Honors & Awards

  • American Association of Physicians, - (-)
  • American Society of Clinical Investigation, - (-)
  • Rackham Award, University of Michigan (-)

Professional Education

  • M.D., Indiana University (1977)
  • B.A., Indiana University (1973)

Current Research and Scholarly Interests

Dr. Michael F. Clarke is the Karel and Avice Beekhuis Professor in Cancer Biology and Associate Director of the Stanford Institute for Stem Cell and Regenerative Medicine. He is a board certified oncologist with extensive training in molecular biology and stem cell biology. In addition to his clinical duties in the division of Oncology, Dr. Clarke maintains a laboratory focused on two areas of research: i) the control of self-renewal of normal stem cells and their malignant counterparts; and ii) the identification and characterization of cancer stem cells. The main objectives of his laboratory are to pursue how perturbations in the self-renewal machinery contribute to human diseases and to use the findings to aid the development of more effective treatment therapies.

His laboratory has a long history of innovative findings which include: the first to demonstrate that inappropriate expression of a normal gene could cause a tumor; the first to identify a dominant-negative splice variant of an oncogene; the first to identify a molecular regulator of stem cell self-renewal; the first to identify a solid tumor stem cell (in breast cancer) and the first to demonstrate a molecular linkage of a self-renewal program used by normal mammary stem cells and breast cancer cells. Recently, his group described a molecular mechanism that confers resistance to radiation in breast cancer stem cells.

His group was the first to discover that the proto-oncogene Bmi-1 regulates stem cell self-renewal via an epigenetic mechanism. By examining the pathways upstream and downstream of Bmi1, hence the molecular pathways that regulate self-renewal, his laboratory found that USP16, a protein that dampens Bmi1 signals, causes a stem cell defect in various stem cells in Down’s syndrome, including neural stem cells.

Since cancers arise as a result of a series of genetic mutations, a better understanding of the consequences of these mutations on the underlying biology of the neoplastic cells will help the development of more effective therapies. Solid tumors such as breast cancers contain heterogeneous populations of neoplastic cells. Through collaboration, his group pioneered and organized a team to use single cell genomics to understand complex tissue hierarchy in normal and malignant cells present in human breast, colon and head and neck cancer tumors. Only a small minority of cancer cells had the capacity to form new tumors in a xenograft model. This tumorigenic cell population could be identified prospectively and consistently had definable and identical phenotype. The tumorigenic cells displayed stem cell-like properties in that they were capable of generating new tumors containing additional stem cells as well as regenerating the phenotypically mixed populations of non-tumorigenic cells present in the original tumor. Effective treatment of cancer will require therapeutic strategies that are able to target and eliminate this tumorigenic subset of cells. His laboratory is pursuing the identification of cancer stem cells in other tumors so that they can be studied. Finally, the laboratory is actively pursuing how cancer stem cells self-renew to maintain themselves and escape the genetic constraints on unlimited self-renewal that regulate normal stem cell numbers. Differences in self-renewal pathways between normal and malignant stem cells could be targeted by new therapeutic agents to eliminate cancer stem cells.

Clinical Trials

  • Biopsy of Human Tumors for Cancer Stem Cell Characterization: a Feasibility Study Not Recruiting

    To see if a limited sampling of tumor tissue from human subjects is a feasible way to gather adequate tissue for cancer stem cell quantification.

    Stanford is currently not accepting patients for this trial. For more information, please contact Ruth Lira, 650-723-1367.

    View full details

2018-19 Courses

Stanford Advisees

All Publications

  • Stromal Gli2 activity coordinates a niche signaling program for mammary epithelial stem cells SCIENCE Zhao, C., Cai, S., Shin, K., Lim, A., Kalisky, T., Lu, W., Clarke, M. F., Beachy, P. A. 2017; 356 (6335): 284-?
  • A Quiescent Bcl11b High Stem Cell Population Is Required for Maintenance of the Mammary Gland. Cell stem cell Cai, S., Kalisky, T., Sahoo, D., Dalerba, P., Feng, W., Lin, Y., Qian, D., Kong, A., Yu, J., Wang, F., Chen, E. Y., Scheeren, F. A., Kuo, A. H., Sikandar, S. S., Hisamori, S., van Weele, L. J., Heiser, D., Sim, S., Lam, J., Quake, S., Clarke, M. F. 2017; 20 (2): 247-260 e5


    Stem cells in many tissues sustain themselves by entering a quiescent state to avoid genomic insults and to prevent exhaustion caused by excessive proliferation. In the mammary gland, the identity and characteristics of quiescent epithelial stem cells are not clear. Here, we identify a quiescent mammary epithelial cell population expressing high levels of Bcl11b and located at the interface between luminal and basal cells. Bcl11b(high) cells are enriched for cells that can regenerate mammary glands in secondary transplants. Loss of Bcl11b leads to a Cdkn2a-dependent exhaustion of ductal epithelium and loss of epithelial cell regenerative capacity. Gain- and loss-of-function studies show that Bcl11b induces cells to enter the G0 phase of the cell cycle and become quiescent. Taken together, these results suggest that Bcl11b acts as a central intrinsic regulator of mammary epithelial stem cell quiescence and exhaustion and is necessary for long-term maintenance of the mammary gland.

    View details for DOI 10.1016/j.stem.2016.11.007

    View details for PubMedID 28041896

    View details for PubMedCentralID PMC5341693

  • Role of epithelial to mesenchymal transition associated genes in mammary gland regeneration and breast tumorigenesis. Nature communications Sikandar, S. S., Kuo, A. H., Kalisky, T., Cai, S., Zabala, M., Hsieh, R. W., Lobo, N. A., Scheeren, F. A., Sim, S., Qian, D., Dirbas, F. M., Somlo, G., Quake, S. R., Clarke, M. F. 2017; 8 (1): 1669


    Previous studies have proposed that epithelial to mesenchymal transition (EMT) in breast cancer cells regulates metastasis, stem cell properties and chemo-resistance; most studies were based on in vitro culture of cell lines and mouse transgenic cancer models. However, the identity and function of cells expressing EMT-associated genes in normal murine mammary gland homeostasis and human breast cancer still remains under debate. Using in vivo lineage tracing and triple negative breast cancer (TNBC) patient derived xenografts we demonstrate that the repopulating capacity in normal mammary epithelial cells and tumorigenic capacity in TNBC is independent of expression of EMT-associated genes. In breast cancer, while a subset of cells with epithelial and mesenchymal phenotypes have stem cell activity, in many cells that have lost epithelial characteristics with increased expression of mesenchymal genes, have decreased tumor-initiating capacity and plasticity. These findings have implications for the development of effective therapeutic agents targeting tumor-initiating cells.

    View details for DOI 10.1038/s41467-017-01666-2

    View details for PubMedID 29162812

    View details for PubMedCentralID PMC5698470

  • Targeted chromatin ligation, a robust epigenetic profiling technique for small cell numbers. Nucleic acids research Zarnegar, M. A., Reinitz, F., Newman, A. M., Clarke, M. F. 2017; 45 (17): e153


    The complexity and inefficiency of chromatin immunoprecipitation strategies restrict their sensitivity and application when examining rare cell populations. We developed a new technique that replaces immunoprecipitation with a simplified chromatin fragmentation and proximity ligation step that eliminates bead purification and washing steps. We present a simple single tube proximity ligation technique, targeted chromatin ligation, that captures histone modification patterns with only 200 cells. Our technique eliminates loss of material and sensitivity due to multiple inefficient steps, while simplifying the workflow to enhance sensitivity and create the potential for novel applications.

    View details for DOI 10.1093/nar/gkx648

    View details for PubMedID 28973448

    View details for PubMedCentralID PMC5622369

  • CDX2 as a Prognostic Biomarker in Stage II and Stage III Colon Cancer NEW ENGLAND JOURNAL OF MEDICINE Dalerba, P., Sahoo, D., Paik, S., Guo, X., Yothers, G., Song, N., Wilcox-Fogel, N., Forgo, E., Rajendran, P. S., Miranda, S. P., Hisamori, S., Hutchison, J., Kalisky, T., Qian, D., Wolmark, N., Fisher, G. A., van de Rijn, M., Clarke, M. F. 2016; 374 (3): 211-222
  • A cell-intrinsic role for TLR2-MYD88 in intestinal and breast epithelia and oncogenesis. Nature cell biology Scheeren, F. A., Kuo, A. H., van Weele, L. J., Cai, S., Glykofridis, I., Sikandar, S. S., Zabala, M., Qian, D., Lam, J. S., Johnston, D., Volkmer, J. P., Sahoo, D., van de Rijn, M., Dirbas, F. M., Somlo, G., Kalisky, T., Rothenberg, M. E., Quake, S. R., Clarke, M. F. 2014; 16 (12): 1238-1248


    It has been postulated that there is a link between inflammation and cancer. Here we describe a role for cell-intrinsic toll-like receptor-2 (TLR2; which is involved in inflammatory response) signalling in normal intestinal and mammary epithelial cells and oncogenesis. The downstream effectors of TLR2 are expressed by normal intestinal and mammary epithelia, including the stem/progenitor cells. Deletion of MYD88 or TLR2 in the intestinal epithelium markedly reduces DSS-induced colitis regeneration and spontaneous tumour development in mice. Limiting dilution transplantations of breast epithelial cells devoid of TLR2 or MYD88 revealed a significant decrease in mammary repopulating unit frequency compared with the control. Inhibition of TLR2, its co-receptor CD14, or its downstream targets MYD88 and IRAK1 inhibits growth of human breast cancers in vitro and in vivo. These results suggest that inhibitors of the TLR2 pathway merit investigation as possible therapeutic and chemoprevention agents.

    View details for DOI 10.1038/ncb3058

    View details for PubMedID 25362351

  • Usp16 contributes to somatic stem-cell defects in Down's syndrome. Nature Adorno, M., Sikandar, S., Mitra, S. S., Kuo, A., Nicolis Di Robilant, B., Haro-Acosta, V., Ouadah, Y., Quarta, M., Rodriguez, J., Qian, D., Reddy, V. M., Cheshier, S., Garner, C. C., Clarke, M. F. 2013; 501 (7467): 380-384


    Down's syndrome results from full or partial trisomy of chromosome 21. However, the consequences of the underlying gene-dosage imbalance on adult tissues remain poorly understood. Here we show that in Ts65Dn mice, which are trisomic for 132 genes homologous to genes on human chromosome 21, triplication of Usp16 reduces the self-renewal of haematopoietic stem cells and the expansion of mammary epithelial cells, neural progenitors and fibroblasts. In addition, Usp16 is associated with decreased ubiquitination of Cdkn2a and accelerated senescence in Ts65Dn fibroblasts. Usp16 can remove ubiquitin from histone H2A on lysine 119, a critical mark for the maintenance of multiple somatic tissues. Downregulation of Usp16, either by mutation of a single normal Usp16 allele or by short interfering RNAs, largely rescues all of these defects. Furthermore, in human tissues overexpression of USP16 reduces the expansion of normal fibroblasts and postnatal neural progenitors, whereas downregulation of USP16 partially rescues the proliferation defects of Down's syndrome fibroblasts. Taken together, these results suggest that USP16 has an important role in antagonizing the self-renewal and/or senescence pathways in Down's syndrome and could serve as an attractive target to ameliorate some of the associated pathologies.

    View details for DOI 10.1038/nature12530

    View details for PubMedID 24025767

    View details for PubMedCentralID PMC3816928

  • Identification of a cKit(+) Colonic Crypt Base Secretory Cell That Supports Lgr5(+) Stem Cells in Mice GASTROENTEROLOGY Rothenberg, M. E., Nusse, Y., Kalisky, T., Lee, J. J., Dalerba, P., Scheeren, F., Lobo, N., Kulkarni, S., Sim, S., Qian, D., Beachy, P. A., Pasricha, P. J., Quake, S. R., Clarke, M. F. 2012; 142 (5): 1195-?


    Paneth cells contribute to the small intestinal niche of Lgr5(+) stem cells. Although the colon also contains Lgr5(+) stem cells, it does not contain Paneth cells. We investigated the existence of colonic Paneth-like cells that have a distinct transcriptional signature and support Lgr5(+) stem cells.We used multicolor fluorescence-activated cell sorting to isolate different subregions of colon crypts, based on known markers, from dissociated colonic epithelium of mice. We performed multiplexed single-cell gene expression analysis with quantitative reverse transcriptase polymerase chain reaction followed by hierarchical clustering analysis to characterize distinct cell types. We used immunostaining and fluorescence-activated cell sorting analyses with in vivo administration of a Notch inhibitor and in vitro organoid cultures to characterize different cell types.Multicolor fluorescence-activated cell sorting could isolate distinct regions of colonic crypts. Four major epithelial subtypes or transcriptional states were revealed by gene expression analysis of selected populations of single cells. One of these, the goblet cells, contained a distinct cKit/CD117(+) crypt base subpopulation that expressed Dll1, Dll4, and epidermal growth factor, similar to Paneth cells, which were also marked by cKit. In the colon, cKit(+) goblet cells were interdigitated with Lgr5(+) stem cells. In vivo, this colonic cKit(+) population was regulated by Notch signaling; administration of a γ-secretase inhibitor to mice increased the number of cKit(+) cells. When isolated from mouse colon, cKit(+) cells promoted formation of organoids from Lgr5(+) stem cells, which expressed Kitl/stem cell factor, the ligand for cKit. When organoids were depleted of cKit(+) cells using a toxin-conjugated antibody, organoid formation decreased.cKit marks small intestinal Paneth cells and a subset of colonic goblet cells that are regulated by Notch signaling and support Lgr5(+) stem cells.

    View details for DOI 10.1053/j.gastro.2012.02.006

    View details for Web of Science ID 000303113600038

    View details for PubMedID 22333952

    View details for PubMedCentralID PMC3911891

  • Single-cell dissection of transcriptional heterogeneity in human colon tumors NATURE BIOTECHNOLOGY Dalerba, P., Kalisky, T., Sahoo, D., Rajendran, P. S., Rothenberg, M. E., Leyrat, A. A., Sim, S., Okamoto, J., Johnston, D. M., Qian, D., Zabala, M., Bueno, J., Neff, N. F., Wang, J., Shelton, A. A., Visser, B., Hisamori, S., Shimono, Y., Van De Wetering, M., Clevers, H., Clarke, M. F., Quake, S. R. 2011; 29 (12): 1120-U11


    Cancer is often viewed as a caricature of normal developmental processes, but the extent to which its cellular heterogeneity truly recapitulates multilineage differentiation processes of normal tissues remains unknown. Here we implement single-cell PCR gene-expression analysis to dissect the cellular composition of primary human normal colon and colon cancer epithelia. We show that human colon cancer tissues contain distinct cell populations whose transcriptional identities mirror those of the different cellular lineages of normal colon. By creating monoclonal tumor xenografts from injection of a single (n = 1) cell, we demonstrate that the transcriptional diversity of cancer tissues is largely explained by in vivo multilineage differentiation and not only by clonal genetic heterogeneity. Finally, we show that the different gene-expression programs linked to multilineage differentiation are strongly associated with patient survival. We develop two-gene classifier systems (KRT20 versus CA1, MS4A12, CD177, SLC26A3) that predict clinical outcomes with hazard ratios superior to those of pathological grade and comparable to those of microarray-derived multigene expression signatures.

    View details for DOI 10.1038/nbt.2038

    View details for Web of Science ID 000298038700023

    View details for PubMedID 22081019

    View details for PubMedCentralID PMC3237928

  • Downregulation of miRNA-200c Links Breast Cancer Stem Cells with Normal Stem Cells CELL Shimono, Y., Zabala, M., Cho, R. W., Lobo, N., Dalerba, P., Qian, D., Diehn, M., Liu, H., Panula, S. P., Chiao, E., Dirbas, F. M., Somlo, G., Pera, R. A., Lao, K., Clarke, M. F. 2009; 138 (3): 592-603


    Human breast tumors contain a breast cancer stem cell (BCSC) population with properties reminiscent of normal stem cells. We found 37 microRNAs that were differentially expressed between human BCSCs and nontumorigenic cancer cells. Three clusters, miR-200c-141, miR-200b-200a-429, and miR-183-96-182 were downregulated in human BCSCs, normal human and murine mammary stem/progenitor cells, and embryonal carcinoma cells. Expression of BMI1, a known regulator of stem cell self-renewal, was modulated by miR-200c. miR-200c inhibited the clonal expansion of breast cancer cells and suppressed the growth of embryonal carcinoma cells in vitro. Most importantly, miR-200c strongly suppressed the ability of normal mammary stem cells to form mammary ducts and tumor formation driven by human BCSCs in vivo. The coordinated downregulation of three microRNA clusters and the similar functional regulation of clonal expansion by miR-200c provide a molecular link that connects BCSCs with normal stem cells.

    View details for DOI 10.1016/j.cell.2009.07.011

    View details for Web of Science ID 000268771900022

    View details for PubMedID 19665978

    View details for PubMedCentralID PMC2731699

  • Association of reactive oxygen species levels and radioresistance in cancer stem cells NATURE Diehn, M., Cho, R. W., Lobo, N. A., Kalisky, T., Dorie, M. J., Kulp, A. N., Qian, D., Lam, J. S., Ailles, L. E., Wong, M., Joshua, B., Kaplan, M. J., Wapnir, I., Dirbas, F. M., Somlo, G., Garberoglio, C., Paz, B., Shen, J., Lau, S. K., Quake, S. R., Brown, J. M., Weissman, I. L., Clarke, M. F. 2009; 458 (7239): 780-U123


    The metabolism of oxygen, although central to life, produces reactive oxygen species (ROS) that have been implicated in processes as diverse as cancer, cardiovascular disease and ageing. It has recently been shown that central nervous system stem cells and haematopoietic stem cells and early progenitors contain lower levels of ROS than their more mature progeny, and that these differences are critical for maintaining stem cell function. We proposed that epithelial tissue stem cells and their cancer stem cell (CSC) counterparts may also share this property. Here we show that normal mammary epithelial stem cells contain lower concentrations of ROS than their more mature progeny cells. Notably, subsets of CSCs in some human and murine breast tumours contain lower ROS levels than corresponding non-tumorigenic cells (NTCs). Consistent with ROS being critical mediators of ionizing-radiation-induced cell killing, CSCs in these tumours develop less DNA damage and are preferentially spared after irradiation compared to NTCs. Lower ROS levels in CSCs are associated with increased expression of free radical scavenging systems. Pharmacological depletion of ROS scavengers in CSCs markedly decreases their clonogenicity and results in radiosensitization. These results indicate that, similar to normal tissue stem cells, subsets of CSCs in some tumours contain lower ROS levels and enhanced ROS defences compared to their non-tumorigenic progeny, which may contribute to tumour radioresistance.

    View details for DOI 10.1038/nature07733

    View details for Web of Science ID 000265193600045

    View details for PubMedID 19194462

    View details for PubMedCentralID PMC2778612

  • Long-term haematopoietic reconstitution by Trp53(-/-)p16(Ink4a-/-)p19(Arf-/-) multipotent progenitors NATURE Akala, O. O., Park, I., Qian, D., Pihalja, M., Becker, M. W., Clarke, M. F. 2008; 453 (7192): 228-U12


    Haematopoiesis is maintained by a hierarchical system where haematopoietic stem cells (HSCs) give rise to multipotent progenitors, which in turn differentiate into all types of mature blood cells. HSCs maintain themselves for the lifetime of the organism because of their ability to self-renew. However, multipotent progenitors lack the ability to self-renew, therefore their mitotic capacity and expansion potential are limited and they are destined to eventually stop proliferating after a finite number of cell divisions. The molecular mechanisms that limit the proliferation capacity of multipotent progenitors and other more mature progenitors are not fully understood. Here we show that bone marrow cells from mice deficient in three genes genetically downstream of Bmi1--p16Ink4a, p19Arf and Trp53 (triple mutant mice; p16Ink4a and p19Arf are alternative reading frames of the same gene (also called Cdkn2a) that encode different proteins)--have an approximately 10-fold increase in cells able to reconstitute the blood long term. This increase is associated with the acquisition of long-term reconstitution capacity by cells of the phenotype c-kit+Sca-1+Flt3+CD150-CD48-Lin-, which defines multipotent progenitors in wild-type mice. The pattern of triple mutant multipotent progenitor response to growth factors resembles that of wild-type multipotent progenitors but not wild-type HSCs. These results demonstrate that p16Ink4a/p19Arf and Trp53 have a central role in limiting the expansion potential of multipotent progenitors. These pathways are commonly repressed in cancer, suggesting a mechanism by which early progenitor cells could gain the ability to self-renew and become malignant with further oncogenic mutations.

    View details for DOI 10.1038/nature06869

    View details for Web of Science ID 000255592400041

    View details for PubMedID 18418377

  • The prognostic role of a gene signature from tumorigenic breast-cancer cells. NEW ENGLAND JOURNAL OF MEDICINE Liu, R., Wang, X., Chen, G. Y., Dalerba, P., Gurney, A., Hoey, T., Sherlock, G., Lewicki, J., Shedden, K., Clarke, M. F. 2007; 356 (3): 217-226


    Breast cancers contain a minority population of cancer cells characterized by CD44 expression but low or undetectable levels of CD24 (CD44+CD24-/low) that have higher tumorigenic capacity than other subtypes of cancer cells.We compared the gene-expression profile of CD44+CD24-/low tumorigenic breast-cancer cells with that of normal breast epithelium. Differentially expressed genes were used to generate a 186-gene "invasiveness" gene signature (IGS), which was evaluated for its association with overall survival and metastasis-free survival in patients with breast cancer or other types of cancer.There was a significant association between the IGS and both overall and metastasis-free survival (P<0.001, for both) in patients with breast cancer, which was independent of established clinical and pathological variables. When combined with the prognostic criteria of the National Institutes of Health, the IGS was used to stratify patients with high-risk early breast cancer into prognostic categories (good or poor); among patients with a good prognosis, the 10-year rate of metastasis-free survival was 81%, and among those with a poor prognosis, it was 57%. The IGS was also associated with the prognosis in medulloblastoma (P=0.004), lung cancer (P=0.03), and prostate cancer (P=0.01). The prognostic power of the IGS was increased when combined with the wound-response (WR) signature.The IGS is strongly associated with metastasis-free survival and overall survival for four different types of tumors. This genetic signature of tumorigenic breast-cancer cells was even more strongly associated with clinical outcomes when combined with the WR signature in breast cancer.

    View details for Web of Science ID 000243488100004

    View details for PubMedID 17229949

  • A CD47-associated super-enhancer links pro-inflammatory signalling to CD47 upregulation in breast cancer NATURE COMMUNICATIONS Betancur, P. A., Abraham, B. J., Yiu, Y. Y., Willingham, S. B., Khameneh, F., Zarnegar, M., Kuo, A. H., McKenna, K., Kojima, Y., Leeper, N. J., Ho, P., Gip, P., Swigut, T., Sherwood, R. I., Clarke, M. F., Somlo, G., Young, R. A., Weissman, I. L. 2017; 8


    CD47 is a cell surface molecule that inhibits phagocytosis of cells that express it by binding to its receptor, SIRPα, on macrophages and other immune cells. CD47 is expressed at different levels by neoplastic and normal cells. Here, to reveal mechanisms by which different neoplastic cells generate this dominant 'don't eat me' signal, we analyse the CD47 regulatory genomic landscape. We identify two distinct super-enhancers (SEs) associated with CD47 in certain cancer cell types. We show that a set of active constituent enhancers, located within the two CD47 SEs, regulate CD47 expression in different cancer cell types and that disruption of CD47 SEs reduces CD47 gene expression. Finally we report that the TNF-NFKB1 signalling pathway directly regulates CD47 by interacting with a constituent enhancer located within a CD47-associated SE specific to breast cancer. These results suggest that cancers can evolve SE to drive CD47 overexpression to escape immune surveillance.

    View details for DOI 10.1038/ncomms14802

    View details for Web of Science ID 000398343600001

    View details for PubMedID 28378740

  • KIT Signaling Promotes Growth of Colon Xenograft Tumors in Mice and Is Up-Regulated in a Subset of Human Colon Cancers. Gastroenterology Chen, E. C., Karl, T. A., Kalisky, T., Gupta, S. K., O'Brien, C. A., Longacre, T. A., van de Rijn, M., Quake, S. R., Clarke, M. F., Rothenberg, M. E. 2015; 149 (3): 705-17 e2


    Receptor tyrosine kinase (RTK) inhibitors have advanced colon cancer treatment. We investigated the role of the RTK KIT in development of human colon cancer.An array of 137 patient-derived colon tumors and their associated xenografts were analyzed by immunohistochemistry to measure levels of KIT and its ligand KITLG. KIT and/or KITLG was stably knocked down by expression of small hairpin RNAs from lentiviral vectors in DLD1, HT29, LS174T, and COLO320 DM colon cancer cell lines, and in UM-COLON#8 and POP77 xenografts; cells transduced with only vector were used as controls. Cells were analyzed by real-time quantitative reverse transcription polymerase chain reaction, single-cell gene expression analysis, flow cytometry, and immunohistochemical, immunoblot, and functional assays. Xenograft tumors were grown from control and KIT-knockdown DLD1 and UM-COLON#8 cells in immunocompromised mice and compared. Some mice were given the RTK inhibitor imatinib after injection of cancer cells; tumor growth was measured based on bioluminescence. We assessed tumorigenicity using limiting dilution analysis.KIT and KITLG were expressed heterogeneously by a subset of human colon tumors. Knockdown of KIT decreased proliferation of colon cancer cell lines and growth of xenograft tumors in mice compared with control cells. KIT knockdown cells had increased expression of enterocyte markers, decreased expression of cycling genes, and, unexpectedly, increased expression of LGR5 associated genes. No activating mutations in KIT were detected in DLD1, POP77, or UM-COLON#8 cells. However, KITLG-knockdown DLD1 cells formed smaller xenograft tumors than control cells. Gene expression analysis of single CD44(+) cells indicated that KIT can promote growth via KITLG autocrine and/or paracrine signaling. Imatinib inhibited growth of KIT(+) colon cancer organoids in culture and growth of xenograft tumors in mice. Cancer cells with endogenous KIT expression were more tumorigenic in mice.KIT and KITLG are expressed by a subset of human colon tumors. KIT signaling promotes growth of colon cancer cells and organoids in culture and xenograft tumors in mice via its ligand, KITLG, in an autocrine or paracrine manner. Patients with KIT-expressing colon tumors can benefit from KIT RTK inhibitors.

    View details for DOI 10.1053/j.gastro.2015.05.042

    View details for PubMedID 26026391

    View details for PubMedCentralID PMC4550533

  • Quantitative assessment of single-cell RNA-sequencing methods. Nature methods Wu, A. R., Neff, N. F., Kalisky, T., Dalerba, P., Treutlein, B., Rothenberg, M. E., Mburu, F. M., Mantalas, G. L., Sim, S., Clarke, M. F., Quake, S. R. 2014; 11 (1): 41-46


    Interest in single-cell whole-transcriptome analysis is growing rapidly, especially for profiling rare or heterogeneous populations of cells. We compared commercially available single-cell RNA amplification methods with both microliter and nanoliter volumes, using sequence from bulk total RNA and multiplexed quantitative PCR as benchmarks to systematically evaluate the sensitivity and accuracy of various single-cell RNA-seq approaches. We show that single-cell RNA-seq can be used to perform accurate quantitative transcriptome measurement in individual cells with a relatively small number of sequencing reads and that sequencing large numbers of single cells can recapitulate bulk transcriptome complexity.

    View details for DOI 10.1038/nmeth.2694

    View details for PubMedID 24141493

  • miR-142 regulates the tumorigenicity of human breast cancer stem cells through the canonical WNT signaling pathway. eLife Isobe, T., Hisamori, S., Hogan, D. J., Zabala, M., Hendrickson, D. G., Dalerba, P., Cai, S., Scheeren, F., Kuo, A. H., Sikandar, S. S., Lam, J. S., Qian, D., Dirbas, F. M., Somlo, G., Lao, K., Brown, P. O., Clarke, M. F., Shimono, Y. 2014; 3


    MicroRNAs (miRNAs) are important regulators of stem and progenitor cell functions. We previously reported that miR-142 and miR-150 are upregulated in human breast cancer stem cells (BCSCs) as compared to the non-tumorigenic breast cancer cells. In this study, we report that miR-142 efficiently recruits the APC mRNA to an RNA-induced silencing complex, activates the canonical WNT signaling pathway in an APC-suppression dependent manner, and activates the expression of miR-150. Enforced expression of miR-142 or miR-150 in normal mouse mammary stem cells resulted in the regeneration of hyperproliferative mammary glands in vivo. Knockdown of endogenous miR-142 effectively suppressed organoid formation by BCSCs and slowed tumor growth initiated by human BCSCs in vivo. These results suggest that in some tumors, miR-142 regulates the properties of BCSCs at least in part by activating the WNT signaling pathway and miR-150 expression.

    View details for DOI 10.7554/eLife.01977

    View details for PubMedID 25406066

  • Usp16 contributes to somatic stem-cell defects in Down's syndrome. Nature Adorno, M., Sikandar, S., Mitra, S. S., Kuo, A., Nicolis Di Robilant, B., Haro-Acosta, V., Ouadah, Y., Quarta, M., Rodriguez, J., Qian, D., Reddy, V. M., Cheshier, S., Garner, C. C., Clarke, M. F. 2013; 501 (7467): 380-384


    Down's syndrome results from full or partial trisomy of chromosome 21. However, the consequences of the underlying gene-dosage imbalance on adult tissues remain poorly understood. Here we show that in Ts65Dn mice, which are trisomic for 132 genes homologous to genes on human chromosome 21, triplication of Usp16 reduces the self-renewal of haematopoietic stem cells and the expansion of mammary epithelial cells, neural progenitors and fibroblasts. In addition, Usp16 is associated with decreased ubiquitination of Cdkn2a and accelerated senescence in Ts65Dn fibroblasts. Usp16 can remove ubiquitin from histone H2A on lysine 119, a critical mark for the maintenance of multiple somatic tissues. Downregulation of Usp16, either by mutation of a single normal Usp16 allele or by short interfering RNAs, largely rescues all of these defects. Furthermore, in human tissues overexpression of USP16 reduces the expansion of normal fibroblasts and postnatal neural progenitors, whereas downregulation of USP16 partially rescues the proliferation defects of Down's syndrome fibroblasts. Taken together, these results suggest that USP16 has an important role in antagonizing the self-renewal and/or senescence pathways in Down's syndrome and could serve as an attractive target to ameliorate some of the associated pathologies.

    View details for DOI 10.1038/nature12530

    View details for PubMedID 24025767

    View details for PubMedCentralID PMC3816928

  • Oncogenic miRNAs and the perils of losing control of a stem cell's epigenetic identity. Cell stem cell Dalerba, P., Clarke, M. F. 2013; 13 (1): 5-6


    Pathways that regulate epigenetic control of stem cell identity are critical to the molecular etiology of cancer. In back-to-back articles in Cell and Cell Stem Cell, Song et al. identify miR-22 as both a repressor of TET proteins and a powerful oncogene in the mammary epithelium and hematopoietic system.

    View details for DOI 10.1016/j.stem.2013.06.012

    View details for PubMedID 23827702

  • Identifying the metastatic seeds of breast cancer. Nature biotechnology Kuo, A. H., Clarke, M. F. 2013; 31 (6): 504-505

    View details for DOI 10.1038/nbt.2599

    View details for PubMedID 23752434

  • MicroRNA-30c inhibits human breast tumour chemotherapy resistance by regulating TWF1 and IL-11 NATURE COMMUNICATIONS Bockhorn, J., Dalton, R., Nwachukwu, C., Huang, S., Prat, A., Yee, K., Chang, Y., Huo, D., Wen, Y., Swanson, K. E., Qiu, T., Lu, J., Park, S. Y., Dolan, M. E., Perou, C. M., Olopade, O. I., Clarke, M. F., Greene, G. L., Liu, H. 2013; 4


    Chemotherapy resistance frequently drives tumour progression. However, the underlying molecular mechanisms are poorly characterized. Epithelial-to-mesenchymal transition has been shown to correlate with therapy resistance, but the functional link and signalling pathways remain to be elucidated. Here we report that microRNA-30c, a human breast tumour prognostic marker, has a pivotal role in chemoresistance by a direct targeting of the actin-binding protein twinfilin 1, which promotes epithelial-to-mesenchymal transition. An interleukin-6 family member, interleukin-11 is identified as a secondary target of twinfilin 1 in the microRNA-30c signalling pathway. Expression of microRNA-30c inversely correlates with interleukin-11 expression in primary breast tumours and low interleukin-11 correlates with relapse-free survival in breast cancer patients. Our study demonstrates that microRNA-30c is transcriptionally regulated by GATA3 in breast tumours. Identification of a novel microRNA-mediated pathway that regulates chemoresistance in breast cancer will facilitate the development of novel therapeutic strategies.

    View details for DOI 10.1038/ncomms2393

    View details for Web of Science ID 000316614600063

    View details for PubMedID 23340433

  • MicroRNA-30c targets cytoskeleton genes involved in breast cancer cell invasion BREAST CANCER RESEARCH AND TREATMENT Bockhorn, J., Yee, K., Chang, Y., Prat, A., Huo, D., Nwachukwu, C., Dalton, R., Huang, S., Swanson, K. E., Perou, C. M., Olopade, O. I., Clarke, M. F., Greene, G. L., Liu, H. 2013; 137 (2): 373-382


    Metastasis remains a significant challenge in treating cancer. A better understanding of the molecular mechanisms underlying metastasis is needed to develop more effective treatments. Here, we show that human breast tumor biomarker miR-30c regulates invasion by targeting the cytoskeleton network genes encoding twinfilin 1 (TWF1) and vimentin (VIM). Both VIM and TWF1 have been shown to regulate epithelial-to-mesenchymal transition. Similar to TWF1, VIM also regulates F-actin formation, a key component of cellular transition to a more invasive mesenchymal phenotype. To further characterize the role of the TWF1 pathway in breast cancer, we found that IL-11 is an important target of TWF1 that regulates breast cancer cell invasion and STAT3 phosphorylation. The miR-30c-VIM/TWF1 signaling cascade is also associated with clinical outcome in breast cancer patients.

    View details for DOI 10.1007/s10549-012-2346-4

    View details for Web of Science ID 000313201100005

    View details for PubMedID 23224145

    View details for PubMedCentralID PMC3583223

  • Innate immune response to homologous rotavirus infection in the small intestinal villous epithelium at single-cell resolution PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Sen, A., Rothenberg, M. E., Mukherjee, G., Feng, N., Kalisky, T., Nair, N., Johnstone, I. M., Clarke, M. F., Greenberg, H. B. 2012; 109 (50): 20667-20672


    "Bulk" measurements of antiviral innate immune responses from pooled cells yield averaged signals and do not reveal underlying signaling heterogeneity in infected and bystander single cells. We examined such heterogeneity in the small intestine during rotavirus (RV) infection. Murine RV EW robustly activated type I IFNs and several antiviral genes (IFN-stimulated genes) in the intestine by bulk analysis, the source of induced IFNs primarily being hematopoietic cells. Flow cytometry and microfluidics-based single-cell multiplex RT-PCR allowed dissection of IFN responses in single RV-infected and bystander intestinal epithelial cells (IECs). EW replicates in IEC subsets differing in their basal type I IFN transcription and induces IRF3-dependent and IRF3-augmented transcription, but not NF-κB-dependent or type I IFN transcripts. Bystander cells did not display enhanced type I IFN transcription but had elevated levels of certain IFN-stimulated genes, presumably in response to exogenous IFNs secreted from immune cells. Comparison of IRF3 and NF-κB induction in STAT1(-/-) mice revealed that murine but not simian RRV mediated accumulation of IkB-α protein and decreased transcription of NF-κB-dependent genes. RRV replication was significantly rescued in IFN types I and II, as well as STAT1 (IFN types I, II, and III) deficient mice in contrast to EW, which was only modestly sensitive to IFNs I and II. Resolution of "averaged" innate immune responses in single IECs thus revealed unexpected heterogeneity in both the induction and subversion of early host antiviral immunity, which modulated host range.

    View details for DOI 10.1073/pnas.1212188109

    View details for Web of Science ID 000312605600104

    View details for PubMedID 23188796

  • Remodeling of Endogenous Mammary Epithelium by Breast Cancer Stem Cells STEM CELLS Parashurama, N., Lobo, N. A., Ito, K., Mosley, A. R., Habte, F. G., Zabala, M., Smith, B. R., Lam, J., Weissman, I. L., Clarke, M. F., Gambhir, S. S. 2012; 30 (10): 2114-2127


    Poorly regulated tissue remodeling results in increased breast cancer risk, yet how breast cancer stem cells (CSC) participate in remodeling is unknown. We performed in vivo imaging of changes in fluorescent, endogenous duct architecture as a metric for remodeling. First, we quantitatively imaged physiologic remodeling of primary branches of the developing and regenerating mammary tree. To assess CSC-specific remodeling events, we isolated CSC from MMTV-Wnt1 (mouse mammary tumor virus long-term repeat enhancer driving Wnt1 oncogene) breast tumors, a well studied model in which tissue remodeling affects tumorigenesis. We confirm that CSC drive tumorigenesis, suggesting a link between CSC and remodeling. We find that normal, regenerating, and developing gland maintain a specific branching pattern. In contrast, transplantation of CSC results in changes in the branching patterns of endogenous ducts while non-CSC do not. Specifically, in the presence of CSC, we identified an increased number of branches, branch points, ducts which have greater than 40 branches (5/33 for CSC and 0/39 for non-CSC), and histological evidence of increased branching. Moreover, we demonstrate that only CSC implants invade into surrounding stroma with structures similar to developing mammary ducts (nine for CSC and one for non-CSC). Overall, we demonstrate a novel approach for imaging physiologic and pathological remodeling. Furthermore, we identify unique, CSC-specific, remodeling events. Our data suggest that CSC interact with the microenvironment differently than non-CSC, and that this could eventually be a therapeutic approach for targeting CSC.

    View details for DOI 10.1002/stem.1205

    View details for Web of Science ID 000308928300005

    View details for PubMedID 22899386

  • The CD47-signal regulatory protein alpha (SIRPa) interaction is a therapeutic target for human solid tumors PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Willingham, S. B., Volkmer, J., Gentles, A. J., Sahoo, D., Dalerba, P., Mitra, S. S., Wang, J., Contreras-Trujillo, H., Martin, R., Cohen, J. D., Lovelace, P., Scheeren, F. A., Chao, M. P., Weiskopf, K., Tang, C., Volkmer, A. K., Naik, T. J., Storm, T. A., Mosley, A. R., Edris, B., Schmid, S. M., Sun, C. K., Chua, M., Murillo, O., Rajendran, P., Cha, A. C., Chin, R. K., Kim, D., Adorno, M., Raveh, T., Tseng, D., Jaiswal, S., Enger, P. O., Steinberg, G. K., Li, G., So, S. K., Majeti, R., Harsh, G. R., van de Rijn, M., Teng, N. N., Sunwoo, J. B., Alizadeh, A. A., Clarke, M. F., Weissman, I. L. 2012; 109 (17): 6662-6667


    CD47, a "don't eat me" signal for phagocytic cells, is expressed on the surface of all human solid tumor cells. Analysis of patient tumor and matched adjacent normal (nontumor) tissue revealed that CD47 is overexpressed on cancer cells. CD47 mRNA expression levels correlated with a decreased probability of survival for multiple types of cancer. CD47 is a ligand for SIRPα, a protein expressed on macrophages and dendritic cells. In vitro, blockade of CD47 signaling using targeted monoclonal antibodies enabled macrophage phagocytosis of tumor cells that were otherwise protected. Administration of anti-CD47 antibodies inhibited tumor growth in orthotopic immunodeficient mouse xenotransplantation models established with patient tumor cells and increased the survival of the mice over time. Anti-CD47 antibody therapy initiated on larger tumors inhibited tumor growth and prevented or treated metastasis, but initiation of the therapy on smaller tumors was potentially curative. The safety and efficacy of targeting CD47 was further tested and validated in immune competent hosts using an orthotopic mouse breast cancer model. These results suggest all human solid tumor cells require CD47 expression to suppress phagocytic innate immune surveillance and elimination. These data, taken together with similar findings with other human neoplasms, show that CD47 is a commonly expressed molecule on all cancers, its function to block phagocytosis is known, and blockade of its function leads to tumor cell phagocytosis and elimination. CD47 is therefore a validated target for cancer therapies.

    View details for DOI 10.1073/pnas.1121623109

    View details for Web of Science ID 000303249100065

    View details for PubMedID 22451913

    View details for PubMedCentralID PMC3340046

  • Stimulation of natural killer cells with a CD137-specific antibody enhances trastuzumab efficacy in xenotransplant models of breast cancer JOURNAL OF CLINICAL INVESTIGATION Kohrt, H. E., Houot, R., Weiskopf, K., Goldstein, M. J., Scheeren, F., Czerwinski, D., Colevas, A. D., Weng, W., Clarke, M. F., Carlson, R. W., Stockdale, F. E., Mollick, J. A., Chen, L., Levy, R. 2012; 122 (3): 1066-1075


    Trastuzumab, a monoclonal antibody targeting human epidermal growth factor receptor 2 (HER2; also known as HER-2/neu), is indicated for the treatment of women with either early stage or metastatic HER2(+) breast cancer. It kills tumor cells by several mechanisms, including antibody-dependent cellular cytotoxicity (ADCC). Strategies that enhance the activity of ADCC effectors, including NK cells, may improve the efficacy of trastuzumab. Here, we have shown that upon encountering trastuzumab-coated, HER2-overexpressing breast cancer cells, human NK cells become activated and express the costimulatory receptor CD137. CD137 activation, which was dependent on NK cell expression of the FcγRIII receptor, occurred both in vitro and in the peripheral blood of women with HER2-expressing breast cancer after trastuzumab treatment. Stimulation of trastuzumab-activated human NK cells with an agonistic mAb specific for CD137 killed breast cancer cells (including an intrinsically trastuzumab-resistant cell line) more efficiently both in vitro and in vivo in xenotransplant models of human breast cancer, including one using a human primary breast tumor. The enhanced cytotoxicity was restricted to antibody-coated tumor cells. This sequential antibody strategy, combining a tumor-targeting antibody with a second antibody that activates the host innate immune system, may improve the therapeutic effects of antibodies against breast cancer and other HER2-expressing tumors.

    View details for DOI 10.1172/JCI61226

    View details for Web of Science ID 000301021500029

    View details for PubMedID 22326955

    View details for PubMedCentralID PMC3287235

  • Removal of lactate dehydrogenase-elevating virus from human-in-mouse breast tumor xenografts by cell-sorting JOURNAL OF VIROLOGICAL METHODS Liu, H., Bockhorn, J., Dalton, R., Chang, Y., Qian, D., Zitzow, L. A., Clarke, M. F., Greene, G. L. 2011; 173 (2): 266-270


    Lactate dehydrogenase-elevating virus (LDV) can infect transplantable mouse tumors or xenograft tumors in mice through LDV-contaminated mouse biological materials, such as Matrigel, or through mice infected with LDV. LDV infects specifically mouse macrophages and alters immune system and tumor phenotype. The traditional approaches to remove LDV from tumor cells, by transplanting tumors into rats or culturing tumor cells in vitro, are inefficient, labor-intensive and time-consuming. Furthermore, these approaches are not feasible for primary tumor cells that cannot survive tissue culture conditions or that may change phenotype in rats. This study reports that fluorescence-activated cell sorting (FACS) is a simple and efficient approach for purifying living primary human breast tumor cells from LDV(+) mouse stromal cells, which can be completed in a few hours. When purified from Matrigel contaminated LDV(+) tumors, sorted human breast tumor cells, as well as tumors grown from sorted cells, were shown to be LDV-free, as tested by PCR. The results demonstrate that cell sorting is effective, much faster and less likely to alter tumor cell phenotype than traditional methods for removing LDV from xenograft models. This approach may also be used to remove other rodent-specific viruses from models derived from distinct tissues or species with sortable markers, where virus does not replicate in the cells to be purified.

    View details for DOI 10.1016/j.jviromet.2011.02.015

    View details for Web of Science ID 000290836400014

    View details for PubMedID 21354210

  • Cancer stem cells from human breast tumors are involved in spontaneous metastases in orthotopic mouse models PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Liu, H., Patel, M. R., Prescher, J. A., Patsialou, A., Qian, D., Lin, J., Wen, S., Chang, Y., Bachmann, M. H., Shimono, Y., Dalerba, P., Adorno, M., Lobo, N., Bueno, J., Dirbas, F. M., Goswami, S., Somlo, G., Condeelis, J., Contag, C. H., Gambhir, S. S., Clarke, M. F. 2010; 107 (42): 18115-18120


    To examine the role of breast cancer stem cells (BCSCs) in metastasis, we generated human-in-mouse breast cancer orthotopic models using patient tumor specimens, labeled with optical reporter fusion genes. These models recapitulate human cancer features not captured with previous models, including spontaneous metastasis in particular, and provide a useful platform for studies of breast tumor initiation and progression. With noninvasive imaging approaches, as few as 10 cells of stably labeled BCSCs could be tracked in vivo, enabling studies of early tumor growth and spontaneous metastasis. These advances in BCSC imaging revealed that CD44(+) cells from both primary tumors and lung metastases are highly enriched for tumor-initiating cells. Our metastatic cancer models, combined with noninvasive imaging techniques, constitute an integrated approach that could be applied to dissect the molecular mechanisms underlying the dissemination of metastatic CSCs (MCSCs) and to explore therapeutic strategies targeting MCSCs in general or to evaluate individual patient tumor cells and predict response to therapy.

    View details for DOI 10.1073/pnas.1006732107

    View details for Web of Science ID 000283184800050

    View details for PubMedID 20921380

    View details for PubMedCentralID PMC2964232

  • The Myc Connection: ES Cells and Cancer CELL Rothenberg, M. E., Clarke, M. F., Diehn, M. 2010; 143 (2): 184-186


    Gene profiling experiments have revealed similarities between cancer and embryonic stem (ES) cells. Kim et al. (2010) dissect the gene expression signature of ES cells into three functional modules and find that the Myc module, including genes targeted by Myc-interacting proteins, accounts for most of the similarity between ES and cancer cells.

    View details for DOI 10.1016/j.cell.2010.09.046

    View details for Web of Science ID 000283052200007

    View details for PubMedID 20946977

  • DLL4 Blockade Inhibits Tumor Growth and Reduces Tumor-Initiating Cell Frequency CELL STEM CELL Hoey, T., Yen, W., Axelrod, F., Basi, J., Donigian, L., Dylla, S., Fitch-Bruhns, M., Lazetic, S., Park, I., Sato, A., Satyal, S., Wang, X., Clarke, M. F., Lewicki, J., Gurney, A. 2009; 5 (2): 168-177


    Previous studies have shown that blocking DLL4 signaling reduced tumor growth by disrupting productive angiogenesis. We developed selective anti-human and anti-mouse DLL4 antibodies to dissect the mechanisms involved by analyzing the contributions of selectively targeting DLL4 in the tumor or in the host vasculature and stroma in xenograft models derived from primary human tumors. We found that each antibody inhibited tumor growth and that the combination of the two antibodies was more effective than either alone. Treatment with anti-human DLL4 inhibited the expression of Notch target genes and reduced proliferation of tumor cells. Furthermore, we found that specifically inhibiting human DLL4 in the tumor, either alone or in combination with the chemotherapeutic agent irinotecan, reduced cancer stem cell frequency, as shown by flow cytometric and in vivo tumorigenicity studies.

    View details for DOI 10.1016/j.stem.2009.05.019

    View details for Web of Science ID 000269511900010

    View details for PubMedID 19664991

  • RADIATION THERAPY ONCOLOGY GROUP TRANSLATIONAL RESEARCH PROGRAM STEM CELL SYMPOSIUM: INCORPORATING STEM CELL HYPOTHESES INTO CLINICAL TRIALS INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Woodward, W. A., Bristow, R. G., Clarke, M. F., Coppes, R. P., Cristofanilli, M., Duda, D. G., Fike, J. R., Hambardzumyan, D., Hill, R. P., Jordan, C. T., Milas, L., Pajonk, F., Curran, W. J., Dicker, A. P., Chen, Y. 2009; 74 (5): 1580-1591


    At a meeting of the Translation Research Program of the Radiation Therapy Oncology Group held in early 2008, attendees focused on updating the current state of knowledge in cancer stem cell research and discussing ways in which this knowledge can be translated into clinical use across all disease sites. This report summarizes the major topics discussed and the future directions that research should take. Major conclusions of the symposium were that the flow cytometry of multiple markers in fresh tissue would remain the standard technique of evaluating cancer-initiating cells and that surrogates need to be developed for both experimental and clinical use.

    View details for DOI 10.1016/j.ijrobp.2009.03.047

    View details for Web of Science ID 000268346100041

    View details for PubMedID 19540073

  • Automated microfluidic chromatin immunoprecipitation from 2,000 cells LAB ON A CHIP Wu, A. R., Hiatt, J. B., Lu, R., Attema, J. L., Lobo, N. A., Weissman, I. L., Clarke, M. F., Quake, S. R. 2009; 9 (10): 1365-1370


    Chromatin immunoprecipitation (ChIP) is a powerful assay used to probe DNA-protein interactions. Traditional methods of implementing this assay are lengthy, cumbersome and require a large number of cells, making it difficult to study rare cell types such as certain cancer and stem cells. We have designed a microfluidic device to perform sensitive ChIP analysis on low cell numbers in a rapid, automated fashion while preserving the specificity of the assay. Comparing ChIP results for two modified histone protein targets, we showed our automated microfluidic ChIP (AutoChIP) from 2,000 cells to be comparable to that of conventional ChIP methods using 50,000-500,000 cells. This technology may provide a solution to the need for a high sensitivity, rapid, and automated ChIP assay, and in doing so facilitate the use of ChIP for many interesting and valuable applications.

    View details for DOI 10.1039/b819648f

    View details for Web of Science ID 000268227400008

    View details for PubMedID 19417902

  • Therapeutic Implications of the Cancer Stem Cell Hypothesis SEMINARS IN RADIATION ONCOLOGY Diehn, M., Cho, R. W., Clarke, M. F. 2009; 19 (2): 78-86


    A growing body of evidence indicates that subpopulations of cancer stem cells (CSCs) drive and maintain many types of human malignancies. These findings have important implications for the development and evaluation of oncologic therapies and present opportunities for potential gains in patient outcome. The existence of CSCs mandates careful analysis and comparison of normal tissue stem cells and CSCs to identify differences between the two cell types. The development of CSC-targeted treatments will face a number of potential hurdles, including normal stem cell toxicity and the acquisition of treatment resistance, which must be considered in order to maximize the chance that such therapies will be successful.

    View details for DOI 10.1016/j.semradonc.2008.11.002

    View details for Web of Science ID 000264310800003

    View details for PubMedID 19249645

    View details for PubMedCentralID PMC2789266

  • Dysregulated gene expression networks in human acute myelogenous leukemia stem cells PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Majetl, R., Becker, M. W., Tian, Q., Lee, T. M., Yan, X., Liu, R., Chiang, J., Hood, L., Clarke, M. F., Weissman, I. L. 2009; 106 (9): 3396-3401


    We performed the first genome-wide expression analysis directly comparing the expression profile of highly enriched normal human hematopoietic stem cells (HSC) and leukemic stem cells (LSC) from patients with acute myeloid leukemia (AML). Comparing the expression signature of normal HSC to that of LSC, we identified 3,005 differentially expressed genes. Using 2 independent analyses, we identified multiple pathways that are aberrantly regulated in leukemic stem cells compared with normal HSC. Several pathways, including Wnt signaling, MAP Kinase signaling, and Adherens Junction, are well known for their role in cancer development and stem cell biology. Other pathways have not been previously implicated in the regulation of cancer stem cell functions, including Ribosome and T Cell Receptor Signaling pathway. This study demonstrates that combining global gene expression analysis with detailed annotated pathway resources applied to highly enriched normal and malignant stem cell populations, can yield an understanding of the critical pathways regulating cancer stem cells.

    View details for DOI 10.1073/pnas.0900089106

    View details for Web of Science ID 000263844100075

    View details for PubMedID 19218430

    View details for PubMedCentralID PMC2642659

  • Colorectal Cancer Stem Cells Are Enriched in Xenogeneic Tumors Following Chemotherapy PLOS ONE Dylla, S. J., Beviglia, L., Park, I., Chartier, C., Raval, J., Ngan, L., Pickell, K., Aguilar, J., Lazetic, S., Smith-Berdan, S., Clarke, M. F., Hoey, T., Lewicki, J., Gurney, A. L. 2008; 3 (6)


    Patients generally die of cancer after the failure of current therapies to eliminate residual disease. A subpopulation of tumor cells, termed cancer stem cells (CSC), appears uniquely able to fuel the growth of phenotypically and histologically diverse tumors. It has been proposed, therefore, that failure to effectively treat cancer may in part be due to preferential resistance of these CSC to chemotherapeutic agents. The subpopulation of human colorectal tumor cells with an ESA(+)CD44(+) phenotype are uniquely responsible for tumorigenesis and have the capacity to generate heterogeneous tumors in a xenograft setting (i.e. CoCSC). We hypothesized that if non-tumorigenic cells are more susceptible to chemotherapeutic agents, then residual tumors might be expected to contain a higher frequency of CoCSC.Xenogeneic tumors initiated with CoCSC were allowed to reach approximately 400 mm(3), at which point mice were randomized and chemotherapeutic regimens involving cyclophosphamide or Irinotecan were initiated. Data from individual tumor phenotypic analysis and serial transplants performed in limiting dilution show that residual tumors are enriched for cells with the CoCSC phenotype and have increased tumorigenic cell frequency. Moreover, the inherent ability of residual CoCSC to generate tumors appears preserved. Aldehyde dehydrogenase 1 gene expression and enzymatic activity are elevated in CoCSC and using an in vitro culture system that maintains CoCSC as demonstrated by serial transplants and lentiviral marking of single cell-derived clones, we further show that ALDH1 enzymatic activity is a major mediator of resistance to cyclophosphamide: a classical chemotherapeutic agent.CoCSC are enriched in colon tumors following chemotherapy and remain capable of rapidly regenerating tumors from which they originated. By focusing on the biology of CoCSC, major resistance mechanisms to specific chemotherapeutic agents can be attributed to specific genes, thereby suggesting avenues for improving cancer therapy.

    View details for DOI 10.1371/journal.pone.0002428

    View details for Web of Science ID 000263280700013

    View details for PubMedID 18560594

  • Isolation and molecular characterization of cancer stem cells in MMTV-Wnt-1 murine breast tumors STEM CELLS Cho, R. W., Wang, X., Diehn, M., Shedden, K., Chen, G. Y., Sherlock, G., Gurney, A., Lewicki, J., Clarke, M. F. 2008; 26 (2): 364-371


    In human breast cancers, a phenotypically distinct minority population of tumorigenic (TG) cancer cells (sometimes referred to as cancer stem cells) drives tumor growth when transplanted into immunodeficient mice. Our objective was to identify a mouse model of breast cancer stem cells that could have relevance to the study of human breast cancer. To do so, we used breast tumors of the mouse mammary tumor virus (MMTV)-Wnt-1 mice. MMTV-Wnt-1 breast tumors were harvested, dissociated into single-cell suspensions, and sorted by flow cytometry on Thy1, CD24, and CD45. Sorted cells were then injected into recipient background FVB/NJ female syngeneic mice. In six of seven tumors examined, Thy1+CD24+ cancer cells, which constituted approximately 1%-4% of tumor cells, were highly enriched for cells capable of regenerating new tumors compared with cells of the tumor that did not fit this profile ("not-Thy1+CD24+"). Resultant tumors had a phenotypic diversity similar to that of the original tumor and behaved in a similar manner when passaged. Microarray analysis comparing Thy1+CD24+ tumor cells to not-Thy1+CD24+ cells identified a list of differentially expressed genes. Orthologs of these differentially expressed genes predicted survival of human breast cancer patients from two different study groups. These studies suggest that there is a cancer stem cell compartment in the MMTV-Wnt-1 murine breast tumor and that there is a clinical utility of this model for the study of cancer stem cells.

    View details for DOI 10.1634/stemcells.2007-0440

    View details for Web of Science ID 000253372600008

    View details for PubMedID 17975224

  • Recent advances in cancer stem cells CURRENT OPINION IN GENETICS & DEVELOPMENT Cho, R. W., Clarke, M. F. 2008; 18 (1): 48-53


    The theory of cancer stem cells states that a subset of cancer cells within a tumor has the ability to self-renew and differentiate. Only those cells within a tumor that have these two properties are called cancer stem cells. This concept was first demonstrated in the study of leukemia where only cells with specific surface antigen profiles were able to cause leukemia when engrafted into immunodeficient mice. In recent years solid tumors were studied utilizing similar techniques in mice. Human tumors where evidence of cancer stem cells has been published include tumors of the breast, brain, pancreas, head and neck, and colon. If this difference in tumorigenicity of cancer cells also occurs in patients, then the ability to enrich for cancer stem cells lays an important groundwork for future studies where mechanisms involved in cancer stem cells can now be investigated.

    View details for DOI 10.1016/j.gde.2008.01.017

    View details for Web of Science ID 000256954100008

    View details for PubMedID 18356041

  • What can we learn about breast cancer from stem cells? 5th International Symposium on Hormonal Carcinogenesis Clarke, M. F. SPRINGER-VERLAG BERLIN. 2008: 17–22

    View details for Web of Science ID 000253701800002

    View details for PubMedID 18497027

  • Cancer stem cells and tumor metastasis: First steps into uncharted territory CELL STEM CELL Dalerba, P., Clarke, M. F. 2007; 1 (3): 241-242


    In several forms of human cancer, only a phenotypic subset of cancer cells, usually termed "cancer stem cells" (CSC), can initiate tumor growth when transplanted. In this issue of Cell Stem Cell, Hermann et al. (2007) analyze the relationship between CSC and tumor metastasis.

    View details for DOI 10.1016/j.stem.2007.08.012

    View details for Web of Science ID 000251055200003

    View details for PubMedID 18371356

  • Bmi-1-green fluorescent protein-knock-in mice reveal the dynamic regulation of Bmi-1 expression in normal and leukemic hematopoietic cells STEM CELLS Hosen, N., Yamane, T., Muijtjens, M., Pham, K., Clarke, M. F., Weissman, I. L. 2007; 25 (7): 1635-1644


    The ability to self-renew is essential for all kinds of stem cells regardless of tissue type. One of the best candidate genes involved in conferring self-renewal capacity is Bmi-1, which has been proven to be essential for the maintenance of both normal adult hematopoietic and leukemia stem cells, as well as adult neural stem cells. To investigate the possible role of Bmi-1 in other cell types that also self-renew, we generated Bmi-1-green fluorescent protein (GFP)-knock-in mice, in which GFP was expressed under the endogenous transcriptional regulatory elements of the Bmi-1 gene. Using these targeted reporter mice, we demonstrated that Bmi-1 is expressed in hematopoietic stem cells (HSCs) at its highest levels and downregulated upon commitment to differentiation. An in vivo reconstitution assay revealed that the frequency of HSCs was 1/16 in Bmi-1high c-kit+ lin -Sca-1+ bone marrow (BM) cells and 1/49 in Bmi-1 high lin- BM cells, suggesting that Bmi-1 may serve as a marker for normal HSCs. In murine leukemia models induced by P210BCR/ABL or TEL/PDGFbetaR + AML1/ETO, Bmi-1 was not overexpressed in leukemic HSCs, despite the increase in the HSC numbers. Bmi-1 was expressed at its highest levels in undifferentiated leukemia cells. Furthermore, in several other nonhematopoietic tissues, cells could be separated into distinct subpopulations with differential Bmi-1 expression. Thus, these mice allow for the isolation of viable Bmi-1-expressing cells and have the potential to become a useful tool for understanding the role of Bmi-1 in normal and cancer stem cells in multiple tissue types. Disclosure of potential conflicts of interest is found at the end of this article.

    View details for DOI 10.1634/stemcells.2006-0229

    View details for Web of Science ID 000247722100006

    View details for PubMedID 17395774

  • Phenotypic characterization of human colorectal cancer stem cells PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Dalerba, P., Dylla, S. J., Park, I., Liu, R., Wang, X., Cho, R. W., Hoey, T., Gurney, A., Huang, E. H., Simeone, D. M., Shelton, A. A., Parmiani, G., Castelli, C., Clarke, M. F. 2007; 104 (24): 10158-10163


    Recent observations indicate that, in several types of human cancer, only a phenotypic subset of cancer cells within each tumor is capable of initiating tumor growth. This functional subset of cancer cells is operationally defined as the "cancer stem cell" (CSC) subset. Here we developed a CSC model for the study of human colorectal cancer (CRC). Solid CRC tissues, either primary tissues collected from surgical specimens or xenografts established in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice, were disaggregated into single-cell suspensions and analyzed by flow cytometry. Surface markers that displayed intratumor heterogeneous expression among epithelial cancer cells were selected for cell sorting and tumorigenicity experiments. Individual phenotypic cancer cell subsets were purified, and their tumor-initiating properties were investigated by injection in NOD/SCID mice. Our observations indicate that, in six of six human CRC tested, the ability to engraft in vivo in immunodeficient mice was restricted to a minority subpopulation of epithelial cell adhesion molecule (EpCAM)(high)/CD44+ epithelial cells. Tumors originated from EpCAM(high)/CD44+ cells maintained a differentiated phenotype and reproduced the full morphologic and phenotypic heterogeneity of their parental lesions. Analysis of the surface molecule repertoire of EpCAM(high)/CD44+ cells led to the identification of CD166 as an additional differentially expressed marker, useful for CSC isolation in three of three CRC tested. These results validate the stem cell working model in human CRC and provide a highly robust surface marker profile for CRC stem cell isolation.

    View details for DOI 10.1073/pnas.0703478104

    View details for Web of Science ID 000247363000044

    View details for PubMedID 17548814

  • Identification of pancreatic cancer stem cells CANCER RESEARCH Li, C., Heidt, D. G., Dalerba, P., Burant, C. F., Zhang, L., Adsay, V., Wicha, M., Clarke, M. F., Simeone, D. M. 2007; 67 (3): 1030-1037


    Emerging evidence has suggested that the capability of a tumor to grow and propagate is dependent on a small subset of cells within a tumor, termed cancer stem cells. Although data have been provided to support this theory in human blood, brain, and breast cancers, the identity of pancreatic cancer stem cells has not been determined. Using a xenograft model in which primary human pancreatic adenocarcinomas were grown in immunocompromised mice, we identified a highly tumorigenic subpopulation of pancreatic cancer cells expressing the cell surface markers CD44, CD24, and epithelial-specific antigen (ESA). Pancreatic cancer cells with the CD44(+)CD24(+)ESA(+) phenotype (0.2-0.8% of pancreatic cancer cells) had a 100-fold increased tumorigenic potential compared with nontumorigenic cancer cells, with 50% of animals injected with as few as 100 CD44(+)CD24(+)ESA(+) cells forming tumors that were histologically indistinguishable from the human tumors from which they originated. The enhanced ability of CD44(+)CD24(+)ESA(+) pancreatic cancer cells to form tumors was confirmed in an orthotopic pancreatic tail injection model. The CD44(+)CD24(+)ESA(+) pancreatic cancer cells showed the stem cell properties of self-renewal, the ability to produce differentiated progeny, and increased expression of the developmental signaling molecule sonic hedgehog. Identification of pancreatic cancer stem cells and further elucidation of the signaling pathways that regulate their growth and survival may provide novel therapeutic approaches to treat pancreatic cancer, which is notoriously resistant to standard chemotherapy and radiation.

    View details for DOI 10.1158/0008-5472.CAN-06-2030

    View details for Web of Science ID 000244137300026

    View details for PubMedID 17283135

  • Identification of a subpopulation of cells with cancer stem cell properties in head and neck squamous cell carcinoma PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Prince, M. E., Sivanandan, R., Kaczorowski, A., Wolf, G. T., Kaplan, M. J., Dalerba, P., Weissman, I. L., Clarke, M. F., Ailles, L. E. 2007; 104 (3): 973-978


    Like many epithelial tumors, head and neck squamous cell carcinoma (HNSCC) contains a heterogeneous population of cancer cells. We developed an immunodeficient mouse model to test the tumorigenic potential of different populations of cancer cells derived from primary, unmanipulated human HNSCC samples. We show that a minority population of CD44(+) cancer cells, which typically comprise <10% of the cells in a HNSCC tumor, but not the CD44(-) cancer cells, gave rise to new tumors in vivo. Immunohistochemistry revealed that the CD44(+) cancer cells have a primitive cellular morphology and costain with the basal cell marker Cytokeratin 5/14, whereas the CD44(-) cancer cells resemble differentiated squamous epithelium and express the differentiation marker Involucrin. The tumors that arose from purified CD44(+) cells reproduced the original tumor heterogeneity and could be serially passaged, thus demonstrating the two defining properties of stem cells: ability to self-renew and to differentiate. Furthermore, the tumorigenic CD44(+) cells differentially express the BMI1 gene, at both the RNA and protein levels. By immunohistochemical analysis, the CD44(+) cells in the tumor express high levels of nuclear BMI1, and are arrayed in characteristic tumor microdomains. BMI1 has been demonstrated to play a role in self-renewal in other stem cell types and to be involved in tumorigenesis. Taken together, these data demonstrate that cells within the CD44(+) population of human HNSCC possess the unique properties of cancer stem cells in functional assays for cancer stem cell self-renewal and differentiation and form unique histological microdomains that may aid in cancer diagnosis.

    View details for DOI 10.1073/pnas.0610117104

    View details for Web of Science ID 000243761100053

    View details for PubMedID 17210912

  • Chromosome 5q deletion and epigenetic suppression of the gene encoding alpha-catenin (CTNNA1) in myeloid cell transformation NATURE MEDICINE Liu, T. X., Becker, M. W., Jelinek, J., Wu, W., Deng, M., Mikhalkevich, N., Hsu, K., Bloomfield, C. D., Stone, R. M., DeAngelo, D. J., Galinsky, I. A., Issa, J., Clarke, M. F., Look, A. T. 2007; 13 (1): 78-83


    Interstitial loss of all or part of the long arm of chromosome 5, or del(5q), is a frequent clonal chromosomal abnormality in human myelodysplastic syndrome (MDS, a preleukemic disorder) and acute myeloid leukemia (AML), and is thought to contribute to the pathogenesis of these diseases by deleting one or more tumor-suppressor genes. Although a major commonly deleted region (CDR) has been delineated on chromosome band 5q31.1 (refs. 3-7), attempts to identify tumor suppressors within this band have been unsuccessful. We focused our analysis of gene expression on RNA from primitive leukemia-initiating cells, which harbor 5q deletions, and analyzed 12 genes within the CDR that are expressed by normal hematopoietic stem cells. Here we show that the gene encoding alpha-catenin (CTNNA1) is expressed at a much lower level in leukemia-initiating stem cells from individuals with AML or MDS with a 5q deletion than in individuals with MDS or AML lacking a 5q deletion or in normal hematopoietic stem cells. Analysis of HL-60 cells, a myeloid leukemia line with deletion of the 5q31 region, showed that the CTNNA1 promoter of the retained allele is suppressed by both methylation and histone deacetylation. Restoration of CTNNA1 expression in HL-60 cells resulted in reduced proliferation and apoptotic cell death. Thus, loss of expression of the alpha-catenin tumor suppressor in hematopoietic stem cells may provide a growth advantage that contributes to human MDS or AML with del(5q).

    View details for DOI 10.1038/nm1512

    View details for Web of Science ID 000243301800039

    View details for PubMedID 17159988

  • The biology of cancer stem cells ANNUAL REVIEW OF CELL AND DEVELOPMENTAL BIOLOGY Lobo, N. A., Shimono, Y., Qian, D., Clarke, M. F. 2007; 23: 675-699


    Cancers originally develop from normal cells that gain the ability to proliferate aberrantly and eventually turn malignant. These cancerous cells then grow clonally into tumors and eventually have the potential to metastasize. A central question in cancer biology is, which cells can be transformed to form tumors? Recent studies elucidated the presence of cancer stem cells that have the exclusive ability to regenerate tumors. These cancer stem cells share many characteristics with normal stem cells, including self-renewal and differentiation. With the growing evidence that cancer stem cells exist in a wide array of tumors, it is becoming increasingly important to understand the molecular mechanisms that regulate self-renewal and differentiation because corruption of genes involved in these pathways likely participates in tumor growth. This new paradigm of oncogenesis has been validated in a growing list of tumors. Studies of normal and cancer stem cells from the same tissue have shed light on the ontogeny of tumors. That signaling pathways such as Bmi1 and Wnt have similar effects in normal and cancer stem cell self-renewal suggests that common molecular pathways regulate both populations. Understanding the biology of cancer stem cells will contribute to the identification of molecular targets important for future therapies.

    View details for DOI 10.1146/annurev.cellbio.22.010305.104154

    View details for Web of Science ID 000250896200025

    View details for PubMedID 17645413

  • Cancer stem cells: Models and concepts ANNUAL REVIEW OF MEDICINE Dalerba, P., Cho, R. W., Clarke, M. F. 2007; 58: 267-284


    Although monoclonal in origin, most tumors appear to contain a heterogeneous population of cancer cells. This observation is traditionally explained by postulating variations in tumor microenvironment and coexistence of multiple genetic subclones, created by progressive and divergent accumulation of independent somatic mutations. An additional explanation, however, envisages human tumors not as mere monoclonal expansions of transformed cells, but rather as complex tridimensional tissues where cancer cells become functionally heterogeneous as a result of differentiation. According to this second scenario, tumors act as caricatures of their corresponding normal tissues and are sustained in their growth by a pathological counterpart of normal adult stem cells, cancer stem cells. This model, first developed in human myeloid leukemias, is today being extended to solid tumors, such as breast and brain cancer. We review the biological basis and the therapeutic implications of the stem cell model of cancer.

    View details for DOI 10.1146/annurev.med.58.062105.204854

    View details for Web of Science ID 000244461500018

    View details for PubMedID 17002552

  • Cancer stem cells and radiotherapy: New insights into tumor radioresistance JOURNAL OF THE NATIONAL CANCER INSTITUTE Diehn, M., Clarke, M. F. 2006; 98 (24): 1755-1757

    View details for DOI 10.1093/jnci/djj505

    View details for Web of Science ID 000242973400002

    View details for PubMedID 17179471

  • Cancer stem cells--perspectives on current status and future directions: AACR Workshop on cancer stem cells. Cancer research Clarke, M. F., Dick, J. E., Dirks, P. B., Eaves, C. J., Jamieson, C. H., Jones, D. L., Visvader, J., Weissman, I. L., Wahl, G. M. 2006; 66 (19): 9339-9344

    View details for PubMedID 16990346

  • Hematopoietic stem cell self-renewal CURRENT OPINION IN GENETICS & DEVELOPMENT Akala, O. O., Clarke, M. F. 2006; 16 (5): 496-501


    Recent studies have begun to elucidate the mechanisms controlling hematopoietic stem cell (HSC) self-renewal. Self-renewal requires the integration of survival signals and proliferation controls with the maintenance of an undifferentiated state. This demands a complex crosstalk between extrinsic signals from the microenvironment and the cell-intrinsic regulators of self-renewal. The Polycomb protein Bmi1 is absolutely required for the maintenance of both adult HSCs and neural stem cells. Evidence from studies in murine and human embryonic stem cells indicates that Polycomb group proteins play a dynamic role in concert with master transcriptional regulators in actively maintaining an undifferentiated state, suggesting that this mechanism applies to multiple types of stem cell. Recently, various new players that regulate HSC maintenance (e.g. Mcl1, Tel/Etv6, Gfi1, Pten and Stat5) have been identified. In order to better understand HSC self-renewal, we need to understand how these pathways are coordinated.

    View details for DOI 10.1016/j.gde.2006.08.011

    View details for Web of Science ID 000241320300009

    View details for PubMedID 16919448

  • Stem cells: The real culprits in cancer? SCIENTIFIC AMERICAN Clarke, M. F., Becker, M. W. 2006; 295 (1): 52-59

    View details for Web of Science ID 000238326700034

    View details for PubMedID 16830680

  • Stem cells and cancer: Two faces of eve CELL Clarke, M. F., Fuller, M. 2006; 124 (6): 1111-1115


    Recent evidence suggests that a subset of cancer cells within some tumors, the so-called cancer stem cells, may drive the growth and metastasis of these tumors. Understanding the pathways that regulate proliferation, self-renewal, survival, and differentiation of malignant and normal stem cells may shed light on mechanisms that lead to cancer and suggest better modes of treatment.

    View details for DOI 10.1016/j.cell.2006.03.011

    View details for Web of Science ID 000237241400007

    View details for PubMedID 16564000

  • Oncogenes, self-renewal and cancer PATHOLOGIE BIOLOGIE Clarke, M. F. 2006; 54 (2): 109-111


    Cancers arise in a tissue as the culmination of a series of mutations that activate oncogenes and inactivate tumor suppressor genes. Many of these mutations affect cell proliferation and survival. Recently, it has become apparent that some oncogenes and tumor suppressor genes also regulate self-renewal, the process by which stem cells maintain themselves. In some cancer cells, the process of self-renewal is de-regulated resulting in expansion of these cells and tumors. It is likely that targeting cancer cell self-renewal pathways will result in more effective cancer therapies.

    View details for DOI 10.1016/j.patbio.2006.01.004

    View details for Web of Science ID 000236287600008

    View details for PubMedID 16524671

  • A self-renewal assay for cancer stem cells. Cancer chemotherapy and pharmacology Clarke, M. F. 2005; 56: 64-68


    Cancers of epithelial origin are responsible for the majority of cancer-related deaths in the USA. Unfortunately, although chemotherapy and/or radiation therapy can sometimes shrink tumors, metastatic cancers of epithelial origin are essentially incurable. It is clear that new approaches are needed to treat these diseases. Although cancer cell lines provide invaluable information, their biological properties often differ in crucial ways from de novo cancer cells. Our laboratory has developed a novel mouse model that reliably permits individual cancer cells isolated directly from patients' tumors to be assayed. This will allow the characterization of crucial signaling pathways involved in processes such as self-renewal that are critical for tumor formation by the cancer cells within de novo tumors. These tools should lead to new insights into the cellular and molecular mechanisms that drive human breast cancer growth and invasion.

    View details for PubMedID 16273355

  • Self-renewal and solid-tumor stem cells Tandem BMT Meeting 2005 Clarke, M. F. ELSEVIER SCIENCE INC. 2005: 14–16

    View details for Web of Science ID 000227329300006

    View details for PubMedID 15682169

  • Epigenetic regulation of normal and cancer stem cells 5th International Conference on Hematopoietic Stem Cells Clarke, M. F. NEW YORK ACAD SCIENCES. 2005: 90–93


    In many tissues, a cellular hierarchy exists in which a small population of stem cells is responsible for the production of the mature cells of the organ. The stem cells maintain themselves through a process known as self-renewal. Similarly, tumors contain a minority population of cancer stem cells that maintain the tumor. Some factors that regulate this process of self-renewal are conserved from fruit fly to humans. Disruption of the regulation of self-renewal results in cancer. Thus understanding the mechanisms that regulate stem cell generation has implications for normal development and disease.

    View details for DOI 10.1196/annals.1349.012

    View details for Web of Science ID 000230894100011

    View details for PubMedID 15958701

  • Neurobiology: At the root of brain cancer NATURE Clarke, M. F. 2004; 432 (7015): 281-282

    View details for DOI 10.1038/432281a

    View details for Web of Science ID 000225161400025

    View details for PubMedID 15549078

  • Self-renewal and solid tumor stem cells ONCOGENE Al-Hajj, M., Clarke, M. F. 2004; 23 (43): 7274-7282


    Solid tumors arise in organs that contain stem cell populations. The tumors in these tissues consist of heterogeneous populations of cancer cells that differ markedly in their ability to proliferate and form new tumors. In both breast cancers and central nervous system tumors, cancer cells differ in their ability to form tumors. While the majority of the cancer cells have a limited ability to divide, a population of cancer stem cells that has the exclusive ability to extensively proliferate and form new tumors can be identified based on marker expression. Growing evidence suggests that pathways that regulate the self-renewal of normal stem cells are deregulated in cancer stem cells resulting in the continuous expansion of self-renewing cancer cells and tumor formation. This suggests that agents that target the defective self-renewal pathways in cancer cells might lead to improved outcomes in the treatment of these diseases.

    View details for DOI 10.1038/sj.onc.1207947

    View details for Web of Science ID 000223998800013

    View details for PubMedID 15378087

  • Chronic myelogenous leukemia - Identifying the hydra's heads NEW ENGLAND JOURNAL OF MEDICINE Clarke, M. F. 2004; 351 (7): 634-636

    View details for Web of Science ID 000223225500005

    View details for PubMedID 15306664

  • Therapeutic implications of cancer stem cells CURRENT OPINION IN GENETICS & DEVELOPMENT Al-Hajj, M., Becker, M. W., Wichal, M., Weissman, I., Clarke, M. F. 2004; 14 (1): 43-47


    Most cancers comprise a heterogenous population of cells with marked differences in their proliferative potential as well as the ability to reconstitute the tumor upon transplantation. Cancer stem cells are a minor population of tumor cells that possess the stem cell property of self-renewal. In addition, dysregulation of stem cell self-renewal is a likely requirement for the development of cancer. This new model for cancer will have significant ramifications for the way we study and treat cancer. In addition, through targeting the cancer stem cell and its dysregulated self-renewal, our therapies for treating cancer are likely to improve.

    View details for DOI 10.1016/j.gde.2003.11.007

    View details for Web of Science ID 000188978200008

    View details for PubMedID 15108804

  • Bmi1, stem cells, and senescence regulation JOURNAL OF CLINICAL INVESTIGATION Park, I. K., Morrison, S. J., Clarke, M. F. 2004; 113 (2): 175-179


    Stem cells generate the differentiated cell types within many organs throughout the lifespan of an organism and are thus ultimately responsible for the longevity of multicellular organisms. Therefore, senescence of stem cells must be prevented. Bmi1 is required for the maintenance of adult stem cells in some tissues partly because it represses genes that induce cellular senescence and cell death.

    View details for DOI 10.1172/JCI200420800

    View details for Web of Science ID 000188195600005

    View details for PubMedID 14722607

  • Applying the principles of stem-cell biology to cancer NATURE REVIEWS CANCER Pardal, R., Clarke, M. F., Morrison, S. J. 2003; 3 (12): 895-902

    View details for DOI 10.1038/nrc1232

    View details for Web of Science ID 000187068700011

    View details for PubMedID 14737120

  • Bmi-1 dependence distinguishes neural stem cell self-renewal from progenitor proliferation NATURE Molofsky, A. V., Pardal, R., Iwashita, T., Park, I. K., Clarke, M. F., Morrison, S. J. 2003; 425 (6961): 962-967


    Stem cells persist throughout life by self-renewing in numerous tissues including the central and peripheral nervous systems. This raises the issue of whether there is a conserved mechanism to effect self-renewing divisions. Deficiency in the polycomb family transcriptional repressor Bmi-1 leads to progressive postnatal growth retardation and neurological defects. Here we show that Bmi-1 is required for the self-renewal of stem cells in the peripheral and central nervous systems but not for their survival or differentiation. The reduced self-renewal of Bmi-1-deficient neural stem cells leads to their postnatal depletion. In the absence of Bmi-1, the cyclin-dependent kinase inhibitor gene p16Ink4a is upregulated in neural stem cells, reducing the rate of proliferation. p16Ink4a deficiency partially reverses the self-renewal defect in Bmi-1-/- neural stem cells. This conserved requirement for Bmi-1 to promote self-renewal and to repress p16Ink4a expression suggests that a common mechanism regulates the self-renewal and postnatal persistence of diverse types of stem cell. Restricted neural progenitors from the gut and forebrain proliferate normally in the absence of Bmi-1. Thus, Bmi-1 dependence distinguishes stem cell self-renewal from restricted progenitor proliferation in these tissues.

    View details for DOI 10.1038/nature02060

    View details for Web of Science ID 000186230600042

    View details for PubMedID 14574365

  • Stem cells in normal breast development and breast cancer CELL PROLIFERATION Dontu, G., Al-Hajj, M., Abdallah, W. A., Clarke, M. F., Wicha, M. S. 2003; 36: 59-72


    The main focus of this review is the role of mammary stem cells in normal breast development and carcinogenesis. We have developed a new in vitro culture system that permits, for the first time, the propagation of mammary stem and progenitor cells in an undifferentiated state, which should facilitate the elucidation of pathways that regulate normal mammary stem-cell self-renewal and differentiation. Furthermore, we propose a model in which transformation of stem cells, or early progenitor cells, results in carcinogenesis. A key event in this process is the deregulation of normal self-renewal in these cells. Transformed mammary stem or progenitor cells undergo aberrant differentiation processes that result in generation of the phenotypic heterogeneity found in human and rodent breast cancers. This phenotypic diversity is driven by a small subset of mammary tumour stem cells. We will discuss the important implications of this mammary tumour stem-cell model.

    View details for Web of Science ID 000186360800006

    View details for PubMedID 14521516

  • Bmi-1 is required for maintenance of adult self-renewing haematopoietic stem cells NATURE Park, I. K., Qian, D. L., Kiel, M., Becker, M. W., Pihalja, M., Weissman, I. L., Morrison, S. J., Clarke, M. F. 2003; 423 (6937): 302-305


    A central issue in stem cell biology is to understand the mechanisms that regulate the self-renewal of haematopoietic stem cells (HSCs), which are required for haematopoiesis to persist for the lifetime of the animal. We found that adult and fetal mouse and adult human HSCs express the proto-oncogene Bmi-1. The number of HSCs in the fetal liver of Bmi-1-/- mice was normal. In postnatal Bmi-1-/- mice, the number of HSCs was markedly reduced. Transplanted fetal liver and bone marrow cells obtained from Bmi-1-/- mice were able to contribute only transiently to haematopoiesis. There was no detectable self-renewal of adult HSCs, indicating a cell autonomous defect in Bmi-1-/- mice. A gene expression analysis revealed that the expression of stem cell associated genes, cell survival genes, transcription factors, and genes modulating proliferation including p16Ink4a and p19Arf was altered in bone marrow cells of the Bmi-1-/- mice. Expression of p16Ink4a and p19Arf in normal HSCs resulted in proliferative arrest and p53-dependent cell death, respectively. Our results indicate that Bmi-1 is essential for the generation of self-renewing adult HSCs.

    View details for DOI 10.1038/nature01587

    View details for Web of Science ID 000182853100046

    View details for PubMedID 12714971

  • In vitro propagation and transcriptional profiling of human mammary stem/progenitor cells GENES & DEVELOPMENT Dontu, G., Abdallah, W. M., Foley, J. M., Jackson, K. W., Clarke, M. F., Kawamura, M. J., Wicha, M. S. 2003; 17 (10): 1253-1270


    Although the existence of mammary stem cells has been suggested by serial transplantation studies in mice, their identification has been hindered by the lack of specific surface markers, and by the absence of suitable in vitro assays for testing stem cell properties: self-renewal and ability to generate differentiated progeny. We have developed an in vitro cultivation system that allows for propagation of human mammary epithelial cells (HMECs) in an undifferentiated state, based on their ability to proliferate in suspension, as nonadherent mammospheres. We demonstrate that nonadherent mammospheres are enriched in early progenitor/stem cells and able to differentiate along all three mammary epithelial lineages and to clonally generate complex functional structures in reconstituted 3D culture systems. Gene expression analysis of cells isolated from nonadherent mammospheres revealed overlapping genetic programs with other stem and progenitor cells and identified new markers that may be useful in the identification of mammary stem cells. The isolation and characterization of these stem cells should help elucidate the molecular pathways that govern normal mammary development and carcinogenesis.

    View details for DOI 10.1101/gad.1061803

    View details for Web of Science ID 000182941000008

    View details for PubMedID 12756227

  • Prospective identification of tumorigenic breast cancer cells PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Al-Hajj, M., Wicha, M. S., Benito-Hernandez, A., Morrison, S. J., Clarke, M. F. 2003; 100 (7): 3983-3988


    Breast cancer is the most common malignancy in United States women, accounting for >40,000 deaths each year. These breast tumors are comprised of phenotypically diverse populations of breast cancer cells. Using a model in which human breast cancer cells were grown in immunocompromised mice, we found that only a minority of breast cancer cells had the ability to form new tumors. We were able to distinguish the tumorigenic (tumor initiating) from the nontumorigenic cancer cells based on cell surface marker expression. We prospectively identified and isolated the tumorigenic cells as CD44(+)CD24(-/low)Lineage(-) in eight of nine patients. As few as 100 cells with this phenotype were able to form tumors in mice, whereas tens of thousands of cells with alternate phenotypes failed to form tumors. The tumorigenic subpopulation could be serially passaged: each time cells within this population generated new tumors containing additional CD44(+)CD24(-/low)Lineage(-) tumorigenic cells as well as the phenotypically diverse mixed populations of nontumorigenic cells present in the initial tumor. The ability to prospectively identify tumorigenic cancer cells will facilitate the elucidation of pathways that regulate their growth and survival. Furthermore, because these cells drive tumor development, strategies designed to target this population may lead to more effective therapies.

    View details for DOI 10.1073/pnas.0530291100

    View details for Web of Science ID 000182058400082

    View details for PubMedID 12629218

    View details for PubMedCentralID PMC153034

  • SLUGging away at cell death CANCER CELL Becker, M. W., Clarke, M. F. 2002; 2 (4): 249-251


    Programmed cell death (PCD) plays an important role in normal and malignant hematopoieis. In this issue of Cancer Cell, Inoue et al. (2002) demonstrate that the CED-1 homolog, Slug, is a key regulator of apoptosis in the response of early hematopoietic progenitors to gamma radiation.

    View details for Web of Science ID 000178717500001

    View details for PubMedID 12398886

  • New oncolytic adenoviruses with hypoxia- and estrogen receptor-regulated replication HUMAN GENE THERAPY Hernandez-Alcoceba, R., Pihalja, M., Qian, D. L., Clarke, M. F. 2002; 13 (14): 1737-1750


    Oncolytic adenoviruses with restricted replication can be produced if the expression of crucial transcription units of the virus is controlled by tissue- or tumor-specific promoters. Here we describe a method for the rapid incorporation of exogenous promoters into the E1A and E4 regions of the human adenovirus type 5 genome. Using this system, we have generated AdEHT2 and AdEHE2F, two conditionally replicative adenoviruses for the treatment of breast cancer. The expression of the E1A gene in both viruses is controlled by a minimal dual-specificity promoter that responds to estrogens and hypoxia. The tight regulation of E1A expression correlated with the ability of these viruses to replicate and kill human cancer cells that express estrogen receptors, or are maintained under hypoxic conditions. The telomerase reverse transcriptase (TERT) promoter and the E2F-1 promoter are preferentially activated in cancer cells. They were introduced into the E4 region of AdEHT2 and AdEHE2F, respectively. The telomerase core promoter failed to block the replication of the virus in telomerase-negative cells. In contrast, AdEHE2F was attenuated in nontransformed quiescent cells growing under normoxic conditions, suggesting that an intact pRB pathway with low levels of E2F transcription factors acts as a negative modulator for the virus. These data indicate that the simultaneous regulation of E1A and E4 viral transcription units by the appropriate combination of promoters can increase the tumor selectivity of oncolytic adenoviruses.

    View details for Web of Science ID 000178077600006

    View details for PubMedID 12396626

  • Differential gene expression profiling of adult murine hematopoietic stem cells BLOOD Park, I. K., He, Y. Q., Lin, F. M., Laerum, O. D., Tian, Q., Bumgarner, R., Klug, C. A., Li, K. J., Kuhr, C., Doyle, M. J., Xie, T., Schummer, M., Sun, Y., GOLDSMITH, A., Clarke, M. F., Weissman, I. L., Hood, L., Li, L. H. 2002; 99 (2): 488-498


    Hematopoietic stem cells (HSCs) have self-renewal capacity and multilineage developmental potentials. The molecular mechanisms that control the self-renewal of HSCs are still largely unknown. Here, a systematic approach using bioinformatics and array hybridization techniques to analyze gene expression profiles in HSCs is described. To enrich mRNAs predominantly expressed in uncommitted cell lineages, 54 000 cDNA clones generated from a highly enriched population of HSCs and a mixed population of stem and early multipotent progenitor (MPP) cells were arrayed on nylon membranes (macroarray or high-density array), and subtracted with cDNA probes derived from mature lineage cells including spleen, thymus, and bone marrow. Five thousand cDNA clones with very low hybridization signals were selected for sequencing and further analysis using microarrays on glass slides. Two populations of cells, HSCs and MPP cells, were compared for differential gene expression using microarray analysis. HSCs have the ability to self-renew, while MPP cells have lost the capacity for self-renewal. A large number of genes that were differentially expressed by enriched populations of HSCs and MPP cells were identified. These included transcription factors, signaling molecules, and previously unknown genes.

    View details for Web of Science ID 000173215900013

    View details for PubMedID 11781229

  • A genetic determinant that specifically regulates the frequency of hematopoietic stem cells JOURNAL OF IMMUNOLOGY Morrison, S. J., Qian, D., Jerabek, L., Thiel, B. A., Park, I. K., Ford, P. S., Kiel, M. J., Schork, N. J., Weissman, I. L., Clarke, M. F. 2002; 168 (2): 635-642


    The regulation of hematopoietic stem cell (HSC) homeostasis is not well understood. We screened for genetic polymorphisms that were linked to differences between mouse strains in the numbers of long-term reconstituting HSCs or restricted progenitors in the bone marrow. AKR/J mice had significantly higher frequencies and numbers of both HSCs and restricted progenitors in their bone marrow than C57BL/Ka-Thy-1.1 mice. The C57BL/Ka-Thy-1.1 alleles were partially dominant. A locus on chromosome 17, including the H-2 complex, was significantly linked to the frequency of long-term self-renewing HSCs but showed no evidence of linkage to the frequency of restricted progenitors. Conversely, a chromosome 1 locus exhibited suggestive linkage to restricted progenitor frequencies but was not linked to HSC frequency. This demonstrates that there are distinct genetic determinants of the frequencies of HSCs and restricted progenitors in vivo. The AKR/J chromosome 17 locus was not sufficient to increase HSC frequencies when bred onto a C57BL background. This suggests that to affect HSC frequencies, the product(s) of this locus likely depend on interactions with unlinked modifying loci.

    View details for Web of Science ID 000173193700014

    View details for PubMedID 11777956

  • Stem cells, cancer, and cancer stem cells NATURE Reya, T., Morrison, S. J., Clarke, M. F., Weissman, I. L. 2001; 414 (6859): 105-111


    Stem cell biology has come of age. Unequivocal proof that stem cells exist in the haematopoietic system has given way to the prospective isolation of several tissue-specific stem and progenitor cells, the initial delineation of their properties and expressed genetic programmes, and the beginnings of their utility in regenerative medicine. Perhaps the most important and useful property of stem cells is that of self-renewal. Through this property, striking parallels can be found between stem cells and cancer cells: tumours may often originate from the transformation of normal stem cells, similar signalling pathways may regulate self-renewal in stem cells and cancer cells, and cancer cells may include 'cancer stem cells' - rare cells with indefinite potential for self-renewal that drive tumorigenesis.

    View details for Web of Science ID 000171898900054

    View details for PubMedID 11689955

  • Clinical protocol. Purging of autologous stem cell sources with bcl-x(s) adenovirus for women undergoing high-dose chemotherapy for stage IV breast carcinoma. Human gene therapy Ayash, L. J., Clarke, M., Adams, P., Ferrara, J., Ratanatharathorn, V., Reynolds, C., Roessler, B., Silver, S., Strawderman, M., Uberti, J., Wicha, M. 2001; 12 (16): 2023-2025


    High-dose chemotherapy (HDCT) and autologous bone marrow transplantation (BMT) is frequently used to treat patients with metastatic cancer including breast cancer and neuroblastoma. However, the bone marrow of such patients is often contaminated with tumor cells. Recently, we have found that a recombinant adenovirus vector that contains a bcl-x, minigene (a dominant negative inhibitor of the bcl-2 family), called the bcl-x(s) adenovirus, is lethal to cancer cells derived from epithelial tissues, but not to normal human hematopoietic cells. To determine the mechanism, by which this virus spares normal hematopoietic cells, we isolated normal mouse hematopoietic stem cells and infected them with an adenovirus that contains a beta-galactosidase minigene. Such cells do not express beta-galactosidase, indicating that hematopoietic stem cells do not express transgene encoded by adenovirus vectors based upon the RSV-AD5 vector system. When breast cancer cells mixed with hematopoietic cells were infected with the bcl-x(s) adenovirus, cancer cells were selectively killed by the suicide adenoviruses. Hematopoietic cells exposed to the suicide vectors were able to reconstitute the bone marrow of mice exposed to lethal doses of y-irradiation. These studies suggest that adenovirus suicide vectors may provide a simple and effective method to selectively eliminate cancer cells derived from epithelial tissue that contaminate bone marrow to be used for autologous BMT. We therefore propose to initiate a phase I clinical trial to test the safety of this virus in women with breast cancer undergoing high does chemotherapy and autologous BMT.

    View details for PubMedID 11727734

  • Regulation of p53 localization EUROPEAN JOURNAL OF BIOCHEMISTRY Liang, S. H., Clarke, M. F. 2001; 268 (10): 2779-2783


    Despite intensive study of p53, the regulation of p53 cellular localization is still poorly understood. This is an overview of the elements and molecules involved in p53 nucleocytoplasmic transportation. These include the nuclear import and export signals of p53, inhibition of p53 nuclear import and export by oligomerization, MDM2-mediated p53 nuclear export, and possible roles of p53 phosphorylation in regulating p53 cellular localization. Finally, questions regarding p53 cellular trafficking will also be discussed.

    View details for Web of Science ID 000168968300004

    View details for PubMedID 11358492

  • Double dose-intensive chemotherapy with autologous stem cell support for relapsed and refractory testicular cancer: the University of Michigan experience and literature review BONE MARROW TRANSPLANTATION Ayash, L. J., Clarke, M., Silver, S. M., Braun, T., Uberti, J., Ratanatharathorn, V., Reynolds, C., Ferrara, J., Broun, E. R., Adams, P. T. 2001; 27 (9): 939-947


    Testicular cancer patients refractory or in relapse after primary chemotherapy have < or =25% 5-year progression-free survival with salvage. To improve prognosis, patients entered a phase I/II tandem dose-escalation trial of carboplatin (1500-2100 mg/m(2)) and etoposide (1200-2250 mg/m(2)) with ABMT. Patients were eligible for a second cycle if disease progression was absent and performance status allowed. From August 1990 to June 1998, 29 males (25 NSGCT) were treated. At the time of ABMT, 10 were chemosensitive, four were chemoresistant, and 10 were absolutely refractory to platinum. Disease status (no. patients) at transplant: primary refractory disease (six), first relapse (10), second relapse (eight), third relapse (five). Fifteen (52%) received both transplants. Treatment-related mortality was 10%. Best response after ABMT included: two CR, one CR surgically NED, five PR, three PR surgically NED, seven SD, and eight PD. Eight (28%) patients are continuously progression-free a median 60 months (range, 31-93) from first ABMT. Three seminoma patients remain progression-free. Of five long-term NSGCT survivors, four were treated in first relapse with platinum-sensitive disease. Eighteen relapses occurred a median of 4 months after ABMT I (two late relapses at 28 and 44 months). The median PFS and OS for the whole group are 4 and 14 months, respectively. Patients with relapsed/ refractory testicular cancer benefit most from ABMT if they have platinum-sensitive disease in first relapse. Patients who do poorly despite ABMT have a mediastinal primary site, true cisplatin-refractory disease, disease progression prior to ABMT, and/or markedly elevated betaHCG at ABMT. New treatment modalities are needed for the latter group.

    View details for Web of Science ID 000169201800006

    View details for PubMedID 11436104

  • Evaluation of a new dual-specificity promoter for selective induction of apoptosis in breast cancer cells CANCER GENE THERAPY Hernandez-Alcoceba, R., Pihalja, M., Nunez, G., Clarke, M. F. 2001; 8 (4): 298-307


    The conditional expression of lethal genes in tumor cells is a promising gene therapy approach for the treatment of cancer. The identification of promoters that are preferentially active in cancer cells is the starting point for this strategy. The combination of tissue-specific and tumor-specific elements offers the possibility to artificially develop such promoters. We describe the construction and characterization of a hybrid promoter for transcriptional targeting of breast cancer. In many cases, breast cancer cells retain the expression of estrogen receptors, and most solid tumors suffer from hypoxia as a consequence of their aberrant vascularization. Estrogen response elements and hypoxia-responsive elements were combined to activate transcription in cells that present at least one of these characteristics. When a promoter containing these elements is used to control the expression of the pro-apoptotic gene harakiri, the induction of cell death can be activated by estrogens and hypoxia, and inhibited by antiestrogens such as tamoxifen. Finally, we show evidence that these properties are maintained in the context of an adenoviral vector (AdEHhrk). Therefore, infection with this virus preferentially kills estrogen receptor-positive breast cancer cells, or cells growing under hypoxic conditions. We propose the use of this promoter for transcriptional targeting of breast cancer.

    View details for Web of Science ID 000168861600008

    View details for PubMedID 11393283

  • Molecular cloning and characterization of a novel regulator of G-protein signaling from mouse hematopoietic stem cells JOURNAL OF BIOLOGICAL CHEMISTRY Parks, I. K., Klug, C. A., Li, K. J., Jerabek, L., Li, L. H., Nanamori, M., Neubig, R. R., Hood, L., Weissman, I. L., Clarke, M. F. 2001; 276 (2): 915-923


    A novel regulator of G-protein signaling (RGS) has been isolated from a highly purified population of mouse long-term hematopoietic stem cells, and designated RGS18. It has 234 amino acids consisting of a central RGS box and short divergent NH(2) and COOH termini. The calculated molecular weight of RGS18 is 27,610 and the isoelectric point is 8.63. Mouse RGS18 is expressed from a single gene and shows tissue specific distribution. It is most highly expressed in bone marrow followed by fetal liver, spleen, and then lung. In bone marrow, RGS18 level is highest in long-term and short-term hematopoietic stem cells, and is decreased as they differentiate into more committed multiple progenitors. The human RGS18 ortholog has a tissue-specific expression pattern similar to that of mouse RGS18. Purified RGS18 interacts with the alpha subunit of both G(i) and G(q) subfamilies. The results of in vitro GTPase single-turnover assays using Galpha(i) indicated that RGS18 accelerates the intrinsic GTPase activity of Galpha(i). Transient overexpression of RGS18 attenuated inositol phosphates production via angiotensin receptor and transcriptional activation through cAMP-responsive element via M1 muscarinic receptor. This suggests RGS18 can act on G(q)-mediated signaling pathways in vivo.

    View details for Web of Science ID 000166430900009

    View details for PubMedID 11042171

  • A novel, conditionally replicative adenovirus for the treatment of breast cancer that allows controlled replication of E1a-deleted adenoviral vectors HUMAN GENE THERAPY Hernandez-Alcoceba, R., Pihalja, M., Wicha, M. S., Clarke, M. F. 2000; 11 (14): 2009-2024


    The efficiency of gene therapy strategies against cancer is limited by the poor distribution of the vectors in the malignant tissues. To solve this problem, a new generation of tumor-specific, conditionally replicative adenoviruses is being developed. To direct the replication of the virus to breast cancer, we have considered one characteristic present in a great proportion of these cancers, which is the expression of estrogen receptors (ERs). On the basis of the wild-type adenovirus type 5, we have constructed a conditionally replicative adenovirus (Ad5ERE2) in which the E1a and E4 promoters have been replaced by a portion of the pS2 promoter containing two estrogen-responsive elements (EREs). This promoter induces transcriptional activation of the E1a and E4 units in response to estrogens in cells that express the ERs. Ad5ERE2 is able to kill ER(+) human breast cancer cell lines as efficiently as the wild-type virus, but has decreased capacity to affect ER(-) cells. By complementation of the E1a protein in trans, Ad5ERE2 allows restricted replication of a conventional E1a-deleted adenoviral vector. When a virus expressing the proapoptotic gene Bc1-xs (Clarke et al., Proc. Natl. Acad. Sci. U.S.A. 1995;92:11024-11028) is used in combination with Ad5ERE2, the ability of both viruses to induce cell death is dramatically increased, and the effect can be modulated by addition of the antiestrogen tamoxifen.

    View details for Web of Science ID 000089592300005

    View details for PubMedID 11020800

  • A bipartite nuclear localization signal is required for p53 nuclear import regulated by a carboxyl-terminal domain JOURNAL OF BIOLOGICAL CHEMISTRY Liang, S. H., Clarke, M. F. 1999; 274 (46): 32699-32703


    Abnormal p53 cellular localization has been considered to be one of the mechanisms that could inactivate p53 function. To understand the regulation of p53 cellular trafficking, we have previously identified two p53 domains involved in its localization. A basic domain, Lys(305)-Arg(306), is required for p53 nuclear import, and a carboxyl-terminal domain, namely the cytoplasmic sequestration domain (CSD) from residues 326-355, could block the nuclear import of Lys(305) or Arg(306) mutated p53. To characterize further the function of these two domains, we demonstrate in this report that the previously described major nuclear localization signal works together with Lys(305)-Arg(306) to form a bipartite and functional nuclear localization sequence (NLS) for p53 nuclear import. The CSD could block the binding of p53 to the NLS receptor, importin alpha, and reduce the efficiency of p53 nuclear import in MCF-7, H1299, and Saos-2 cells. The blocking effect of the CSD is not due to the enhancement of nuclear export or oligomerization of the p53. These results indicate that the CSD can regulate p53 nuclear import by controlling access of the NLS to importin alpha binding.

    View details for Web of Science ID 000083623000026

    View details for PubMedID 10551826

  • Germ cell tumor: Differentiation of viable tumor, mature teratoma, and necrotic tissue with FDG PET and kinetic modeling RADIOLOGY Sugawara, Y., Zasadny, K. R., Grossman, H. B., Francis, I. R., Clarke, M. F., Wahl, R. L. 1999; 211 (1): 249-256


    To evaluate the feasibility of positron emission tomography (PET) with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) in patients with germ cell tumor (GCT) to monitor treatment and differentiate residual masses after chemotherapy.Twenty-six FDG PET studies were performed in 21 patients with GCT, FDG uptake of tumors was interpreted visually, and the lean standardized uptake value (SUVlean) was determined. Tumor kinetic rate constants (K1, k2, k3) and net rate of FDG phosphorylation (K = [K1.k3]/[k2 + k3]) in tumors were calculated from the dynamic data by means of a three-compartment model, assuming k4 = 0.Viable tumors (n = 10) showed intense FDG uptake and could easily be differentiated visually from mature teratoma (n = 6) and necrosis or scar (n = 10). The SUVlean of residual viable tumors (4.51 +/- 1.34 [mean +/- SD]) was higher than that of mature teratoma (1.38 +/- 0.71) and necrosis or scar (1.05 +/- 0.29) (P < .05). Although neither the visual interpretation nor SUVlean differentiated mature teratoma from necrosis or scar, there were statistically significant differences in the kinetic rate constants K1 and K between mature teratoma and necrosis or scar as follows: K1, 0.113 mL/min/g +/- 0.026 versus 0.036 mL/min/g +/- 0.005 (P < .05); K, 0.005 mL/min/g +/- 0.003 versus 0.0008 mL/min/g +/- 0.0001 (P < .05).FDG PET with kinetic analysis appears to be a promising method for management of disease in patients with GCT after treatment.

    View details for Web of Science ID 000079323200036

    View details for PubMedID 10189480

  • The nuclear import of p53 is determined by the presence of a basic domain and its relative position to the nuclear localization signal ONCOGENE Liang, S. H., Clarke, M. F. 1999; 18 (12): 2163-2166


    It has been reported that Lysine-305 is needed for the nuclear import of the p53 protein (Liang et al., 1998). In the present study, further mutagenesis analyses were carried out between Lys-305 and the major nuclear localization signal (NLS I) of p53. It was found that a single mutation of Arg-306 resulted in the defect of p53 nuclear import. This effect is the same as that of Lys-305 mutation. Other mutations between Arg-306 and NLS I have no effect on the nuclear import of p53. However, deletions of more than two amino acids between this region abolished the transport of p53 into the nucleus. These results indicate that a basic domain other than the well defined NLS is required for the nuclear import of p53. A spacer between this basic domain and NLS I is necessary for the entrance of p53 into the cell nucleus.

    View details for Web of Science ID 000079346200015

    View details for PubMedID 10321742

  • Role of p53 in the regulation of irradiation-induced apoptosis in neuroblastoma cells MOLECULAR GENETICS AND METABOLISM Jasty, R., Lu, J. Y., Irwin, T., Suchard, S., Clarke, M. F., Castle, V. P. 1998; 65 (2): 155-164


    Wild-type p53 plays a crucial role in the control of apoptosis following ionizing radiation (IR); conversely, mutant p53 is associated with IR resistance. Although wild-type p53 is expressed in virtually all neuroblastoma tumors, treatment failures secondary to inadequate local control with radiotherapy are a problem in patients with advanced stage disease. This apparent paradox is the focus of our interest. The Shep-1 neuroblastoma cell line is highly resistant to IR. This cell line contains a wild-type p53 gene and is an ideal model for studying the mechanism of IR resistance in this disease. Following high-dose IR, cell fractionation demonstrated that p53 is induced and targeted to the nucleus. The induced p53 is functional as p53-responsive genes (Waf-1 and MDM-2) are appropriately induced following IR. Intriguingly, overexpression of p53 could reverse the inherent IR resistance of Shep-1 cells. Multiple cell lines expressing variable levels of exogenous temperature-sensitive p53 were generated. Pulse induction of p53 alone did not affect Shep-1 cell viability, while induction of p53, followed by IR, resulted in cell death and DNA fragmentation proportional to the dose of IR and the level of p53 expression. These findings demonstrate that p53 overexpression renders Shep-1 cells IR-sensitive and suggest that large quantities of exogenous p53 can overcome the factors inhibiting p53-mediated, IR-induced apoptosis.

    View details for Web of Science ID 000076744000010

    View details for PubMedID 9787107

  • Cooperation of a single lysine mutation and a C-terminal domain in the cytoplasmic sequestration of the p53 protein JOURNAL OF BIOLOGICAL CHEMISTRY Liang, S. H., Hong, D., Clarke, M. F. 1998; 273 (31): 19817-19821


    Cytoplasmic sequestration of the p53 tumor suppresser protein has been proposed as a mechanism involved in abolishing p53 function. However, the mechanisms regulating p53 subcellular localization remain unclear. In this report, we analyzed the possible existence of cis-acting sequences involved in intracellular trafficking of the p53 protein. To study p53 trafficking, the jellyfish green fluorescent protein (GFP) was fused to the wild-type or mutated p53 proteins for fast and sensitive analysis of protein localization in human MCF-7 breast cancer, RKO colon cancer, and SAOS-2 sarcoma cells. The wild-type p53/GFP fusion protein was localized in the cytoplasm, the nucleus, or both compartments in a subset of the cells. Mutagenesis analysis demonstrated that a single amino acid mutation of Lys-305 (mt p53) caused cytoplasmic sequestration of the p53 protein in the MCF-7 and RKO cells, whereas the fusion protein was distributed in both the cytoplasm and the nucleus of SAOS-2 cells. In SAOS-2 cells, the mutant p53 was a less efficient inducer of p21/CIP1/WAF1 expression. Cytoplasmic sequestration of the mt p53 was dependent upon the C-terminal region (residues 326-355) of the protein. These results indicated the involvement of cis-acting sequences in the regulation of p53 subcellular localization. Lys-305 is needed for nuclear import of p53 protein, and amino acid residues 326-355 can sequester mt p53 in the cytoplasm.

    View details for Web of Science ID 000075125200067

    View details for PubMedID 9677415

  • A method of limited replication for the efficient in vivo delivery of adenovirus to cancer cells HUMAN GENE THERAPY Han, J. S., Qian, D. L., Wicha, M. S., Clarke, M. F. 1998; 9 (8): 1209-1216


    Replication-deficient viral vectors are currently being used in gene transfer strategies to treat cancer cells. Unfortunately, viruses are limited in their ability to diffuse through tissue. This makes it virtually impossible to infect the majority of tumor cells in vivo and results in inadequate gene transfer. This problem can be addressed by allowing limited viral replication. Limited viral replication facilitates greater penetration of virions into tissue and can improve gene transfer. We have developed a strategy of limited viral replication using AdRSVlaclys, a chemically modified E1-deleted adenovirus, to codeliver an exogenous plasmid encoding the adenovirus E1 region. This system allows one round of viral replication. We examined the effect of this limited adenovirus replication in vitro and in vivo. In culture, codelivery of virus and pE1 resulted in a large increase in infected cells when compared with control cells exposed to virus and pUC19. In experiments on nude mice bearing HeLa ascites tumors, intraperitoneal injection of AdRSVlaclys/pE1 resulted in a significantly higher percentage of infected HeLa cells as compared with the PBS controls (p < 0.05) or the AdRSVlaclys/pUC19 controls (p < 0.01). These data demonstrate that the transcomplementation of replication-deficient adenovirus with exogenous E1 DNA leads to limited replication, and this controlled replication enhances gene transfer efficiency of adenovirus in vivo.

    View details for Web of Science ID 000073794800011

    View details for PubMedID 9625260

  • Targeting cancer cell death with a bcl-x(s) adenovirus SPRINGER SEMINARS IN IMMUNOPATHOLOGY Han, J. S., Nunez, G., Wicha, M. S., Clarke, M. F. 1998; 19 (3): 279-288


    Transformation is a complex cellular process that requires several genetic abnormalities. In many cases, one of these abnormalities is an inhibition of PCD, which provides a selective advantage for tumor cells. This has been recently shown in an in vivo model, where overexpression of Bcl-XL, is a crucial step in the progression from hyperplasia to neoplasia and is accompanied by a significant decrease in tumor apoptosis [56]. Frequently, overexpression of a member of the Bcl-2 family results in a block in cell death and appears to nullify many built-in cellular defense mechanisms against cancer. Such a block presents a problem because radiation and chemotherapy, standard cancer treatments, ultimately exert their effect by induction of apoptosis and would also be made less effective. Therefore, to better treat cancer it may be necessary to develop novel methods to overcome the effects of the Bcl-2 family. One way to approach this problem is to target the cause--the molecular machinery that allows a cancer cell to survive. Advances in our understanding of apoptosis has identified the Bcl-2 family as a mediator of most apoptosis pathways, including those initiated by oncogenes, tumor suppressor genes, growth factor withdrawal, and external damaging signals. Therefore, functional inhibition of Bcl-2 family members is lethal to many cancer cells. Using gene transfer technology, we can now deliver genes that accomplish this goal. Further investigation will reveal whether this translates to improved therapy in the future.

    View details for Web of Science ID 000072317400002

    View details for PubMedID 9580270

  • Prevention of fluorodeoxyuridine-induced cytotoxicity and DNA damage in HT29 colon carcinoma cells by conditional expression of wild-type p53 phenotype MOLECULAR PHARMACOLOGY Parsels, L. A., Zellars, R. C., Loney, T. L., Parsels, J. D., Clarke, M. F., MERCHANT, A. K., Lawrence, T. S., Maybaum, J. 1997; 52 (4): 600-605


    We have examined the effects of conditionally expressing wild-type p53 activity in HT29 cells on DNA damage and cytotoxicity caused by exposure to fluorodeoxyuridine (FdUrd). Expression of wild-type p53 phenotype for 24 hr before FdUrd treatment provided HT29 cells with virtually complete protection from cytotoxicity caused by this drug. In addition, wild-type p53 expression also prevented FdUrd-induced DNA double-strand breaks and, unexpectedly, single-strand breaks in parental (mature) DNA. Temporary expression of wild-type p53 activity in the absence of drug treatment caused some loss of clonogenicity, although the magnitude of this cytotoxic effect was small compared with the level of cell kill obtained by treatment with cytotoxic drugs for similar periods of time, indicating that HT29 cells are not highly sensitive to induction of programmed cell death by wild-type p53. Because these observations conflict with previously suggested models for FdUrd-induced damage to parental DNA, we propose an alternative model to explain how incorporation of uracil into nascent DNA might result in single-strand breaks in the opposite (parental) strand and how these breaks might be converted to the double-strand breaks that produce cell death.

    View details for Web of Science ID A1997YA26800007

    View details for PubMedID 9380022

  • Bcl-x(s) enhances adenoviral vector-induced apoptosis in neuroblastoma cells CANCER RESEARCH Dole, M. G., Clarke, M. F., Holman, P., Benedict, M., Lu, J. Y., Jasty, R., EIPERS, P., Thompson, C. B., Rode, C., Bloch, C., Nunez, G., Castle, V. P. 1996; 56 (24): 5734-5740


    bcl-x is a member of the bcl-2 family of genes and by alternative splicing gives rise to two distinct mRNAs: bcl-xL and bcl-xS. We have previously investigated the expression of Bcl-x in neuroblastoma (NB) cell lines and have shown that Bcl-xL is expressed and functions to inhibit chemotherapy-induced apoptosis. However, none of the NB cell lines expressed Bcl-xS. The aim of the present study was to determine the effects of Bcl-xS expression on the viability of NB cells. A panel of NB cell lines (CHP-382, GOTO, SHEP-1, SHSY-5Y, and GI-CA-N) were infected with either a bcl-xS adenovirus (pAdRSV-bcl-xS) or a control virus (pAdRSV-lac-z). NB cells showed loss of viability with both viruses, although the bcl-xS virus was most toxic. Importantly, infection with the bcl-xS adenovirus resulted in rapid loss of cell viability, DNA fragmentation, and morphological features of apoptosis even in NB cells transfected to overexpress Bcl-2 and Bcl-xL. These findings suggest that deregulated expression of Bcl-xS using an adenovirus may provide a novel mechanism for initiating cell death in tumors that express Bcl-2 or Bcl-xL.

    View details for Web of Science ID A1996VX88000036

    View details for PubMedID 8971184

  • Retroviral infection is limited by Brownian motion HUMAN GENE THERAPY CHUCK, A. S., Clarke, M. F., Palsson, B. O. 1996; 7 (13): 1527-1534


    Replication-defective retroviruses are frequently used as gene carriers for gene transfer into target cells. Here we show that the short half-lives of retroviruses limit the distance that they can effectively travel in solution by Brownian motion, and thus the possibility of successful gene transfer. This physiochemical limitation can be overcome, and effective contact between the retroviral gene carrier and the target cell can be obtained, by using net convective flow of retrovirus-containing medium through a layer of target cells. Using model cell lines (NIH-3T3 and CV-1), it was shown that gene transfer rates can be increased by more than an order of magnitude using the same concentration infection medium. High transduction rates could be obtained even in the absence of polycations, such as Polybrene, which heretofore have been required to achieve reasonable transduction rates. This development may play an important role in realizing human gene therapy.

    View details for Web of Science ID A1996WD32200005

    View details for PubMedID 8864753

  • bcl-x(s) gene therapy induces apoptosis of human mammary tumors in nude mice CANCER RESEARCH Ealovega, M. W., McGinnis, P. K., Sumantran, V. N., Clarke, M. F., Wicha, M. S. 1996; 56 (9): 1965-1969


    Bcl-xs is a dominant negative repressor of Bcl-2 and Bcl-xL, both of which inhibit apoptosis. We used a replication-deficient adenoviral vector to transiently overexpress Bcl-xs in MCF-7 human breast cancer cells, which overexpress Bcl-xL. Infection with this vector induced apoptosis in vitro. We then determined the effects of intratumoral injection of bcl-xs adenovirus on solid MCF-7 tumors in nude mice. Tumors injected four times with the bcl-xs adenovirus showed a 50% reduction in size. Using terminal transferase-mediated dUTP-digoxigenin nick end labeling, we observed apoptotic cells at sites of bcl-xs adenoviral injection. These experiments demonstrate the feasibility of using bcl-xs gene therapy to induce apoptosis in human breast tumors.

    View details for Web of Science ID A1996UG75600003

    View details for PubMedID 8616832

  • A RECOMBINANT BCL-X(S) ADENOVIRUS SELECTIVELY INDUCES APOPTOSIS IN CANCER-CELLS BUT NOT IN NORMAL BONE-MARROW CELLS PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Clarke, M. F., Apel, I. J., Benedict, M. A., Eipers, P. G., Sumantran, V., GONZALEZGARCIA, M., Doedens, M., Fukunaga, N., Davidson, B., Dick, J. E., Minn, A. J., Boise, L. H., Thompson, C. B., Wicha, M., Nunez, G. 1995; 92 (24): 11024-11028


    Many cancers overexpress a member of the bcl-2 family of inhibitors of apoptosis. To determine the role of these proteins in maintaining cancer cell viability, an adenovirus vector that expresses bcl-xs, a functional inhibitor of these proteins, was constructed. Even in the absence of an exogenous apoptotic signal such as x-irradiation, this virus specifically and efficiently kills carcinoma cells arising from multiple organs including breast, colon, stomach, and neuroblasts. In contrast, normal hematopoietic progenitor cells and primitive cells capable of repopulating severe combined immunodeficient mice were refractory to killing by the bcl-xs adenovirus. These results suggest that Bcl-2 family members are required for survival of cancer cells derived from solid tissues. The bcl-xs adenovirus vector may prove useful in killing cancer cells contaminating the bone marrow of patients undergoing autologous bone marrow transplantation.

    View details for Web of Science ID A1995TF89100042

    View details for PubMedID 7479929

  • RETROVIRAL-MEDIATED GENE-TRANSFER IN HUMAN BONE-MARROW CELLS GROWN IN CONTINUOUS PERFUSION CULTURE VESSELS BLOOD Eipers, P. G., Krauss, J. C., Palsson, B. O., Emerson, S. G., Todd, R. F., Clarke, M. F. 1995; 86 (10): 3754-3762


    Hematopoietic stem cell gene therapy holds the promise of being able to treat a variety of inherited and acquired diseases of the hematopoietic stem cell. However, to date, genetic modification of the human hematopoietic stem cell has been relatively inefficient. Here, we report the results of using a bioreactor system to expand hematopoietic cells after a brief retrovirus infection using a high titer, replication defective virus encoding for murine CD18. The retrovirus transduced culture continued to produce genetically modified hematopoietic progenitors for up to 6 weeks, the duration of the culture period. Up to one-third of the long-term culture initiating cell (LTC-IC) are genetically modified by the culture conditions. Murine CD18 can be expressed on the cell surface of up to 20% of the mature cells generated by the culture system, suggesting that clinically significant levels of gene transfer may be occurring. These results demonstrate the feasibility of using continuous perfusion bioreactors as a method of efficiently modifying human hematopoietic stem cells.

    View details for Web of Science ID A1995TE58500016

    View details for PubMedID 7579342

  • BCL-X(L) PROTECTS CANCER-CELLS FROM P53-MEDIATED APOPTOSIS ONCOGENE Schott, A. F., Apel, I. J., Nunez, G., Clarke, M. F. 1995; 11 (7): 1389-1394


    Oncogenesis is a process resulting from genetic events which cause loss of growth control or inhibition of appropriate cell death. The Bcl-XL protein is a recently discovered member of the bcl-2 family which has been shown to protect cells from some forms of programmed cell death, but has not yet been implicated in the genesis of human carcinomas. In this report we explore the role of Bcl-XL overexpression in protecting cancer cells from p53-mediated apoptosis. Increased levels of Bcl-XL were found in a subset of primary human breast carcinomas, as well as in the breast cancer line, T47D. T47D cells were then transfected with a temperature-sensitive mutant of the tumor suppressor p53 (p53ts). Although many tumor cell lines undergo apoptosis when p53 is expressed, the T47D transfectants remained viable at temperatures permitting wild-type p53 phenotype. This suggested that endogenous Bcl-XL could protect cancer cells from p53-mediated apoptosis. To test this hypothesis, murine erythroleukemia cells were transfected with bcl-XL and p53ts. While cell lines expressing p53 alone rapidly died, those cells co-expressing Bcl-XL survived. These results demonstrate that Bcl-XL is capable of protecting cells from p53-mediated apoptosis, and suggest a possible mechanism by which tumors expressing Bcl-XL are able to partly overcome the tumor suppressor functions of p53.

    View details for Web of Science ID A1995RY96700021

    View details for PubMedID 7478561



    To better understand the molecular basis of radiation-induced cell death, we studied the role of the bcl-2 oncogene and the p53 tumor suppressor gene in this process. A temperature-sensitive mutant of murine p53 (p53Val-135) and/or bcl-2 was transfected into murine erythroleukemia cells (MEL, DP16-1, which are null in p53). We demonstrate that radiation-induced cell death occurs by both p53-dependent and -independent pathways and overexpression of bcl-2 modulates both pathways. When viability was measured 24 h post-radiation, cells that had been briefly exposed to wtp53 immediately after X-ray irradiation had decreased survival as compared to unirradiated cells expressing wtp53 or X-ray irradiated DP16-1 cells. However, at later times X-ray irradiated parental DP16-1 cells also had decreased survival compared to the unirradiated control. This decrease in survival began 48 h following radiation. Bcl-2 prevented radiation-induced cell death in DP16-1 cells expressing wtp53 and delayed radiation-induced cell death in DP16-1 cells without wtp53. X-ray irradiated cells expressing wtp53 displayed microscopic and biochemical characteristics consistent with cell death due to apoptosis. DP16-1 cells which were untransfected or co-transfected with wtp53 and bcl-2 displayed characteristics of cells undergoing necrosis. These results suggest that radiation-induced cell death occurs by both p53-dependent and p53-independent pathways. The p53-dependent pathway results in cell death via apoptosis and occurs approximately 24 h following radiation. The p53-independent pathway does not appear to involve apoptosis and occurs at a later time, starting 48 h after X-ray exposure. Thus, bcl-2 protects cells from p53-dependent radiation-induced apoptotic cell death and attenuates p53-independent radiation-induced cell death.

    View details for Web of Science ID A1995RP92400014

    View details for PubMedID 7634401

  • OVEREXPRESSION OF BCL-X(S), SENSITIZES MCF-7 CELLS TO CHEMOTHERAPY-INDUCED APOPTOSIS CANCER RESEARCH Sumantran, V. N., Ealovega, M. W., Nunez, G., Clarke, M. F., Wicha, M. S. 1995; 55 (12): 2507-2510


    Resistance to apoptosis plays an important role in tumors that are refractory to chemotherapy. We report that Bcl-XL, which functions like Bcl-2 to inhibit apoptosis, is highly expressed in MCF-7 human breast carcinoma cells. We used Bcl-XS, a dominant negative inhibitor of Bcl-2 and Bcl-XL, to demonstrate the role of these genes in modulating chemotherapy-induced apoptosis. Bcl-XS overexpressed in MCF-7 cells by stable transfection does not affect viability by itself but induces a marked increase in chemosensitivity to VP-16 or taxol. Using an ELISA assay which quantitates DNA damage, we demonstrate that this sensitization is due to apoptosis, suggesting the therapeutic utility of targeting this pathway.

    View details for Web of Science ID A1995RC93600007

    View details for PubMedID 7780958

  • In vitro expansion of hematopoietic cells for clinical application. Cancer treatment and research Emerson, S. G., Palsson, B. O., Clarke, M. F., Silver, S. M., Adams, P. T., Koller, M. R., Van Zant, G., Rummel, S., Armstrong, R. D., MALUTA, J. 1995; 76: 215-223

    View details for PubMedID 7577336

  • The Bcl-2 family of proteins: regulators of cell death and survival. Trends in cell biology Nuñez, G., Clarke, M. F. 1994; 4 (11): 399-403


    The Bcl-2 protein inhibits apoptosis induced by a variety of signals, in a range of cell types and in diverse organisms, and it is implicated in both normal development and oncogenesis. Despite this central role, the mechanism of action of Bcl-2 is not yet clear. Recent studies have uncovered a number of Bcl-2-related gene products that regulate apoptosis either negatively or positively, and Bcl-2 forms heterodimers with at least one of these proteins, Bax. This article discusses the role of the Bcl-2 family of proteins in the light of these findings.

    View details for PubMedID 14731816



    Programmed cell death, or apoptosis, may play an important role in the regulation of hematopoiesis. The tumor suppressor protein p53 has been identified as a key regulator of apoptosis in both normal and malignant hematopoietic cells. Modulation of p53 function is of interest, therefore, both in understanding the control of apoptosis and as a potential therapeutic intervention. In this study we describe the effect on murine erythroleukemia cells, transfected with a temperature-sensitive mutant p53, of exposure to the differentiating agent dimethylsulfoxide (DMSO). Rather than terminally differentiating, these cells are induced to undergo apoptosis. Interestingly, exposure to DMSO leads to an alteration of the protein conformation of the p53 mutant to one recognized by a wild-type specific monoclonal antibody. This is accompanied by a translocation of the p53 protein from the cytoplasm to the nucleus. These results suggest that the activity of some mutant p53 proteins can be functionally modified by exogenous compounds.

    View details for Web of Science ID A1994PC47400008

    View details for PubMedID 8065163



    We have studied the ability of c-myc and bcl-2 oncogenes to modulate p53 function. Our studies show that coincident expression of human Bcl-2 protein with p53 prolongs survival of murine erythroleukemia cells. This effect was associated with a loss of the G1 specificity of p53-mediated cell cycle arrest. Furthermore, we found that the c-myc and bcl-2 genes cooperate to inhibit p53 functions. Coexpression of bcl-2 and c-myc can totally overcome p53-induced apoptosis and cell cycle arrest by altering the subcellular trafficking of p53 during the cell cycle: the p53 remains in the cytoplasm of the cotransfected cells during a critical period in G1. This finding suggests a mechanism by which normal hematopoietic progenitors can survive and proliferate despite p53 expression and by which the inappropriate expression of bcl-2 and c-myc can cooperate in transformation.

    View details for Web of Science ID A1994NT46100030

    View details for PubMedID 8016082



    A temperature-sensitive mutant of murine p53 (p53Val-135) was transfected by electroporation into murine erythroleukemia cells (DP16-1) lacking endogenous expression of p53. While the transfected cells grew normally in the presence of mutant p53 (37.5 degrees C), wild-type p53 (32.5 degrees C) was associated with a rapid loss of cell viability. Genomic DNA extracted at 32.5 degrees C was seen to be fragmented into a characteristic ladder consistent with cell death due to apoptosis. Following synchronization by density arrest, transfected cells released into G1 at 32.5 degrees C were found to lose viability more rapidly than did randomly growing cultures. Following release into G1, cells became irreversibly committed to cell death after 4 h at 32.5 degrees C. Commitment to cell death correlated with the first appearance of fragmented DNA. Synchronized cells allowed to pass out of G1 prior to being placed at 32.5 degrees C continued to cycle until subsequently arrested in G1; loss of viability occurred following G1 arrest. In contrast to cells in G1, cells cultured at 32.5 degrees C for prolonged periods during S phase and G2/M, and then returned to 37.5 degrees C, did not become committed to cell death. G1 arrest at 37.5 degrees C, utilizing either mimosine or isoleucine deprivation, does not lead to rapid cell death. Upon transfer to 32.5 degrees C, these G1 synchronized cell populations quickly lost viability. Cells that were kept density arrested at 32.5 degrees C (G0) lost viability at a much slower rate than did cells released into G1. Taken together, these results indicate that wild-type p53 induces cell death in murine erythroleukemia cells and that this effect occurs predominantly in the G1 phase of actively cycling cells.

    View details for Web of Science ID A1993KD78500072

    View details for PubMedID 8417361

  • C-MYB EFFECTS ON KINETIC EVENTS DURING MEL CELL-DIFFERENTIATION ONCOGENE Danish, R., ELAWAR, O., Weber, B. L., Langmore, J., Turka, L. A., Ryan, J. J., Clarke, M. F. 1992; 7 (5): 901-907


    During dimethylsulfoxide (DMSO)-induced differentiation of Friend mouse erythroleukemia (MEL) cells there is a biphasic fall in c-myb mRNA levels. We have previously shown that constitutive expression of c-myb blocks differentiation. To delineate more accurately the point at which Myb blocks differentiation, MEL cells were transfected with a human c-myb construct under the control of the beta-globin promoter and enhancers. In concert with endogenous DMSO-induced globin transcription during MEL cell differentiation, the beta-globin c-myb transcription unit of the transfected plasmid is activated after 3-5 days of culture in media containing DMSO. Here we describe c-myb-transformed MEL clones which undergo delayed expression of the exogenous c-myb following 3-5 days of culture in DMSO. In contrast to wild-type MEL cells, both clones failed to display phenotypic markers of differentiation and continued to proliferate for up to 10 days of culture. These data suggest that the late fall in c-myb levels may be required in order for differentiation to occur. Additionally, we suggest that constitutive expression of c-myb does not block early commitment events such as activation of histone Hl', subsequent chromatin condensation, and alteration of proliferation-related gene expression. Taken together, these results show that c-myb acts very late in the process of differentiation.

    View details for Web of Science ID A1992HP64200009

    View details for PubMedID 1533276



    High-level expression of the c-sis oncogene, which encodes the beta chain of platelet-derived growth factor, transforms immortalized rodent fibroblasts in vitro to a malignant phenotype. c-sis gene expression has been demonstrated in a variety of human tumors, although generally at levels much lower than those shown to transform cells in vitro. We examined the effect of lower levels of c-sis expression on the phenotype of NIH 3T3 fibroblasts. Clones with various levels of c-sis expression were generated by transfecting NIH 3T3 cells with a plasmid that expressed the human c-sis cDNA and the TN5 neomycin-resistance gene. G418-resistant clones, which expressed the c-sis cDNA, were selected and characterized. Alterations in the phenotype of the clones that expressed c-sis ranged from increased growth in soft agar to malignant tumor formation in nude and syngeneic mice. Increased levels of c-sis cDNA expression correlated with the acquisition of features of transformation in a dose-dependent manner and altered the cellular phenotype in a manner consistent with the progression of cells towards malignancy. These data support a model in which low levels of sis gene expression in tumors contribute to the acquisition of some features of transformation but require complementation by other genes or factors to produce a fully malignant phenotype.

    View details for Web of Science ID A1992JB22100010

    View details for PubMedID 1323300



    The stromal cell layer is believed to play an important role in long-term human bone marrow cultures (LTHBMCs). At present, neither the role that the stromal cell extra-cellular matrix (ECM) plays in influencing stroma behavior is well understood nor are the effects of stroma aging. Rapid medium exchanged LTHBMCs were established on surfaces precoated with human natural fibronectin and type 1 rat tail collagen. Although initial adhesion of hematopoietic cells was improved by the presence of both ECMs, the overall progenitor and nonadherent cell productivity was not improved nor did the stroma grow to confluency faster. Thus, the ECMs used did not significantly influence the cell productivity of LTHBMCs. To examine the influence of stromal cell layer aging, conditioned medium was obtained from the first two weeks of LTHBMCs that was subsequently concentrated and used as a medium supplement in a second set of slowly exchanged LTHBMCs. The presence of the concentrated conditioned medium (conCM) enhanced the production of nonadherent cells three-fold compared with control over an eight week culture period. Control cultures that were exposed to conCM after 4 weeks in culture significantly improved their cell productivity during the latter 4 weeks of culture compared with control. The productivity of cultures exposed to conCM for 4 weeks dropped significantly when unsupplemented medium was used for the latter 4 weeks of culture. Interestingly, phytohemagglutin-stimulated leukocyte-conditioned medium stimulated LTHMBCs in a similar fashion, as did conditioned medium from early LTHBMCs. Taken together, these results strongly suggest that the stromal cell layer does produce important factors for active hematopoiesis during its growth to confluence.

    View details for Web of Science ID A1992KX78000004

    View details for PubMedID 1369237



    The in vitro culture of mouse bone marrow (Dexter cultures) has allowed a detailed analysis of the biology of murine hematopoiesis. However, attempts to develop stable long-term human bone marrow cultures have been unsuccessful. Available culture systems all have finite and relatively short lifetimes. The reasons for the limited longevity are unknown. Utilizing computer-assisted integration techniques, we have theoretically simulated culture cell production kinetics to help identify factors that may be responsible for culture decay, as well as to suggest possible means of improving culture longevity. The simulation demonstrates that removal of stem cells is a possible mechanism leading to culture decline. Under the standard bone marrow culture conditions, even with a high stem cell renewal rate, the cultures appear to be destined to fail. Thus, the development of proper sampling techniques or improved stem cell retention may be critical to obtain successful long-term cultures.

    View details for Web of Science ID A1992GX27300015

    View details for PubMedID 1577098



    We studied the effect of the combination of rapid culture medium exchange with the addition of the human hematopoietic growth factors interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and erythropoietin (Epo) on the proliferation and differentiation of human long-term bone marrow cultures (LTBMCs). Individually and in combinations, IL-3, GM-CSF, and Epo were added to the culture medium of LTBMCs that were maintained with 50% medium volume exchange per day. The combination of IL-3 + GM-CSF + Epo generated the most prolific cultures with an order of magnitude increase in nonadherent cell production from weeks 2 through 8 in culture as compared with unsupplemented controls. Under these conditions, the cultures produced as many cells as were inoculated every 2 weeks and led to a greater than 2.5-fold expansion in terms of the number of nonadherent cells produced over a 6- to 8-week period. Furthermore, the LTBMCs produced nonadherent colony-forming unit-GM (CFU-GM) for more than 20 weeks. The rapid medium exchange combined with the addition of human hematopoietic CSFs significantly enhances the proliferation and differentiation of LTBMCs. These results indicate that addition of combinations of hematopoietic CSFs, together with a rapid medium exchange rate, can provide culture conditions that are suitable for the expansion of the progenitor cell pool and perhaps for the increased survival of hematopoietic stem cells in culture. Although these culture conditions still fall short of full reconstitution of functional human bone marrow, they provide an improved approach to hematopoietic cell culture that may permit the expansion and manipulation of progenitor cells in vitro.

    View details for Web of Science ID A1991GV58400008

    View details for PubMedID 1742483



    Biotinylated granulocyte/macrophage colony-stimulating factor (GM-CSF) analogues with different linkage chemistries and levels of conjugated biotin were synthesized by reacting recombinant human GM-CSF with sulfosuccinimidyl 6-biotinamidohexanoate or biotin hydrazide/1-[3-(dimethylamino)-propyl]-3-ethylcarbodiimide. These chemically reactive forms of biotin produced derivatives biotinylated at amine or carboxyl groups, respectively. Amine-derivatized analogues of 1.2 and 3.8 mol of biotin/mol of protein (N1-bGM-CSF and N4-bGM-CSF) and a carboxyl-modified analogue of 4.6 mol of biotin/mol of protein (C5-bGM-CSF) were synthesized. These analogues were compared to determine the effect of biotinylation on biological activity and GM-CSF receptor binding characteristics. The biotinylated proteins migrated with the same molecular weight as the native, unmodified protein as determined by SDS-PAGE and could be detected by Western blotting with alkaline phosphatase conjugated streptavidin, thus demonstrating the biotin linkage. All three analogues retained full agonist activity relative to the native protein (EC50 = 10-15 pM) when assayed for the stimulation of human bone marrow progenitor cell growth. Cell surface GM-CSF receptor binding was characterized by the binding of the analogues to human neutrophils, with detection by fluorescein-conjugated avidin and fluorescence-activated cell sorting. The N-bGM-CSFs demonstrated GM-CSF receptor specific binding that was displaceable by excess underivatized protein, with the detected fluorescence signal decreasing with increasing biotin to protein molar ratio. In contrast, C5-bGM-CSF binding above background fluorescence could not be detected using this system, suggesting that this derivative could bind to and activate the receptor, but not simultaneously bind fluorescein-conjugated avidin. The amine-derivatized biotinylated GM-CSF analogues retained biological activity, could specifically label cell surface receptors, and may be useful nonradioactive probes with which to study GM-CSF receptor cytochemistry and receptor modulation by flow cytometry.

    View details for Web of Science ID A1991GR93700016

    View details for PubMedID 1839606



    The successful ex vivo reconstruction of human bone marrow is an extraordinarily important basic scientific and clinical goal. Fundamentally, the system is the paradigm of a complex interactive tissue, in which the proliferation and regulated differentiation of one parenchymal cell type (the hematopoietic stem cell) is governed by the surrounding stromal cells. Understanding and reproducing the molecular interactions between bone marrow stromal cells and stem cells in tissue culture models is therefore the critical step in successful bone marrow tissue culture. Clinically, successful reconstruction of human bone marrow would permit the controlled production of mature blood cells for transfusion therapy, and immature bone marrow stem cells for bone marrow transplantation. In approaching the bone marrow culture system, we recognize the critical role that hematopoietic growth factors (HGFs) play in hematopoiesis. Since stromal cells in traditional human bone marrow cultures produce little HGFs, we have begun by asking whether local supplementation of hematopoietic growth factors via genetically engineered stromal cells might augment hematopoiesis in liquid cultures. The results indicate that locally produced GM-CSF and IL-3 do augment hematopoiesis for several weeks in culture. In combination with geometric and dynamic approaches to reconstructing physiological bone marrow microenvironments, we believe that this approach has promise for reconstructing human bone marrow ex vivo, thereby permitting its application to a variety of basic and clinical problems.

    View details for Web of Science ID A1991FC72500007

    View details for PubMedID 2066377



    The metabolic and secretory characteristics of NIH-3T3 fibroblasts transfected with a cDNA encoding human granulocyte-macrophage colony stimulating factor (GM-CSF) were examined as a function of the culture medium exchange schedule. The rates of glucose and glutamine consumption and of lactate and ammonia production were measured over exchange schedules ranging from complete medium replacement weekly (1/week) to complete medium replacement daily (7/week). All measured metabolic rates increased with increased medium exchange rates and accelerated sharply between exchange rates of 3.5/week and 7/week. The lactate/glucose and ammonia/glutamine yield coefficients, however, remained invariant at about 1.9 and 1.0 mol/mol, respectively, under all medium perfusion conditions. A shift-up in medium perfusion rates from 3.5/week to 7/week resulted in increased metabolic rates that resembled those observed in the cultures that were exchanged at the 7/week rate throughout, showing that the metabolic rates could be directly controlled by the perfusion rate. Differential regulation of medium versus serum perfusion demonstrated that increased NIH-3T3 cell metabolism was directly proportional to the serum flux to which the cells were exposed. Thus a limiting serum component is responsible for the altered metabolic and growth rates. The GM-CSF production by the transfected 3T3 cells was stable but exhibited substantial transient increases during periods of cell proliferation, demonstrating that the secretion of transfected gene products can be highly modulated even when the cDNA is driven from a constitutive promoter. These studies show that the metabolic and secretory behavior of genetically engineered cells is influenced by the medium exchange schedule.

    View details for Web of Science ID A1991EY27300001

    View details for PubMedID 1366977



    C-myb, the normal cellular homolog of the retroviral transforming gene v-myb, encodes a nuclear, transcriptional regulatory protein (p75c-myb). C-myb is involved in regulating normal human hematopoiesis, and inhibits dimethyl sulfoxide-induced differentiation of Friend murine erythroleukemia (F-MEL) cells. An alternately spliced c-myb mRNA encodes a truncated version of p75c-myb (mbm2) that includes the DNA binding region and nuclear localization signal present in the c-myb protein, but does not contain the transcriptional regulatory regions. Constitutive expression of mbm2, in contrast to c-myb, here resulted in enhanced differentiation of F-MEL cells. These data suggest that the c-myb protooncogene encodes alternately spliced mRNA species with opposing effects on differentiation.

    View details for Web of Science ID A1990DY35100036

    View details for PubMedID 2205003

  • ALTERNATIVE SPLICING OF THE HUMAN C-MYB GENE ONCOGENE Westin, E. H., Gorse, K. M., Clarke, M. F. 1990; 5 (8): 1117-1124


    Two cDNA clones of the human c-myb gene have been isolated from a CCRF-CEM leukemia cell cDNA library and sequenced in their entirety. These sequences, when compared with those previously reported for the human c-myb gene, reveal an alternative splicing process that generates at least four forms of the c-myb message. Three of these forms co-migrate on Northern blots and are co-expressed in several human hematopoietic cell types. Data on sequence comparisons with mouse and chicken homologues of c-myb coupled with oligonucleotide hybridization to genomic clones of the human c-myb gene indicate that this alternative splicing process utilizes three closely spaced splice donor sites and two unique exons present between viral defined exons 5 and 6. In one clone, the alternative splicing would generate a predicted myb protein with a three amino acid deletion in the region involved in transcription activation. In the other clone, incorporation of a new exon leads to introduction of a translation stop codon leading to loss of the entire carboxy terminus of the protein. This includes loss of a portion of the region involved in transcription activation as well as a separate highly conserved domain. The effect of these changes on protein function is currently unknown.

    View details for Web of Science ID A1990DX36100002

    View details for PubMedID 2202948


    View details for Web of Science ID A1989T821800013

    View details for PubMedID 2648086



    A full-length human c-myb cDNA clone has been isolated from a CCRF-CEM leukemia cell cDNA library. The plasmid vector contains simian virus 40-derived promotor, splice, and polyadenylation sequences as well as a transcription unit for a dihydrofolate reductase cDNA. We have introduced this construct into Friend erythroleukemia (F-MEL) cells and have isolated a number of clones which contain intact and transcriptionally active human c-myb sequences. F-MEL clones expressing the highest levels of the human c-myb mRNA differentiate poorly in response to dimethyl sulfoxide. Two clones which initially expressed low levels of human c-myb transcripts and which differentiated normally were subsequently inhibited in their ability to differentiate when grown in successively higher concentrations of methotrexate, due to amplification and enhanced expression of plasmid sequences. The inhibitory effect on F-MEL differentiation appeared to be independent of the early decline in c-myc transcripts which were normally regulated in all cases examined. Our results indicate that constitutive expression of a nontruncated human c-myb cDNA can exert profound effects on erythroid differentiation and argue for a causal role of c-myb in the F-MEL differentiation process.

    View details for Web of Science ID A1988L925300043

    View details for PubMedID 2832742



    A cDNA library was constructed from the HUT102 cell line established from a patient with adult T-cell leukemia/lymphoma and screened for cDNA clones that contain (i) cellular sequences abundantly expressed in HUT102 cells and not in the virus-negative T-cell line HUT78, and (ii) viral long terminal repeat (LTR) sequences either in the 5' end or in the 3' end. One such cDNA clone, KT1, was isolated and its nucleotide sequence was determined. It contains three regions: a KpnI repeat, a unique cellular region (UCR), and the U3 + R sequence of the human T-lymphotropic virus type I LTR. The arrangement of this clone suggests that its RNA transcript was activated by provirus integration in cis, possibly by the activity of a downstream provirus enhancer. Analysis of HUT102 DNA shows that one allele of the KT1 UCR is rearranged. The expression of the KT1 UCR is unique to HUT102. These data are consistent with the idea that the human T-lymphotropic virus type I LTR contains an enhancer which can activate upstream sequences in cis. The possible significance of this finding is discussed.

    View details for Web of Science ID A1986A778300041

    View details for PubMedID 3007468

  • Sequence-specific interaction of histones with the simian virus 40 enhancer region in vitro. journal of biological chemistry Clarke, M. F., Fitzgerald, P. C., Brubaker, J. M., Simpson, R. T. 1985; 260 (23): 12394-12397


    DNA fragments containing either one or both of the 72-base pair (bp) elements which constitute the SV40 enhancer and the three adjacent 21-bp repeats were associated with histone octomers from chicken erythrocytes in vitro. Both fragments formed complexes with electrophoretic mobilities of nucleosomes containing the appropriate length of DNA. Analysis of DNase I cutting of uniquely end-labeled complexes suggests that the fragment containing a single 72-bp element forms a positioned core particle. Control experiments show that positioning is not due to the 21-bp repeats or to end effects. The fragment with a tandem repeat of the 72-bp element also does not associate randomly with histones. The data are consistent with formation of a core particle on one or the other of the repeated enhancer sequences. We discuss possible functional consequences of such nucleosome positioning.

    View details for PubMedID 2995375

  • DNA METHYLATION AND EXPRESSION OF HLA-DR-ALPHA MOLECULAR AND CELLULAR BIOLOGY Reitz, M. S., Mann, D. L., Eiden, M., Trainor, C. D., Clarke, M. F. 1984; 4 (5): 890-897


    B-cell lines established from two individuals with T-cell acute lymphocytic leukemia (T-ALL) express HLA-DR antigens, whereas the isogenic T-cells do not. The lack of expression correlates with a lack of detectable HLA-DR mRNA. All of the DR alpha DNA sequences detected by a cloned DR alpha cDNA probe are contained in a BglII fragment which varies slightly in size (4.0 to 4.8 kilobases) from one individual to another. In DNA from the T-cells not expressing DR alpha mRNA, all of the potential HpaII sites within the BglII fragment appeared to be methylated. In contrast, at least some of these sites were not methylated in DNA from the B-cells expressing high levels of DR alpha mRNA. Treatment of these T-cells with 5-azacytidine resulted in the induction of DR surface antigen expression, the appearance of DR alpha mRNA, and the partial demethylation of the DR alpha DNA sequences. T-cell lines established from human T-cell leukemia-lymphoma virus associated T-cell neoplasias, in contrast to the T-cell acute lymphocytic leukemia cell lines, expressed both DR antigens and DR alpha mRNA; the HpaII sites within the BglII fragment of DR alpha DNA of these human T-cell leukemia-lymphoma virus-positive T-cell lines were in all cases at least partially unmethylated. Uncultured peripheral blood T-cells from human T-cell leukemia-lymphoma virus-infected individuals expressed DR antigens at a low level, and the DR alpha locus was partially unmethylated. After 48 h in culture, DR antigen expression was substantially increased, but no significant changes were observed in methylation of the DR alpha locus or in the amount of DR mRNA which was present. This suggests that expression of DR antigens also can be modulated post-transcriptionally.

    View details for Web of Science ID A1984SP90200011

    View details for PubMedID 6328275



    Leukemic peripheral blood lymphocytes from individuals infected with the human T-cell leukemia/lymphoma virus (HTLV) were found to express little or no viral RNA before being put into tissue culture. Within 24-48 hr, viral RNA expression increased at least four- to eightfold. Established HTLV-infected cell lines constitutively express viral RNA. Southern blots of DNA from HTLV-infected cells digested with the methylation-sensitive restriction enzyme HpaII showed that the proviral DNA was methylated in all of the uncultured peripheral blood cells tested. In contrast, no proviral methylation was detected in any of the cell lines examined, suggesting a functional correlation between methylation and viral RNA expression. However, DNA from HTLV-infected lymphocytes cultured for 48 hr (by which time increases in viral RNA expression are evident) did not differ detectably with respect to proviral DNA methylation from uncultured cells, suggesting that the increase in viral RNA expression after short-term culture is mediated by mechanisms independent of changes in DNA methylation.

    View details for Web of Science ID A1984SV56900010

    View details for PubMedID 6328756



    The nucleotide sequence of a transforming human c-sis complementary DNA shows an open reading frame 723 base pairs in length located downstream from an in-phase terminator thymine-guanine-adenine codon. Sequences within this region were identical to those previously determined for the exons of the normal human c-sis gene. Thus, the predicted transforming product, a protein of 27,281 daltons, may be the actual precursor for normal human platelet-derived growth factor chain A.

    View details for Web of Science ID A1984TC73000037

    View details for PubMedID 6740330



    We have previously shown that two human T-cell lines (HSB and 8402) derived from patients with childhood T-cell ALL (T-ALL) do not synthesize detectable mRNA for HLA-DR alpha. The DR alpha genes in both cell lines are hypermethylated relative to the same genes in T-cell lines infected with human T-cell leukemia virus (HTLV) and derived from patients with adult T-cell leukemia/lymphoma (ATL). These latter cell lines do express HLA-DR alpha-mRNA, as well as HLA-DR surface antigens. We report here that the genes for HLA class I antigens are also highly methylated in the T-ALL T-cell lines relative to the same genes in the ATL T-cell lines, normal peripheral blood T cells, and autologous normal B-cell lines. In spite of substantial differences in the extent of methylation of class I-related genes, no obvious differences exist among these cell types in their levels of expression of HLA-A and -B antigens. The data clearly indicate, however, that the class I and class II components of the major histocompatibility complex are unusually hypermethylated in several T-ALL-derived cell lines, while ATL T-cell lines do not substantially differ in this respect from normal peripheral blood T-cells.

    View details for Web of Science ID A1984TY56600006

    View details for PubMedID 6096637

  • TRANSFORMATION OF NIH 3T3-CELLS BY A HUMAN C-SIS CDNA CLONE NATURE Clarke, M. F., Westin, E., Schmidt, D., Josephs, S. F., Ratner, L., WONGSTAAL, F., Gallo, R. C., Reitz, M. S. 1984; 308 (5958): 464-467


    The mechanism of leukaemogenic transformation by human T-cell leukaemia/lymphoma virus (HTLV), a retrovirus implicated in the aetiology of certain adult T-cell leukaemias and lymphomas, is unknown but is conceivably associated with the expression of the cellular analogues of retroviral oncogenes. The HUT-102 cell line, derived from a cutaneous T-cell lymphoma and infected with HTLV, expresses several cellular oncogenes. It is unusual among haemopoietic cell lines in that one of these is c-sis, the gene from which the oncogene v-sis of the simian sarcoma virus was derived, and perhaps the gene for platelet-derived growth factor (PDGF). To explore the possible role of c-sis expression in HTLV-induced disease, we have obtained cDNA clones of c-sis from HUT-102 cells. Here we describe two such clones and report that one of them transforms NIH-3T3 cells. This is the first example of transformation of NIH-3T3 cells by a human onc gene other than c-ras or Blym, as well as the first demonstration of transformation by a human cDNA clone.

    View details for Web of Science ID A1984SJ97500057

    View details for PubMedID 6323994



    Cell lines were established from the peripheral blood of two patients with adult T cell leukemia. In contrast to our previous experience, where all such lines expressed T cell markers, these two cell lines expressed B cell antigens and Ig light chains (kappa on CF-2, lambda on HS). Human T cell lymphoma proviral (HTLV) sequences were demonstrated in both cell lines. Since only a portion of the cells in culture expressed Ig light chains, experiments were carried out to exclude the possibility that the cultures were not a mixture of B and T or non-B cells. Cells that expressed kappa- or lambda-light chains were separated by cell sorting from kappa- or lambda-negative cells and replaced in culture. Light chain negative cells reexpressed light chains after time in culture. After 5-azacytidine treatment of the cell lines, all cells expressed Ig light chains. These studies show that the human retrovirus HTLV, which has been demonstrated to be associated with certain T cell malignancies, can infect B cells or B cell precursors.

    View details for Web of Science ID A1984SY22400007

    View details for PubMedID 6330177

  • Presence of HTLV in a subset of T cells from an infected patient: some immunochemical properties of the infected cells. Haematology and blood transfusion Reitz, M. S., Mann, D., Clarke, M. F., Kalyanaraman, V. S., Robert-Guroff, M., Popovic, M., Gallo, R. C. 1983; 28: 459-461

    View details for PubMedID 6602749

  • HOMOLOGY OF HUMAN T-CELL LEUKEMIA-VIRUS ENVELOPE GENE WITH CLASS-I HLA-GENE NATURE Clarke, M. F., Gelmann, E. P., Reitz, M. S. 1983; 305 (5929): 60-62


    Human T-cell leukaemia virus (HTLV), first isolated in the United States from a patient with cutaneous T-cell lymphoma, is a unique horizontally transmitted retrovirus which is highly associated with certain adult T-cell malignancies. Also, HTLV can be transmitted in vitro to cord blood T-lymphocytes. In the accompanying paper it was shown that all T cells producing HTLV, whether cultured from infected persons or infected in vitro, bind a monoclonal antibody (4D12) which recognizes an epitope shared by certain cross-reactive class I major histocompatibility antigens. This antigen may account for the extra HLA-A and -B specificities detected in HTLV-infected cells using alloantisera. Because of the unusual findings of apparently inappropriate HLA antigens in HTLV infected cells, we had previously looked for rearrangement of class I-related genes in HTLV infected cells but failed to find any. Here, using molecular clones of HTLV and human major histocompatibility antigen DNA, we have shown homology between the envelope gene region of HTLV and the region of an HLA-B locus gene which codes for the extracellular portion of a class I histocompatibility antigen.

    View details for Web of Science ID A1983RE64300046

    View details for PubMedID 6888550



    We have examined the respiratory burst and arachidonic acid oxygenation that accompany phagocytosis in macrophages. Guinea pig alveolar macrophages were stimulated with opsonized zymosan in the presence of inhibitors of arachidonic acid metabolism: ASA, indomethacin, and ETYA, ASA, at concentrations as high as 60 micrograms/ml, had no effect on either oxygen consumption or superoxide ion formation. Indomethacin (4 x 10(-4) M) and ETYA (2 x 10(-5) M) did inhibit oxygen utilization and superoxide production. However, no indomethacin or ETYA inhibition of oxygen utilization was detected in the presence of 1 mM KCN, suggesting that the inhibitable portion of the respiratory burst observed with indomethacin or ETYA was dependent on mitochondrial respiration. Further study with ETYA showed that the inhibitor at 2 x 10(-5) M had little effect on uptake of 125I-labeled zymosan but did abolish the conversion of 14C-arachidonic acid to a compound that co-migrated with authentic 12-HETE on silica gel plates. Lower concentrations of ETYA (5 x 10(-6) M), which had no effect on the respiratory burst of phagocytosing alveolar macrophages, also inhibited arachidonic acid metabolism. We conclude therefore that the inhibition of oxygen consumption and superoxide production by ETYA at 2 x 10(-5) M is unrelated to inhibition of arachidonic acid metabolism. Furthermore, the oxygenation of arachidonic acid requires little of the oxygen consumed by phagocytosing alveolar macrophages.

    View details for Web of Science ID A1982NS41700015

    View details for PubMedID 6281348