Dr. Edwin Chang obtained his PhD (1992) at McGill University from the Department of Medicine, Division of Experimental Medicine. From 1993 onwards, he began work at Geron Corporation (Menlo Park, California) in which he studied the mechanism of cellular immortalization as well as cellular aging and applied his findings in the search for therapies against both cardiovascular diseases and cancer. In 2002, he joined Stanford University where he initially utilized his experience from Geron Corporation to research cardiovascular and endothelial progenitor cell function. In 2009, he became part of the Molecular Imaging Program at Stanford (MIPS) where he explored the applicability of various modalities (PET, BLI, CT, MRI, US) for many projects related to cancer and to vascular function. In 2012, he became a member of the Canary Center at Stanford University where he has leveraged his experience in cell and preclinical studies to develop imaging modalities to track therapeutic responses against cancer as well as detecting early stage cancers. Currently, he is exploring not only diagnostics against cancers but therapeutics as well. As a result, Dr. Chang has explored the relevance of medicinal compounds from the Ayurvedic medical tradition, in particular Withaferin A from the winter cherry plant, in stopping cancers such as glioblastomas. He has also examined the cooperativity of Withaferin A with other interventions that are known to inhibit gliomas such as combination therapies of Withaferin A with temozolomide, with other ginsenosides and with alternating electric fields (known as tumor treating fields or TTFields).
Current Role at Stanford
Lab Manager and Lab Scientist at Canary Center at Stanford
Honors & Awards
Canadian Heart and Stroke Foundation Post-doctoral research fellowship, McMaster University/ Geron Corporation (1992-1995)
First prize at Ninth Annual Student Research Seminar, McGill University (1989)
Canadian Medical Research Council Graduate Scholarship, University of British Columbia (1984-1986)
Gordon Roy Findley Chemistry Award, Brock University (1983-1984)
NSERC Summer Undergraduate Scholarship, Brock University (1982-1984)
Scholler In-House Scholarship for scholastic excellence, Brock University (1984)
Scholler In-House Scholarship for scholastic excellence, Brock University (1983)
Scholler In-House Scholarship for scholastic excellence, Brock University (1982)
Gail Thompson Award for English Essay Composition, Sir Winston Churchill Secondary School (1979)
Education & Certifications
PhD, McGill University, School of Medicine, Montreal, PQ, Canada, Experimental Medicine (1991)
MSc, University of British Columbia, Vancouver, B.C., Canada, Biochemistry (1984)
BSc, Brock University, St. Catharines, ON, Canada, Biology/Chemistry (1986)
Edwin Chang. "United States Patent 18-275 Novel cell membrane permeability mechanism of tumor treating fields on cancer cells", Leland Stanford Junior University, Jun 18, 2018
Edwin Chang. "United States Patent 17-238 Prevention and Treatment of Teratoma Formation During Stem Cell Therapy using Alternating Electric Fields", Leland Stanford Junior University, Jun 13, 2017
Edwin Chang. "United States Patent 13-017 Blood Biomarkers for Monitoring Response to anti-EGFR Therapy", Leland Stanford Junior University, Jan 16, 2013
Edwin Chang. "United States Patent 10-184 Use of 18F-FPPRGD2 tracer to monitor drug therapy and evolving hypoxic status in ischemic wound healinag", Leland Stanford Junior University, Jun 7, 2010
Dr. Chang has explored the relevance of medicinal compounds from the Ayurvedic medical tradition, in particular Withaferin A from the winter cherry plant, in stopping cancers such as glioblastomas. He has also examined the cooperativity of Withaferin A with other interventions that are known to inhibit gliomas such as combination therapies of Withaferin A with temozolomide, with other ginsenosides and with alternating electric fields (known as tumor treating fields or TTFields). He also has professional interests in stem cell research, the biology of aging, cancer as well as telomere and telomerase biology.
Lab Manager and Lab Scientist with Dept. of Radiology at Stanford, Stanford University (9/1/2011 - Present)
3155 Porter Drive, Palo Alto, CA, USA, 94304
Tumor Treating Fields Increases Membrane Permeability in Glioblastoma Cells
Cell Death Discovery
View details for DOI 10.1038/s41420-018-0130-x
A blood biomarker for monitoring response to anti-EGFR therapy.
Cancer biomarkers : section A of Disease markers
BACKGROUND AND OBJECTIVE: To monitor therapies targeted to epidermal growth factor receptors (EGFR) in non-small cell lung cancer (NSCLC), we investigated Peroxiredoxin 6 (PRDX6) as a biomarker of response to anti-EGFR agents.METHODS: We studied cells that are sensitive (H3255, HCC827) or resistant (H1975, H460) to gefitinib. PRDX6 was examined with either gefitinib or vehicle treatment using enzyme-linked immunosorbent assays. We created xenograft models from one sensitive (HCC827) and one resistant cell line (H1975) and monitored serum PRDX6 levels during treatment.RESULTS: PRDX6 levels in cell media from sensitive cell lines increased significantly after gefitinib treatment vs. vehicle, whereas there was no significant difference for resistant lines. PRDX6 accumulation over time correlated positively with gefitinib sensitivity. Serum PRDX6 levels in gefitinib-sensitive xenograft models increased markedly during the first 24 hours of treatment and then decreased dramatically during the following 48 hours. Differences in serum PRDX6 levels between vehicle and gefitinib-treated animals could not be explained by differences in tumor burden.CONCLUSIONS: Our results show that changes in serum PRDX6 during the course of gefitinib treatment of xenograft models provide insight into tumor response and such an approach offers several advantages over imaging-based strategies for monitoring response to anti-EGFR agents.
View details for PubMedID 29689709
The Exosome Total Isolation Chip.
Circulating tumor-derived extracellular vesicles (EVs) have emerged as a promising source for identifying cancer biomarkers for early cancer detection. However, the clinical utility of EVs has thus far been limited by the fact that most EV isolation methods are tedious, nonstandardized, and require bulky instrumentation such as ultracentrifugation (UC). Here, we report a size-based EV isolation tool called ExoTIC (exosome total isolation chip), which is simple, easy-to-use, modular, and facilitates high-yield and high-purity EV isolation from biofluids. ExoTIC achieves an EV yield ∼4-1000-fold higher than that with UC, and EV-derived protein and microRNA levels are well-correlated between the two methods. Moreover, we demonstrate that ExoTIC is a modular platform that can sort a heterogeneous population of cancer cell line EVs based on size. Further, we utilize ExoTIC to isolate EVs from cancer patient clinical samples, including plasma, urine, and lavage, demonstrating the device's broad applicability to cancers and other diseases. Finally, the ability of ExoTIC to efficiently isolate EVs from small sample volumes opens up avenues for preclinical studies in small animal tumor models and for point-of-care EV-based clinical testing from fingerprick quantities (10-100 μL) of blood.
View details for DOI 10.1021/acsnano.7b04878
View details for PubMedID 29090896
Synergistic inhibition of glioma cell proliferation by Withaferin A and tumor treating fields.
Journal of neuro-oncology
Glioblastoma (GBM) is the most aggressive and lethal form of brain cancer. Standard therapies are non-specific and often of limited effectiveness; thus, efforts are underway to uncover novel, unorthodox therapies against GBM. In previous studies, we investigated Withaferin A, a steroidal lactone from Ayurvedic medicine that inhibits proliferation in cancers including GBM. Another novel approach, tumor treating fields (TTFields), is thought to disrupt mitotic spindle formation and stymie proliferation of actively dividing cells. We hypothesized that combining TTFields with Withaferin A would synergistically inhibit proliferation in glioblastoma. Human glioblastoma cells (GBM2, GBM39, U87-MG) and human breast adenocarcinoma cells (MDA-MB-231) were isolated from primary tumors. The glioma cell lines were genetically engineered to express firefly luciferase. Proliferative potential was assessed either by bioluminescence imaging or cell counting via hemocytometer. TTFields (4 V/cm) significantly inhibited growth of the four cancer cell lines tested (n = 3 experiments per time point, four measurements per sample, p < 0.02 at least; 2-way ANOVA, control vs. treatment). The combination of Withaferin A (10-100 nM) with TTFields significantly inhibited the growth of the glioma cells to a degree beyond that of Withaferin A or TTFields alone. The interaction of the Withaferin A and TTFields on glioma cells was found to be synergistic in nature (p < 0.01, n = 3 experiments). These findings were validated by both bioluminescence and hemocytometric measurements. The combination of Withaferin A with TTFields represents a novel approach to treat GBM in a manner that is likely better than either treatment alone and that is synergistic.
View details for PubMedID 28681243
A novel theranostic strategy for MMP-14 expressing glioblastomas impacts survival.
Molecular cancer therapeutics
Glioblastoma (GBM) has a dismal prognosis. Evidence from preclinical tumor models and human trials indicates the role of GBM initiating cells (GIC) in GBM drug resistance. Here, we propose a new treatment option with tumor enzyme-activatable, combined therapeutic and diagnostic (theranostic) nanoparticles, which caused specific toxicity against GBM tumor cells and GICs. The theranostic cross-linked iron oxide nanoparticles (CLIO) were conjugated to a highly potent vascular disrupting agent (ICT) and secured with a matrix-metalloproteinase (MMP-14) cleavable peptide. Treatment with CLIO-ICT disrupted tumor vasculature of MMP-14 expressing GBM, induced GIC apoptosis and significantly impaired tumor growth. In addition, the iron core of CLIO-ICT enabled in vivo drug tracking with MR imaging. Treatment with CLIO-ICT plus temozolomide achieved tumor remission and significantly increased survival of human GBM bearing mice by more than 2 fold compared to treatment with temozolomide alone. Thus, we present a novel therapeutic strategy with significant impact on survival and great potential for clinical translation.
View details for PubMedID 28659432
Withaferin A and its potential role in glioblastoma (GBM)
JOURNAL OF NEURO-ONCOLOGY
2017; 131 (2): 201-211
Within the Ayurvedic medical tradition of India, Ashwagandha (Withania somnifera) is a well-known herb. A large number of withanolides have been isolated from both its roots and its leaves and many have been assessed for their pharmacological activities. Amongst them, Withaferin A is one of its most bioactive phytoconstituents. Due to the lactonal steroid's potential to modulate multiple oncogenic pathways, Withaferin A has gained much attention as a possible anti-neoplastic agent. This review focuses on the use of Withaferin A alone, or in combination with other treatments, as a newer option for therapy against the most aggressive variant of brain tumors, Glioblastoma. We survey the various studies that delineate Withaferin A's anticancer mechanisms, its toxicity profiles, its pharmacokinetics and pharmacodynamics and its immuno-modulating properties.
View details for DOI 10.1007/s11060-016-2303-x
View details for Web of Science ID 000394342500001
View details for PubMedID 27837436
AshwaMAX and Withaferin A inhibits gliomas in cellular and murine orthotopic models
JOURNAL OF NEURO-ONCOLOGY
2016; 126 (2): 253-264
Glioblastoma multiforme (GBM) is an aggressive, malignant cancer Johnson and O'Neill (J Neurooncol 107: 359-364, 2012). An extract from the winter cherry plant (Withania somnifera ), AshwaMAX, is concentrated (4.3 %) for Withaferin A; a steroidal lactone that inhibits cancer cells Vanden Berghe et al. (Cancer Epidemiol Biomark Prev 23: 1985-1996, 2014). We hypothesized that AshwaMAX could treat GBM and that bioluminescence imaging (BLI) could track oral therapy in orthotopic murine models of glioblastoma. Human parietal-cortical glioblastoma cells (GBM2, GBM39) were isolated from primary tumors while U87-MG was obtained commercially. GBM2 was transduced with lentiviral vectors that express Green Fluorescent Protein (GFP)/firefly luciferase fusion proteins. Mutational, expression and proliferative status of GBMs were studied. Intracranial xenografts of glioblastomas were grown in the right frontal regions of female, nude mice (n = 3-5 per experiment). Tumor growth was followed through BLI. Neurosphere cultures (U87-MG, GBM2 and GBM39) were inhibited by AshwaMAX at IC50 of 1.4, 0.19 and 0.22 µM equivalent respectively and by Withaferin A with IC50 of 0.31, 0.28 and 0.25 µM respectively. Oral gavage, every other day, of AshwaMAX (40 mg/kg per day) significantly reduced bioluminescence signal (n = 3 mice, p < 0.02, four parameter non-linear regression analysis) in preclinical models. After 30 days of treatment, bioluminescent signal increased suggesting onset of resistance. BLI signal for control, vehicle-treated mice increased and then plateaued. Bioluminescent imaging revealed diffuse growth of GBM2 xenografts. With AshwaMAX, GBM neurospheres collapsed at nanomolar concentrations. Oral treatment studies on murine models confirmed that AshwaMAX is effective against orthotopic GBM. AshwaMAX is thus a promising candidate for future clinical translation in patients with GBM.
View details for DOI 10.1007/s11060-015-1972-1
View details for Web of Science ID 000368728300005
- ROS and Brain Diseases: The Good, the Bad, and the Ugly OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2013
Cerenkov Luminescence Imaging (CLI) for Cancer Therapy Monitoring
JOVE-JOURNAL OF VISUALIZED EXPERIMENTS
In molecular imaging, positron emission tomography (PET) and optical imaging (OI) are two of the most important and thus most widely used modalities. PET is characterized by its excellent sensitivity and quantification ability while OI is notable for non-radiation, relative low cost, short scanning time, high throughput, and wide availability to basic researchers. However, both modalities have their shortcomings as well. PET suffers from poor spatial resolution and high cost, while OI is mostly limited to preclinical applications because of its limited tissue penetration along with prominent scattering optical signals through the thickness of living tissues. Recently a bridge between PET and OI has emerged with the discovery of Cerenkov Luminescence Imaging (CLI). CLI is a new imaging modality that harnesses Cerenkov Radiation (CR) to image radionuclides with OI instruments. Russian Nobel laureate Alekseyevich Cerenkov and his colleagues originally discovered CR in 1934. It is a form of electromagnetic radiation emitted when a charged particle travels at a superluminal speed in a dielectric medium. The charged particle, whether positron or electron, perturbs the electromagnetic field of the medium by displacing the electrons in its atoms. After passing of the disruption photons are emitted as the displaced electrons return to the ground state. For instance, one (18)F decay was estimated to produce an average of 3 photons in water. Since its emergence, CLI has been investigated for its use in a variety of preclinical applications including in vivo tumor imaging, reporter gene imaging, radiotracer development, multimodality imaging, among others. The most important reason why CLI has enjoyed much success so far is that this new technology takes advantage of the low cost and wide availability of OI to image radionuclides, which used to be imaged only by more expensive and less available nuclear imaging modalities such as PET. Here, we present the method of using CLI to monitor cancer drug therapy. Our group has recently investigated this new application and validated its feasibility by a proof-of-concept study. We demonstrated that CLI and PET exhibited excellent correlations across different tumor xenografts and imaging probes. This is consistent with the overarching principle of CR that CLI essentially visualizes the same radionuclides as PET. We selected Bevacizumab (Avastin; Genentech/Roche) as our therapeutic agent because it is a well-known angiogenesis inhibitor. Maturation of this technology in the near future can be envisioned to have a significant impact on preclinical drug development, screening, as well as therapy monitoring of patients receiving treatments.
View details for DOI 10.3791/4341
View details for Web of Science ID 000209226000031
Diffusible amyloid oligomers trigger systemic amyloidosis in mice
2008; 415: 207-215
AA (amyloid protein A) amyloidosis in mice is markedly accelerated when the animals are given, in addition to an inflammatory stimulus, an intravenous injection of protein extracted from AA-laden mouse tissue. Previous findings affirm that AA fibrils can enhance the in vivo amyloidogenic process by a nucleation seeding mechanism. Accumulating evidence suggests that globular aggregates rather than fibrils are the toxic entities responsible for cell death. In the present study we report on structural and morphological features of AEF (amyloid-enhancing factor), a compound extracted and partially purified from amyloid-laden spleen. Surprisingly, the chief amyloidogenic material identified in the active AEF was diffusible globular oligomers. This partially purified active extract triggered amyloid deposition in vital organs when injected intravenously into mice. This implies that such a phenomenon could have been inflicted through the nucleation seeding potential of toxic oligomers in association with altered cytokine induction. In the present study we report an apparent relationship between altered cytokine expression and AA accumulation in systemically inflamed tissues. The prevalence of serum AA monomers and proteolytic oligomers in spleen AEF is consistent to suggest that extrahepatic serum AA processing might lead to local accumulation of amyloidogenic proteins at the serum AA production site.
View details for DOI 10.1042/BJ20071696
View details for Web of Science ID 000260158400004
View details for PubMedID 18564059
Aging and diabetes compromises endothelial progenitor cell function and differentiation
WILEY-BLACKWELL PUBLISHING, INC. 2008: A24
View details for Web of Science ID 000253761000076
Human EPC mobilization and differentiation is influenced by exercise and by aging
WILEY-BLACKWELL PUBLISHING, INC. 2008: A24–A24
View details for Web of Science ID 000253761000075
Ischemia-induced mobilization of bone marrow resident mesenchymal stem cells is impaired in diabetes
93rd Annual Clinical Congress of the American-College-of-Surgeons
ELSEVIER SCIENCE INC. 2007: S64–S64
View details for Web of Science ID 000249397300134
Adipose-derived mesenchymal stem cells mobilize to sites of ischemia and participate in postnatal neovascularization
5th Annual Scientific Meeting of the International-Federation-of-Adipose-Therapeutics-and-Science
WILEY-BLACKWELL. 2007: 3283–84
View details for Web of Science ID 000251707200063
Endothelial progenitor cells participate in nicotine-mediated angiogenesis
JOURNAL OF THE AMERICAN COLLEGE OF CARDIOLOGY
2006; 48 (12): 2553-2560
We aimed to determine the role of endothelial progenitor cells (EPCs) in cholinergic angiogenesis.Recently, we provided evidence for a new angiogenic pathway mediated by endothelial nicotinic acetylcholine receptors (nAChR). Increasing evidence suggests that circulating EPCs also contribute to postnatal neovascularization by homing to sites of neovascularization, a process termed postnatal vasculogenesis. Therefore, we investigated whether nAChR activation increases mobilization and/or recruitment of EPCs to a site of angiogenesis.To identify EPCs from reservoirs both inside and outside of the bone marrow and to avoid the adverse effects of total body irradiation, we employed a murine parabiosis model with tie-2-LacZ FvB/N mice connected to wild-type FvB/N mice and induced unilateral hind limb ischemia in the wild-type animal.Administration of nicotine increased capillary density in the ischemic hind limb, and increased soluble Kit ligand plasma levels. The effect of systemic administration was greater than that of local delivery of nicotine (45% vs. 76% increase in capillary density by comparison to vehicle control, intramuscular vs. oral administration of nicotine; p < 0.05). Ischemia-induced incorporation of EPC in the control group was rare, but was increased 5-fold by systemic administration of nicotine. Exposure to nicotine in vitro increased EPC count and EPC transmigration. Finally, systemic administration of nicotine increased EPC number in the bone marrow and spleen during hind limb ischemia.Nicotine treatment increased the number of EPCs in the bone marrow and spleen, and increased their incorporation into the vasculature of ischemic tissue. Administration of nicotine increased markers of EPC mobilization. This study indicates that the known angiogenic effect of nicotine may be mediated in part by mobilization of precursor cells.
View details for DOI 10.1016/j.jacc.2006.07.066
View details for Web of Science ID 000242916100022
View details for PubMedID 17174197
A central role for nicotinic cholinergic receptor-dependent pathways in regulation of endothelial cell migration - Novel insights into angiogenesis
LIPPINCOTT WILLIAMS & WILKINS. 2004: 219
View details for Web of Science ID 000224783501207
Nicotine administration significantly alters peripheral, bone marrow and splenic stem cell populations in C57/BI6 mice
53rd Annual Scientific Session of the American-College-of-Cardiology
ELSEVIER SCIENCE INC. 2004: 490A–490A
View details for Web of Science ID 000189388502073
Genetic determinants of nicotine-induced angiogenesis
52nd Annual Scientific Session of the American-College-of-Cardiology
ELSEVIER SCIENCE INC. 2003: 256A–257A
View details for Web of Science ID 000181669501116
Aging and survival of cutaneous microvasculature
JOURNAL OF INVESTIGATIVE DERMATOLOGY
2002; 118 (5): 752-758
The growth and turnover of blood vessels in the skin is fundamental in normal development, wound repair, hair follicle cycling, tumor cell metastasis, and in many different states of cutaneous pathology. Whereas many investigations are focused on mechanisms of angiogenesis in the skin, the influence of cellular aging and replicative senescence (i.e., the inability, after a critical number of population doublings, to replicate) on microvascular remodeling events has received relatively less attention. In this article, we review the clinical and pathologic relationships associated with cutaneous vascular aging and update current knowledge of endothelial cell survival characteristics. A hypothesis is presented in which endothelial cell aging and survival are linked to molecular mechanisms controlling cell proliferation, quiescence, apoptosis, and cellular senescence. We review recent results demonstrating how activation of telomerase in human dermal microvascular endothelial cells affects their durability both in vitro and in vivo and conclude by linking these studies with current concepts involving endothelial cell precursors, control of postnatal somatic cell telomerase activity, and murine model systems.
View details for Web of Science ID 000175472300003
View details for PubMedID 11982751
eNOS activity is reduced in senescent human endothelial cells - Preservation by hTERT immortalization
2001; 89 (9): 793-798
Advanced age is associated with endothelial dysfunction and increased risk for atherosclerosis. However, the mechanisms for these observed effects are not clear. To clarify the association between aging and loss of endothelial function, young human aortic endothelial cells (HAECs), senescent HAECs transfected with control vector, and immortalized HAECs containing human telomerase reverse transcriptase (hTERT) were compared for expression of endothelial nitric oxide synthase (eNOS) and production of NO. To investigate a specific function modulated by endothelial NO, adhesion of monocytes under basal conditions as well as after exposure to TNF-alpha was assessed. A decrease in eNOS mRNA, protein, and activity was observed in endothelial cells at senescence as compared with young HAEC; this effect was blunted in hTERT cells. In all cells, shear stress induced a greater increase in the expression of eNOS protein with the final result being higher levels in hTERT compared with senescent cells. Basal monocyte binding was significantly elevated on aged endothelial cells compared with parental and hTERT cells. Exposure of TNF-alpha resulted in a 2-fold increase in monocyte adhesion in senescent cells, whereas this effect was reduced in cells transfected with hTERT. Prior exposure to fluid flow significantly reduced subsequent monocyte adhesion in all groups. These studies demonstrate that replicative aging results in decreased endothelial expression of eNOS accompanied by enhanced monocyte binding. Stable expression of hTERT results in endothelial cells with a younger phenotype with greater amount of eNOS and NO activity. Thus, telomerase transfection may have important functional consequences on endothelial cells.
View details for Web of Science ID 000171974800010
View details for PubMedID 11679409
Microarray analysis of replicative senescence
1999; 9 (17): 939–45
Limited replicative capacity is a defining characteristic of most normal human cells and culminates in senescence, an arrested state in which cells remain viable but display an altered pattern of gene and protein expression. To survey widely the alterations in gene expression, we have developed a DNA microarray analysis system that contains genes previously reported to be involved in aging, as well as those involved in many of the major biochemical signaling pathways.Senescence-associated gene expression was assessed in three cell types: dermal fibroblasts, retinal pigment epithelial cells, and vascular endothelial cells. Fibroblasts demonstrated a strong inflammatory-type response, but shared limited overlap in senescent gene expression patterns with the other two cell types. The characteristics of the senescence response were highly cell-type specific. A comparison of early- and late-passage cells stimulated with serum showed specific deficits in the early and mid G1 response of senescent cells. Several genes that are constitutively overexpressed in senescent fibroblasts are regulated during the cell cycle in early-passage cells, suggesting that senescent cells are locked in an activated state that mimics the early remodeling phase of wound repair.Replicative senescence triggers mRNA expression patterns that vary widely and cell lineage strongly influences these patterns. In fibroblasts, the senescent state mimics inflammatory wound repair processes and, as such, senescent cells may contribute to chronic wound pathologies.
View details for DOI 10.1016/S0960-9822(99)80420-5
View details for Web of Science ID 000082518200018
View details for PubMedID 10508581
Telomerase expression in human somatic cells does not induce changes associated with a transformed phenotype
1999; 21 (1): 111–14
Expression of the human telomerase catalytic component, hTERT, in normal human somatic cells can reconstitute telomerase activity and extend their replicative lifespan. We report here that at twice the normal number of population doublings, telomerase-expressing human skin fibroblasts (BJ-hTERT) and retinal pigment epithelial cells (RPE-hTERT) retain normal growth control in response to serum deprivation, high cell density, G1 or G2 phase blockers and spindle inhibitors. In addition, we observed no cell growth in soft agar and detected no tumour formation in vivo. Thus, we find that telomerase expression in normal cells does not appear to induce changes associated with a malignant phenotype.
View details for DOI 10.1038/5056
View details for Web of Science ID 000077960700020
View details for PubMedID 9916802
Expression of telomerase increases the lifespan of primary cells without induction of transformation.
W B SAUNDERS CO. 1998: 198A
View details for Web of Science ID 000077121300800
Identification and cloning of a sequence homologue of dopamine beta-hydroxylase
1998; 218 (1-2): 111–20
We have identified and cloned a cDNA encoding a new member of the monooxygenase family of enzymes. This novel enzyme, which we call MOX (monooxygenase X; unknown substrate) is a clear sequence homologue of the enzyme dopamine beta-hydroxylase (DBH). MOX maintains many of the structural features of DBH, as evidenced by the retention of most of the disulfide linkages and all of the peptidyl ligands to the active site copper atoms. Unlike DBH, MOX lacks a signal peptide sequence and therefore is unlikely to be a secreted molecule. The steady-state mRNA levels of MOX are highest in the kidney, lung, and adrenal gland, indicating that the tissue distribution of MOX is broader than that of DBH. Antisera raised to a fusion protein of MOX identifies a single band of the expected mobility by Western blot analysis. MOX mRNA levels are elevated in some fibroblast cell strains at replicative senescence, through this regulation is not apparent in all primary cell strains. The gene for MOX resides on the q arm of chromosome 6 and the corresponding mouse homolog has been identified.
View details for DOI 10.1016/S0378-1119(98)00344-8
View details for Web of Science ID 000076204300014
View details for PubMedID 9751809
TELOMERE LENGTH AND REPLICATIVE AGING IN HUMAN VASCULAR TISSUES
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1995; 92 (24): 11190–94
Because repeated injury of the endothelium and subsequent turnover of intimal and medial cells have been implicated in atherosclerosis, we examined telomere length, a marker of somatic cell turnover, in cells from these tissues. Telomere lengths were assessed by Southern analysis of terminal restriction fragments (TRFs) generated by HinfI/Rsa I digestion of human genomic DNA. Mean TRF length decreased as a function of population doublings in human endothelial cell cultures from umbilical veins, iliac arteries, and iliac veins. When endothelial cells were examined for mean TRF length as a function of donor age, there was a significantly greater rate of decrease for cells from iliac arteries than from iliac veins (102 bp/yr vs. 47 bp/yr, respectively, P < 0.05), consistent with higher hemodynamic stress and increased cell turnover in arteries. Moreover, the rate of telomere loss as a function of donor age was greater in the intimal DNA of iliac arteries compared to that of the internal thoracic arteries (147 bp/yr vs. 87 bp/yr, respectively, P < 0.05), a region of the arterial tree subject to less hemodynamic stress. This indicates that the effect is not tissue specific. DNA from the medial tissue of the iliac and internal thoracic arteries showed no significant difference in the rates of decrease, suggesting that chronic stress leading to cellular senescence is more pronounced in the intima than in the media. These observations extend the use of telomere size as a marker for the replicative history of cells and are consistent with a role for focal replicative senescence in cardiovascular diseases.
View details for DOI 10.1073/pnas.92.24.11190
View details for Web of Science ID A1995TF89100076
View details for PubMedID 7479963
View details for PubMedCentralID PMC40597
TELOMERE SHORTENING IS ASSOCIATED WITH CELL-DIVISION IN-VITRO AND IN-VIVO
EXPERIMENTAL CELL RESEARCH
1995; 220 (1): 194–200
In humans, the amount of terminal (TTAGGG)n, telomeric DNA decreases during aging of various somatic cell types in vitro and in vivo. While the factors accounting for telomere shortening have not been thoroughly established, the inability of the DNA replication machinery to completely copy chromosomal termini (the "end replication problem") and the absence in somatic cells of telomerase, the enzyme that synthesizes telomeric DNA de novo, is a likely mechanism. One prediction of this hypothesis is that telomere shortening should be dependent on cell division. Thus we analyzed telomere length in actively dividing and quiescent cells in vitro and in vivo. In circular outgrowths of cultured human diploid fibroblasts (HDF), cells at the outer periphery had a significantly lower mean terminal restriction fragment (TRF) length (P = 0.011) and telomeric signal intensity (P = 0.024) than cells at the center. Also, the rate of telomere shortening over time for HDFs held quiescent was not statistically significant (m = -12 bp/day, P = 0.16) while that for serially passaged cells was significant (m = -34 bp/day, P = 0.017). To examine the rate of telomere shortening for quiescent cells in vivo, we measured mean TRF length in brain tissue from adult donors ranging in age from 32-75 years. No significant decrease was observed as a function of donor age (P = 0.087), in contrast to the shortening of telomere length that occurs during in vivo aging of mitotically active cells (P = 0.0001). These observations show that telomere shortening is largely, if not entirely, dependent on cell division and support the end replication problem as a mechanism for this process and the use of telomere length as a biomarker for replicative capacity.
View details for DOI 10.1006/excr.1995.1306
View details for Web of Science ID A1995RR76300022
View details for PubMedID 7664836
THE RNA COMPONENT OF HUMAN TELOMERASE
1995; 269 (5228): 1236–41
Eukaryotic chromosomes are capped with repetitive telomere sequences that protect the ends from damage and rearrangements. Telomere repeats are synthesized by telomerase, a ribonucleic acid (RNA)-protein complex. Here, the cloning of the RNA component of human telomerase, termed hTR, is described. The template region of hTR encompasses 11 nucleotides (5'-CUAACCCUAAC) complementary to the human telomere sequence (TTAGGG)n. Germline tissues and tumor cell lines expressed more hTR than normal somatic cells and tissues, which have no detectable telomerase activity. Human cell lines that expressed hTR mutated in the template region generated the predicted mutant telomerase activity. HeLa cells transfected with an antisense hTR lost telomeric DNA and began to die after 23 to 26 doublings. Thus, human telomerase is a critical enzyme for the long-term proliferation of immortal tumor cells.
View details for DOI 10.1126/science.7544491
View details for Web of Science ID A1995RR84200024
View details for PubMedID 7544491