All Publications

  • Deconstructing p53 pathways in tumor suppression. Mello, S., Bieging-Rolett, K., Kaiser, A., Valente, E., Raj, N., McClendon, J., Flowers, B., Morgens, D., Bassik, M., Attardi, L. AMER ASSOC CANCER RESEARCH. 2018: 17
  • A p53 Super-tumor Suppressor Reveals a Tumor Suppressive p53-Ptpn14-Yap Axis in Pancreatic Cancer. Cancer cell Mello, S. S., Valente, L. J., Raj, N., Seoane, J. A., Flowers, B. M., McClendon, J., Bieging-Rolett, K. T., Lee, J., Ivanochko, D., Kozak, M. M., Chang, D. T., Longacre, T. A., Koong, A. C., Arrowsmith, C. H., Kim, S. K., Vogel, H., Wood, L. D., Hruban, R. H., Curtis, C., Attardi, L. D. 2017; 32 (4): 460–73.e6


    The p53 transcription factor is a critical barrier to pancreatic cancer progression. To unravel mechanisms of p53-mediated tumor suppression, which have remained elusive, we analyzed pancreatic cancer development in mice expressing p53 transcriptional activation domain (TAD) mutants. Surprisingly, the p5353,54 TAD2 mutant behaves as a "super-tumor suppressor," with an enhanced capacity to both suppress pancreatic cancer and transactivate select p53 target genes, including Ptpn14. Ptpn14 encodes a negative regulator of the Yap oncoprotein and is necessary and sufficient for pancreatic cancer suppression, like p53. We show that p53 deficiency promotes Yap signaling and that PTPN14 and TP53 mutations are mutually exclusive in human cancers. These studies uncover a p53-Ptpn14-Yap pathway that is integral to p53-mediated tumor suppression.

    View details for PubMedID 29017057

  • Combined loss of PUMA and p21 accelerates c-MYC-driven lymphoma development considerably less than loss of one allele of p53 ONCOGENE VALENTE, L. J., Grabow, S., Vandenberg, C. J., Strasser, A., Janic, A. 2016; 35 (29): 3866-3871


    The tumor suppressor p53 is mutated in ~50% of human cancers. P53 is activated by a range of stimuli and regulates several cellular processes, including apoptotic cell death, cell cycle arrest, senescence and DNA repair. P53 induces apoptosis via transcriptional induction of the BH3-only proteins PUMA (p53-upregulated modulator of apoptosis) and NOXA, and cell cycle arrest via p21. Induction of these processes was proposed to be critical for p53-mediated tumor suppression. It is therefore surprising that mice lacking PUMA, NOXA and p21, as well as mice bearing mutations in p53 that impair the transcriptional activation of these genes, are not tumor prone, unlike mice lacking p53 function, which spontaneously develop tumors with 100% incidence. These p53 target genes and the processes they regulate may, however, impact differently on tumor development depending on the oncogenic drivers. For example, loss of PUMA enhances c-MYC-driven lymphoma development in mice, but, interestingly, the acceleration was less impressive compared with that caused by the loss of even a single p53 allele. Different studies have reported that loss of p21 can accelerate, delay or have no impact on tumorigenesis. In an attempt to resolve this controversy, we examined whether loss of p21-mediated cell cycle arrest cooperates with PUMA deficiency in accelerating lymphoma development in Eμ-Myc mice (overexpressing c-MYC in B-lymphoid cells). We found that Eμ-Myc mice lacking both p21 and PUMA (Eμ-Myc;Puma(-/-);p21(-/-)) developed lymphoma at a rate comparable to Eμ-Myc;Puma(-/-) animals, notably with considerably longer latency than Eμ-Myc;p53(+/-)mice. Loss of p21 had no impact on the numbers, cycling or survival of pre-leukemic Eμ-Myc B-lymphoid cells, even when PUMA was lost concomitantly. These results demonstrate that even in the context of deregulated c-MYC expression, p53 must suppress tumor development by activating processes apart from, or in addition to, PUMA-mediated apoptosis and p21-induced cell cycle arrest.

    View details for DOI 10.1038/onc.2015.457

    View details for Web of Science ID 000380753200011

    View details for PubMedID 26640149

  • Therapeutic Response to Non-genotoxic Activation of p53 by Nutlin3a Is Driven by PUMA-Mediated Apoptosis in Lymphoma Cells CELL REPORTS Valente, L. J., Aubrey, B. J., Herold, M. J., Kelly, G. L., Happo, L., Scott, C. L., Newbold, A., Johnstone, R. W., Huang, D. C., Vassilev, L. T., Strasser, A. 2016; 14 (8): 1858-1866


    Nutlin3a is a small-molecule antagonist of MDM2 that promotes non-genotoxic activation of p53 through p53 protein stabilization and transactivation of p53 target genes. Nutlin3a is the forerunner of a class of cancer therapeutics that have reached clinical trials. Using transgenic and gene-targeted mouse models lacking the critical p53 target genes, p21, Puma, and Noxa, we found that only loss of PUMA conferred profound protection against Nutlin3a-induced killing in both non-transformed lymphoid cells and Eμ-Myc lymphomas in vitro and in vivo. CRISPR/Cas9-mediated targeting of the PUMA gene rendered human hematopoietic cancer cell lines markedly resistant to Nutlin3a-induced cell death. These results demonstrate that PUMA-mediated apoptosis, but not p21-mediated cell-cycle arrest or senescence, is a critical determinant of the therapeutic response to non-genotoxic p53 activation by Nutlin3a. Importantly, in human cancer, PUMA expression may predict patient responses to treatment with MDM2 antagonists.

    View details for DOI 10.1016/j.celrep.2016.01.059

    View details for Web of Science ID 000371217700006

    View details for PubMedID 26904937

  • MCL-1 but not BCL-XL is critical for the development and sustained expansion of thymic lymphoma in p53-deficient mice BLOOD Grabow, S., Delbridge, A. R., Valente, L. J., Strasser, A. 2014; 124 (26): 3939-3946


    Apoptosis plays a role in normal lymphopoiesis and lymphoid malignancies. Pro-survival MCL-1 is essential for survival of T-cell progenitors, BCL-XL for immature thymocytes, and BCL-2 for mature T cells. Conversely, little is known about the regulators that are required for the survival of T-cell lymphomas. We used constitutive and conditionally gene-targeted mice to investigate which pro-survival BCL-2 family member is required for the sustained survival of thymic lymphomas initiated by loss of p53. Constitutive loss of a single Mcl-1 allele delayed tumor onset. In contrast, lymphomas emerging in p53(-/-) mice in which Mcl-1 could be conditionally deleted had been selected for retention of MCL-1 expression. In contrast, complete loss of BCL-XL had no impact on lymphoma development in p53(-/-) mice. These results demonstrate that thymic lymphomas elicited by loss of p53 must arise from cancer-initiating cells that require MCL-1 for their survival. Acute deletion of both Mcl-1 alleles abrogated the expansion of p53(-/-) lymphomas in mice, whereas inducible loss of BCL-XL had little impact. This reveals that MCL-1 is essential for the sustained survival of these malignant cells and suggests that targeting MCL-1 may be an attractive strategy for the treatment of T-cell lymphoma.

    View details for DOI 10.1182/blood-2014-09-601567

    View details for Web of Science ID 000347468200017

    View details for PubMedID 25368374

  • Targeting of MCL-1 kills MYC-driven mouse and human lymphomas even when they bear mutations in p53 GENES & DEVELOPMENT Kelly, G. L., Grabow, S., Glaser, S. P., Fitzsimmons, L., Aubrey, B. J., Okamoto, T., Valente, L. J., Robati, M., Tai, L., Fairlie, W. D., Lee, E. F., Lindstrom, M. S., Wiman, K. G., Huang, D. C., Bouillet, P., Rowe, M., Rickinson, A. B., Herold, M. J., Strasser, A. 2014; 28 (1): 58-70


    The transcriptional regulator c-MYC is abnormally overexpressed in many human cancers. Evasion from apoptosis is critical for cancer development, particularly c-MYC-driven cancers. We explored which anti-apoptotic BCL-2 family member (expressed under endogenous regulation) is essential to sustain c-MYC-driven lymphoma growth to reveal which should be targeted for cancer therapy. Remarkably, inducible Cre-mediated deletion of even a single Mcl-1 allele substantially impaired the growth of c-MYC-driven mouse lymphomas. Mutations in p53 could diminish but not obviate the dependency of c-MYC-driven mouse lymphomas on MCL-1. Importantly, targeting of MCL-1 killed c-MYC-driven human Burkitt lymphoma cells, even those bearing mutations in p53. Given that loss of one allele of Mcl-1 is well tolerated in healthy tissues, our results suggest that therapeutic targeting of MCL-1 would be an attractive therapeutic strategy for MYC-driven cancers.

    View details for DOI 10.1101/gad.232009.113

    View details for Web of Science ID 000329293500007

    View details for PubMedID 24395247

  • p53 Efficiently Suppresses Tumor Development in the Complete Absence of Its Cell-Cycle Inhibitory and Proapoptotic Effectors p21, Puma, and Noxa CELL REPORTS Valente, L. J., Gray, D. H., Michalak, E. M., Pinon-Hofbauer, J., Egle, A., Scott, C. L., Janic, A., Strasser, A. 2013; 3 (5): 1339-1345


    Activation of apoptosis through transcriptional induction of Puma and Noxa has long been considered to constitute the critical (if not sole) process by which p53 suppresses tumor development, although G1/S boundary cell-cycle arrest via induction of the CDK inhibitor p21 has also been thought to contribute. Recent analyses of mice bearing mutations that impair p53-mediated induction of select target genes have indicated that activation of apoptosis and G1/S cell-cycle arrest may, in fact, be dispensable for p53-mediated tumor suppression. However, the expression of Puma, Noxa, and p21 was not abrogated in these mutants, only reduced; therefore, the possibility that the reduced levels of these critical effectors of p53-mediated apoptosis and G1/S-cell-cycle arrest sufficed to prevent tumorigenesis could not be excluded. To resolve this important issue, we have generated mice deficient for p21, Puma, and Noxa (p21-/-puma-/-noxa-/- mice). Cells from these mice were deficient in their ability to undergo p53-mediated apoptosis, G1/S cell-cycle arrest, and senescence. Nonetheless, these animals remained tumor free until at least 500 days, in contrast to p53-deficient mice, which had all succumbed to lymphoma or sarcoma by 250 days. Interestingly, DNA lesions induced by γ-irradiation persisted longer in p53-deficient cells compared to wild-type or p21-/-puma-/-noxa-/- cells, and the former failed to transcriptionally activate several p53 target genes implicated in DNA repair. These results demonstrate beyond a doubt that the induction of apoptosis, cell-cycle arrest, and possibly senescence is dispensable for p53-mediated suppression of spontaneous tumor development and indicate that coordination of genomic stability and possibly other processes, such as metabolic adaptation, may instead be critical.

    View details for DOI 10.1016/j.celrep.2013.04.012

    View details for Web of Science ID 000321899300003

    View details for PubMedID 23665218

  • Role of p63 and the Notch pathway in cochlea development and sensorineural deafness PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Terrinoni, A., Serra, V., Bruno, E., Strasser, A., Valente, E., Flores, E. R., van Bokhoven, H., Lu, X., Knight, R. A., Melino, G. 2013; 110 (18): 7300-7305


    The ectodermal dysplasias are a group of inherited autosomal dominant syndromes associated with heterozygous mutations in the Tumor Protein p63 (TRP63) gene. Here we show that, in addition to their epidermal pathology, a proportion of these patients have distinct levels of deafness. Accordingly, p63 null mouse embryos show marked cochlea abnormalities, and the transactivating isoform of p63 (TAp63) protein is normally found in the organ of Corti. TAp63 transactivates hairy and enhancer of split 5 (Hes5) and atonal homolog 1 (Atoh1), components of the Notch pathway, known to be involved in cochlear neuroepithelial development. Strikingly, p63 null mice show morphological defects of the organ of Corti, with supernumerary hair cells, as also reported for Hes5 null mice. This phenotype is related to loss of a differentiation property of TAp63 and not to loss of its proapoptotic function, because cochleas in mice lacking the critical Bcl-2 homology domain (BH-3) inducers of p53- and p63-mediated apoptosis--Puma, Noxa, or both--are normal. Collectively, these data demonstrate that TAp63, acting via the Notch pathway, is crucial for the development of the organ of Corti, providing a molecular explanation for the sensorineural deafness in ectodermal dysplasia patients with TRP63 mutations.

    View details for DOI 10.1073/pnas.1214498110

    View details for Web of Science ID 000318682300047

    View details for PubMedID 23589895

  • Distinct target genes and effector processes appear to be critical for p53-activated responses to acute DNA damage versus p53-mediated tumour suppression BIODISCOVERY Valente, L. J., Strasser, A. 2013; 8 (3)
  • The Role of the Apoptotic Machinery in Tumor Suppression COLD SPRING HARBOR PERSPECTIVES IN BIOLOGY Delbridge, A. R., Valente, L. J., Strasser, A. 2012; 4 (11)


    Multicellular organisms have evolved processes to prevent abnormal proliferation or inappropriate tissue infiltration of cells, and these tumor suppressive mechanisms serve to prevent tissue hyperplasia, tumor development, and metastatic spread of tumors. These include potentially reversible processes such as cell cycle arrest and cellular senescence, as well as apoptotic cell death, which in contrast eliminates dangerous cells that may initiate tumor development. Tumor suppressive processes are organized as complex, extensive signaling networks, controlled by central "nodes." These "nodes" are prominent tumor suppressors, such as P53 or PTEN, whose loss is responsible for the development of the majority of human cancers. In this review we discuss the processes by which some of these prominent tumor suppressors trigger apoptotic cell death and how this process protects us from cancer development.

    View details for DOI 10.1101/cshperspect.a008789

    View details for Web of Science ID 000312348400007

    View details for PubMedID 23125015