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Carl Maki, Ph.D.Regulated Activity and Degradation of p53 and p53-pathway ProteinsResearch SummaryWild-type p53 is a tumor suppressor protein and potent growth inhibitor. Inactivation of p53 or its downstream pathway is considered essential for the development of most human cancers. It is therefore important to determine how p53 is normally regulated, and how this regulation is disrupted in cancer. Wild-type p53 is an unstable protein that is normally expressed at low levels due to the action of MDM2 and other ubiquitin-system E3 ligases that bind p53 and promote its degradation. In contrast, p53 is stabilized and its levels increase in response to various stresses, such as DNA damage, hypoxia, and inappropriate growth signals. Increased levels of p53 can halt cell proliferation through at least two mechanisms. First, nuclear p53 is a transcription factor and activates expression of genes that promote either growth arrest (e.g. p21) or apoptosis (e.g. PUMA, bax). Second, cytoplasmic p53 can localize to the mitochondria and interact with pro- and anti-apoptotic members of the Bcl-2 protein family, increasing release of pro-apoptotic factors from the mitochondria to promote apoptosis. Over 50% of human cancers harbor mutations within the P53 gene, and mutant forms of p53 are commonly expressed in tumors. Many of these tumor-associated p53 mutants have been shown to lack the ability to function as a transcription factor or disrupt the mitochondria, indicating these functions are important for p53-mediated tumor suppression.Our research during the next 5 years will focus on three areas. First, we have made the observation that MDM2 binding can promote a conformational change in p53, evidenced by exposure of the “mutant-specific” pAb240 epitope. We will examine the mechanism by which MDM2 binding promotes this conformational change, and how it affects p53 stability, activity, and interaction with other proteins. Second, we have found that p53 activation by Nutlin-3a promotes a dramatic cytoskeletal rearrangement and loss of focal adhesions. We will examine the basis for this and determine if it translates to decreased cancer cell migration and invasion. Third, we have found that transient p53 activation by Nutlin-3a promotes endoreduplication and the formation of therapy-resistant tetraploid cells. This represents a potentially adverse side-effect of therapies designed to activate p53 in cancer. We will examine the formation and resistance of tetraploid cells.
Selected PapersGeyer, RK, Yu, ZK, Maki, CG. The MDM2 RING-finger domain is required to promote p53 nuclear export. Nature Cell Biol. 2: 569-573, 2000.Yu, ZK, Geyer, RK, Maki, CG. MDM2-dependent ubiquitination of nuclear and cytoplasmic p53. Oncogene. 19: 5892-5897, 2000. Inoue, T, Geyer, RK, Howard, D, Yu, ZK, and Maki, CG. MDM2 can promote the ubiquitination, nuclear export, and degradation of p53 in the absence of direct binding. J. Biol. Chem. 276: 45255-45260, 2001. Inoue, T, Stuart, J, Leno, R, and Maki, CG. Nuclear import and export signals in control of the p53-related protein p73. J. Biol. Chem. 277: 15053-15060, 2002. Wei, X, Yu, ZK, Ramalingam, A, Grossmann, SR, Yu, JH, Bloch, DB, and Maki, CG. Physical and functional interactions between PML and MDM2. J. Biol. Chem. 278: 29288-29297, 2003. Zhu, H, Wu, L, and Maki, C.G. MDM2 and promyelocytic leukemia antagonize each other through their direct interaction with p53. J. Biol. Chem. 278: 49286-49292, 2003. Wu, L, Zhu, H, and Maki, C.G. A link between p73 transcriptional activity and p73 degradation. Oncogene 23: 4032-4036, 2004. Zhu, H, Nie, L, and Maki, C.G. Cdk2-dependent inhibition of p21 stability via a C-terminal cyclin-binding motif. J. Biol. Chem. 280: 29282-29288, 2005. Zhang, L, Nie, L, and Maki, C.G. P53 and p73 differ in their ability to inhibit glucocorticoid receptor (GR) transcriptional activity. Mol. Cancer 6: 68, 2006. Sasaki, M, Nie, L, and Maki, C.G. MDM2 binding induces a conformational change in p53 that is opposed by heat shock protein 90 and precedes p53 proteasomal degradation. J. Biol. Chem. 282: 14626-14634, 2007. Nie, L, Sasaki, M, and Maki, C.G. Regulation of p53 nuclear export through sequential changes in conformation and ubiquitination. J. Biol. Chem. 282: 14616-14625, 2007. Moran, D, Gawlak, G, Jayaprakash, M, Mayar, S, and Maki, C.G. Geldanamycin promotes premature mitotic entry and micronucleation in irradiated p53/p21 deficient colon carcinoma cells. Oncogene 2008 (in press). Shen, H, Moran, D, and Maki, C.G. Transient Nutlin-3a treatment promotes endoreduplication and the generation of therapy-resistant tetraploid cells. Cancer Res 2008 (in press). |
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Biomedical Sciences
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The University of Chicago, 5841 S. Maryland Avenue MC 6027, Chicago,
Illinois 60637
biomed@huggins.bsd.uchicago.edu
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