Browsing by Subject "p73"

Now showing 1 - 3 of 3
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    Mutant and wild-type p53 form complexes with p73 upon phosphorylation by the kinase JNK
    (2018-04) Wolf, Eric R.; McAtarsney, Ciaran P.; Bredhold, Kristin E.; Kline, Amber M.; Mayo, Lindsey D.; Pediatrics, School of Medicine
    The transcription factors p53 and p73 are critical to the induction of apoptotic cell death, particularly in response to cell stress that activates c-Jun N-terminal kinase (JNK). Mutations in the DNA-binding domain of p53, which are commonly seen in cancers, result in conformational changes that enable p53 to interact with and inhibit p73, thereby suppressing apoptosis. In contrast, wild-type p53 reportedly does not interact with p73. We found that JNK-mediated phosphorylation of Thr81 in the proline-rich domain (PRD) of p53 enabled wild-type p53, as well as mutant p53, to form a complex with p73. Structural algorithms predicted that phosphorylation of Thr81 exposes the DNA-binding domain in p53 to enable its binding to p73. The dimerization of wild-type p53 with p73 facilitated the expression of apoptotic target genes [such as those encoding p53–up-regulated modulator of apoptosis (PUMA) and Bcl-2-associated X protein (BAX)] and, subsequently, the induction of apoptosis in response to JNK activation by cell stress in various cells. Thus, JNK phosphorylation of mutant and wild-type p53 promotes the formation of a p53/p73 complex that determines cell fate: apoptosis in the context of wild-type p53 or cell survival in the context of the mutant. These findings refine our current understanding of both the mechanistic links between p53 and p73 and the functional role for Thr81 phosphorylation.
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    Potentiation of Carboplatin-Mediated DNA Damage by the Mdm2 Modulator Nutlin-3a in a Humanized Orthotopic Breast-to-Lung Metastatic Model
    (American Association for Cancer Research, 2015-12) Tonsing-Carter, Eva; Bailey, Barbara J.; Saadatzadeh, M. Reza; Ding, Jixin; Wang, Haiyan; Sinn, Anthony L.; Peterman, Kacie M.; Spragins, Tiaishia K.; Silver, Jayne M.; Sprouse, Alyssa A.; Georgiadis, Taxiarchis M.; Gunter, T. Zachary; Long, Eric C.; Minto, Robert E.; Marchal, Christophe C.; Batuello, Christopher N.; Safa, Ahmad R.; Hanenberg, Helmut; Territo, Paul R.; Sandusky, George E.; Mayo, Lindsey D.; Eischen, Christine M.; Shannon, Harlan E.; Pollok, Karen E.; Department of Pharmacology and Toxicology, IU School of Medicine
    Triple-negative breast cancers (TNBC) are typically resistant to treatment, and strategies that build upon frontline therapy are needed. Targeting the murine double minute 2 (Mdm2) protein is an attractive approach, as Mdm2 levels are elevated in many therapy-refractive breast cancers. The Mdm2 protein-protein interaction inhibitor Nutlin-3a blocks the binding of Mdm2 to key signaling molecules such as p53 and p73α and can result in activation of cell death signaling pathways. In the present study, the therapeutic potential of carboplatin and Nutlin-3a to treat TNBC was investigated, as carboplatin is under evaluation in clinical trials for TNBC. In mutant p53 TMD231 TNBC cells, carboplatin and Nutlin-3a led to increased Mdm2 and was strongly synergistic in promoting cell death in vitro. Furthermore, sensitivity of TNBC cells to combination treatment was dependent on p73α. Following combination treatment, γH2AX increased and Mdm2 localized to a larger degree to chromatin compared with single-agent treatment, consistent with previous observations that Mdm2 binds to the Mre11/Rad50/Nbs1 complex associated with DNA and inhibits the DNA damage response. In vivo efficacy studies were conducted in the TMD231 orthotopic mammary fat pad model in NOD.Cg-Prkdc(scid)Il2rg(tm1Wjl)/SzJ (NSG) mice. Using an intermittent dosing schedule of combined carboplatin and Nutlin-3a, there was a significant reduction in primary tumor growth and lung metastases compared with vehicle and single-agent treatments. In addition, there was minimal toxicity to the bone marrow and normal tissues. These studies demonstrate that Mdm2 holds promise as a therapeutic target in combination with conventional therapy and may lead to new clinical therapies for TNBC.
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    Specific Functions of the Tumor Suppressor P53 are Activated by P73 and VHL
    (2019-07) Wolf, Eric R.; Mayo, Lindsey; Goebl, Mark; Ivan, Mircea; Mendonca, Marc; Wells, Clark
    The transcription factor and tumor suppressor protein p53 critically regulates cell survival or death in response to cellular stress. p53 can activate genes involved in a wide variety of processes, including apoptosis, cell cycle arrest, angiogenesis, metabolism, and senescence. Mutations in p53 are common in cancer and alter its interactions with other proteins, but there are other mechanisms and posttranslational modifications that can alter these interactions as well. In some tumors, such as renal cell carcinoma, p53 is commonly inactive even though mutations to TP53 are rare. This suggests that there are other biochemical mechanisms of inhibition, which we explore in this study. Mutations in the DNA-binding domain of p53 result in conformational changes that enable p53 to interact with and inhibit its family member p73, thereby promoting cell survival instead of apoptosis. In contrast, it has been reported that wild-type p53 does not bind to p73. We found that JNK-mediated phosphorylation of Thr81 in the proline-rich domain (PRD) of p53 enabled wild-type p53 to form a complex with p73. The dimerization of wild-type p53 with p73 facilitated the expression of apoptotic target genes such as PUMA and BAX, as well as the induction of apoptosis. In addition to the apoptotic function of p53, the tumor suppressor also plays a major role in the inhibition of angiogenesis. Here we also report a new mechanism where the Mdm2 oncoprotein can indirectly inactive p53 through the regulation of the tumor suppressor VHL. In response to hypoxia, VHL can bind p53, which results in activation of several anti-angiogenic targets of p53 such as THBS1 and COL18A1. Mdm2 regulates the VHL-p53 interaction by conjugating nedd8 to VHL within a region that is important for the VHL-p53 interaction, blocking the induction of anti-angiogenic genes and resulting in a proangiogenic phenotype. Due to its positive regulation of major proangiogenic proteins and its negative regulation of potent inhibitors of angiogenesis, we propose that the oncoprotein Mdm2 is the angiogenic switch. These findings refine our understanding of p53 interactions and activation, specifically for p53-p73 induced cell death and p53-VHL inhibition of angiogenesis.