Previous work by our lab (and by other groups) has determined that Mdm2 is the master regulator of the p53 tumor suppressor during development and in multiple tissues of neonates and adults. Mdm2 binds with p53 to block the p53's ability to alter transcription. In addition, Mdm2-p53 binding also promotes p53 ubiquitination, nuclear export, and proteosomal degradation, thereby inhibiting all p53 activities within the cell. Through these mechanisms, Mdm2 negatively regulates the ability of p53 to suppress tumorigenesis, and amplification and/or overexpression of the MDM2 gene is observed in a very significant percentage of human cancers. In this proposal, we summarize the progress we have made in our previous studies on p53 regulation by Mdm2 and its homologue, Mdm4 (MdmX). We describe recent studies examining the effects of ATM- mediated phosphorylation of Mdm2 on the regulation of p53 stability and activity, and discuss the generation of new Mdm2 alleles in mice that are compromised in their capacity to be phosphorylated by the DNA damage effector kinases ATM, c-Abl, or Akt. Based upon the preliminary data we present, we propose to utilize these models to examine in vivo the effects of Mdm2 phosphorylation on Mdm2-p53 signaling and on p53's ability to govern cell growth, the DNA damage response, cell metabolism, and to suppress tumorigenesis. As with our previous in vivo studies, this proposed research should greatly increase our understanding of the functional roles of the Mdm2-p53 signaling axis in regulating cell growth and death, and should help identify new targets for the treatment of radiation sickness and cancer.

Public Health Relevance

Mdm2 is a key negative regulator of the p53 tumor suppressor. Although much has been learned from biochemical assays and transfection studies regarding Mdm2 inhibition of p53 and the effects of DNA damage-induced kinases on Mdm2 post-translational modifications, analysis of genetically modified mice has proven critical in substantiating or refuting the numerous and often conflicting models derived from previous cell-based studies. Analysis of genetically altered mice has also led to new theories regarding Mdm2 functions and the role of Mdm2-p53 signaling in cancer. In this proposal, we will analyze several new mouse models we have generated to explore the effects of Mdm2 phosphorylation on Mdm2 and p53 levels and functions. Based upon our preliminary data, our proposed research should establish Mdm2 phosphorylation as the critical signaling event in the p53-mediated acute DNA damage response and in the regulation of p53 suppression of spontaneous and oncogene induced tumorigenesis. The results of these experiments have much clinical relevance, as an understanding of the regulatory mechanisms that control p53 activity in normal cell growth, in the acute DNA damage response, and in tumorigenesis is a critical prerequisite to developing new therapies to treat radiation-induced pathology and cancer.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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Cancer Molecular Pathobiology Study Section (CAMP)
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Johnson, Ronald L
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University of Massachusetts Medical School Worcester
Anatomy/Cell Biology
Schools of Medicine
United States
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