MDM2 and its homolog MDMX are important regulators of the p53 tumor suppressor. Knockout experiments showed that both are essential for viability of mouse embryos. In human tumor cells, MDMX knockdown inhibits tumor xenograft formation, whereas MDMX overexpression increases tumor resistance to chemotherapy. Unlike MDM2, MDMX does not have E3 ligase activity and its mechanism of p53 regulation is poorly understood. We found that MDMX is an integral part of signaling pathways that activate p53. DNA damage induces MDMX phosphorylation by ATM and Chk2, leading to its degradation by MDM2. Oncogenic and nucleolar stress also induce MDMX degradation by ARF and L11 regulation of MDM2. Therefore, accelerated MDMX degradation is a common mechanism for p53 activation. We found that 14-3-3 proteins regulate MDMX degradation after DNA damage by binding to a Chk2 phosphorylation site (S367) on MDMX. We have also identified CK11 as an MDMX binding partner that phosphorylates MDMX S289 and enhances the ability of MDMX to inhibit p53. We hypothesize that signaling to p53 is in part mediated through regulation of MDMX phosphorylation and degradation. The following experiments are proposed to further study the function and regulation of MDMX during stress response. (1) Determine the mechanism of p53 inhibition by MDMX. (2) Investigate the regulation of MDMX-p53 interaction by Chk2 and CK1?. (3) Investigate the regulation of MDMX degradation. (4) Test the in vivo functions of MDMX interactions with 14-3-3 and CK1?. These experiments should lead to a better understanding of the mechanisms that regulate MDMX and may identify novel strategy for targeting MDMX in human cancer.

Public Health Relevance

The proposal will study the regulation of the mdmx oncoprotein and the mechanism of p53 inactivation by mdmx. The experiments are based on recent findings on the regulation of mdmx degradation by phosphorylation and interactions with kinases and ribosomal proteins. The experiments will also use mouse models to test the physiological functions of mdmx modifications. Understanding the mechanisms of mdmx regulation may lead to new strategies to activate p53 in cancer cells.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA109636-08
Application #
8196878
Study Section
Cancer Etiology Study Section (CE)
Program Officer
Watson, Joanna M
Project Start
2004-07-01
Project End
2014-11-30
Budget Start
2011-12-01
Budget End
2012-11-30
Support Year
8
Fiscal Year
2012
Total Cost
$264,493
Indirect Cost
$106,114
Name
H. Lee Moffitt Cancer Center & Research Institute
Department
Type
DUNS #
139301956
City
Tampa
State
FL
Country
United States
Zip Code
33612
Cheng, Qian; Song, Tanjing; Chen, Lihong et al. (2014) Autoactivation of the MDM2 E3 ligase by intramolecular interaction. Mol Cell Biol 34:2800-10
Zheng, H; Chen, L; Pledger, W J et al. (2014) p53 promotes repair of heterochromatin DNA by regulating JMJD2b and SUV39H1 expression. Oncogene 33:734-44
Yang, Leixiang; Song, Tanjing; Chen, Lihong et al. (2013) Regulation of SirT1-nucleomethylin binding by rRNA coordinates ribosome biogenesis with nutrient availability. Mol Cell Biol 33:3835-48
Cross, Brittany; Chen, Lihong; Cheng, Qian et al. (2011) Inhibition of p53 DNA binding function by the MDM2 protein acidic domain. J Biol Chem 286:16018-29
Muppidi, Avinash; Li, Xiaolong; Chen, Jiandong et al. (2011) Conjugation of spermine enhances cellular uptake of the stapled peptide-based inhibitors of p53-Mdm2 interaction. Bioorg Med Chem Lett 21:7412-5
Cheng, Qian; Cross, Brittany; Li, Baozong et al. (2011) Regulation of MDM2 E3 ligase activity by phosphorylation after DNA damage. Mol Cell Biol 31:4951-63
Madden, Michael M; Muppidi, Avinash; Li, Zhenyu et al. (2011) Synthesis of cell-permeable stapled peptide dual inhibitors of the p53-Mdm2/Mdmx interactions via photoinduced cycloaddition. Bioorg Med Chem Lett 21:1472-5
Phan, Jason; Li, Zhenyu; Kasprzak, Agnieszka et al. (2010) Structure-based design of high affinity peptides inhibiting the interaction of p53 with MDM2 and MDMX. J Biol Chem 285:2174-83
Li, Baozong; Cheng, Qian; Li, Zhenyu et al. (2010) p53 inactivation by MDM2 and MDMX negative feedback loops in testicular germ cell tumors. Cell Cycle 9:1411-20
Chen, Lihong; Li, Zhenyu; Zwolinska, Aleksandra K et al. (2010) MDM2 recruitment of lysine methyltransferases regulates p53 transcriptional output. EMBO J 29:2538-52

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