MDM2 and its homolog MDMX are important regulators of the p53 tumor suppressor. MDMX overexpression occurs in a subset of human tumors and is an alternative mechanism for inactivating p53. MDMX is resistant to MDM2 inhibitors such as Nutlin, therefore MDMX overexpression may reduce the efficacy of MDM2 inhibitors currently entering clinical trials. Understanding the structure and regulation of MDMX will be critical for the successful targeting of p53 pathway in cancer therapy. MDMX does not have E3 ligase activity and its mechanism of p53 regulation is poorly understood. We showed that MDMX is an important target of signaling pathways that activate p53. DNA damage induces MDMX phosphorylation by ATM/Chk2, promotes MDMX nuclear translocation and degradation, and inhibits MDMX binding to CK1? and p53. To elucidate the mechanism of MDMX regulation and signal integration, we established a novel assay for the detection of protein intra-molecular interactions. We demonstrate that different MDMX domains engage in intra-molecular binding, which results in auto inhibition by p53 mimicry. We hypothesize that the intra-molecular interactions in MDMX are important for its function and regulation. The following experiments are proposed to further study the MDMX internal interactions during stress response. (1) Investigate the regulation of MDMX internal interactions using a novel proteolytic fragment release assay. (2) Determine the mechanism of p53 inhibition by MDMX and CK1?. (3) Investigate the mechanism of senescence stimulation by MDMX. (4) Determine the physiological functions of MDMX internal interactions using mouse model. 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.
This proposal investigates the molecular mechanisms by which cells control the activity of the p53 tumor suppressor. Wild type p53 stabilization and activation in response to stress is critical for its tumor suppressor function. MDMX is a critical regulator of p53 and a mediator of stress signaling. Elucidating the mechanisms that regulate MDMX function may provide novel therapeutic strategies that activate p53 in tumors. This proposal will investigate the novel finding that MDMX domains undergo multiple intra-molecular binding that are important in signal transduction and p53 regulation. The experiments will test the functions of these interactions using biochemical assays, and will also test the physiological functions in a mouse model.
| Huang, Qingling; Chen, Lihong; Yang, Leixiang et al. (2018) MDMX acidic domain inhibits p53 DNA binding in vivo and regulates tumorigenesis. Proc Natl Acad Sci U S A 115:E3368-E3377 |
| Yang, Leixiang; Fang, Jia; Chen, Jiandong (2017) Tumor cell senescence response produces aggressive variants. Cell Death Discov 3:17049 |
| Borcherds, Wade; Becker, Andreas; Chen, Lihong et al. (2017) Optimal Affinity Enhancement by a Conserved Flexible Linker Controls p53 Mimicry in MdmX. Biophys J 112:2038-2042 |
| Chen, Jiandong (2016) Intra molecular interactions in the regulation of p53 pathway. Transl Cancer Res 5:639-649 |
| Wei, Xi; Wu, Shaofang; Song, Tanjing et al. (2016) Secondary interaction between MDMX and p53 core domain inhibits p53 DNA binding. Proc Natl Acad Sci U S A 113:E2558-63 |
