Function and regulation of MDMX intra-molecular interactions

 描述(申请人提供)：MDM2及其同系物MDMX是P53肿瘤抑制因子的重要调节因子。MDMX的过度表达发生在人类肿瘤的一个亚群中，是灭活P53的另一种机制。MDMX对努特林等MDM2抑制剂具有耐药性，因此过度表达MDMX可能会降低目前进入临床试验的MDM2抑制剂的疗效。了解MDMX的结构和调控对于成功靶向p53通路在肿瘤治疗中的作用至关重要。MDMX不具有E3连接酶活性，其对P53的调控机制尚不清楚。我们发现MDMX是激活P53的信号通路的重要靶点。DNA损伤可诱导mdmx通过atm/chk2磷酸化，促进mdmx核转位和降解，并抑制mdmx与CK1和P53的结合。为了阐明MDMX调控和信号整合的机制，我们建立了一种新的检测蛋白质分子内相互作用的方法。我们证明了不同的MDMX结构域参与了分子内结合，这导致了P53模仿的自身抑制。我们假设MDMX中的分子内相互作用对其功能和调控是重要的。为了进一步研究MDMX在应力响应过程中的内部相互作用，建议进行以下实验。(1)用一种新的蛋白降解片段释放法研究MDMX内部相互作用的调节。(2)探讨MDMX和CK1抑制P53的作用机制。(3)探讨MDMX促进衰老的作用机制。(4)用小鼠模型确定MDMX内部相互作用的生理功能。这些实验应该有助于更好地理解调控MDMX的机制，并可能确定靶向人类癌症MDMX的新策略。

 DESCRIPTION (provided by applicant): 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.