Role of MRK in DNA Damage Response

描述(由申请人提供)：细胞对DNA损伤的反应通过诱导细胞周期停滞和为损伤修复提供时间来促进癌症的辐射抗性。这项提议的长期目标是确定DNA损伤反应的信号成分，这些成分可能是降低癌细胞辐射抵抗力的靶点。控制细胞周期停滞的监视机制被称为检查点，由控制DNA修复和细胞周期停滞等功能的复杂信号通路网络组成。位于BRCT基序蛋白MCD1、Nbs1和53BP1下游的ATM-Chk2/Chk1-CDc25A级联通路在伽玛射线诱导的S和G2期细胞周期停滞中发挥重要作用。蛋白激酶MRK受辐射激活，导致S期和G2期细胞周期停滞。研究发现，MRK通过直接磷酸化Chk2参与辐射诱导的Chk2活化。此外，通过RNA干扰敲除MRK可以减少53BP1对DNA损伤部位的定位，并使癌细胞对伽马射线的致死效应敏感。本研究的目的是通过检验以下假设来阐明MRK在DNA损伤诱导的细胞周期停滞中的作用机制：MRK作用于MDC1、Nbs1、53BP1和ATM的下游，在级联反应中导致Chk2激活和CDc25A降解，以响应伽玛辐射。这些特定的目标将通过以下几个方面来验证这些假说：1)定义在MRK通路中对伽马辐射做出反应的元件；以及2)通过结构-功能研究确定MRK激活的分子机制。对MRK功能的分子分析将提高我们对DNA损伤后细胞周期检查点调控的理解，并可能为开发旨在降低肿瘤辐射抗性的抗肿瘤药物寻找新的靶点。

DESCRIPTION (provided by applicant): The cellular response to DNA damage contributes to radiation resistance in cancer by inducing cell cycle arrest and allowing time for damage repair. The long-term objective of this proposal is to identify signaling components of the DNA damage response that could be targeted to decrease radiation resistance in cancer cells. The surveillance mechanisms that control cell cycle arrest are called checkpoints and consist of a complex network of signaling pathways that control DNA repair as well as cell cycle arrest among other functions. The ATM-Chk2/Chkl-Cdc25A cascade, downstream of the BRCT-motif-containing proteins MCD1, Nbsl and 53BP1, plays an important role in gamma-radiation-induced cell cycle arrest in S and G2 phase. The protein kinase MRK is activated by gamma-radiation and contributes to S-phase and G2-phase cell cycle arrest. MRK was found to participate in the gamma-radiation-induced Chk2 activation by directly phosphorylating Chk2. In addition, MRK knockdown by RNA interference reduces 53BP1 localization to sites of DNA damage and sensitizes cancer cells to the lethal effects of gamma-radiation. The goal of this study is to elucidate the mechanism through which MRK contributes to DNA-damage-induced cell cycle arrest by testing the following hypothesis: MRK operates downstream ofMDC1, Nbsl, 53BP1 and ATM, in the cascade that leads to Chk2 activation and Cdc25A degradation in response to, gamma-radiation. The specific aims will test these hypotheses by: 1) Defining the elements that operate in the MRK pathway in response to gamma-radiation; and 2) Defining the molecular mechanism of MRK activation through structure-function studies. The molecular analysis of the function of MRK will improve our understanding of cell cycle checkpoint regulation following DNA damage and could identify novel targets for the development of antineoplastic agents aimed at decreasing tumor radiation resistance.