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并为损伤修复留出时间，有助于癌症的辐射抗性。这项提案的长期目标是确定DNA损伤反应的信号成分，这些信号成分可以被靶向降低癌细胞的辐射抗性。控制细胞周期停滞的监视机制被称为检查点，由控制DNA修复以及细胞周期停滞等功能的信号通路的复杂网络组成。ATM-Chk 2/Chkl-Cdc 25 A级联在γ辐射诱导的细胞周期S期和G2期阻滞中起重要作用，其位于含有BRCT基序的蛋白质MCD 1、Nbs 1和53 BP 1的下游。蛋白激酶MRK被γ辐射激活，并有助于S期和G2期细胞周期停滞。MRK通过直接磷酸化Chk 2参与γ射线诱导的Chk 2活化。此外，通过RNA干扰敲除MRK减少了53 BP 1定位于DNA损伤位点，并使癌细胞对γ辐射的致死作用敏感。本研究的目的是通过测试以下假设来阐明MRK有助于DNA损伤诱导的细胞周期停滞的机制：MRK在MDC 1、Nbs 1、53 BP 1和ATM的下游工作，在级联反应中导致Chk 2激活和Cdc 25 A降解以响应γ-辐射。具体目标将通过以下方式测试这些假设：1）定义MRK通路中响应γ辐射的元件; 2）通过结构-功能研究定义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，并可以为开发旨在降低肿瘤辐射抗性的药物确定新的靶点。

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.