The mismatch repair system is required for S-phase checkpoint activation
The mismatch repair system is required for S-phase checkpoint activation
复制标题
DOI：
10.1038/ng1052
复制
发表时间：
2003-01-01
期刊：
影响因子：
30.8
通讯作者：
Baskaran, R
中科院分区：
文献类型：
--
作者：
Brown, KD;Rathi, A;Baskaran, R
有缺陷的S期检查点激活导致在遗传毒性损伤如暴露于电离辐射后不能下调DNA复制。这种“抗辐射DNA合成”（RDS）是共济失调-毛细血管扩张症的表型标志（1），这是一种由ATM突变引起的癌症倾向性疾病（2）。错配修复系统主要纠正复制过程中出现的核苷酸错配（3）。在这里，我们表明，错配修复系统是激活S期检查点响应电离辐射所必需的。错配修复蛋白缺陷的细胞显示RDS，错配修复功能的恢复恢复了正常的S期检查点功能。ATM的催化活化和ATM介导的NBS 1蛋白磷酸化（也称为nitrile）的发生独立于错配修复。然而，ATM依赖性磷酸化和激活的检查点激酶CHK 2和随后的降解其下游目标，CDC 25 A，被废除在细胞缺乏错配修复。体外和体内方法均显示MSH 2与CHK 2结合，MLH 1与ATM结合。这些发现表明，在DNA损伤位点形成的错配修复复合物促进ATM对CHK 2的磷酸化，并且该机制中的缺陷形成了在错配修复缺陷的细胞中观察到的RDS的分子基础。
Defective S-phase checkpoint activation results in an inability to downregulate DNA replication following genotoxic insult such as exposure to ionizing radiation. This 'radioresistant DNA synthesis' (RDS) is a phenotypic hallmark of ataxia-telangiectasia(1), a cancer-prone disorder caused by mutations in ATM(2). The mismatch repair system principally corrects nucleotide mismatches that arise during replication(3). Here we show that the mismatch repair system is required for activation of the S-phase checkpoint in response to ionizing radiation. Cells deficient in mismatch repair proteins showed RDS, and restoration of mismatch repair function restored normal S-phase checkpoint function. Catalytic activation of ATM and ATM-mediated phosphorylation of the protein NBS1 (also called nibrin) occurred independently of mismatch repair. However, ATM-dependent phosphorylation and activation of the checkpoint kinase CHK2 and subsequent degradation of its downstream target, CDC25A, was abrogated in cells lacking mismatch repair. In vitro and in vivo approaches both show that MSH2 binds to CHK2 and that MLH1 associates with ATM. These findings indicate that the mismatch repair complex formed at the sites of DNA damage facilitates the phosphorylation of CHK2 by ATM, and that defects in this mechanism form the molecular basis for the RDS observed in cells deficient in mismatch repair.