Cheng Wen-Hsing, Muftic Diana, Muftuoglu Meltem, Dawut Lale, Morris Christa, Helleday Thomas, Shiloh Yosef, Bohr Vilhelm A
Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
Mol Biol Cell. 2008 Sep;19(9):3923-33. doi: 10.1091/mbc.e07-07-0698. Epub 2008 Jul 2.
Werner syndrome (WS) is a human genetic disorder characterized by extensive clinical features of premature aging. Ataxia-telengiectasia (A-T) is a multisystem human genomic instability syndrome that includes premature aging in some of the patients. WRN and ATM, the proteins defective in WS and A-T, respectively, play significant roles in the maintenance of genomic stability and are involved in several DNA metabolic pathways. A role for WRN in DNA repair has been proposed; however, this study provides evidence that WRN is also involved in ATM pathway activation and in a S-phase checkpoint in cells exposed to DNA interstrand cross-link-induced double-strand breaks. Depletion of WRN in such cells by RNA interference results in an intra-S checkpoint defect, and interferes with activation of ATM as well as downstream phosphorylation of ATM target proteins. Treatment of cells under replication stress with the ATM kinase inhibitor KU 55933 results in a S-phase checkpoint defect similar to that observed in WRN shRNA cells. Moreover, gamma H2AX levels are higher in WRN shRNA cells than in control cells 6 and 16 h after exposure to psoralen DNA cross-links. These results suggest that WRN and ATM participate in a replication checkpoint response, in which WRN facilitates ATM activation in cells with psoralen DNA cross-link-induced collapsed replication forks.
沃纳综合征（WS）是一种人类遗传性疾病，其特征为具有广泛的早衰临床特征。共济失调毛细血管扩张症（A-T）是一种多系统人类基因组不稳定综合征，部分患者存在早衰现象。分别在WS和A-T中存在缺陷的蛋白质WRN和ATM，在维持基因组稳定性方面发挥着重要作用，并参与多种DNA代谢途径。有人提出WRN在DNA修复中发挥作用；然而，本研究提供的证据表明，WRN还参与ATM途径的激活以及暴露于DNA链间交联诱导的双链断裂的细胞中的S期检查点。通过RNA干扰使此类细胞中的WRN缺失会导致S期检查点缺陷，并干扰ATM的激活以及ATM靶蛋白的下游磷酸化。用ATM激酶抑制剂KU 55933处理处于复制应激状态的细胞会导致类似于在WRN shRNA细胞中观察到的S期检查点缺陷。此外，在暴露于补骨脂素DNA交联后6小时和16小时，WRN shRNA细胞中的γH2AX水平高于对照细胞。这些结果表明，WRN和ATM参与复制检查点反应，其中WRN促进补骨脂素DNA交联诱导的复制叉塌陷的细胞中ATM的激活。
