Wechsler Thomas, Chen Benjamin P C, Harper Ryan, Morotomi-Yano Keiko, Huang Betty C B, Meek Katheryn, Cleaver James E, Chen David J, Wabl Matthias
Department of Microbiology and Immunology and UCSF Cancer Center, University of California, San Francisco, CA 94143, USA.
Proc Natl Acad Sci U S A. 2004 Feb 3;101(5):1247-52. doi: 10.1073/pnas.0307765100. Epub 2004 Jan 20.
Unrepaired DNA double-strand breaks can lead to apoptosis or tumorigenesis. In mammals double-strand breaks are repaired mainly by nonhomologous end-joining mediated by the DNA-PK complex. The core protein of this complex, DNA-PKcs, is a DNA-dependent serine/threonine kinase that phosphorylates protein targets as well as itself. Although the (auto)phosphorylation activity has been shown to be essential for repair of both random double-strand breaks and induced breaks at the immunoglobulin locus, the corresponding phosphatase has been elusive. In fact, to date, none of the putative phosphatases in DNA double-strand break repair has been identified. Here we show that protein phosphatase 5 interacts with DNA-PKcs and dephosphorylates with surprising specificity at least two functional sites. Cells with either hypo- or hyperphosphorylation of DNA-PKcs at these sites show increased radiation sensitivity.
未修复的DNA双链断裂可导致细胞凋亡或肿瘤发生。在哺乳动物中，双链断裂主要通过由DNA-PK复合物介导的非同源末端连接进行修复。该复合物的核心蛋白DNA-PKcs是一种依赖DNA的丝氨酸/苏氨酸激酶，可磷酸化蛋白质靶点以及其自身。尽管（自身）磷酸化活性已被证明对于随机双链断裂和免疫球蛋白基因座处的诱导断裂的修复至关重要，但相应的磷酸酶却难以捉摸。事实上，迄今为止，DNA双链断裂修复中假定的磷酸酶均未被鉴定出来。在此我们表明，蛋白磷酸酶5与DNA-PKcs相互作用，并以惊人的特异性使至少两个功能位点去磷酸化。在这些位点DNA-PKcs磷酸化不足或过度磷酸化的细胞显示出辐射敏感性增加。
