Bomgarden Ryan D, Lupardus Patrick J, Soni Deena V, Yee Muh-Ching, Ford James M, Cimprich Karlene A
Department of Molecular Pharmacology, Stanford University, Stanford, CA 94305-5174, USA.
EMBO J. 2006 Jun 7;25(11):2605-14. doi: 10.1038/sj.emboj.7601123. Epub 2006 May 4.
An essential component of the ATR (ataxia telangiectasia-mutated and Rad3-related)-activating structure is single-stranded DNA. It has been suggested that nucleotide excision repair (NER) can lead to activation of ATR by generating such a signal, and in yeast, DNA damage processing through the NER pathway is necessary for checkpoint activation during G1. We show here that ultraviolet (UV) radiation-induced ATR signaling is compromised in XPA-deficient human cells during S phase, as shown by defects in ATRIP (ATR-interacting protein) translocation to sites of UV damage, UV-induced phosphorylation of Chk1 and UV-induced replication protein A phosphorylation and chromatin binding. However, ATR signaling was not compromised in XPC-, CSB-, XPF- and XPG-deficient cells. These results indicate that damage processing is not necessary for ATR-mediated S-phase checkpoint activation and that the lesion recognition function of XPA may be sufficient. In contrast, XP-V cells deficient in the UV bypass polymerase eta exhibited enhanced ATR signaling. Taken together, these results suggest that lesion bypass and not lesion repair may raise the level of UV damage that can be tolerated before checkpoint activation, and that XPA plays a critical role in this activation.
共济失调毛细血管扩张症突变和Rad3相关蛋白（ATR）激活结构的一个重要组成部分是单链DNA。有人提出，核苷酸切除修复（NER）可通过产生这样一种信号导致ATR激活，并且在酵母中，通过NER途径进行的DNA损伤处理对于G1期的检查点激活是必要的。我们在此表明，在S期，紫外线（UV）辐射诱导的ATR信号在XPA缺陷的人类细胞中受损，这表现为ATR相互作用蛋白（ATRIP）向UV损伤位点的易位缺陷、UV诱导的Chk1磷酸化以及UV诱导的复制蛋白A磷酸化和染色质结合缺陷。然而，ATR信号在XPC、CSB、XPF和XPG缺陷的细胞中并未受损。这些结果表明，损伤处理对于ATR介导的S期检查点激活并非必要，并且XPA的损伤识别功能可能就足够了。相比之下，缺乏紫外线跨损伤聚合酶η的XP-V细胞表现出增强的ATR信号。综上所述，这些结果表明，损伤绕过而非损伤修复可能会提高在检查点激活之前可耐受的紫外线损伤水平，并且XPA在这种激活中起关键作用。
