Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, 15261, USA.
J Cell Sci. 2013 Oct 1;126(Pt 19):4414-23. doi: 10.1242/jcs.128272. Epub 2013 Jul 18.
Single-strand breaks (SSBs) are the most common type of oxidative DNA damage and they are related to aging and many genetic diseases. The scaffold protein for repair of SSBs, XRCC1, accumulates at sites of poly(ADP-ribose) (pAR) synthesized by PARP, but it is retained at sites of SSBs after pAR degradation. How XRCC1 responds to SSBs after pAR degradation and how this affects repair progression are not well understood. We found that XRCC1 dissociates from pAR and is translocated to sites of SSBs dependent on its BRCTII domain and the function of PARG. In addition, phosphorylation of XRCC1 is also required for the proper dissociation kinetics of XRCC1 because (1) phosphorylation sites mutated in XRCC1 (X1 pm) cause retention of XRCC1 at sites of SSB for a longer time compared to wild type XRCC1; and (2) phosphorylation of XRCC1 is required for efficient polyubiquitylation of XRCC1. Interestingly, a mutant of XRCC1, LL360/361DD, which abolishes pAR binding, shows significant upregulation of ubiquitylation, indicating that pARylation of XRCC1 prevents the poly-ubiquitylation. We also found that the dynamics of the repair proteins DNA polymerase beta, PNK, APTX, PCNA and ligase I are regulated by domains of XRCC1. In summary, the dynamic damage response of XRCC1 is regulated in a manner that depends on modifications of polyADP-ribosylation, phosphorylation and ubiquitylation in live cells.
单链断裂(SSBs)是最常见的氧化 DNA 损伤类型,与衰老和许多遗传疾病有关。修复 SSBs 的支架蛋白 XRCC1 聚集在 PARP 合成的多聚 ADP-核糖(pAR)部位,但在 pAR 降解后仍保留在 SSBs 部位。XRCC1 在 pAR 降解后如何响应 SSBs,以及这如何影响修复进展尚不清楚。我们发现 XRCC1 从 pAR 解离并依赖于其 BRCTII 结构域和 PARG 的功能转移到 SSBs 部位。此外,XRCC1 的磷酸化对于 XRCC1 的适当解离动力学也是必需的,因为(1)XRCC1 中的磷酸化位点突变(X1 pm)导致 XRCC1 在 SSB 部位的滞留时间比野生型 XRCC1 长;(2)XRCC1 的磷酸化对于 XRCC1 的有效多泛素化是必需的。有趣的是,一种 XRCC1 突变体 LL360/361DD,它消除了 pAR 结合,显示出显著的泛素化上调,表明 XRCC1 的 pAR 化阻止了多泛素化。我们还发现,修复蛋白 DNA 聚合酶β、PNK、APTX、PCNA 和 ligase I 的动力学受到 XRCC1 结构域的调节。总之,XRCC1 的动态损伤反应以依赖于多 ADP-核糖基化、磷酸化和泛素化修饰的方式在活细胞中受到调节。