Yan Jun, Jetten Anton M
Cell Biology Section, Division of Intramural Research, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, United States.
Cancer Lett. 2008 Nov 28;271(2):179-90. doi: 10.1016/j.canlet.2008.04.046. Epub 2008 Jun 11.
Chromosomal double-strand breaks (DSBs) in eukaryotes provoke a rapid, extensive modification in chromatin flanking the breaks. The DNA damage response (DDR) coordinates activation of cell cycle checkpoints, apoptosis, and DNA repair networks, to ensure accurate repair and genomic integrity. The checkpoint kinase ATM plays a critical role in the initiation of DDR in response to DSBs. The early ATM-mediated phosphorylation of the histone variant H2AX proteins near DSBs leads to the subsequent binding of MDC1, which functions as a scaffold for the recruitment and assembly of many DDR mediators and effectors, including BRCA1. Recent studies have provided new insights into the mechanism by which BRCA1 and associated proteins are recruited to DNA damage foci and revealed key roles for the receptor-associated protein 80 (RAP80) and the E3 ligase RNF8 in this process. RAP80 is an ubiquitin-interaction motif (UIM) containing protein that is associated with a BRCA1/BARD1 complex through its interaction with CCDC98 (Abraxas). The UIMs of RAP80 are critical for targeting this protein complex to DSB sites. Additional studies revealed that after binding gamma-H2AX, ATM-phosphorylated MDC1 is recognized by the FHA domain of RNF8, which subsequently binds the E2 conjugating enzyme UBC13. This complex catalyzes K63-linked polyubiquitination of histones H2A and gamma-H2AX, which are then recognized by the UIMs of RAP80, thereby facilitating the recruitment of the BRCA1/BARD1/CCDC98/RAP80 protein complex to DSB sites. Depletion of RAP80 or RNF8 impairs the translocation of BRCA1 to DNA damage sites and results in defective cell cycle checkpoint control and DSB repair. In this review, we discuss this cascade of protein phosphorylation and ubiquitination and the role it plays in the control of cellular responses to genotoxic stress by regulating the interactions, localization, and function of DDR proteins.
真核生物中的染色体双链断裂（DSB）会引发断裂位点两侧染色质的快速、广泛修饰。DNA损伤反应（DDR）协调细胞周期检查点、细胞凋亡和DNA修复网络的激活，以确保准确修复和基因组完整性。检查点激酶ATM在响应DSB时启动DDR过程中起着关键作用。DSB附近组蛋白变体H2AX蛋白的早期ATM介导的磷酸化导致MDC1随后结合，MDC1作为许多DDR介质和效应器（包括BRCA1）募集和组装的支架。最近的研究为BRCA1及相关蛋白被募集到DNA损伤位点的机制提供了新见解，并揭示了受体相关蛋白80（RAP80）和E3连接酶RNF8在此过程中的关键作用。RAP80是一种含有泛素相互作用基序（UIM）的蛋白质，通过与CCDC98（Abraxas）相互作用与BRCA1/BARD1复合物相关联。RAP80的UIM对于将该蛋白复合物靶向DSB位点至关重要。进一步研究表明，在结合γ-H2AX后，ATM磷酸化的MDC1被RNF8的FHA结构域识别，随后RNF8结合E2共轭酶UBC13。该复合物催化组蛋白H2A和γ-H2AX的K63连接的多聚泛素化，然后被RAP80的UIM识别，从而促进BRCA1/BARD1/CCDC98/RAP80蛋白复合物向DSB位点的募集。RAP80或RNF8的缺失会损害BRCA1向DNA损伤位点的转位，并导致细胞周期检查点控制和DSB修复缺陷。在本综述中，我们讨论了这种蛋白质磷酸化和泛素化级联反应，以及它通过调节DDR蛋白的相互作用、定位和功能在控制细胞对基因毒性应激反应中所起的作用。
