Qi Leilei, Chakravarthy Reka, Li Monica M, Deng Chu-Xia, Li Rong, Hu Yanfen
Department of Anatomy and Cell Biology, the George Washington University, School of Medicine and Health Sciences, Washington DC20037, USA.
Cancer Center, Faculty of Health Sciences, University of Macau, Macau, SAR China.
iScience. 2022 Aug 15;25(9):104944. doi: 10.1016/j.isci.2022.104944. eCollection 2022 Sep 16.
BRCA1 maintains genome stability by promoting homologous recombination (HR)-mediated DNA double-strand break (DSB) repair. Mutation of mouse BRCA1-S1152, corresponding to an ATM phosphorylation site in its human counterpart, resulted in increased genomic instability and tumor incidence. In this study, we report that BRCA1-S1152 is part of a feedback loop that sustains ATM activity. BRCA1-S1152A mutation impairs recruitment of the E3 ubiquitin ligase SKP2. This in turn attenuates NBS1-K63 ubiquitination by SKP2 at DSB, impairs sustained ATM activation, and ultimately leads to deficient end resection, the commitment step in the HR repair pathway. Auto-phosphorylation of human ATM at S1981 is known to be important for its kinase activation; we mutated the corresponding amino acid residue in mouse ATM (S1987A) to characterize potential roles of mouse ATM-S1987 in the BRCA1-SKP2-NBS1-ATM feedback loop. Unexpectedly, MEFs carrying the ATM-S1987A knockin mutation maintain damage-induced ATM kinase activation, suggesting a species-specific function of human ATM auto-phosphorylation.
BRCA1通过促进同源重组（HR）介导的DNA双链断裂（DSB）修复来维持基因组稳定性。小鼠BRCA1-S1152发生突变，该位点对应于其人类同源物中的一个ATM磷酸化位点，导致基因组不稳定性增加和肿瘤发生率上升。在本研究中，我们报告BRCA1-S1152是维持ATM活性的反馈回路的一部分。BRCA1-S1152A突变会损害E3泛素连接酶SKP2的募集。这反过来会减弱SKP2在DSB处对NBS1的K63泛素化，损害ATM的持续激活，并最终导致末端切除缺陷，这是HR修复途径中的关键步骤。已知人类ATM在S1981处的自磷酸化对其激酶激活很重要；我们将小鼠ATM中的相应氨基酸残基（S1987A）进行突变，以表征小鼠ATM-S1987在BRCA1-SKP2-NBS1-ATM反馈回路中的潜在作用。出乎意料的是，携带ATM-S1987A敲入突变的小鼠胚胎成纤维细胞（MEFs）维持损伤诱导的ATM激酶激活，这表明人类ATM自磷酸化具有物种特异性功能。
