Isono Mayu, Niimi Atsuko, Oike Takahiro, Hagiwara Yoshihiko, Sato Hiro, Sekine Ryota, Yoshida Yukari, Isobe Shin-Ya, Obuse Chikashi, Nishi Ryotaro, Petricci Elena, Nakada Shinichiro, Nakano Takashi, Shibata Atsushi
Advanced Scientific Research Leaders Development Unit, Gunma University, Maebashi, Gunma 371-8511, Japan; Gunma University Heavy Ion Medical Center, Gunma University, Maebashi, Gunma 371-8511, Japan.
Gunma University Initiative for Advanced Research, Gunma University, Maebashi, Gunma 371-8511, Japan.
Cell Rep. 2017 Jan 10;18(2):520-532. doi: 10.1016/j.celrep.2016.12.042.
BRCA1 promotes homologous recombination (HR) by activating DNA-end resection. By contrast, 53BP1 forms a barrier that inhibits DNA-end resection. Here, we show that BRCA1 promotes DNA-end resection by relieving the 53BP1-dependent barrier. We show that 53BP1 is phosphorylated by ATM in S/G phase, promoting RIF1 recruitment, which inhibits resection. 53BP1 is promptly dephosphorylated and RIF1 released, despite remaining unrepaired DNA double-strand breaks (DSBs). When resection is impaired by CtIP/MRE11 endonuclease inhibition, 53BP1 phosphorylation and RIF1 are sustained due to ongoing ATM signaling. BRCA1 depletion also sustains 53BP1 phosphorylation and RIF1 recruitment. We identify the phosphatase PP4C as having a major role in 53BP1 dephosphorylation and RIF1 release. BRCA1 or PP4C depletion impairs 53BP1 repositioning, EXO1 recruitment, and HR progression. 53BP1 or RIF1 depletion restores resection, RAD51 loading, and HR in PP4C-depleted cells. Our findings suggest that BRCA1 promotes PP4C-dependent 53BP1 dephosphorylation and RIF1 release, directing repair toward HR.
BRCA1通过激活DNA末端切除来促进同源重组（HR）。相比之下，53BP1形成一种屏障，抑制DNA末端切除。在此，我们表明BRCA1通过解除53BP1依赖性屏障来促进DNA末端切除。我们发现53BP1在S/G期被ATM磷酸化，促进RIF1募集，从而抑制切除。尽管DNA双链断裂（DSB）仍未修复，但53BP1会迅速去磷酸化且RIF1会被释放。当通过抑制CtIP/MRE11核酸内切酶损害切除时，由于持续的ATM信号传导，53BP1磷酸化和RIF1会持续存在。BRCA1缺失也会使53BP1磷酸化和RIF1募集持续存在。我们确定磷酸酶PP4C在53BP1去磷酸化和RIF1释放中起主要作用。BRCA1或PP4C缺失会损害53BP1重新定位、EXO1募集和HR进程。53BP1或RIF1缺失可恢复PP4C缺失细胞中的切除、RAD51加载和HR。我们的研究结果表明，BRCA1促进PP4C依赖性的53BP1去磷酸化和RIF1释放，将修复导向HR。
