BRCA1 Directs the Repair Pathway to Homologous Recombination by Promoting 53BP1 Dephosphorylation.

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/G2 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.

Isono M ，Niimi A ，Oike T ，Hagiwara Y ，Sato H ，Sekine R ，Yoshida Y ，Isobe SY ，Obuse C ，Nishi R ，Petricci E ，Nakada S ，Nakano T ，Shibata A ... -  《Cell Reports》

Regulation of repair pathway choice at two-ended DNA double-strand breaks.

A DNA double-strand break (DSB) is considered to be a critical DNA lesion because its misrepair can cause severe mutations, such as deletions or chromosomal translocations. For the precise repair of DSBs, the repair pathway that is optimal for the particular circumstance needs to be selected. Non-homologous end joining (NHEJ) functions in G1/S/G2 phase, while homologous recombination (HR) becomes active only in S/G2 phase after DNA replication. DSB end structure is another factor affecting the repair pathway. For example, one-ended DSBs in S phase are mainly repaired by HR due to the lack of a partner DSB end for NHEJ. In contrast, two-ended DSBs, which are mainly induced by ionizing radiation, are repaired by either NHEJ or HR in G2 cells. Under the current model in terms of DSB repair pathway usage in G2 phase, NHEJ repairs ∼70% of two-ended DSBs, whereas HR repairs only ∼30%. Recent studies propose that NHEJ factors can bind all the DSB ends and are then either used to progress that pathway of DSB repair, or the repair proceeds by HR. In addition, molecular regulation by BRCA1 and 53BP1 has also been proposed. At DSB sites, BRCA1 functions to alleviate the 53BP1 barrier to resection by promoting 53BP1 dephosphorylation, followed by RIF1 release and 53BP1 repositioning. This timely 53BP1 repositioning may be important for the establishment of a chromatin environment that promotes the recruitment of EXO1 for resection in HR. This review summarizes current knowledge on factors regulating DSB repair pathway choice in terms of spatiotemporal regulation by focusing on the repair events at two-ended DSBs in G2 cells.

Shibata A 《-》

Impaired 53BP1/RIF1 DSB mediated end-protection stimulates CtIP-dependent end resection and switches the repair to PARP1-dependent end joining in G1.

Bakr A ，Köcher S ，Volquardsen J ，Petersen C ，Borgmann K ，Dikomey E ，Rothkamm K ，Mansour WY ... -  《Oncotarget》

A cell cycle-dependent regulatory circuit composed of 53BP1-RIF1 and BRCA1-CtIP controls DNA repair pathway choice.

DNA double-strand break (DSB) repair pathway choice is governed by the opposing activities of 53BP1 and BRCA1. 53BP1 stimulates nonhomologous end joining (NHEJ), whereas BRCA1 promotes end resection and homologous recombination (HR). Here we show that 53BP1 is an inhibitor of BRCA1 accumulation at DSB sites, specifically in the G1 phase of the cell cycle. ATM-dependent phosphorylation of 53BP1 physically recruits RIF1 to DSB sites, and we identify RIF1 as the critical effector of 53BP1 during DSB repair. Remarkably, RIF1 accumulation at DSB sites is strongly antagonized by BRCA1 and its interacting partner CtIP. Lastly, we show that depletion of RIF1 is able to restore end resection and RAD51 loading in BRCA1-depleted cells. This work therefore identifies a cell cycle-regulated circuit, underpinned by RIF1 and BRCA1, that governs DSB repair pathway choice to ensure that NHEJ dominates in G1 and HR is favored from S phase onward.

Escribano-Díaz C ，Orthwein A ，Fradet-Turcotte A ，Xing M ，Young JT ，Tkáč J ，Cook MA ，Rosebrock AP ，Munro M ，Canny MD ，Xu D ，Durocher D ... -  《-》

H4K20me2 distinguishes pre-replicative from post-replicative chromatin to appropriately direct DNA repair pathway choice by 53BP1-RIF1-MAD2L2.

Simonetta M ，de Krijger I ，Serrat J ，Moatti N ，Fortunato D ，Hoekman L ，Bleijerveld OB ，Altelaar AFM ，Jacobs JJL ... -  《-》