SHLD 2/ FAM 35A co‐operates with REV 7 to coordinate DNA double‐strand break repair pathway choice

Abstract

DNA double‐strand breaks (DSBs) can be repaired by two major pathways: non‐homologous end‐joining (NHEJ) and homologous recombination (HR). DNA repair pathway choice is governed by the opposing activities of 53BP1, in complex with its effectors RIF1 and REV7, and BRCA1. However, it remains unknown how the 53BP1/RIF1/REV7 complex stimulates NHEJ and restricts HR to the S/G2 phases of the cell cycle. Using a mass spectrometry (MS)‐based approach, we identify 11 high‐confidence REV7 interactors and elucidate the role of SHLD2 (previously annotated as FAM35A and RINN2) as an effector of REV7 in the NHEJ pathway. FAM35A depletion impairs NHEJ‐mediated DNA repair and compromises antibody diversification by class switch recombination (CSR) in B cells. FAM35A accumulates at DSBs in a 53BP1‐, RIF1‐, and REV7‐dependent manner and antagonizes HR by limiting DNA end resection. In fact, FAM35A is part of a larger complex composed of REV7 and SHLD1 (previously annotated as C20orf196 and RINN3), which promotes NHEJ and limits HR. Together, these results establish SHLD2 as a novel effector of REV7 in controlling the decision‐making process during DSB repair.

53BP1: a DSB escort

“…Concerning the mechanism by which 53BP1 limits the formation of ssDNA at DNA breaks, there are two main models ( Fig. 7; Barazas et al 2018;Dev et al 2018;Findlay et al 2018;Gao et al 2018;Ghezraoui et al 2018;Gupta et al 2018;Mirman et al 2018;Noordermeer et al 2018). In the first model, 53BP1 uses the loading of Shieldin onto the ssDNA to protect the 5 ′ end from resection (Fig.…”

“…7A). The finding that Shld2 alone or in complex with Shld1 can bind to ssDNA is promising in this regard (Dev et al 2018;Findlay et al 2018;Gao et al 2018;Noordermeer et al 2018), but it remains to be seen whether Shieldin binds sufficiently close to the 5 ′ end to form a barrier to nucleolytic attack. For Shieldin to block resection upon engaging the DNA end, at least some ssDNA must B A Figure 7.…”

“…The length of this 3 ′ overhang is not yet clear since the minimal binding site of the whole Shieldin complex has not been determined. In vitro, Shld2/Shld1 complexes bind to oligonucleotides of 60-100 nt (Dev et al 2018;Findlay et al 2018;Gao et al 2018;Noordermeer et al 2018).…”

Mapping global and local coevolution across 600 species to identify novel homologous recombination repair genes

“…NPP uses a continuous scale of conservation instead of a defining cutoff for the protein being lost or retained and normalizes gene conservation relative to the expected conservation of other genes between the species. We applied NPP to reveal genetic interactions and novel genes in the RNA interference pathway, in RNA methylation, and in different human diseases including cancer (Schwartz et al 2013;Tabach et al 2013a,b;Sadreyev et al 2015;Findlay et al 2018;Malcov-Brog et al 2018;Nordlinger et al 2018;Omar et al 2018).…”

Ubiquitylation at the Fork: Making and Breaking Chains to Complete DNA Replication

“…Interestingly, one of the mutations falls within the HORMA domain of REV7, known to mediate its interaction with REV1 and REV3L suggesting that the incapacity of patient cells to form an active Pol ζ is responsible for the defect in ICL repair [ 271 ]. The TLS-independent function of REV7 as part of the end-joining SHIELDIN complex that controls the extent of DNA resection at DSBs could suggest defects in downstream ICL repair steps in REV7 mutant cells as well [ 272 , 273 , 274 , 275 , 276 , 277 , 278 , 279 ]. Finally, the recent implication of the RFWD3 ubiquitin ligase in the FA pathway supports roles for ubiquitylation beyond cross-link unhooking, nuclease recruitment and translesion synthesis into the HR-dependent steps of ICL repair [ 68 , 93 , 94 ].…”