RIF1 Is Essential for 53BP1-Dependent Nonhomologous End Joining and Suppression of DNA Double-Strand Break Resection

Abstract

SummaryThe appropriate execution of DNA double-strand break (DSB) repair is critical for genome stability and tumor avoidance. 53BP1 and BRCA1 directly influence DSB repair pathway choice by regulating 5′ end resection, but how this is achieved remains uncertain. Here we report that Rif1−/− mice are severely compromised for 53BP1-dependent class switch recombination (CSR) and fusion of dysfunctional telomeres. The inappropriate accumulation of RIF1 at DSBs in S phase is antagonized by BRCA1, and deletion of Rif1 suppresses toxic nonhomologous end joining (NHEJ) induced by PARP inhibition in Brca1-deficient cells. Mechanistically, RIF1 is recruited to DSBs via the N-terminal phospho-SQ/TQ domain of 53BP1, and DSBs generated by ionizing radiation or during CSR are hyperresected in the absence of RIF1. Thus, RIF1 and 53BP1 cooperate to block DSB resection to promote NHEJ in G1, which is antagonized by BRCA1 in S phase to ensure a switch of DSB repair mode to homologous recombination.

The FHA and BRCT domains recognize ADP-ribosylation during DNA damage response

“…Accumulated evidence suggests that 53BP1 is a key downstream effector in the ATM-dependent pathway and could be phosphorylated by ATM and CHK2 (Anderson et al 2001;Rappold et al 2001;Ward et al 2003). Phosphorylated 53BP1 is known to regulate its functional partners to govern the transient G2/M checkpoint and DNA damage repair (DiTullio et al 2002;Fernandez-Capetillo et al 2002;Callen et al 2013;Chapman et al 2013), which is consistent with our observations. Moreover, the PARdependent early ATM activation controls the transient G2/M checkpoint, which plays an important role in maintaining genomic stability.…”

“…During DNA damage response, 53BP1 is a key downstream effector of the ATM pathway (Anderson et al 2001;Rappold et al 2001;Ward et al 2003). Accumulated evidence suggests that ATM-dependent 53BP1 phosphorylation activates both the G2/M checkpoint and DNA damage repair (DiTullio et al 2002;Fernandez-Capetillo et al 2002;Callen et al 2013;Chapman et al 2013). Thus, we asked whether PAR regulates the ATM-dependent 53BP1 phosphorylation.…”

Rif1 and Exo1 regulate the genomic instability following telomere losses

“…Similarly, elevated levels of Rif1 were found in breast cancer and teratocarcinomas (Wang et al ., 2009; Li et al ., 2015). Since mammalian Rif1 participates in suppressing the HDR repair pathway in the G1 phase (Chapman et al ., 2013; Di Virgilio et al ., 2013; Escribano‐Díaz et al ., 2013; Zimmermann et al ., 2013), it was suggested that too much Rif1 drives illicit and error‐prone DSB repair, which alters the genome. However, our study shows that Rif1 can drive genomic instability in the absence of DSB repair.…”

CtIP-mediated resection is essential for viability and can operate independently of BRCA1

“…It was shown that 53BP1 inhibits resection, but that BRCA1 antagonizes 53BP1, allowing the nucleolytic processing of DNA ends in S phase (Bunting et al, 2010;Chapman et al, 2012). Furthermore PTIP and RIF1, both of which act downstream of 53BP1, inhibit BRCA1-associated DNA metabolism (Callen et al, 2013;Chapman et al, 2013;EscribanoDíaz et al, 2013;Feng et al, 2013;Zimmermann et al, 2013). Nevertheless, the mediators of resection in BRCA1/53BP1, BRCA1/PTIP, and BRCA1/RIF double-deficient cells have not been identified.…”