CHAMP1-POGZ counteracts the inhibitory effect of 53BP1 on homologous recombination and affects PARP inhibitor resistance.

DNA double-strand break (DSB) repair-pathway choice regulated by 53BP1 and BRCA1 contributes to genome stability. 53BP1 cooperates with the REV7-Shieldin complex and inhibits DNA end resection to block homologous recombination (HR) and affects the sensitivity to inhibitors for poly (ADP-ribose) polymerases (PARPs) in BRCA1-deficient cells. Here, we show that a REV7 binding protein, CHAMP1 (chromosome alignment-maintaining phosphoprotein 1), has an opposite function of REV7 in DSB repair and promotes HR through DNA end resection together with POGZ (POGO transposable element with ZNF domain). CHAMP1 was recruited to laser-micro-irradiation-induced DSB sites and promotes HR, but not NHEJ. CHAMP1 depletion suppressed the recruitment of BRCA1, but not the recruitment of 53BP1, suggesting that CHAMP1 regulates DSB repair pathway in favor of HR. Depletion of either CHAMP1 or POGZ impaired the recruitment of phosphorylated RPA2 and CtIP (CtBP-interacting protein) at DSB sites, implying that CHAMP1, in complex with POGZ, promotes DNA end resection for HR. Furthermore, loss of CHAMP1 and POGZ restored the sensitivity to a PARP inhibitor in cells depleted of 53BP1 together with BRCA1. These data suggest that CHAMP1and POGZ counteract the inhibitory effect of 53BP1 on HR by promoting DNA end resection and affect the resistance to PARP inhibitors.