Ring Finger Nuclear Factor RNF168 Is Important for Defects in Homologous Recombination Caused by Loss of the Breast Cancer Susceptibility Factor BRCA1

The RING finger nuclear factor RNF168 is required for recruitment of several DNA damage response factors to double strand breaks (DSBs), including 53BP1 and BRCA1. Because 53BP1 and BRCA1 function antagonistically during the DSB repair pathway homologous recombination (HR), the influence of RNF168 on HR has been unclear. We report that RNF168 depletion causes an elevated frequency of two distinct HR pathways (homology-directed repair and single strand annealing), suppresses defects in HR caused by BRCA1 silencing, but does not suppress HR defects caused by disruption of CtIP, RAD50, BRCA2, or RAD51. Furthermore, RNF168-depleted cells can form ionizing radiation-induced foci of the recombinase RAD51 without forming BRCA1 ionizing radiation-induced foci, indicating that this loss of BRCA1 recruitment to DSBs does not reflect a loss of function during HR. Additionally, we find that RNF168 and 53BP1 have a similar influence on HR. We suggest that RNF168 is important for HR defects caused by BRCA1 loss.