Compensatory functions and interdependency of the DNABinding domain of BRCA2 with the BRCA1-PALB2-BRCA2 complex

BRCA1, BRCA2, and PALB2 are key players in cellular tolerance to chemotherapeutic agents, including camptothecin, cisplatin, and PARP inhibitor. The N-terminal segment of BRCA2 interacts with PALB2, thus contributing to the formation of the BRCA1-PALB2-BRCA2 complex. To understand the role played by BRCA2 in this complex, we deleted its N-terminal segment and generated BRCA2DN mutant cells. Although previous studies have suggested that BRCA1-PALB2 plays a role in the recruitment of BRCA2 to DNA-damage sites, BRCA2DN mutant cells displayed a considerably milder phenotype than did BRCA2^-/- null-deficient cells. We hypothesized that the DNA-binding domain (DBD) of BRCA2 might compensate for a defect in BRCA2DN that prevented stable interaction with PALB2. To test this hypothesis, we disrupted the DBD of BRCA2 in wild-type and BRCA2DN cells. Remarkably, although the resulting BRCA2DDBD cells displayed a moderate phenotype, the BRCA2DN+DDBD cells displayed a very severe phenotype, as did the BRCA2^-/- cells, suggesting that the N-terminal segment and the DBD play a substantially overlapping role in the functionality of BRCA2. We also showed that the formation of both the BRCA1-PALB2-BRCA2 complex and the DBD is required for efficient recruitment of BRCA2 to DNA-damage sites. Our study revealed the essential role played by both the BRCA1-PALB2-BRCA2 complex and the DBD in the functionality of BRCA2, as each can compensate for the other in the recruitment of BRCA2 to DNA-damage sites. This knowledge adds to our ability to accurately predict the efficacy of antimalignant therapies for patients carrying mutations in the BRCA2 gene.