Abstract IA014: BRCA2 promotes genomic integrity and therapy resistance primarily through its role in homology-directed repair

Abstract

Abstract Tumor suppressor BRCA2 functions in multiple pathways. The role of BRCA2 in homologous recombination, also termed homology-directed repair (HDR), is particularly well known. We also showed that it has a key role in the protection of stalled replication forks from the MRE11 nuclease. Moreover, BRCA2 also suppresses the formation of single-stranded gaps during replication. We have attempted to delineate the relative contributions of these three pathways to the maintenance of genome integrity and chemotherapy response using separation of function alleles. First, we report that mouse and human cells require a RAD51 filament stabilization motif in BRCA2 for both fork protection and gap suppression but not HDR. In mice, loss of fork protection and gap suppression do not compromise genome instability or shorten tumor latency. By contrast, HDR deficiency increases spontaneous and replication stress-induced chromosome aberrations and tumor predisposition. Unlike with HDR, fork protection and gap suppression defects are also observed in Brca2 heterozygous cells from mice, likely due to reduced RAD51 stabilization at stalled forks and gaps. Sensitivity to the PARP inhibitor olaparib is greatest for HDR-deficient cells, although fork protection/gap suppression-defective cells show a weak sensitivity. Gaps arise from PRIMPOL activity, which is associated with sensitivity to 5-hydroxymethyl-2’-deoxyuridine (hmdU) and DNPH1 inhibition due to the formation of SMUG1-generated abasic sites and is exacerbated by poly(ADP-ribose) polymerase inhibition. In summary, this work demonstrates that HDR deficiency has the major role in generating sensitivity to chemotherapeutics, although gap suppression deficiency may be targeted by specific agents. Citation Format: Pei Xin Lim, Maria Jasin. BRCA2 promotes genomic integrity and therapy resistance primarily through its role in homology-directed repair [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Damage Repair: From Basic Science to Future Clinical Application; 2024 Jan 9-11; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2024;84(1 Suppl):Abstract nr IA014.