BRCA2
tumor suppressor protein ensures genome integrity by mediating DNA repair via homologous recombination (HR). This function is executed in part by its canonical
DNA binding domain located at the C-terminus (BRCA2CTD), the only folded domain of the
protein. Most germline pathogenic missense variants are located in this highly conserved region which binds to
single-stranded DNA (ssDNA) and to the acidic
protein DSS1. These interactions are essential for the HR function of BRCA2. Here, we report that the variant R2645G, identified in
breast cancer and located at the DSS1 interface, unexpectedly increases the ssDNA binding activity of BRCA2CTDin vitro. Human cells expressing this variant display a hyper-recombination phenotype,
chromosomal instability in the form of chromatid gaps when exposed to DNA damage, and increased
PARP inhibitor sensitivity. In mouse embryonic stem cells (mES), this variant alters viability and confers sensitivity to
cisplatin and
Mitomycin C. These results suggest that BRCA2 interaction with ssDNA needs to be tightly regulated to limit HR and prevent
chromosomal instability and we propose that this control mechanism involves DSS1. Given that several missense variants located within this region have been identified in
breast cancer patients, these findings might have clinical implications for carriers.