Overexpression of the BRC repeat 8 of BRCA2 hyperstabilizes RAD51 and alters DNA repair dynamics

Background RAD51 plays an essential role in maintaining genomic stability via homologous recombination (HR). Aberrant RAD51 expression compromises genomic integrity and influences cellular responses to DNA-damaging agents. RAD51 expression is tightly regulated in normal cells, and its increased expression is associated with therapeutic resistance and poor prognosis in various cancers. BRCA2, a tumor suppressor gene product, promotes HR by directly interacting with RAD51 through eight evolutionarily conserved BRC repeats (BRC1–8). Individual BRC repeats in BRCA2 share a relatively low sequence similarity and possess distinct biochemical properties. We previously reported that the expression of certain BRC repeats alters RAD51 protein levels, suggesting that individual BRC repeats distinctly affect RAD51 expression. Methods and Results We aimed to determine the specific BRC repeat regions that affect RAD51 protein levels. Notably, BRC8 expression significantly elevated protein levels and foci formation, possibly due to the inhibition of ubiquitin-mediated RAD51 degradation. Paradoxically, despite increased RAD51 foci formation, BRC8 expression significantly reduced HR repair efficiency and sensitivity to DNA-damaging agents. Conclusion Our findings suggest that BRC8 overexpression stabilizes RAD51 by inhibiting ubiquitin-dependent degradation of RAD51, leading to increased persistence in RAD51 foci, indicating impaired timely removal of RAD51 from DNA damage sites and reduced HR efficiency. Additionally, altered cell cycle distribution may contribute to reduced non-homologous end-joining (NHEJ) efficiency, thereby further enhancing cellular sensitivity to DNA-damaging agents. These findings provide a basis for exploring the potential of BRC8-based peptides as tools for modulating RAD51 stability and sensitizing cells to DNA damage.