Expression of BRC repeats in breast cancer cells disrupts the BRCA2- Rad51 complex and leads to radiation hypersensitivity and loss of G₂/M checkpoint control

BRCA2 is a breast tumor suppressor with a potential function in the cellular response to DNA damage. BRCA2 binds to Rad51 through its BRC repeats. In support of the biological significance of this interaction, we found that the complex of BRCA2 and Rad51 in breast cancer MCF-7 cells was diminished upon conditional expression of a wild-type, but not a mutated, BRC4 repeat using the tetracycline-inducible system. Cells expressing a wild- type BRC4 repeat showed hypersensitivity to γ-irradiation, an inability to form Rad51 radiation-induced foci, and a failure of radiation-induced G₂/M, but not G₁/S, checkpoint control. These results strongly suggest that the interaction between BRCA2 and Rad51 mediated by BRC repeats is critical for the cellular response to DNA damage.