The breast cancer susceptibility gene BRCA1 is required for subnuclear assembly of Rad51 and survival following treatment with the DNA cross-linking agent cisplatin

Mutations in breast cancer tumor susceptibility genes, BRCA1 and BRCA2, pre dispose women to early onset breast cancer and other malignancies. The Brca genes are involved in multiple cellular processes in response to DNA damag e including checkpoint activation, gene transcription, and DNA repair. Bioc hemical interaction with the recombinational repair protein Rad51 (Scully, R., Chen, J., Ochs, R. L., Keegan, M., Hoekstra, M., Feunteun, J., and Livi ngston, D. M. (1997) Cell 90, 425-435), as well as genetic evidence (Moynah an, M. E., Chiu, J.W., holler, B. H., and Jasin, M. (1999) Mol. Cell 4, 511 -818 and Snouwaert, J. N., Gowen, L. C., Latour, A. M., Mohn, A. R., Xiao, A., DiBiase, L., and Roller, B. H. (1999) Oncogene 18, 7900-7907), demonstr ates that Brca1 is involved in recombinational repair of DNA double strand breaks. Using isogenic Brca1(+/+) and brca1(-/-) mouse embryonic stem (ES) cell lines, we investigated the rob of Brca1 in the cellular response to tw o different categories of DNA damage: x-ray induced damage and cross-linkin g damage caused by the chemotherapeutic agent, cisplatinum, Immunoflouresce nce studies with normal and brca1(-/-) mutant mouse ES cell lines indicate that Brca1 promotes assembly of subnuclear Rad51 foci following both types of DNA damage. These foci are likely to be oligomeric complexes of Rad51 en gaged in repair of DNA lesions or in processes that allow cells to tolerate such lesions during DNA replication. Clonogenic assays show that brca1(-/- ) mutants are 5-fold more sensitive to cisplatinum compared with wild-type cells. Our studies suggest that Brca1 contributes to damage repair and/or t olerance by promoting assembly of Rad51. This function appears to be shared with Brca2.