BRCA2 is required for ionizing radiation-induced assembly of rad51 complexin vivo

Mutations in BRCA1 and BRCA2 account for the majority of familial breast ca ncers. Cells with mutated BRCA1 or BRCA2 are hypersensitive to ionizing rad iation (IR) and exhibit defective DNA repair. Both BRCA1 and BRCA2 have bee n reported to bind Rad51, a protein essential for homologous recombination and the recombinational repair of DNA double-strand breaks. In normal cells , a redistribution of Rad51 protein, manifested as formation of Rad51 nucle ar foci, is seen upon IR treatment. Here we demonstrate that In-induced Rad 51 foci formation is aberrant in BRCA2- but not BRCA1-deficient tumor cells . In Capan-1 cells, which do not express functional BRCA2, there was little Rad51 foci formation in response to a wide range of radiation dosages, Mor eover, forced expression of a fusion protein containing green fluorescent p rotein and the first Rad51-binding BRC repeat of BRCA2 in cells with wild;t ype BRCA2 rendered them hypersensitive to IR and cisplatin and compromised IR-induced Rad51 foci formation. In HCC1937 cells, which harbor mutation of BRCA1, In-induced Rad51 foci were readily detected, This study suggests a requirement of BRCA2 protein for the IR-induced assembly of Rad51 complex i n vivo.