Yuan S S, Lee S Y, Chen G, Song M, Tomlinson G E, Lee E Y
Department of Molecular Medicine/Institute of Biotechnology, University of Texas Health Science Center at San Antonio, 78245, USA.
Cancer Res. 1999 Aug 1;59(15):3547-51.
Mutations in BRCA1 and BRCA2 account for the majority of familial breast cancers. Cells with mutated BRCA1 or BRCA2 are hypersensitive to ionizing radiation (IR) and exhibit defective DNA repair. Both BRCA1 and BRCA2 have been 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 nuclear foci, is seen upon IR treatment. Here we demonstrate that IR-induced Rad51 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. Moreover, forced expression of a fusion protein containing green fluorescent protein and the first Rad51-binding BRC repeat of BRCA2 in cells with wild-type BRCA2 rendered them hypersensitive to IR and cisplatin and compromised IR-induced Rad51 foci formation. In HCC1937 cells, which harbor mutation of BRCA1, IR-induced Rad51 foci were readily detected. This study suggests a requirement of BRCA2 protein for the IR-induced assembly of Rad51 complex in vivo.
BRCA1和BRCA2基因的突变是大多数家族性乳腺癌的病因。携带BRCA1或BRCA2基因突变的细胞对电离辐射（IR）高度敏感，且DNA修复存在缺陷。据报道，BRCA1和BRCA2均能与Rad51结合，Rad51是一种对同源重组和DNA双链断裂的重组修复至关重要的蛋白质。在正常细胞中，经IR处理后，可观察到Rad51蛋白重新分布，表现为Rad51核灶形成。在此，我们证明，在BRCA2缺陷而非BRCA1缺陷的肿瘤细胞中，IR诱导的Rad51灶形成异常。在不表达功能性BRCA2的Capan-1细胞中，无论辐射剂量如何，几乎都没有Rad51灶形成。此外，在具有野生型BRCA2的细胞中，强制表达包含绿色荧光蛋白和BRCA2的首个Rad51结合BRC重复序列的融合蛋白，会使细胞对IR和顺铂高度敏感，并损害IR诱导的Rad51灶形成。在携带BRCA1突变的HCC1937细胞中，很容易检测到IR诱导的Rad灶。这项研究表明，体内IR诱导的Rad51复合物组装需要BRCA2蛋白。
