Down regulation of BRCA2 causes radio-sensitization of human tumor cells in vitro and in vivo

In order to study the role of BRCA2 protein in homologous recombination(HR) repair and radio-sensitization, we utilized RNA interference (RNAi)strategy in vitro and in vivo with human tumor cells. HeLa cellstransfected with BRCA2 siRNA (Qiagen) as well as negative-control siRNAfor 48 hours were irradiated, and several critical end points wereexamined. The radiation cell survival level was significantly reduced inHeLa cells with BRCA2 siRNA when compared with mock- or negative controlsiRNA transfected cells. DNA double strand break (DSB) repair asmeasured by constant field gel-electrophoresis showed a clear inhibitionin cells with BRCA2 siRNA, while little inhibition was observed in cellswith negative control siRNA. Our immuno-staining experiments revealed asignificant delay in Rad51 foci formation in cells with BRCA2 siRNA whencompared with the control populations. However, none of the NHEJproteins nor the phosphorylation of DNA-PKcs was affected in cellstransfected with BRCA2 siRNA. In addition, the combined treatment withradiation and BRCA2 siRNA in xenograft model with HeLa cells showed anefficient inhibition of in vivo tumor growth. Our results demonstratedown-regulation of BRCA2 leads to radio-sensitization mainly through theinhibition of HRR type DSB repair; a possibility of using BRCA2 siRNA asan effective radiosensitizer in tumor radiotherapy may arise