Minichromosome maintenance complex facilitates the recruitment of BRCA1 onto chromatin and foci formation in A549 cells

Lung cancer is the most frequent cancer and the leading cause of cancer death worldwide. Therefore, a better understanding of DNA damage repair in cells might be helpful to treat cancers. The present study was aimed to investigate the potential interaction between breast cancer 1 (BRCA1) and minichromosome maintenance proteins (MCMs) during DNA damage in lung carcinoma A549 cells. The recombinant vectors of BRCA1 and MCMs with different tags were constructed and transfected into A549 cells. Immunoprecipitation (IP), immunoblot (IB), and mass spectrometry were performed to screen the possible interactions between BRCA1 and MCMs. In addition, the expression of MCM2 and MCM6 was knocked down by specific short hairpin RNAs (shRNAs). The cells were incubated with camptothecin (CPT) or bleomycin to induce DNA damage, and then the interaction between MCM2 and BRCA1, chromatin fraction, and foci formation of BRCA1 were examined. The results showed that MCM2/3/5/6 was immunoprecipitated against the hemaglutinin (HA)-BRCA1 in A549 nuclei. Upon DNA damage, the interaction between MCM2 and BRCA1 was reduced. Moreover, downregulation of MCM2 or MCM6 could increase the nonchromatin level of BRCA1, but decrease the chromatin level of BRCA1. Knockdown of MCM2 or MCM6 could statistically inhibit foci formation of BRCA1 in A549 nuclei upon bleomycin-induced DNA damage (P < 0.05). Our results suggest that there is an interaction between BRCA1 and MCMs in A549 cell nuclei. Down-regulation of MCMs could prevent chromatin fraction and foci formation of BRCA1 upon DNA damage.