Proteomic analysis of BRCA1-depleted cell line reveals a putative role for replication protein A2 up-regulation in BRCA1 breast tumor development

Purpose: Germline mutations in BRCA1 result in a strong predisposition to breast cancer, with frequent loss of heterozygosity of the remaining wild-type allele. The development of BRCA1 tumors is likely to depend on additional genetic alterations and gene expression changes which follow growth and DNA repair defects associated with BRCA1 deficiency. The identification of these modifications offers an opportunity to find surrogate markers of BRCA1 tumors. Here, we sought to identify differentially expressed proteins related to BRCA1 depletion.

Experimental design: We used isogenic HeLa cells either stably knocked-down or not for BRCA1 (BRCA1(KD) ) and compared protein profiles of these cells by DIGE.

Results: We detected increased levels of Replication protein A2 (RPA2) in BRCA1(KD) cells as compared to control cells. RPA2 is an essential protein required for DNA replication and repair. We further demonstrated that depletion of RPA2 subunit delays growth of BRCA1(KD) respect to isogenic control cells. Strikingly, elevated levels of RPA2 were more frequently observed in BRCA1 tumors when triple-negative tumors from BRCA1 mutation carriers (n=13) and non-carriers (n=36) were stained in situ for RPA2.

Conclusions and clinical relevance: RPA2 up-regulation may thus be involved in the growth and/or survival of BRCA1 tumor cells and useful in immunohistochemical discrimination of triple-negative BRCA1 tumors.