Abstract 3384: ER-α: The paramount facet predisposing BRCA1 defective tumors

BRCA1 and BRCA2 are key tumor-suppressor proteins that aid in DNA damage repair and hence, play a pivotal role in ensuring the cellular genomic stability. Though BRCA1 protein is indispensable for all the cells, there is a restriction of cancers due to BRCA1 mutation, largely to the breast and the ovary. To date, a valid explanation for this predisposition does not prevail; nevertheless, a link between estrogen receptor-α (ER-α) and BRCA1 has been reported. Thus, it could be speculated that BRCA1 functions are being manifested through numerous interacting partners, which once identified, might unravel the enigma behind the BRCA1 defective selective tumorigenesis. These factors thus led us to the current study, which aims to analyze the role of ER-α in BRCA1-mediated DNA damage repair and its association with breast tumorigenesis. The direct interaction between BRCA1 and ER-α has been extensively elucidated and BRCA1 mutation has been well known to be associated with cancers in tissues where ER-α is overexpressed; consequently, its role in DNA damage repair could be a definite possibility. To deduce the exact function of ER-α in BRCA1-mediated DNA damage repair, ER-α proficient and BRCA1 wild-type breast cancer cell line, MCF-7, was used for the study. Stable clones of MCF-7 cell lines deficient in ER-α as well as BRCA1 were generated by independent shRNA transfections. Repairable DSBs were created in the cell lines using specific concentration of the platinum-based drug, cisplatin (cis-diamminedichloridoplatinum). Nuclear damage (DNA-DSB) and the ability of cells to sense and repair the DSBs due to cisplatin treatment in ER-α/ BRCA1 deficeint and proficient cells was detected by the scoring of phosphorylation in the histone variant H2AX (γ-H2AX) by immunocytochemistry and Western blot analysis. Damage repair events like phosphorylation of BRCA1 and its recruitment to the nuclear damage site as foci and direct interaction between these proteins during damage repair were analyzed by varying experimental procedures. Finally, the DNA DSB repair efficiency of these cells were directly measured using specific DNA DSB repair assays. The results obtained from microscopy, immunocytochemistry, Western blot analysis and other assays noticeably indicated that the DNA damage repair efficiency was significantly reduced in the ER-deficient condition. Together, these results supply clues to the indispensable role of ER-α in DNA DSB repair. The current study acts as basic evidence in understanding the molecular biology behind the predisposition of BRCA1 mutations to breast or ovarian cancers, which otherwise remains elusive. Unveiling these hidden mechanisms might pave the way for the identification of new target,s which would enable better therapeutics for these cancers. Citation Format: Arathi Rajan, Neetha Rajan Latha, Priya Srinivas. ER-α: The paramount facet predisposing BRCA1 defective tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3384.