Estrogen receptor (ER) signaling in normal, BRCA (B) 1 and B2 mutation associated, and ER-positive breast cancer (BC) mammary cells.

Abstract

576 Background: ER is expressed in ≈70% of sporadic BC and activates genes driving cell proliferation and tumorigenesis. B1 and B2 mutation associated BC have predominant triple negative and ER+ phenotypes respectively, yet hormonal manipulation with oophorectomy reduces BC risk in both B1 and B2 carriers. We have previously performed genome-wide analysis of ER binding sites in MCF-7 BC cells, and identified distinct mechanisms of ER signaling. Here, we seek to elucidate differences in ER signaling between non-malignant (normal, B1 and B2) and ER+ BC mammary cells. Methods: Breast tissue were obtained from patients undergoing reduction mammoplasties (normal), prophylactic mastectomies (B1 and B2 carriers) and surgical excision of ER+ BC. After dissociation into a single-cell suspension, ER+ EpCAM+CD49f- mature luminal (ML) and EpCAM+CD49f+ luminal progenitor (LP) subpopulations were obtained by flow cytometry. Following estrogen stimulation, RNA was extracted for gene microarray analysis. ER chromatin immunoprecipitation and DNA sequencing (ChIP-seq) was performed and DNA libraries prepared and sequenced. Results: Triplicates ofnormal, prophylactic B1 and B2, and ER+ BC tissues were analyzed.Gene ontology analysis indicates different gene expression signatures between non-malignant tissue and MCF-7 BC cells following estrogen stimulation. Genes that promotes cell cycling and proliferation were downregulated in non-malignant tissue, but were upregulated in BC cells (P < 10-5). Hierarchical clustering of the gene microarray by mutation status revealed distinct LP gene signatures in normal, B1 and B2 breast tissue, whilst the ML signatures were largely indistinguishable between the three tissue types. Conclusions: There are contrasting differences in ER signaling between normal mammary and BC cells, with estrogen having anti-proliferative effects in normal luminal cells compared to pro-proliferative effects in BC. Our data suggest that alterations in ER signaling play a major role in breast tumorigenesis. Differences in the LP population between B1 and B2 breast tissue may account for their distinct BC phenotypes.