Abstract PD01-08: Differences in estrogen receptor signaling in non-malignant primary ER-positive breast epithelial cells and breast cancer.

Abstract

Abstract Background: The estrogen receptor (ER) is expressed in ∼70% of sporadic breast cancer and activates genes driving cell proliferation and tumorigenesis. We have previously performed genome-wide analysis of ER binding sites in MCF-7 breast cancer cells, and identified distinct mechanisms of ER signaling. We have also previously used EpCAM and CD49f as markers to enrich for viable ER-positive (ER+) cells obtained from non malignant breast tissue. Here, we seek to elucidate differences in ER signaling between non-malignant and ER+ breast cancer cells. Methods: Primary breast epithelial cells were obtained from patients undergoing reduction mammoplasties and surgical excision of ER+ breast cancer. After dissociation of breast reductions into a single-cell suspension, ER+ mature luminal (ML; EpCAM+CD49f−) and luminal progenitor (LP; EpCAM+CD49f+) 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. These results were compared to MCF-7 breast cancer cells. Results: Reduction mammoplasty and ER+ breast cancer tissues were analyzed, and compared to MCF-7 cells. Gene expression profiles were different between non-malignant tissue and ER+ breast cancer cells following estrogen stimulation, with a 2–3 fold higher number of ER regulated genes in ER+ breast cancer compared to ER+ non malignant cells, and few overlapping estrogen regulated genes. Genes that promotes cell cycling and cell proliferation were downregulated in non-malignant tissue, but were upregulated in breast cancer cells (P < 10–5). CYP1A1, a major estradiol metabolizing enzyme, was upregulated in normal cells but downregulated in ER+ breast cancer cells. Motif analysis of ER ChIP-seq data in normal and ER+ breast cancer tissues demonstrated an enrichment of ER motifs in the overlapping sites and an enrichment of FOXA1 motifs in ER+ breast cancer cells and TCF12 motifs in non-malignant ER+ epithelial cells. Conclusions: There are contrasting differences in ER signaling between normal mammary and breast cancer cells, with estrogen having anti-proliferative effects in normal luminal cells compared to pro-proliferative effects in breast cancer. ER ChIP-Seq has identified TCF12 as a major co-factor in non-malignant breast tissue whilst FOXA1 is a major co-factor in ER+ breast cancer. Our data provides evidence for key alterations in ER-signaling during tumorigenesis, and identifies potential mechanisms to target cancer specific ER signaling. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD01-08.