GSE99680
Estrogen signaling is reprogrammed in breast tumorigenesis
Limited knowledge of the changes in estrogen receptor (ER) signaling during the transformation of the normal mammary gland to breast cancer hinders the development of effective prevention and treatment strategies. Differences in estrogen signaling between normal human primary breast epithelial cells and primary breast tumors obtained immediately following surgical excision were explored. Transcriptional profiling of normal ER+ mature luminal mammary epithelial cells and ER+ breast tumors revealed significant difference in the response to estrogen stimulation. Consistent with these differences in gene expression, the normal and tumor ER cistromes were distinct and sufficient to segregate normal breast tissues from breast tumors. The selective enrichment of the DNA binding motif GRHL2 in the breast cancer-specific ER cistrome suggests that it may play a role in the differential function of ER in breast cancer. Depletion of GRHL2 resulted in altered ER binding and differential transcriptional responses to estrogen stimulation. Furthermore, GRHL2 was demonstrated to be essential for estrogen-stimulated proliferation of ER+ breast cancer cells. DLC1 was also identified as an estrogen-induced tumor suppressor in the normal mammary gland with decreased expression in breast cancer. In clinical cohorts, loss of DLC1 and gain of GRHL2 expression are associated with breast cancer and are independently predictive for worse survival. This study suggests that normal ER signaling is lost and tumor-specific ER signaling is gained during breast tumorigenesis. Unraveling these changes in ER signaling during breast cancer progression should aid the development of more effective prevention strategies and targeted therapeutics. SIGNIFICANCE STATEMENT: Abnormal estrogen receptor (ER) signaling drives the majority of breast cancers and is targeted by endocrine therapies. However, in normal breast tissue, ER signaling has been demonstrated to promote benign functions such as development and differentiation. Using genomic techniques to characterize ER function in normal breast and breast tumors, this study reveals differential patterns of ER signaling, suggesting that normal ER signaling is lost and tumorigenic ER signaling gained during breast tumor formation. Better understanding of this process can aid the development of improved breast cancer prevention strategies and therapies. Overall design: Methods: To model the normal breast epithelium, viable tissue specimens from patients undergoing reduction mammoplasty were obtained and enriched for breast epithelial cells via FACS. Fresh-frozen ER+ breast tumor samples were then obtained for comparison. RNA-seq, ChIP-seq for ER, and genome-wide CRISPR screening in the presence of estrogen stimulation were performed. These various modalities of genomic data were then integrated and analyzed to identify mechanistic patterns in breast tumorigenesis.