Dynamics of mRNA and microRNA Expression in the Estrogen Response of Breast Cancer Cells

Cellular signaling leads to broad changes in gene expression that reprogram the cell and alter cell state. Signaling often begins with cellular receptors binding a ligand and initiating a transcriptional response. One example of this is the estrogen receptor, which binds the ligand estrogen and translocates to the nucleus where it binds to estrogen response elements and regulates the expression numerous target RNAs. The regulatory network of both messenger RNAs (mRNAs) and microRNAs (miRNAs) responding to estrogen stimulation is a complex, dynamic and multilayered program that is critical to the etiology of breast cancer. Estrogen receptor α (ERα) is an important biomarker of breast cancer severity and a common therapeutic target. Recent studies have demonstrated that in addition to its role in promoting proliferation, ERα also protects tumors against metastatic transformation. Current therapeutic strategies inhibit estrogen stimulated signaling and interfere with both beneficial and detrimental signaling pathways regulated by ERα. Additionally, ERα cyclically binds estrogen response elements and induces bursts of transcriptional activity. Together these observations suggest that ERα regulated genes and miRNAs may exhibit temporal variation in expression. Furthermore, it remains unclear if estrogen stimulated pathways exhibit the same temporal expression patterns, or if different pathways exhibit different temporal expression patterns. By combining both RNA-sequencing and small RNA-sequencing of cells responding to estrogen, we uncover the dynamics of both mRNA and miRNA expression in response to estrogen stimulation. Furthermore, we identify a regulatory circuit with potential therapeutic relevance to breast cancer that more specifically inhibits ERα-stimulated growth and survival pathways without interfering with its protective features. In response to estrogen stimulation, MCF7 cells (an estrogen receptor positive model cell line) exhibit induction of miR-503, and repression of the oncogene ZNF217. miR-503 inhibits proliferation in MCF7 cells, in part through its inhibition of the oncogene ZNF217 and the cell-cycle gene CCND1. While numerous regulatory interactions can be mined from this temporal profile of estrogen responsive mRNAs and miRNAs, the induction of the anti-proliferative microRNA, miR-503, both highlights the protective aspects of estrogen signaling and indicates that miR-503 holds promise as a therapeutic for breast cancer.Doctor of Philosoph