Exploring estrogen receptor gene regulatory mechanism in breast cancer
Katchy, Anne Chinenye 1984-
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Estrogen has vital roles in development and maintenance of mammary gland and supports the growth of the majority of primary breast cancer. It carries out its function through the estrogen receptors (ER): ERα and ERβ. In this dissertation, we focused on identifying the functional and genome wide effects of both receptors in breast cancer cell lines (T47D and MCF7). First, we aimed at identifying microRNAs (miRNAs) that are significantly associated with normal or disrupted estrogen signaling in breast cancer cells, and are regulated by ERα and ERβ. Despite the fact that 24h estrogen treatment results in strong changes to expression of about 900 protein-coding transcripts, we found no significant changes in mature miRNA expression levels by 17β-estradiol (E2)-activated ERα in neither T47D nor MCF7 breast cancer cells. On the other hand, when studying the effects of exogenously expressed ERβ, we identified miR-135a, miR-21, miR-200c, and miR-522, among others, as being regulated. Most of the ERβ effects were ligand-independent, but we observed a significant response to E2 in the MCF7-ERβ cells. Also, the MCF7-ERβ showed enhanced stem cell abilities in comparison to the MCF7-Control cells as illustrated by increased mammospheres formation during several generations. Secondly, we aimed at investigating environmental factors and its effect on the risk for breast cancer. We identified the gene expression response for each of these compounds: BPA, genistein (Gen), E2, and soy formula extract (SF) in MCF7 cells, and found that each regulated similar genes in the same manner. Many target genes regulated by BPA, Gen, and SF, were involved in important biological processes identical to those of estrogen. Investigation of non-ERα mediated regulations for these EDCs suggested that these compounds may regulate gene transcription solely through ERα, in the cells and doses used. Furthermore, we found that these compounds acted together in a sub-additive manner, and tumor clustering with the gene expression profile of these EDC compounds revealed a significantly lower disease free survival. Altogether, the data presented in this dissertation would aid in increasing the knowledge of early risk factors for breast cancer. Our work provides data for future use of the estrogen receptors in clinical applications by providing new candidates for pharmaceutical drug development, as well as, biomarkers for diagnosis and prognosis.