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Title:Novel tools to identify estrogen regulated genes important for breast and ovarian cancer cell proliferation
Author(s):Cherian, Mathew Muthuthottathu
Director of Research:Shapiro, David J.
Doctoral Committee Chair(s):Shapiro, David J.
Doctoral Committee Member(s):Kemper, Jongsook K.; Raetzman, Lori; Bolton, Eric C.
Department / Program:Molecular and Integrative Physiology
Discipline:Molecular and Integrative Physiology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Breast Cancer
Abstract:Estrogens are steroid hormones produced by the ovaries and extra ovarian tissues including the adrenal gland and adipose tissue. There are 3 major physiologically relevant estrogens in the human body, the most potent and biologically relevant of which is 17 -estradiol (E2). E2 exerts its physiologic functions by acting through two isoforms of Estrogen Receptor (ER); ER and ER . ERs are normally bound to heat shock chaperone proteins but once E2 diffuses across the cell membrane and binds to the ligand binding pocket of ER it sheds these proteins, homodimerizes and binds to DNA recruiting transcriptional machinery and upregulating a number of target genes including those important for proliferation. Estrogens acting through ER play a central role in the proliferation of breast and ovarian cancer cells as evidenced by the mainstay clinical adjuvant therapies for breast cancer which target the ligand pocket of estrogen receptor by either competitively displacing endogenous ligand, or by inhibiting the rate dependent enzymes responsible for synthesizing the endogenous ligand. While the importance of E2-ER as a central regulator in breast cancer proliferation is unquestioned, it remains unclear how ER is activated when the clear majority of women who develop breast cancer are post-menopausal. After menopause the concentrations of E2 are at their lowest point in a woman's life. Epidemiologic studies show that the level of E2 necessary to increase the risk of breast cancer in a post-menopausal woman is in the picomolar range. However, the known binding affinity of E2 for ER lies between 0.5 and 2 nM. It was not known whether E2 concentrations in the picomolar range can exert biological effects on cell proliferation and gene expression. Moreover, the identity of key regulators of E2-ER induced proliferation are not fully characterized. Recent reports indicate that roughly 15% of the human genome is regulated by Estrogen Receptor. This growing list of ER regulated genes has been compiled, but determining which genes are critical factors in E2 induced proliferation has remained challenging. In order to probe these questions, we developed techniques for studying the effect of low concentrations of E2 on estrogen induced cell proliferation and gene expression. We used this information to begin to identify critical ER regulated genes. Moreover, we developed a new experimental model that allows us to identify genes critical for E2-ER dependent cell proliferation in a nearly isogenic cell system. Through careful removal of exogenous estrogens we have developed a cell culture system in which the growth of ER positive cell lines is solely dependent on the addition of E2 to the system. Therefore, in this system E2 is the missing factor preventing the cells from proliferating. Using this model we found that picomolar concentrations of E2 are able to stimulate near maximal proliferation of MCF-7, T47D, T47D ER D538G, BG1 and PEO4 breast and ovarian cancer cells. Furthermore, picomolar E2 stimulates robust colony formation in anchorage independent soft agar assays. This effect is not primarily mediated through ER 's extra-nuclear activation of the ERK signaling pathway, but rather through ER 's classic nuclear mechanism of action. Utilizing qPCR we analyzed expression of a number of genes and find that some genes are concordantly regulated at picomolar and nanomolar concentrations while other genes, such as FOS, were regulated by nanomolar but not picomolar concentrations of E2. Finally, we show that picomolar concentrations of E2 are sufficient to elicit robust recruitment of ER to regulatory elements in estrogen responsive genes. The second tool described in this work is a set of nearly isogenic cell lines with a specific phenotypic difference. The T47D KBluc cell line was originally developed as a breast cancer cell line stably transfected with a (ERE)3-luciferase reporter in order to detect environmental estrogens. A key difference between this cell line and its parental T47D cell line is that E2 does not stimulate proliferation of the cells. We demonstrate that this cell line contains ER , that the ER is functional and able to regulate both the transfected reporter and endogenous genes. We also tested a panel of known ER regulated genes to see if any of the genes are discordantly regulated between the two cell lines; this would suggest the gene might play a role in E2 induced cell proliferation. These two tools represent an important step in furthering our understanding of E2-ER regulated cell proliferation. Notably, we show experimentally that the extremely low concentrations of estrogen identified as tumorigenic in epidemiological studies are sufficient to induce growth of breast cancer cells in the laboratory. This work demonstrates the potential of a novel approach to pursuing genome wide transcriptome studies of ER action in order to identify critical regulators of ER induced proliferation.
Issue Date:2018-03-20
Rights Information:Copyright 2018 Mathew Cherian
Date Available in IDEALS:2018-09-04
Date Deposited:2018-05

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