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Title:Estradiol regulation of leucine-rich repeat immunoglobulin-like domains protein 1 (LRIG 1) and roles of estrogen receptor in translational regulation in breast cancer cells
Author(s):Funk, Cory C.
Director of Research:Katzenellenbogen, Benita S.
Doctoral Committee Chair(s):Belmont, Andrew S.
Doctoral Committee Member(s):Shapiro, David J.; Freeman, Brian C.; Bellini, Michel; Katzenellenbogen, Benita S.
Department / Program:Cell & Developmental Biology
Discipline:Cell and Developmental Biology
Degree Granting Institution:University of Illinois at Urbana-Champaign
breast cancer
estrogen receptor
gene regulation
Abstract:Among the first diagnostic tests performed upon finding a tumor in the breast is the determination of the expression of three proteins: the Estrogen Receptor α (ERα), the Progesterone Receptor (PR) and Heregulin 2 (HER2). The ER, though often considered responsible for driving tumor growth, is usually indicative of a good prognosis as ER-positive tumors are typically more indolent in nature and responsive to endocrine therapy. Long after estrogens were known to drive the growth of many breast tumors, the estrogen receptor was identified. The ER is a modular transcription factor known to regulate the expression of over a thousand genes in breast cancer cells. As a master regulator of transcription, ER can impact the transcription and subsequent expression of many proteins that ultimately determine the growth and invasiveness of a tumor. As a transcriptional regulator, activation of ER with its cognate ligand, estradiol, results in a cascade of changes beginning with chromatin remodeling of estradiol-regulated genes. In an attempt to identify ER-interacting proteins that aid in this chromatin unfolding activity, we performed a yeast two-hybrid screen using amino acids 420-534 of ERα as bait and identified Eukaryotic translation initiation factor 3 subunit F (eIF3f) as an interaction partner. Fluorescence microscopy suggests that in the presence of estradiol, the location of ERα-eIF3f changes. Though unclear if eIF3f, a translation factor, plays a role in chromatin unfolding, as a translation factor, we suggest that the interaction between eIF3f and ERα establishes a link through which estradiol can regulate translation. In support of this link, we find ERα in polysome profile fractions. Knockdown of eIF3f also appears to change the solubility of ERα within the nucleus. eIF3f knockdown also results in changes in steady-state mRNA levels of specific estradiol-target genes. Upon isolation of mRNA following polysome fractionation, we observe differences in the rate of translation of several estradiol-regulated mRNAs. Unlike other ERα-interacting partners such as Jab1 and E6-AP, eIF3f interacts with a shorter form of ERα. The effects of estradiol on cellular function are pleiotropic. As a transcriptional regulator, ER regulates many genes that can have a subsequent impact on other cellular functions. These so-called secondary effects are often associated as the principle actions of estradiol. We identify leucine-rich repeats and immunoglobulin-like domains protein 1 (LRIG1) as an estradiol-regulated gene. LRIG1 is a negative regulator of Receptor Tyrosine Kinase (RTK) signaling. Up-regulation of LRIG1 mRNA and protein is mediated by the estrogen receptor-α (ERα) and we identified the regions of the LRIG1 gene to which ER binds. LRIG1 regulation by estradiol helps to explain how tumors typically utilize either estradiol or growth factor pathways, but rarely both, as mitogenic stimuli. Increased LRIG1, in response to estradiol, results in decreased signaling through RTK pathways. The impact of LRIG1 regulation by estradiol is cell-type specific. LRIG1 protein levels are important for both the growth of cells as well as colony formation and invasiveness of ERα-positive and HER2-positive BT-474 and ERα-positive and HER2-negative MCF-7 breast cancer cell lines. LRIG1 regulation by estradiol may be important for breast cancer etiology and phenotypic properties by influencing signaling pathways such as the AKT and MAPK pathways, which help to determine the breast tumor subtype as well as responsiveness to cancer treatments.
Issue Date:2011-01-21
Rights Information:Copyright 2010 Cory Funk
Date Available in IDEALS:2013-01-22
Date Deposited:2010-12

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