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Estrogen-Regulated Gene Networks in Human Breast Cancer Cells: Involvement of E2F1 in the Regulation of Cell Proliferation

Departments of Biochemistry (J.D.S.) and Molecular and Integrative Physiology (J.F., B.S.K.), University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3704; Women’s Health and Musculoskeletal Biology (B.K., K.C.N.C.), Wyeth Research, Collegeville, Pennsylvania 19426; and Department of Molecular Biology and Genetics (W.L.K.), Cornell University, Ithaca, New York 14853-4203

Address all correspondence and requests for reprints to: Dr. Benita S. Katzenellenbogen, University of Illinois, Department of Molecular and Integrative Physiology, 524 Burrill Hall, 407 South Goodwin Avenue, Urbana, Illinois 61801-3704. E-mail: katzenel{at}life.uiuc.edu.

Estrogens generally stimulate the proliferation of estrogen receptor (ER)-containing breast cancer cells, but they also suppress proliferation of some ER-positive breast tumors. Using a genome-wide analysis of gene expression in two ER-positive human breast cancer cell lines that differ in their proliferative response to estrogen, we sought to identify genes involved in estrogen-regulated cell proliferation. To this end, we compared the transcriptional profiles of MCF-7 and MDA-MB-231ER+ cells, which have directionally opposite 17ß-estradiol (E2)-dependent proliferation patterns, MCF-7 cells being stimulated and 231ER+ cells suppressed by E2. We identified a set of approximately 70 genes regulated by E2 in both cells, with most being regulated by hormone in an opposite fashion. Using a variety of bioinformatics approaches, we found the E2F binding site to be overrepresented in the potential regulatory regions of many cell cycle-related genes stimulated by estrogen in MCF-7 but inhibited by estrogen in 231ER+ cells. Biochemical analyses confirmed that E2F1 and E2F downstream target genes were increased in MCF-7 and decreased in 231ER+ cells upon estrogen treatment. Furthermore, RNA interference-mediated knockdown of E2F1 blocked estrogen regulation of E2F1 target genes and resulted in loss of estrogen regulation of proliferation. These results demonstrate that regulation by estrogen of E2F1, and subsequently its downstream target genes, is critical for hormone regulation of the proliferative program of these breast cancer cells, and that gene expression profiling combined with bioinformatic analyses of transcription factor binding site enrichment in regulated genes can identify key components associated with nuclear receptor hormonal regulation of important cellular functions.

NURSA Molecule Pages Link:

Nuclear Receptors:   ERα

Coregulators:   NRIP  |  SMAD3

Ligands:   17β-Estradiol  |  Fulvestrant

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