The Role of miR-206 in the Epidermal Growth Factor (EGF) Induced Repression of Estrogen Receptor-α (ERα) Signaling and a Luminal Phenotype in MCF-7 Breast Cancer Cells

• Published in: Molecular endocrinology (Baltimore, Md.) Md.), 2009-08, Vol.23 (8), p.1215-1230
• Main Authors: Adams, Brian D, Cowee, Danielle M, White, Bruce A
• Format: Article
• Language: English
• Subjects: Breast Neoplasms - metabolism; Cell Line, Tumor; Cell Proliferation; Epidermal Growth Factor - metabolism; Estrogen Receptor alpha - metabolism; Humans; In Situ Nick-End Labeling; MicroRNAs - genetics; MicroRNAs - physiology; Models, Biological; Models, Genetic; Open Reading Frames; Phenotype; Polymerase Chain Reaction; Signal Transduction; Trypan Blue - pharmacology
• ISSN: 0888-8809; 1944-9917
• DOI: 10.1210/me.2009-0062

Epidermal growth factor (EGF) receptor (EGFR)/MAPK signaling can induce a switch in MCF-7 breast cancer cells, from an estrogen receptor (ER)α-positive, Luminal-A phenotype, to an ERα-negative, Basal-like phenotype. Although mechanisms for this switch remain obscure, Basal-like cancers are typically high grade and confer a poorer clinical prognosis. We previously reported that miR-206 and ERα repress each other’s expression in MCF-7 cells in a double-negative feedback loop. We show herein that miR-206 coordinately targets mRNAs encoding the coactivator proteins steroid receptor coactivator (SRC)-1 and SRC-3, and the transcription factor GATA-3, all of which contribute to estrogenic signaling and a Luminal-A phenotype. Overexpression of miR-206 repressed estrogen-mediated responses in MCF-7 cells, even in the presence of ERα encoded by an mRNA lacking a 3′-untranslated region, suggesting miR-206 affects estrogen signaling by targeting mRNAs encoding ERα-associated coregulatory proteins. Furthermore, EGF treatments enhanced miR-206 levels in MCF-7 cells and ERα-negative, EGFR-positive MDA-MB-231 cells, whereas EGFR small interfering RNA, or PD153035, an EGFR inhibitor, or U0126, a MAPK kinase inhibitor, significantly reduced miR-206 levels in MDA-MB-231 cells. Blocking EGF-induced enhancement of miR-206 with antagomiR-206 abrogated the EGF-inhibitory effect on ERα, SRC-1, and SRC-3 levels, and on estrogen response element-luciferase activity, indicating that EGFR signaling represses estrogenic responses in MCF-7 cells by enhancing miR-206 activity. Elevated miR-206 levels in MCF-7 cells ultimately resulted in reduced cell proliferation, enhanced apoptosis, and reduced expression of multiple estrogen-responsive genes. In conclusion, miR-206 contributes to EGFR-mediated abrogation of estrogenic responses in MCF-7 cells, contributes to a Luminal-A- to Basal-like phenotypic switch, and may be a measure of EGFR response within Basal-like breast tumors. MicroRNA-206 targets mRNAs encoding ERα, SRC-1, SRC-3 and GATA-3, and contributes to the EGF-induced transition from a “Luminal” to a “Basal-like” subtype in breast cancer.