Estrogen receptor beta exerts growth-inhibitory effects on human mammary epithelial cells.
Estrogen receptor beta (ERbeta) is widely expressed in mammary epithelium. ERbeta expression is reported to decline during carcinogenesis of the breast and other tissues. In this study, we examined the consequences of a loss of ERbeta expression in mammary epithelial cells. We knocked down ERbeta transcript levels in human mammary epithelial MCF-10A cells and in MCF-7 breast cancer cells by means of stable transfection with a specific shRNA plasmid. ERbeta knockdown resulted in a significant growth increase of both cell types in a ligand-independent manner. This effect was accompanied by elevated cyclin A2 expression in MCF-10A cells and by decreased expression of growth-inhibitory p21/WAF and epithelial cell marker cytokeratine 8 in both cell lines. Transfection of ERbeta shRNA did not alter the absent proliferative estrogen response of MCF-10A cells, but conferred sensitivity to selective estrogen receptor modulator tamoxifen to this cell line. In contrast, ERbeta knockdown diminished estrogen responsiveness of MCF-7 breast cancer cells and also weakened the effect of tamoxifen on this cell line. These ligand-dependent effects only observed in MCF-7 cells exhibiting a high ERalpha/beta ratio were accompanied by smaller estrogenic repression of p21/WAF expression, an impaired tamoxifen-triggered induction of this gene and by relative downregulation of ERalpha and cyclin A2 transcript levels. Our data suggest that ERbeta exerts antiproliferative effects both on MCF-10A and MCF-7 cells in a ligand- and ERalpha-independent manner by regulation of p21/WAF or cyclin A2 gene expression. Knockdown of ERbeta in both cell types was sufficient to significantly decrease transcript levels of epithelial cell marker cytokeratin 8. The results of this study support the hypothesis that ERbeta acts as a tumor suppressor in mammary epithelium.
Department of Obstetrics and Gynecology, University of Regensburg, 93053, Regensburg, Germany. otreeck@caritasstjosef.de
Oliver
O
Treeck
Claus
C
Lattrich
Anette
A
Springwald
Olaf
O
Ortmann
D001940:Breast / Q000166:cytology / Q000187:drug effects*; D001943:Breast Neoplasms / Q000473:pathology*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line / Q000166:cytology / Q000187:drug effects; D045744:Cell Line, Tumor / Q000166:cytology / Q000187:drug effects; D056751:Cyclin A2 / Q000096:biosynthesis / Q000235:genetics; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis / Q000235:genetics; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000032:analysis; D047629:Estrogen Receptor beta / Q000235:genetics / Q000502:physiology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006131:Growth Inhibitors / Q000502:physiology*; D006801:Humans; D053533:Keratin-8 / Q000096:biosynthesis / Q000235:genetics; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000502:physiology; D013629:Tamoxifen / Q000494:pharmacology; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000502:physiology*
C503721:CCNA2 protein, human; C493956:CDKN1A protein, human; D056751:Cyclin A2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D006131:Growth Inhibitors; D053533:Keratin-8; D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D025521:Tumor Suppressor Proteins; D013629:Tamoxifen; D004958:Estradiol