title: Estrogen receptor beta binds Sp1 and recruits a corepressor complex to the estrogen receptor alpha gene promoter.
abstract: Human estrogen receptors alpha and beta are crucially involved in the regulation of mammary growth and development. Normal breast tissues display a relative higher expression of ER beta than ER alpha, which drastically changes during breast tumorogenesis. Thus, it is reasonable to suggest that a dysregulation of the two estrogen receptor subtypes may induce breast cancer development. However, the molecular mechanisms underlying the potential opposing roles played by the two estrogen receptors on tumor cell growth remain to be elucidated. In the present study, we have demonstrated that ER beta overexpression in breast cancer cells decreases cell proliferation and down-regulates ER alpha mRNA and protein content, along with a concomitant repression of estrogen-regulated genes. Transient transfection experiments, using a vector containing the human ER alpha promoter region, showed that elevated levels of ER beta down-regulated basal ER alpha promoter activity. Furthermore, site-directed mutagenesis and deletion analysis revealed that the proximal GC-rich motifs at -223 and -214 are critical for the ER beta-induced ER alpha down-regulation in breast cancer cells. This occurred through ER beta-Sp1 protein-protein interactions within the ER alpha promoter region and the recruitment of a corepressor complex containing the nuclear receptor corepressor NCoR, accompanied by hypoacetylation of histone H4 and displacement of RNA-polymerase II. Silencing of NCoR gene expression by RNA interference reversed the down-regulatory effects of ER beta on ER alpha gene expression and cell proliferation. Our results provide evidence for a novel mechanism by which overexpression of ER beta through NCoR is able to down regulate ER alpha gene expression, thus blocking ER alpha's driving role on breast cancer cell growth.
authors.affiliation: Department of Pharmaco-Biology, University of Calabria, Via P. Bucci, 87036 Arcavacata di Rende, CS, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Bartella
authors.forename: P
authors.initials: P
authors.lastname: Rizza
authors.forename: I
authors.initials: I
authors.lastname: Barone
authors.forename: D
authors.initials: D
authors.lastname: Zito
authors.forename: F
authors.initials: F
authors.lastname: Giordano
authors.forename: C
authors.initials: C
authors.lastname: Giordano
authors.forename: S
authors.initials: S
authors.lastname: Catalano
authors.forename: L
authors.initials: L
authors.lastname: Mauro
authors.forename: D
authors.initials: D
authors.lastname: Sisci
authors.forename: M L
authors.initials: ML
authors.lastname: Panno
authors.forename: S A W
authors.initials: SA
authors.lastname: Fuqua
authors.forename: S
authors.initials: S
authors.lastname: Andò
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D047369:Chromatin Immunoprecipitation; D047628:Estrogen Receptor alpha / Q000235:genetics* / Q000378:metabolism; D047629:Estrogen Receptor beta / Q000235:genetics / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D056971:Nuclear Receptor Co-Repressor 1 / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D034622:RNA Interference; D012319:RNA Polymerase II / Q000378:metabolism; D020218:Response Elements; D016329:Sp1 Transcription Factor / Q000378:metabolism*
chemical_list: C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; C539127:NCOR1 protein, human; D056971:Nuclear Receptor Co-Repressor 1; D016329:Sp1 Transcription Factor; D007334:Insulin-Like Growth Factor I; D012319:RNA Polymerase II