title: Unique roles of p160 coactivators for regulation of breast cancer cell proliferation and estrogen receptor-alpha transcriptional activity.
abstract: Each of the three members of the p160 steroid receptor coactivator (SRC) family of coactivators (SRC-1, SRC-2 and SRC-3) stimulates estrogen receptor (ER)-alpha function in trans-activation assays. Consequently, we sought to elucidate their contributions to the ER-regulated processes of cell proliferation, apoptosis, and the expression of ERalpha target genes in MCF-7 breast cancer cells. The small interfering RNA depletion of SRC-2 or SRC-3 but not SRC-1 inhibited growth of MCF-7 cells, and this was reflected in decreased cell cycle progression and increased apoptosis in SRC-2- or SRC-3-depleted cells as well as a reduction in ERalpha transcriptional activity measured on a synthetic reporter gene. However, only SRC-3 depletion blocked estradiol stimulated cell proliferation. Depletion of SRC-1 did not affect these events, and together this reveals functional differences between each of the three SRC family coactivators. Regulation of the endogenous ERalpha target gene, c-myc was not affected by depletion of any of the p160 coactivators although depletion of each of them decreased pS2 mRNA expression in estradiol-treated MCF-7 cells. Moreover, progesterone receptor and cyclin D1 gene expression were decreased in SRC-3 small interfering RNA-treated cells. Expression of mRNA and protein levels for the antiapoptotic gene, Bcl-2 was dependent on SRC-3 expression, whereas Bcl-2 protein but not mRNA expression also was sensitive to SRC-1 depletion. Together these data indicate that the closely related p160 coactivators are not functionally redundant in breast cancer cells because they play gene-specific roles in regulating mRNA and protein expression, and they therefore are likely to make unique contributions to breast tumorigenesis.
authors.affiliation: Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Sudipan
authors.initials: S
authors.lastname: Karmakar
authors.forename: Estrella A
authors.initials: EA
authors.lastname: Foster
authors.forename: Carolyn L
authors.initials: CL
authors.lastname: Smith
mesh_terms: D017209:Apoptosis / Q000235:genetics; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000235:genetics; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019938:Cyclin D1 / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay; D047628:Estrogen Receptor alpha / Q000235:genetics*; D005434:Flow Cytometry; D051548:Histone Acetyltransferases / Q000235:genetics / Q000502:physiology*; D006801:Humans; D056920:Nuclear Receptor Coactivator 1; D051958:Nuclear Receptor Coactivator 2 / Q000235:genetics / Q000502:physiology*; D056921:Nuclear Receptor Coactivator 3; D034741:RNA, Small Interfering / Q000235:genetics / Q000502:physiology; D011980:Receptors, Progesterone / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic / Q000235:genetics*; D014162:Transfection
chemical_list: D047628:Estrogen Receptor alpha; D051958:Nuclear Receptor Coactivator 2; D034741:RNA, Small Interfering; D011980:Receptors, Progesterone; D015534:Trans-Activators; D014157:Transcription Factors; D019938:Cyclin D1; D051548:Histone Acetyltransferases; C538859:NCOA1 protein, human; C538866:NCOA3 protein, human; D056920:Nuclear Receptor Coactivator 1; D056921:Nuclear Receptor Coactivator 3