title: Estrogen receptor alpha and beta heterodimers exert unique effects on estrogen- and tamoxifen-dependent gene expression in human U2OS osteosarcoma cells.
abstract: The 17beta-estradiol (E2) receptor isoforms [estrogen receptor (ER) alpha and ERbeta] bind E2 and selective ER modulators (SERMs) as homodimers (alpha/alpha or beta/beta) or heterodimers (alpha/beta) to regulate gene expression. Although recent studies have shown that ER homodimers regulate unique sets of E2-responsive genes, little information exists regarding the transcriptional actions of the ERalpha/beta heterodimer. This paper describes the development of a U2OS human osteosarcoma (osteoblast) cell line stably expressing both ERalpha and ERbeta isoforms at a ratio of 1:4, a ratio reported to exist in normal, mature osteoblast cells derived from cancellous bone. The regulation of endogenous genes by E2 and 4-hydroxy-tamoxifen were measured in these cells using gene microarrays and real-time RT-PCR. Both E2 and 4-hydroxy-tamoxifen were shown to regulate unique sets of endogenous genes in the U2OS-ERalpha/beta heterodimer cell line (20% and 27% of total, respectively), compared with all the genes regulated in U2OS-ER homodimer cell lines. Furthermore, two novel E2-regulated genes, retinoblastoma binding protein 1 and 7-dehydrocholesterol reductase, were found to contain estrogen response element-like sequences that directly bind the ERalpha/beta heterodimer. These results suggest that the expression of both ER isoforms, forming functional ERalpha/beta heterodimers, result in unique patterns of gene regulation, many of which are distinct from the genes regulated by the ER homodimers.
authors.affiliation: Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, 1601C Guggenheim, 200 1st Street Southwest, Rochester, Minnesota 55905, USA. Monroe.David@mayo.edu
authors.forename: David G
authors.initials: DG
authors.lastname: Monroe
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Secreto
authors.forename: Malayannan
authors.initials: M
authors.lastname: Subramaniam
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Getz
authors.forename: Sundeep
authors.initials: S
authors.lastname: Khosla
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Spelsberg
mesh_terms: D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D047369:Chromatin Immunoprecipitation; D019281:Dimerization; D015536:Down-Regulation; D004958:Estradiol / Q000378:metabolism; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D047629:Estrogen Receptor beta / Q000378:metabolism*; D004967:Estrogens / Q000494:pharmacology*; D005786:Gene Expression Regulation; D006801:Humans; D047468:Immunoprecipitation; D008957:Models, Genetic; D020411:Oligonucleotide Array Sequence Analysis; D010006:Osteoblasts / Q000378:metabolism; D012516:Osteosarcoma / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D020033:Protein Isoforms; D020218:Response Elements; D056465:Retinoblastoma-Binding Protein 1; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013629:Tamoxifen / Q000031:analogs & derivatives / Q000494:pharmacology*
chemical_list: D002352:Carrier Proteins; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D004967:Estrogens; D020033:Protein Isoforms; D056465:Retinoblastoma-Binding Protein 1; D013629:Tamoxifen; C016601:afimoxifene; D004958:Estradiol; D044925:Oxidoreductases Acting on CH-CH Group Donors; C019995:7-dehydrocholesterol reductase