Estradiol and Selective Estrogen Receptor Modulators Differentially Regulate Target Genes with Estrogen Receptors α and β

Estrogens and selective estrogen receptor modulators (SERMs) interact with estrogen receptor (ER) α and β to activate or repress gene transcription. To understand how estrogens and SERMs exert tissue-specific effects, we performed microarray analysis to determine whether ERα or ERβ regulate different target genes in response to estrogens and SERMs. We prepared human U2OS osteosarcoma cells that are stably transfected with a tetracycline-inducible vector to express ERα or ERβ. Western blotting, immunohistochemistry, and immunoprecipitation studies confirmed that U2OS-ERα cells synthesized only ERα and that U2OS-ERβ cells expressed exclusively ERβ. U2OS-ERα and U2OS-ERβ cells were treated either with 17β-estradiol (E₂), raloxifene, and tamoxifen for 18 h. Labeled cRNAs were hybridized with U95Av2 GeneChips (Affymetrix). A total of 228, 190, and 236 genes were significantly activated or repressed at least 1.74-fold in U2OS-ERα and U2OS-ERβ cells by E₂, raloxifene, and tamoxifen, respectively. Most genes regulated in ERα cells in response to E₂, raloxifene, and tamoxifen were distinct from those regulated in ERβ cells. Only 38 of the 228 (17%) genes were regulated by E₂ in both U2OS-ERβ and U2OS-ERβ cells. Raloxifene and tamoxifen regulated only 27% of the same genes in both the ERα and ERβ cells. A subset of genes involved in bone-related activities regulated by E₂, raloxifene, and tamoxifen were also distinct. Our results demonstrate that most genes regulated by ERα are distinct from those regulated by ERβ in response to E₂ and SERMs. These results indicate that estrogens and SERMs exert tissue-specific effects by regulating unique sets of targets genes through ERα and ERβ.