SRA coactivation of estrogen receptor-alpha is phosphorylation-independent, and enhances 4-hydroxytamoxifen agonist activity.
The ability of steroid receptor RNA activator (SRA), an AF-1 coactivator, to contribute to differences in estrogen receptor (ER)-alpha and ERbeta transcriptional activity was tested. In transient transfections, SRA expression increased ERalpha- and ERbeta-dependent gene expression. However, when the receptors' amino-terminal A/B regions were examined as GAL4 DNA binding domain fusions, SRA enhanced the activity of GAL-ABalpha but not GAL-ABbeta. Exogenous SRA also enhanced AF-2 activity for both receptors, indicating that SRA effects are not limited to AF-1. Simultaneously mutating three phosphorylation sites within GAL-ABalpha domain only modestly reduced SRA coactivation of GAL-ABalpha, suggesting that phosphorylation does not play a major role in SRA function relative to this domain. SRA enhanced ERalpha activity stimulated by 4-hydroxytamoxifen, but was unable to convert this mixed antiestrogen to an ERbeta agonist. Thus, SRA is an ERalpha AF-1-specific coactivator that enhances the agonist activity of tamoxifen-bound ERalpha and may contribute to tamoxifen resistance.
Coleman
Kevin M
KM
Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030-3498, USA.
Lam
Vinh
V
Jaber
Basem M
BM
Lanz
Rainer B
RB
Smith
Carolyn L
CL
D015153:Blotting, Western; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D047629:Estrogen Receptor beta / Q000378:metabolism; D017353:Gene Deletion; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000378:metabolism / Q000502:physiology*; D013629:Tamoxifen / Q000819:agonists* / Q000031:analogs & derivatives* / Q000494:pharmacology*; D014158:Transcription, Genetic; D014162:Transfection
D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; C405423:steroid receptor RNA activator; D013629:Tamoxifen; C016601:afimoxifene; D004247:DNA