Role of estrogen receptor ligand and estrogen response element sequence oninteraction with chicken ovalbumin upstream promoter transcription factor (COUP-TF)

Estrogen-responsive genes are regulated by altering the balance of estrogen receptor (ER) interaction with transcription activators and inhibitors. He re we examined the role of ER ligand on ER interaction with the Chicken Ova lbumin Upstream Promoter Transcription Factor (COUP-TF) orphan nuclear rece ptor. COUP-TF binding to half-site estrogen response elements (EREs) was in creased by the addition of estradiol (E-2) -liganded ER (E-2-ER), but not b y ER liganded with the antiestrogens 4-hydroxytamoxifen (4-OHT-ER) or tamox ifen aziridine (TAz-ER). ER did not bind to single half-sites. Conversely, COUP-TF enhanced the ERE binding of purified E-2-ER, but did not affect TAz -ER-ERE binding. In contrast, only antiestrogens enhanced direct interactio n between ER and COUP-TF as assessed by GST pull-down assays. Identical res ults were obtained using either purified bovine or recombinant human ER alp ha. Co-immunoprecipitation assays showed that ER and COUP-TF interact in ex tracts from MCF-7 and ER alpha-transfected MDA-MB-231 cells. Here we docume nt that ER ligand impacts COUP-TF-ER interaction. COUP-TF interaction is me diated by the DNA binding and ligand-binding domains of ER. We suggest that changes in ER conformation induced by DNA binding reduce ER-COUP-TF intera ction. Transient transfection of human MCF-7 breast cancer cells with a COU P-TFI expression vector repressed E-2-induced luciferase reporter gene expr ession from single or multiple tandem copies of a consensus ERE. COUP-TFI s timulated 4-OHT-induced luciferase activity from a minimal ERE. Alone, COUP -TFI increased transcription from ERE half-sites or a single ERE in a seque nce-dependent manner. These data provide evidence that the ERE sequence and its immediate flanking regions influence whether COUP-TF enhances, inhibit s, or has no effect on ER ligand-induced ERE reporter gene expression and t hat COUP-TFI activates gene transcription from ERE half-sites. We suggest t hat COUP-TFI plays a role in mitigating estrogen-responsive gene expression . (C) 1999 Elsevier Science Ltd. All rights reserved.