title: The nuclear orphan receptors COUP-TF and ARP-1 positively regulate the trout estrogen receptor gene through enhancing autoregulation.
abstract: The rainbow trout estrogen receptor (rtER) is a positively autoregulated gene in liver cells. In a previous report, we showed that upregulation is mediated by an estrogen response element (ERE) located in the proximal promoter of the gene and that a half binding site for nuclear receptors (5'-TGACCT-3') located 15 bp upstream of the ERE is involved in the magnitude of the estrogen response. We now report that the human orphan receptor COUP-TF and a COUP-TF-like protein from trout liver are able to bind to the consensus half-site. When cotransfected with the rtER gene proximal promoter, COUP-TF had no regulatory functions on its own. Interestingly, COUP-TF enhanced rtER transactivation properties in the presence of estradiol in a dose-dependent manner when cotransfected with the rtER gene promoter. Unliganded retinoid receptor heterodimers had the same helper function as COUP-TF in the presence of estradiol but were switched to repressors when the ligand all-trans-retinoic acid was added. Mutation of the consensus half-site only slightly reduced COUP-TF helper function, suggesting that it actually results from a complex mechanism that probably involves both DNA binding of COUP-TF to the promoter and protein-protein interaction with another transcription factor bound to the promoter. Nevertheless, a DNA-binding-defective mutant of COUP-TF was also defective in ER helper function. Competition footprinting analysis suggested that COUP-TF actually establishes contacts with the consensus upstream half-site and the downstream ERE half-site that would form a DR-24-like response element. Interaction of COUP-TF with the DR-24 element was confirmed in footprinting assays by using nuclear extracts from Saccharomyces cerevisiae expressing COUP-TF. Finally, interaction of COUP-TF with mutants of the rtER gene promoter showed that COUP-TF recognizes the ERE when the upstream half-site is mutated. These data show that COUP-TF may activate transcription through interaction with other nuclear receptors. This cross-talk between liganded nuclear receptors and orphan receptors is likely to modulate the spectrum of action of a particular ligand-receptor complex and may participate in the cell-type specificity of the ligand effect.
authors.affiliation: UPRES-A CNRS 6026, Equipe Associée d'Endocrinologie Moléculaire des Poissons, INRA, Université de Rennes I, France.
authors.forename: G
authors.initials: G
authors.lastname: Lazennec
authors.forename: L
authors.initials: L
authors.lastname: Kern
authors.forename: Y
authors.initials: Y
authors.lastname: Valotaire
authors.forename: G
authors.initials: G
authors.lastname: Salbert
mesh_terms: D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D051838:COUP Transcription Factor I; D051837:COUP Transcription Factor II; D051836:COUP Transcription Factors; D004247:DNA / Q000378:metabolism; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000502:physiology*; D006706:Homeostasis / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011960:Receptors, Estrogen / Q000235:genetics*; D011965:Receptors, Glucocorticoid / Q000502:physiology*; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism; D011987:Receptors, Steroid / Q000502:physiology*; D012097:Repressor Proteins / Q000502:physiology*; D047488:Retinoid X Receptors; D017210:Tilapia; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015533:Transcriptional Activation
chemical_list: D051838:COUP Transcription Factor I; D051837:COUP Transcription Factor II; D051836:COUP Transcription Factors; D004247:DNA; D004268:DNA-Binding Proteins; D011960:Receptors, Estrogen; D011965:Receptors, Glucocorticoid; D018168:Receptors, Retinoic Acid; D011987:Receptors, Steroid; D012097:Repressor Proteins; D047488:Retinoid X Receptors; D014157:Transcription Factors; C497589:NR2F1 protein, human; C095569:NR2F2 protein, human