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.

COUP-TF Upregulates NGFI-A Gene Expression through an Sp1 Binding Site

“…Only a few promoters have been reported to be transactivated by COUP-TFs; these include the arrestin promoter (36), the phosphoenolpyruvate carboxykinase promoter (21), the trout estrogen receptor gene (30), the vHNF1 promoter (45), and the HIV long terminal repeat (49). Transactivation by COUP-TFs can also be observed in an in vitro system (37).…”

Involvement of cyclic AMP response element binding protein (CREB) and estrogen receptor phosphorylation in the synergistic activation of the estrogen receptor by estradiol and protein kinase activators

“…The magnitude of transcriptional activity is modulated by coactivator complexes [14,15] and proceeds by interaction with chromatin and the pre-initiation complex [15][16][17]. Interaction between estrogen signaling and other nuclear receptors [18,19], protein kinase C [20], general transcription factors [21][22][23] and/or MAP kinase [24,25] is documented, but little is known about the mechanism underlying estrogen/PKA cross-talk.…”

IL-8 expression and its possible relationship with estrogen-receptor-negative status of breast cancer cells

“…For the determination of estrogen-responsiveness of the cells, 2 mg of ERE2-TK.-LUC and 0.8 mg of internal control CMV-GAL per well were cotransfected by lipofection. b-galactosidase and luciferase were determined as previously described (Lazennec et al, 1997).…”