Glucocorticoids exert their metabolic effect via their intracellular receptor, the glucocorticoid receptor (GR). In a yeast two-hybrid screening, we found the chicken ovalbumin upstream promoter transcription factor II (COUP-TFII), an orphan nuclear receptor that plays important roles in glucose, cholesterol, and xenobiotic metabolism, as a partner of GR. In an in vitro glutathione-S-transferase pull-down assay, COUP-TFII interacted via its DNA-binding domain with the hinge regions of both GRα and its splicing variant GRβ, whereas COUP-TFII formed a complex with GRα, but not with GRβ, in an in vivo chromatin immunoprecipitation and a regular immunoprecipitation assay. Accordingly, GRα, but not GRβ, enhanced COUP-TFII-induced transactlvation of the simple COUP-TFII-responsive 7α-hydroxylase promoter through the transcriptlonal activity of its activation function-1 domain, whereas COUP-TFII repressed GRα-induced transactivation of the glucocorticoid-responsive promoter by attracting the silencing mediator for retinoid and thyroid hormone receptors. Importantly, mutual protein-protein interaction of GRα and COUP-TFII was necessary for glucocorticoid-induced enhancement of the promoter activity and the endogenous mRNA expression of the COUP-TFII-responsive phosphoenolpyruvate carboxykinase, the rate-limiting enzyme of hepatic gluconeogenesis. We suggest that COUP-TFII may participate in some of the metabolic effects of glucocorticoids through direct interactions with GRα. These interactions influence the transcription of both COUP-TFII- and GRα-responsive target genes, seem to be promoter specific, and can be in either a positive or negative direction.
ASJC Scopus subject areas
- Molecular Biology