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 GRalpha and its splicing variant GRbeta, whereas COUP-TFII formed a complex with GRalpha, but not with GRbeta, in an in vivo chromatin immunoprecipitation and a regular immunoprecipitation assay. Accordingly, GRalpha, but not GRbeta, enhanced COUP-TFII-induced transactivation of the simple COUP-TFII-responsive 7alpha-hydroxylase promoter through the transcriptional activity of its activation function-1 domain, whereas COUP-TFII repressed GRalpha-induced transactivation of the glucocorticoid-responsive promoter by attracting the silencing mediator for retinoid and thyroid hormone receptors. Importantly, mutual protein-protein interaction of GRalpha 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 GRalpha. These interactions influence the transcription of both COUP-TFII- and GRalpha-responsive target genes, seem to be promoter specific, and can be in either a positive or negative direction.

Glucocorticoids play pivotal roles in the maintenance of homeostasis but, when dysregulated, may also have deleterious effects. Smad6, one of the transforming growth factor ␤ (TGF␤) family downstream transcription factors, interacts with the N-terminal domain of the glucocorticoid receptor (GR) through its Mad homology 2 domain and suppresses GR-mediated transcriptional activity in vitro. Adenovirus-mediated Smad6 overexpression inhibits glucocorticoid action in rat liver in vivo, preventing dexamethasoneinduced elevation of blood glucose levels and hepatic mRNA expression of phosphoenolpyruvate carboxykinase, a well known rate-limiting enzyme of liver gluconeogenesis. Smad6 suppresses GR-induced transactivation by attracting histone deacetylase 3 to DNA-bound GR and by antagonizing acetylation of histone H3 and H4 induced by p160 histone acetyltransferase. These results indicate that Smad6 regulates glucocorticoid actions as a corepressor of the GR. From our results and known cross-talks between glucocorticoids and TGF␤ family molecules, it appears that the anti-glucocorticoid actions of Smad6 may contribute to the neuroprotective, anticatabolic and pro-wound healing properties of the TGF␤ family of proteins.Glucocorticoids play crucial roles in the regulation of basal and stress-related homeostasis (1). They are necessary for maintenance of many important biologic activities, such as homeostasis of intermediary metabolism, central nervous and cardiovascular system functions, and the immune/inflammatory reaction (1). Glucocorticoids also act as potent immunosuppressive and anti-inflammatory agents at "pharmacologic" doses, properties that make them irreplaceable therapeutic means for many inflammatory, autoimmune, allergic, and lymphoproliferative diseases (2). At high levels and over a long duration, glucocorticoids have neurotoxic, catabolic, and anti-wound healing properties as well as promoting gluconeogenesis, adipogenesis, and a shift of the T helper 1 to T helper 2 balance toward T helper 2 predominance (3, 4). Many extracellular and intracellular factors influence the actions of glucocorticoids at the level of their target tissues (5). Some of these are physiologically important, whereas others may also be associated with pathologic processes (5, 6).The actions of glucocorticoids are mediated by the ubiquitous intracellular glucocorticoid receptor (GR), 2 which functions as a hormoneactivated transcription factor of glucocorticoid target genes (3, 7). The GR consists of three domains, the N-terminal or "immunogenic" domain, the central, DNA-binding domain (DBD), and the C-terminal, ligand-binding domain. The functions of the latter two domains have been studied extensively, whereas those of the immunogenic domain are less well known (7). In the unliganded state, the GR is located primarily in the cytoplasm (7). After binding to its agonist ligand, the GR undergoes conformational changes and translocates into the nucleus. Ligand-activated GR then binds to the glucocorticoid response elements (GREs) as a ...