title: Ligand-selective transactivation and transrepression via the glucocorticoid receptor: role of cofactor interaction.
abstract: The mechanisms that determine ligand-selective transcriptional responses by the glucocorticoid receptor (GR) are not fully understood. Using a wide panel of GR ligands, we investigated the relationships between the potency and maximal response for transactivation via a glucocorticoid response element (GRE) and transrepression via both nuclear factor small ka, CyrillicB (NFsmall ka, CyrillicB) and activator protein-1 (AP-1) sites, relative binding affinity for the GR, as well as interaction with both coactivators and corepressors. The results showed ligand-selective differences in potency and efficacy for each promoter, as well as for a particular ligand between the three promoters. Ligand potency correlated with relative affinity for the GR for agonists and partial agonists in transactivation but not for transrepression. Maximal response was unrelated to relative affinity of ligand for GR for both transactivation and transrepression. A good and significant correlation between full length coactivator binding in two-hybrid assays and efficacy as well as potency of different receptor-steroid complexes for both transactivation and transrepression supports a major role for coactivator recruitment in determination of ligand-selective transcriptional activity. Furthermore, ligand-selective GR binding to GRIP-1, as determined by both two-hybrid and DNA pull down assays, correlated positively with ligand-selective efficacy for transactivation of both a synthetic GRE reporter with expressed GR as well as of an endogenous gene via endogenous GR. The receptor interacting domain of the corepressor SMRT exhibited strong interaction with both agonists and partial agonists, similar to the results for coactivators, suggesting a possible role for SMRT in activation of transcription. However, there was no correlation between ligand affinity for the GR and cofactor interaction. These results provide strong quantitative biochemical support for a model in which GR-mediated ligand-selective differential interaction with GRIP-1, SRC-1A, NCoR and SMRT is a major determinant of ligand-selective and promoter-specific differences in potency and efficacy, for both transactivation and transrepression.
authors.affiliation: Department of Biochemistry, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
authors.forename: Katharina
authors.initials: K
authors.lastname: Ronacher
authors.forename: Katie
authors.initials: K
authors.lastname: Hadley
authors.forename: Chanel
authors.initials: C
authors.lastname: Avenant
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Stubsrud
authors.forename: S Stoney
authors.initials: SS
authors.lastname: Simons
authors.forename: Ann
authors.initials: A
authors.lastname: Louw
authors.forename: Janet P
authors.initials: JP
authors.lastname: Hapgood
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D003907:Dexamethasone / Q000378:metabolism; D006801:Humans; D008024:Ligands; D009419:Nerve Tissue Proteins / Q000378:metabolism; D011485:Protein Binding; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques
chemical_list: D002352:Carrier Proteins; C491310:GRIP1 protein, human; D008024:Ligands; C497713:NR3C1 protein, human; D009419:Nerve Tissue Proteins; D011965:Receptors, Glucocorticoid; D012097:Repressor Proteins; C404226:TSC22D3 protein, human; D014157:Transcription Factors; D003907:Dexamethasone; D004247:DNA