RU486-induced glucocorticoid receptor agonism is controlled by the receptor N terminus and by corepressor binding

Glucocorticoid-induced gene transcription has been shown to be mediated by coactivators bound to the glucocorticoid receptor (GR). The glucocorticoid antagonist RU486 interferes with the steroid-mediated activation and can also exhibit partial agonist activity, a response in which corepressors have been implicated. Here we have shown that deletion of the N terminus of GR totally abolishes the agonist activity of RU486. Furthermore, we have demonstrated that corepressors bind directly to the RU486-bound GR as determined by glutathione S-transferase pull-down, mammalian two-hybrid assay, and coimmunoprecipitation. Fine mapping of the interaction regions within GR and the corepressor NCoR reveals a complex interaction profile that involves a number of domains in each protein. Notably, the N and the C termini of GR are both involved in corepressor binding. Thus, the N terminus of GR is a major determinant for RU486-dependent NCoR interaction as well as for RU486-mediated agonist activity.