Physical interaction and functional synergy between glucocorticoid receptor and Ets2 proteins for transcription activation of the rat cytochrome P-450c27 promoter

We demonstrate that dexamethasone-mediated transcription activation of the cytochrome P-450c27 promoter involves a physical interaction and functional synergy between glucocorticoid receptor (GR) and Ets2 factor. Ets2 protein binding to a "weak" Ets-like site of the promoter is dependent on Oh bound to the adjacent cryptic glucocorticoid response element. Coimmunoprecipita tion and chemical cross-linking experiments show physical interaction betwe en GR and Ets2 proteins. Mutational analyses show synergistic effects of Et s2 and GR in dexamethasone-mediated activation of the cytochrome P-450c27 p romoter. The DNA-binding domain of GR, lacking the transcription activation and ligand-binding domains, was fully active in synergistic activation of the promoter with intact Ets2. The DNA-binding domain of Ets2 lacking the t ranscription activation domain showed a dominant negative effect on the tra nscription activity. Finally, a fusion protein consisting of the GR DNA-bin ding domain and the transcription activation domain of Ets2 fully supported the transcription activity, suggesting a novel synergy between the two pro teins, which does not require the transactivation domain of GR. Our results also provide new insights on the role of putative weak consensus Ets sites in transcription activation, possibly through synergistic interaction with other gene-specific transcription activators.