Separate Regions of Glucocorticoid Receptor, Coactivator TIF2, and Comodulator STAMP Modify Different Parameters of GR‐mediated Gene Induction

Abstract

Coregulators, such as TIF2, and comodulators, such as STAMP, modify several aspects of glucocorticoid receptor (GR)‐mediated gene induction. Varying the levels of these factors alters not only the total level of transactivation (Amax) but also both the position of the dose‐response curve (e.g., EC50) for agonists and the amount of partial agonistic activity of antagonists (as a percent of full agonist activity under the same conditions). Our lab has found that TIF2 and STAMP appear to form a complex with GR that results in more than additive changes in Amax, EC50, and percent partial agonist activity for GR‐inducible genes. Using gene activation, mammalian two‐hybrid, and co‐immunoprecipitation (co‐IP) assays with truncated proteins; we find that selected regions of each protein (GR, TIF2, and STAMP) are required in the ternary complex to modify some, but not all, induction properties. Modulation of EC50 requires the most domains of each protein. Smaller fragments are sufficient to modify the Amax and/or percent partial agonist activity. Even less is required to form a complex. The data suggest that the pathways controlling Amax, EC50, and percent partial agonist activity of GR transactivation are physically separable and may utilize different transcriptional cofactors. Thus, greater physiological control of glucocorticoid action may be possible via agents that modify individual induction parameters.Source of research support: NIH Intramural Program