OR12-03 Mineralocorticoid and Glucocorticoid Receptors Adopt Distinct Quaternary Structures and Can Form Heteromultimers That Affect Chromatin-Binding Profiles

The mineralocorticoid and glucocorticoid receptors (MR and GR) are evolutionarily related nuclear receptors with high sequence conservation and a shared hormone response element (HRE). Both receptors are activated by glucocorticoids, but MR can be selectively activated by aldosterone. Using the imaging technique Number & Brightness (N&B) it has recently been proposed that liganded GR dimers form tetramers upon binding to HREs in live cells. We now show that agonist-bound MR adopts a tetrameric organization in the nucleoplasm and forms complexes with an average of 7 receptor units upon binding an HRE. Interestingly, MR antagonists eplerenone and spironolactone induced intermediate oligomerization arrangements, strongly suggesting that higher order oligomerization is essential for receptor activity. Site-directed mutagenesis and deletion analysis suggest that the N-terminus of MR is a main determinant of higher order oligomerization. Both with corticosterone and aldosterone, GR can incorporate into MR complexes partially displacing MR monomers. Genome-wide chromatin binding studies suggest that the presence of GR in the same cells profoundly change MR interaction with distinct sets of enhancers in a ligand-dependent way, contributing to receptor-specific signaling. Certain genes respond to only one receptor while others respond to both receptors. The interaction of these two closely related receptors has important implications for the mechanisms for glucocorticoid signaling and transcription factors in general.