Genome-wide binding potential and regulatory activity of the glucocorticoid receptor's monomeric and dimeric forms

A widely regarded model for glucocorticoid receptor (GR) action postulates that dimeric binding to DNA regulates unfavorable metabolic pathways while monomeric receptor binding promotes repressive gene responses related to its anti-inflammatory effects. This model has been built upon the characterization of the GRdim mutant, reported to be incapable of DNA binding and dimerization. Although quantitative live-cell imaging data shows GRdim as mostly dimeric, genomic studies based on recovery of enriched half-site response elements suggest monomeric engagement on DNA. Here, we perform genome-wide studies on GRdim and a constitutively monomeric mutant. Our results show that impairing dimerization affects binding even to open chromatin. We also find that GRdim does not exclusively bind half-response elements. Our results do not support a physiological role for monomeric GR and are consistent with a common mode of receptor binding via higher order structures that drives both the activating and repressive actions of glucocorticoids. Glucocorticoid receptors (GR) are thought to bind DNA as dimers or monomers, to regulate different transcription pathways. Here, the authors perform genome-wide studies on GRs with mutations that impair dimerization and provide evidence that monomeric GRs do not play a significant physiologic role.