The mineralocorticoid receptor forms higher order oligomers upon DNA binding.

The mineralocorticoid and glucocorticoid receptors (MR and GR) are evolutionary related nuclear receptors with highly conserved DNA- and ligand-binding domains (DBD and LBD), which determine promiscuous activation by corticosteroid hormones (aldosterone and glucocorticoids) and binding to a shared DNA consensus sequence, the hormone response element (HRE). In addition, MR and GR functionally interact, likely through direct formation of heteromeric complexes, potentially contributing to cell-specific corticosteroid signaling. It has recently been proposed that agonist and DNA binding promote GR self-association in tetramers. Here we investigated MR quaternary arrangement after receptor activation. To that end we used a fluorescence imaging technique, Number & Brightness (N&B) analysis, in a cell system where receptor-DNA interaction can be studied in live cells in real time. Our results show that agonist-bound MR is a tetramer in the nucleoplasm, forming higher order oligomers upon binding to HREs. Antagonists form intermediate quaternary arrangements, suggesting that the formation of large oligomeric complexes is essential for function. We also show that divergence between MR and GR quaternary arrangements are driven by different functionality of multimerization interfaces in the DBD and LBD and their interplay with the N-terminal domain. In spite of contrasting quaternary structures, MR and GR are able to form heteromers. Given the importance of both receptors as pharmacological targets and the differential oligomerization induced by antagonists, our findings suggest that influencing quaternary structure may be important to provide selective modulation of corticosteroid signaling.