Steroid nuclear receptors (NR3C) are ligand-modulated transcription factors that typically form homodimers upon binding to specific hormone response elements in chromatin. However, recent evidence challenges this classical model, suggesting alternative quaternary structures and heteromerization among different NR3C family members. We previously demonstrated that the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) can assemble into large hetero-oligomers of up to eight subunits in a DNA- and ligand-dependent manner. Here, we investigated interactions between MR and the progesterone receptor (PR). To this end, we combined advanced fluorescence imaging with transcriptomic analysis to determine whether MR and PR co-expression results in heteromer formation with distinct transcriptional outcomes. Using number and brightness (N&B) analysis and fluorescence cross-correlation, we confirmed ligand-dependent MR-PR heterocomplex formation in living cells. Super-resolution microscopy (dSTORM) further revealed nanoscale colocalization of MR and PR within heteroclusters, whose area varied with ligand identity. Functionally, RNA-seq analysis showed that MR and PR reciprocally modulate each other’s transcriptional activity and specificity. In summary, our findings support a model in which NR3C receptors engage in promiscuous interactions to generate hetero-oligomers with diverse quaternary architectures and altered functional outputs.
Ramos-Hernández et al. (Sun,) studied this question.