Colocalization of mineralocorticoid and EGF receptor at the plasma membrane.

The mineralocorticoid receptor (MR), a ligand-activated transcription factor expressed in various cell types (e.g. epithelial cells, neurons, smooth muscle cells, immune cells), plays important roles in neurohumoral, neuronal, cardiovascular, renal and intestinal function. Pathophysiological relevant signaling mechanisms include nongenomic pathways involving the EGF receptor (EGFR). We investigated whether a MR-EGFR colocalization may underlie the functional MR-EGFR interaction by coimmunoprecipitation, fluorescence resonance energy transfer (FRET) and confocal microscopy in a heterologous expression system. EGFR and a small fraction of MR colocalize at the cell membrane, independently of short time exposure (</=60min) to receptor ligands. Twenty-four-hour-exposure to saturating concentrations of aldosterone (10nmol/l) resulted in an almost complete nuclear translocation of MR and disappearance of MR-EGFR colocalization. EGFR transactivation is enhanced only after MR stimulation. Inhibition of HSP90 by geldanamycin did not reduce the fraction of MR interacting with EGFR. Disruption of cholesterol-rich membrane domains by cyclodextrin reduced MR-EGFR interaction. In conclusion, a subfraction of MR interacts with EGFR at the plasma membrane in our heterologous expression system, possibly at cholesterol-rich domains, to form a steroid receptor/growth factor receptor signaling module.