Specificity in mineralocorticoid versus glucocorticoid action

Area of Science:

• Endocrinology
• Molecular Biology
• Cell Biology

Background:

• Mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) share structural and functional similarities.
• Both receptors can bind to and activate common hormone response elements.
• Specificity of MR and GR action is thought to be primarily mediated by prereceptor mechanisms.

Purpose of the Study:

• To investigate the mechanisms conferring specificity between MR and GR.
• To identify MR-regulated genes in vivo.
• To characterize the in vivo response of candidate genes to corticosteroid activation.

Main Methods:

• In vitro studies using epithelial and fibroblast cell lines.
• In vivo studies in rat distal colon.
• Analysis of gene expression following corticosteroid administration.

Main Results:

• MR and GR exhibit differential transactivation in epithelial cells, mediated by receptor N-termini.
• Intracellular signaling pathways differentially modulate MR and GR activity.
• Four candidate genes (epithelial sodium channel beta and gamma subunits, serum and glucocorticoid-regulated kinase, channel-inducing factor) were rapidly upregulated by both MR and GR activation within 60 minutes.

Conclusions:

• Specificity between MR and GR can be achieved through receptor N-termini and differential modulation by signaling pathways.
• Aldosterone rapidly upregulates key genes involved in sodium transport via MR activation.
• While aldosterone-responsive genes were identified, genes uniquely regulated by aldosterone have not yet been discovered.