Calcineurin increases expression of aldosterone synthase via dephosphorylation of NFATc4

The mineralocorticoid hormone, aldosterone, is secreted by the adrenal zona glomerulosa (ZG) in response to high plasma K+ and hypovolemia and promotes renal Na+ reabsorption and K+ secretion. Hence, the regulation of aldosterone secretion is critical for the control of ion homeostasis and blood pressure. While the kinase pathways regulating aldosterone production are well studied, little is known about the involved phosphatases. Using the human adrenocortical carcinoma cell line NCI-H295R, we found that the mRNA expression of the aldosterone synthase increases significantly within 6 hours after K+ exposure. This increase was inhibited in a dose-dependent manner by the calcineurin inhibitors tacrolimus and cyclosporine A. Calcineurin (Cn) is a serine-threonine-specific, Ca2+ and CaM-activated protein phosphatase essential for lymphocyte, neuronal and cardiac function. The physiologic role of Cn in the ZG cells and the molecular pathways by which Cn regulates the K+-stimulated secretion of aldosterone are unknown. To answer these questions, we stimulated NCI-H295R cells with K+ with or without Tacrolimus and studied the phosphorylation pattern of cytoplasmic proteins by phospho-proteomics. We generated a map of the changes in the Ser/Thr phosphorylation in adrenocortical cells upon stimulation with K+ and identified Cn-regulated phosphoproteins.