Involvement of bone morphogenetic protein-6 in differential regulation of aldosterone production by angiotensin II and potassium in human adrenocortical cells

Aldosterone production is modified by several growth factors that reside in the adrenal. We have recently reported the existence of a bone morphogenetic protein (BMP) system in human adrenocortical cells, in which BMP-6 augments aldosterone synthesis. Here, we investigated functional roles of BMP-\6, focusing on the differential regulation of aldosterone synthesis induced by angiotensin (Ang) II and potassium (K). In human adrenocortical H295R cells, BMP-6 augmented Ang II-induced CYP11B2 transcription and mRNA and aldosterone roduction but had no effect on K-induced aldosterone production. Inhibition of endogenous BMP-6 action by neutralizing antibodies impaired aldosterone production induced by Ang II but not that induced by K. Blockage of ligand-receptor binding using extracellular domain (ECD) of BMP type I receptors revealed that ECDs to activin receptor-like kinase (ALK)-2 and ALK-3 significantly reduced the aldosterone production induced by Ang II. None of the type I-receptor ECDs tested had any effect on K-induced aldosterone levels. Overexpression of a dominant negative-activin type II receptor construct selectively decreased Ang II-induced aldosterone production without having any effect on K-induced aldosterone production. BMP type II receptor-dominant negative had no effect on aldosterone induced by either Ang II or K. These results infer that BMP-6 acts through ALK-2, ALK-3, and activin type II receptor receptors in adrenocortical cells. BMP-6 pretreatment extends the induction of ERK1/2 phosphorylation by Ang II and treatment with ECDs to ALK-2 and ALK-3 impaired Ang II-induced ERK phosphorylation. The specific inhibitor of ERK activation, U0126, suppressed the activation of CYP11B2 transcription induced by BMP-6 without affecting Smad phosphorylation and Tlx2-Luc activity. Collectively, the endogenous BMP-6 system plays critical roles in aldosterone production between Ang II and K through ERK signaling pathway.