Reciprocal influences between the signalling pathways regulating proliferation and steroidogenesis in adrenal glomerulosa cells

The main regulators of aldosterone secretion in adrenal gland zona glomerulosa (ZG) cells are the hormones angiotensin II (Ang II) and adrenocorticotrophin (ACTH) and small increases in the extracellular potassium (K(+)) concentration. The action of these agonists is mediated by different signalling systems - ACTH is mediated by cAMP and activation of protein kinase A while Ang II and K(+) activate two protein kinases, Ca(2+)-calmodulin-dependent protein kinase (CamK) and diacylglycerol-dependent protein kinase (PKC). Ang II, besides being one of the main agonists for the secretion of aldosterone, also stimulates proliferation of ZG cells, a process mediated by mitogen-activated protein kinases (MAPKs). Recent studies aimed at elucidating the molecular mechanisms underlying cell proliferation have shown that calcineurin is the principal regulator of MAPKs activity. The purpose of this review is to discuss experimental evidence of possible reciprocal influences between the signalling pathways regulating proliferation and steroidogenesis in ZG cells.