[Protein kinase C and regulation of specialized steroidogenic functions of the adrenal cortical cell]

Protein kinase C is expressed in adrenal cortex as a single isoenzyme, whereas four isoforms are detected in brain tissue. Of the two major steroidogenic agents (ACTH and angiotensin II), only A II stimulates polyphosphoinositide hydrolysis and thus appears able to induce protein kinase C activation in adrenocortical cell. Although direct activation of the kinase partly mimics the steroidogenic effect of A II, no clear evidence has been obtained for a monodirectional effect of the kinase in the acute activation of adrenocortical cell steroidogenic activity. On the other hand, protein kinase C may play a key role in multidirectional regulatory events, resulting in the modulation of ACTH-responsive adenylate cyclase activity, in feed-back control or subtle transregulation (cross-talk) processes between different adrenocortical cell activation pathways triggered by different hormonal signals.