Stimulatory effect of pituitary adenylate cyclase-activating polypeptide on catecholamine synthesis in cultured bovine adrenal chromaffin cells: involvements of tyrosine hydroxylase phosphorylation caused by Ca2+ influx and cAMP.

In cultured bovine adrenal chromaffin cells, pituitary adenylate cylase-activating polypeptide (PACAP) stimulated [14C]catecholamine synthesis from [14C]tyrosine (but not from [14C]DOPA) in a concentration-dependent manner, causing maximal stimulation at 10(-7) M. The stimulatory action of PACAP was not affected by staurosporine (an inhibitor of protein kinase C) or in the cells in which protein kinase C was down-regulated by prolonged exposure to TPA (an activator of protein kinase C), whereas it was partially attenuated in Ca(2+)-free medium. PACAP (10(-7) M) increased the formation of [3H]inositol phosphates, [Ca2+]i and 45Ca2+ uptake as well as cAMP. The peptide also stimulated the phosphorylation of tyrosine hydroxylase, the enzyme catalyzing the rate-limiting step in catecholamine synthesis. Catecholamine synthesis and tyrosine hydroxylase phosphorylation stimulated by the maximal effective concentration of dibutyryl cAMP or high K+, which activates Ca2+ uptake, were further enhanced by PACAP, suggesting that both cAMP- and Ca(2+)-dependent protein kinases may be involved in the stimulation of tyrosine hydroxylase phosphorylation and catecholamine synthesis caused by PACAP.