Protein kinase a coordinately regulates both basal expression and cyclic AMP-mediated induction of three catecholamine-synthesizing enzyme genes

Studies have shown that the cyclic AMP-regulated pathway is involved in the activation of tyrosine hydroxylase (TH) and in the induction of gene expression of the three catecholamine-synthesizing enzymes, TH, dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PN MT). In the present study we investigated further the role of protein kinase A (PKA) in the regulation of both basal and cyclic AMP-inducible transcription of the three catecholamine-synthesizing enzymes in primary cultured bovine chromaffin cells by using the PKA-specific inhibitor N-[2-(p-bromocinnamylamine)ethyl] -5-isoquinolinesulfonamide (H-89). In the presence of 40 mu M H-89, mRNA levels of TH, DBH, and PNMT were reduced to 17 +/- 8, 19 +/- 8, and 14 +/- 2% of the untreated control, respectively, in 24 h, and intracellular norepinephrine and epinephrine levels were decreased to 20 and 34%, respectively, in 72 h. At 20 mu M, although the basal enzyme gene expression levels were little affected, their induction by forskolin was abolished and norepinephrine and epinephrine levels fell to 55 and 74%. This reduction in catecholamines at 20 mu M was probably due to changes in the phosphorylation state of TH, as its enzymatic activity was found to be decreased to 66 and 69% in 48 and 72 h, respectively. Thus, PKA activity in bovine adrenal medullary cells coordinately regulates both basal and cyclic AMP-inducible gene expression of specific catecholamine-synthesizing enzymes, resulting in changes in intracellular catecholamine levels available for consequent neurohormonal activities.