PROTEIN-KINASE A COORDINATELY REGULATES BOTH BASAL EXPRESSION AND CYCLIC AMP-MEDIATED INDUCTION OF 3 CATECHOLAMINE-SYNTHESIZING ENZYME GENES

Studies have shown that the cyclic AMP-regulated pathway is involved i n the activation of tyrosine hydroxylase (TH) and in the induction of gene expression of the three catecholamine-synthesizing enzymes, TH, d opamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransfe rase (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 enzym es in primary cultured bovine chromaffin cells by using the PKA-specif ic inhibitor N-[2-(p-bromocinnamylamine)ethyl] -5-isoquinolinesulfonam ide (H-89). In the presence of 40 mu M H-89, mRNA levels of TH, DBH, a nd PNMT were reduced to 17 +/- 8, 19 +/- 8, and 14 +/- 2% of the untre ated 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 wer e little affected, their induction by forskolin was abolished and nore pinephrine and epinephrine levels fell to 55 and 74%. This reduction i n catecholamines at 20 mu M was probably due to changes in the phospho rylation state of TH, as its enzymatic activity was found to be decrea sed to 66 and 69% in 48 and 72 h, respectively. Thus, PKA activity in bovine adrenal medullary cells coordinately regulates both basal and c yclic AMP-inducible gene expression of specific catecholamine-synthesi zing enzymes, resulting in changes in intracellular catecholamine leve ls available for consequent neurohormonal activities.