Nicotine increases expression of tyrosine hydroxylase gene. Involvement of protein kinase A-mediated pathway

Nicotine, a major component of tobacco smoke, stimulates catecholamine secretion and activates catecholamine biosynthetic enzymes such as tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) in adrenal medullary cells. We investigated the effect of long term treatment with nicotine on TH and DBH gene expression in rat PC12 pheochromocytoma cells. Nicotine treatment for 1-2 days increased both the TH and DBH mRNA levels. The effect of nicotine on TH mRNA seems to be transcriptionally mediated. Deletion analysis of the 5' promoter region of the TH gene showed that the region containing a cyclic AMP/calcium regulatory element is sufficient for the nicotinic induction of TH. Nicotine did not induce TH mRNA or chloramphenicol acetyltransferase reporter activity in mutant PC12 cells deficient in protein kinase A activity. However, the deficiency in protein kinase A activity did not affect the elevation in intracellular calcium concentration caused by nicotine, indicating normal receptor function. These results suggest that a cAMP-mediated pathway plays a crucial role in the long term nicotine-induced activation of the TH gene.