The long-term goals of this project were: 1) to examine the nature of extracellular and intracellular signals controlling expression of tyrosine hydroxylase (TH), phenylethanolamine-N-methyl-transferase (PNMT), and proenkephalin (pEK) genes; 2) to determine whether these genes are differentially regulated; 3) to determine roles of transcription and post-transcriptional mechanisms in such regulations; and 4) to examine the possible role of nuclear oncogenes in coordinating the regulation of TH, PNMT, and pEK genes. Previous studies identified nicotine and angiotensin receptors as major transsynaptic and hormonal inputs controlling activities and mRNA levels of the catecholamine biosynthetic enzymes in adrenal medullary (AM) cells. The purpose of this study was to further explore the molecular mechanisms underlying these modes of regulation. Incubation of cultured bovine AM cells with nicotine or a stable analog of angiotensin II, sar1-angiotensin II, increased synthesis of TH and PNMT mRNAs, suggesting transcriptional activation of these genes. No effects of nicotine or sar1-angiotensin II on TH and PNMT MRNA levels could be demonstrated in cells treated with cycloheximide or puromycin, suggesting regulation by inducible proteins. Western analysis demonstrated the presence of c-fos, c-jun, and several c-fos- and c-jun-related antigens in control and stimulated AM cells. Sar1-angiotensin II and nicotine Increased steady-state levels of c-fos (1.5- to 2-fold) and c-fos MRNA (10- to 14-fold) and the levels of several c-fos-related antigens (FRA) (2- to 7-fold). Some of FRA showed differential regulation by angiotensin II and nicotinic receptors. The levels of p36-38 c-jun and c-jun mRNA were increased by sarl-angiotensin II (2- to 5-fold) and were less affected by nicotine. In conclusion, our results suggest transcriptional regulation of the TH gene by angiotensin II and nicotinic receptors, through partially different nuclear pathways. The regulation may involve multiple target sites in the TH promoter, inducible proteins. APl-like factors, c-fos and c-fos related antigens.
