Molecular Biology of Stress‐Elicited Induction of Catecholamine Biosynthetic Enzymesa

Abstract

Immobilization stress elevates adrenal mRNA for several catecholamine biosynthetic enzymes. Phenylethanolamine N-methyltransferase (PNMT) mRNA is elevated in response to as little as 5 minutes of immobilization, which appears to be a direct consequence of the large rise of glucocorticoids. Tyrosine hydroxylase (TH) mRNA levels are not elevated under these conditions, but are maximally induced by 30 min of a single immobilization. Dopamine beta-hydroxylase (DBH) requires repeated stress for maximal induction. Transcriptional inhibitor actinomycin D prevented the elevation of TH and PNMT mRNA with a single immobilization. Oligonucleotides corresponding to the AP-1 like element in the TH promoter and an important regulatory element in the DBH promoter were used in binding assays with adrenomedullary extracts of rats exposed to stress. The complexes were UV cross-linked and analyzed by gel electrophoresis. The complex bound to the TH AP-1 site contained c-fos and other proteins (including cJun). The complex to the DBH-1 element contained several proteins, probably including fos related proteins but lacked c-fos. Immunoblots found that c-fos is induced in the adrenal medulla near maximally by one hour immobilization and cJun and JunD are present in higher constitutive levels and are only moderately regulated by immobilization stress. The results indicate that different mechanisms of transcriptional activation are used by several members of the catecholamine biosynthetic pathway.

c‐Fos Deficiency Inhibits Induction of mRNA for Some, but Not All, Neurotransmitter Biosynthetic Enzymes by Immobilization Stress

“…Thus, elevation of PNMT is largely dependent on hormonal regulation at its glucocorticoid regulatory responseelement (Ross et al, 1990), and hypophysectomy prevents the induction of PNMT by stress, whereas TH, DBH, and NPY responses are affected only slightly (Nankova et al, 1994;Viskupic et al, 1994;Sabban et al, 1996). Transsynaptic nicotinic nerve stimulation is essential for the induction of adrenomedullary NPY , whereas immobilization stress was found to enable elevation of TH and c-Fos mRNAs by a nonneuronal, nonpituitarymediated pathway (Nankova et al, 1994;Sabban et al, 1995).In addition to the stress effects in the adrenal medulla, these genes are also elevated by stress in both the noradrenergic neurons of sympathetic ganglia and the locus ceruleus, the major noradrenergic cell bodies in the brainstem (Angulo et al, 1991;Mamalaki et a!., 1992;. However, there appear to be tissue-specific differences.…”

“…Mean levels in wild-type control males were taken as 1.0. *p < 0.05, for pairwise comparisons of the effect of stress for same gender and genotype; * *p < 0.05, for pairwise comparisons of basal levels of males and females of the same genotype.for the induction of TH by repeated immobilization stress is surprising given the parallel induction of cFos and AP-1 DNA binding activity and TH transcription in rats previously observed with stress (Nankova eta!., 1994;Sabban et al, 1995). If c-Fos is involved nonetheless in the induction of TH expression by immobilization in wild-type animals, the loss of c-Fos may be compensated for in this role by another transcription factor in the transgenic animals.…”

“…Stress leads to marked and prolonged elevations in the expression of several gene products in the sympathoadrenal system. In the adrenal medulla, the catecholamine biosynthetic enzymes, tyrosine hydroxylase (TH), dopamine~3-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT), several neuropeptide precursors, such as NPY and preproenkephalin, as well as c-Fos, are transcriptionally induced by stress (Sabban et a!., 1995. Although their expression is elevated by immobilization stress, different mechanisms appear to be responsible for their induction.…”

“…Thus, elevation of PNMT is largely dependent on hormonal regulation at its glucocorticoid regulatory responseelement (Ross et al, 1990), and hypophysectomy prevents the induction of PNMT by stress, whereas TH, DBH, and NPY responses are affected only slightly (Nankova et al, 1994;Viskupic et al, 1994;Sabban et al, 1996). Transsynaptic nicotinic nerve stimulation is essential for the induction of adrenomedullary NPY , whereas immobilization stress was found to enable elevation of TH and c-Fos mRNAs by a nonneuronal, nonpituitarymediated pathway (Nankova et al, 1994;Sabban et al, 1995).…”

“…Different types of stress, including immobilization or restraint stress, increase cfos gene expression in adrenal medulla and specific brain regions (Melia et al, 1994;Senba et a!., 1994;Palkovits et al, 1995;Sabban et al, 1995). c-fos is a 62-kDa nuclear protooncogene that forms heterodimers with members of the Jun family; these complexes bind to AP-1 sites (core consensus of TGAG/CTCA) to regulate transcription (Angel and Karin, 1991).…”