Strain-specific differences in transcription of the gene for the epinephrine-synthesizing enzyme phenylethanolamine N-methyltransferase

Pituitary adenylate cyclase activating polypeptide (PACAP) regulates expression of catecholamine biosynthetic enzyme genes in bovine adrenal chromaffin cells

Pituitary adenylate cyclase activating polypeptide (PACAP) elevates levels of the mRNAs encoding the catecholamine synthesizing enzymes tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) in primary cultures of bovine adrenal chromaffin cells. PACAP potently (in nanomolar concentrations) increases the amount of mRNA for each of the three catecholamine biosynthetic enzymes. At 10 nM PACAP, TH and DBH mRNA levels increase approx 10-fold; 1 nM PACAP produces an approx 2.5-fold elevation of PNMT mRNA. In contrast to depolarizing or cholinergic stimuli, PACAP does not enhance expression of 5' upstream regions of the PNMT gene transiently transfected into chromaffin cells. Nor does PACAP stimulate the rate of PNMT gene transcription, thereby indicating that the effects of this neuropeptide do not involve enhanced transcription of this gene. However, after 16 h in the presence of transcriptional inhibitors, more PNMT mRNA is present in cultures treated with PACAP relative to control cultures, whereas amounts of TH and DBH mRNAs are not changed. PACAP likely elevates PNMT mRNA levels posttranscriptionally, possibly by stabilizing this message against degradation. Thus, although PACAP is an effective regulator for expression of all three catecholamine enzyme genes, its mechanism of action on PNMT mRNA appears to be distinctive from its effects on TH and DBH gene transcription.

Glucocorticoids stimulate transcription of the rat phenylethanolamine N-methyltransferase (PNMT) gene in vivo and in vitro

1. Phenylethanolamine N-methyltransferase (PNMT) is regulated by glucocorticoid hormones. This study investigates the ability of glucocorticoids to modulate transcription of the rat PNMT gene in vivo and in vitro. 2. In the adrenal glands of hypophysectomized (HPX'd) rats, the synthetic glucocorticoid dexamethasone (DEX) stimulates production of PNMT mRNA. Quantitative hybridization reveals that the levels of PNMT mRNA increase approximately threefold in total and poly(A)+RNA after 4 days of DEX treatment of HPX'd rats, a level which is maximal for this treatment. 3. ACTH, the hormonal stimulus of glucocorticoid biosynthesis in the adrenal cortex, enhances PNMT mRNA production to levels comparable to that achieved with DEX in this system. The steroid responsiveness of PNMT message production is specific for glucocorticoids. DEX also increases PNMT mRNA in the brain stem, although the magnitude and speed of response are lower than observed in the adrenal gland. 4. Additional confirmation of the inductive ability of glucocorticoids is demonstrated by the increase in PNMT immunoprecipitated following translation in vitro of adrenal RNAs from DEX-treated rats. Furthermore, the PNMT mRNA signal obtained by in situ hybridization histochemistry in adrenal sections and in primary cultures of dispersed rat adrenal medullae reveals that DEX effects on PNMT mRNA can be elicited both in vivo and in vitro. 5. Specifically, glucocorticoids exert their effects on expression of PNMT mRNA by elevating the rate of PNMT gene transcription: a 2.3-fold increase in PNMT transcription persists for 18 hr following DEX treatment of HPX'd rats. In summary, this study establishes that glucocorticoids directly and rapidly stimulate transcription of the rat PNMT gene.

Phenylethanolamine N-methyltransferase (PNMT)-expressing horizontal cells in the rat retina: a study employing double-label immunohistochemistry

Phenylethanolamine N-methyltransferase (PNMT), the final enzyme in the catecholamine biosynthetic pathway that converts norepinephrine to epinephrine, has been detected in the retinas of various vertebrate species. The expression of PNMT has generally been thought to occur in amacrine cells of the ganglion cell and inner nuclear layers. By using immunohistochemical techniques, we have found a population of PNMT- and neurofilament-positive neurons at the border of the inner nuclear layer and the outer plexiform layer in the rat retina. We have classified these cells as horizontal neurons based on their location adjacent to the outer plexiform layer, their morphology, and their expression of vimentin and neurofilaments.

Species-specific distribution of aromatic L-amino acid decarboxylase in the rodent adrenal gland, cerebellum, and olfactory bulb

Aromatic L-amino acid decarboxylase (AADC), the enzyme that converts L-dopa to dopamine, displayed species-specific differences in both activity and immunoreactivity in the cerebellum, olfactory bulb, and adrenal glands of three rodent species, the hamster, rat, and mouse. Specifically, in the hamster but not the rat or mouse, AADC immunoreactive cells were observed in the cerebellum and adrenal cortex. The unusual distribution of the enzyme was confirmed biochemically. AADC activity was greater in the adrenal gland and the cerebellum in the hamster than in the mouse or rat. In addition, by Western blot analysis, one band of appropriate molecular weight was observed both in the hamster adrenal gland and cerebellum. The rat adrenal gland displayed a similar immunoreactive protein on the Western blot; however, the protein could not be detected in the rat cerebellum by the technique utilized. Tyrosine hydroxylase (TH) immunoreactivity in these same tissues did not differ among the species. In the main olfactory bulb of the mouse, juxtaglomerular cells exhibited very limited immunoreactivity for AADC, but TH-immunoreactivity in these cells was robust. In contrast, juxtaglomerular cells in the rat displayed a similar intensity of immunostaining for both AADC and TH. AADC activity in the mouse, consistent with the reduced immunostaining for the enzyme, was 50% of that in the rat and the hamster. These data demonstrate that AADC protein, which is contained in cells of diverse function, also displays qualitative and quantitative species specific variations in both distribution and amount.