The complete nucleotide sequence and structure of the gene encoding bovine phenylethanolamine N-methyltransferase

Identification of phenylethanolamine N-methyltransferase gene expression in stellate ganglia and its modulation by stress

Phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28) is the terminal enzyme of the catecholaminergic pathway converting noradrenaline to adrenaline. Although preferentially localized in adrenal medulla, evidence exists that PNMT activity and gene expression are also present in the rat heart, kidney, spleen, lung, skeletal muscle, thymus, retina and different parts of the brain. However, data concerning PNMT gene expression in sympathetic ganglia are still missing. In this study, our effort was focused on identification of PNMT mRNA and/or protein in stellate ganglia and, if present, testing the effect of stress on PNMT mRNA and protein levels in this type of ganglia. We identified both PNMT mRNA and protein in stellate ganglia of rats and mice, although in much smaller amounts compared with adrenal medulla. PNMT gene expression and protein levels were also increased after repeated stress exposure in stellate ganglia of rats and wild-type mice. Similarly to adrenal medulla, the immobilization-induced increase was probably regulated by glucocorticoids, as determined indirectly using corticotropin-releasing hormone knockout mice, where immobilization-induced increase of PNMT mRNA was suppressed. Thus, glucocorticoids might play an important role in regulation of PNMT gene expression in stellate ganglia under stress conditions.

Glucocorticoid responsiveness of the rat phenylethanolamine N-methyltransferase gene

Two newly identified, overlapping (1 bp) glucocorticoid response elements (GREs) at -759 and -773 bp in the promoter of the rat phenylethanolamine N-methyltransferase (PNMT; EC 2.1.1.28) gene are primarily responsible for its glucocorticoid sensitivity, rather than the originally identified -533-bp GRE. A dose-dependent increase in PNMT promoter activity was observed in RS1 cells transfected with a wild-type PNMT promoter-luciferase reporter gene construct and treated with dexamethasone (maximum activation at 0.1 microM). The type II glucocorticoid receptor antagonist RU38486 (10 microM) fully inhibited dexamethasone (1 microM) activation of the PNMT promoter, consistent with classical glucocorticoid receptors mediating corticosteroid-stimulated transcriptional activity. Relative IC(50) values from gel mobility shift competition assays showed that the -759-bp GRE has a 2-fold greater affinity for the glucocorticoid receptor than the -773-bp GRE. Site-directed mutation of the -533-, -759-, and -773-bp GREs alone or in tandem demonstrated that the -759-bp GRE was also functionally more important, but both the -759- and -773-bp GREs are required for maximum glucocorticoid responses. Moreover, the -533-bp GRE, rather than increasing glucocorticoid sensitivity of the promoter, may limit corticosteroid responsiveness mediated via the -759- and -773-bp GREs. Finally, the glucocorticoid receptor bound to the -759- and -773-bp GREs interacts cooperatively with Egr-1 and/or AP-2 to stimulate PNMT promoter activity in RS1 cells treated with dexamethasone. In contrast, glucocorticoid receptors bound to the -533-bp GRE only seem to participate in synergistic activation of the PNMT promoter through interaction with activator protein 2.

Human indolethylamine N-methyltransferase: cDNA cloning and expression, gene cloning, and chromosomal localization

Indolethylamine N-methyltransferase (INMT) catalyzes the N-methylation of tryptamine and structurally related compounds. We recently cloned and characterized the rabbit INMT cDNA and gene as a step toward cloning the cDNA and gene for this enzyme in humans. We have now used a PCR-based approach to clone a human INMT cDNA that had a 792-bp open reading frame that encoded a 263-amino-acid protein 88% identical in sequence to rabbit INMT. Northern blot analysis of 35 tissues showed that a 2.7-kb INMT mRNA species was expressed in most tissues. When the cDNA was expressed in COS-1 cells, the recombinant enzyme catalyzed the methylation of tryptamine with an apparent K(m) value of 2.9 mM. The human cDNA was then used to clone the human INMT gene from a human genomic BAC library. The gene was 5471 bp in length, consisted of three exons, and was structurally similar to the rabbit INMT gene as well as genes for nicotinamide N-methyltransferase and phenylethanolamine N-methyltransferase in several species. All INMT exon-intron splice junctions conformed to the "GT-AG" rule, and no canonical TATA or CAAT sequences were present within the 5'-flanking region of the gene. Human INMT mapped to chromosome 7p15.2-p15.3 on the basis of both PCR analysis and fluorescence in situ hybridization. Finally, two possible single nucleotide polymorphisms were identified within exon 3, both of which altered the encoded amino acid. The cloning and expression of a human INMT cDNA, as well as the cloning, structural characterization, and mapping of its gene represent steps toward future studies of the function and regulation of this methyltransferase enzyme in humans.

Glucocorticoids decrease phenylethanolamine N-methyltransferase mRNA expression in the immature foetal sheep adrenal

This study examined the impact of a chronic physiological elevation of plasma cortisol levels on adrenal catecholamine synthetic enzyme and proenkephalin A mRNA expression in foetal sheep. Cortisol (2.5-3. 0 mg.5 ml-1.24 h-1, n=9) or saline (0.9% saline, n=6) was infused into foetal sheep for 7 days between 109 days and 116 days gestation. Foetal plasma cortisol concentrations were higher (P<0.0005) in the cortisol infused foetuses when compared with the saline infused group (43.07+/-4.13 nmol.l-1 vs 1.67+/-0.10 nmol.l-1). There were no differences, however, in the plasma ACTH levels between the two groups. Using Northern blot analysis, adrenal phenylethanolamine N-methyltransferase (PNMT) mRNA expression was found to be reduced (P<0.005) fivefold in the cortisol infused foetuses when compared with the controls, as was the relative area of the adrenal medulla which stained positively with anti-PNMT (28.1+/-2.5% vs 44.8+/-4.8%, P<0.007). No effect of cortisol infusion was observed on adrenal tyrosine hydroxylase mRNA and protein expression or proenkephalin A mRNA expression. We conclude that before birth, adrenaline synthesis may be suppressed by a novel direct, or indirect, inhibitory effect of glucocorticoids on PNMT mRNA expression.

Phenylethanolamine N-methyltransferase gene expression. Sp1 and MAZ potential for tissue-specific expression

Phenylethanolamine N-methyltransferase (PNMT) promoter-luciferase reporter gene constructs (pGL3RP863, pGL3RP444, and pGL3RP392) transfected into COS1, RS1, PC12, NIH/3T3, or Neuro2A cells showed the highest basal luciferase activity in the Neuro2A cells. DNase I footprinting with Neuro2A cell nuclear extract identified protected PNMT promoter regions spanning the -168/-165 and -48/-45 base pair Sp1/Egr-1 binding sites. Gel mobility shift assays and transient transfection assays using site-directed mutant PNMT promoter-luciferase reporter gene constructs indicated that the elevated basal luciferase activity in the Neuro2A cells was mediated by Sp-1. Furthermore, activation of the PNMT promoter by Sp1 depends on both its binding affinity for its cognate target sequences and its intracellular concentrations. When Sp1 levels were increased through an expression plasmid, luciferase reporter gene expression rose well beyond basal wild-type levels, even with either Sp1 binding element mutated. Finally, another transcription factor expressed in the Neuro2A cells competes with Sp1 by interacting with DNA sequences 3' to the -48 base pair Sp1 site to prevent Sp1 binding and induction of the PNMT promoter. The DNA consensus sequence, Southwestern analysis, and gel mobility shift assays with antibodies identify MAZ as the competitive factor. These findings suggest that Sp1 may potentially contribute to the tissue-specific expression of the PNMT gene, with the competition between Sp1 and MAZ conferring additional tissue-specific control.

Tissue-specific alternative mRNA splicing of phenylethanolamine N-methyltransferase (PNMT) during development by intron retention

The expression of phenylethanolamine N-methyl transferase (EC 2. 1.1.2.8, PNMT), the final enzyme in the cascade of catecholamine synthesis, is differentially regulated in adrenergic neurons in the brain and in adrenal chromaffin cells. Using reverse transcription-polymerase chain reaction-based techniques, we detected in the prenatal developing rat brainstem, two species of PNMT mRNA which were produced by a rare alternative splicing mechanism known as intron retention. The spliced, intronless message was downregulated postnatally, while the intron-retained mRNA species continued to be constitutively expressed through adulthood. By contrast in the adrenals, at all stages of development examined, only the intronless message was expressed. In line with previous reports on the failure of glucocorticoids to induce PNMT expression in the brain, the pattern of PNMT splicing in brainstem explants was not affected by the presence of the synthetic glucocorticoid dexamethasone. Undifferentiated sympathoadrenal PC12 pheochromocytoma cells expressed very low basal levels of both mRNA variants, accompanied by a very low basal PNMT enzymatic activity. Exposure of PC12 cells to dexamethasone resulted in the upregulation of only the spliced mRNA variant concomitant with a 3-fold increase in PNMT enzymatic activity. In contrast, treatment of PC 12 cells with nerve growth factor (NGF) enhanced the expression of both the intron-retained and the intronless mRNA species without changes in the basal enzyme activity. This latter result suggests that the translation of the intronless mRNA species may be regulated by the intron-retained mRNA species, which by itself may yield a truncated, yet enzymatically functional translational product. Our data suggest that the tissue-specific regulation of PNMT expression is based on a rare alternative splicing mechanism termed intron retention, and that in the adrenal, but not in the brain, this mechanism is sensitive to regulation by glucocorticoids. Thus, this system is uniquely suited for studying the hormonal control of tissue-specific splicing in the nervous system.

Rabbit lung indolethylamine N-methyltransferase. cDNA and gene cloning and characterization

Indolethylamine N-methyltransferase (INMT) catalyzes the N-methylation of tryptamine and structurally related compounds. This reaction has been studied because of its possible role in the in vivo synthesis of psychoactive compounds or neurotoxins and has been characterized biochemically in preparations of rabbit lung. Therefore, we set out to purify rabbit lung INMT, to clone and express its cDNA, and to clone and structurally characterize its gene as steps toward understanding the function and regulation of this enzyme. Rabbit lung INMT was purified and partial amino acid sequence was obtained. A polymerase chain reaction-based approach was then used to clone a rabbit lung INMT cDNA with a 792-base pair open reading frame that encoded a 263-amino acid protein with a predicted molecular mass of 29 kDa. When the cDNA was expressed in COS-1 cells, the encoded protein catalyzed the methylation of tryptamine and structurally related compounds, and was inhibited by two products of the reaction, S-adenosyl-L-homocysteine (AdoHcy) and N,N-dimethyltryptamine, as well as antimigraine drugs that are structurally related to N,N-dimethyltryptamine. Northern blot analysis demonstrated the presence of 2.0-kilobase mRNA species in rabbit lung, liver and, at lower levels, in brain. The cDNA was then used to clone the rabbit INMT gene. That gene had three exons and was structurally similar to the genes for nicotinamide N-methyltransferase and phenylethanolamine N-methyltransferase in several species. Cloning and expression of a rabbit lung INMT cDNA and cloning of the rabbit INMT gene represent important steps toward determination of the function and regulation of this mammalian methyltransferase enzyme.

Phenylethanolamine N-methyltransferase gene expression: synergistic activation by Egr-1, AP-2 and the glucocorticoid receptor

The gene encoding the epinephrine synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT), is transcriptionally activated by Egr-1, AP-2, and the glucocorticoid receptor (GR). Stimulation by AP-2 requires its synergistic interaction with an activated GR. The present studies show that the GR also cooperates with Egr-1 or the combination of Egr-1 and AP-2 to activate the PNMT promoter. Together Egr-1, AP-2, and the GR can induce PNMT promoter-mediated luciferase reporter gene expression beyond the sum of their independent contributions as well as synergistically activate the endogenous PNMT gene leading to marked increases in PNMT mRNA. Examination of the effects of mutation of the AP-2 or Egr-1 binding sites on PNMT promoter activation by DEX and the factor binding to the remaining intact site or by all three transcriptional activators showed changes in luciferase reporter gene expression which suggest that DNA structure may be altered thereby reducing or enhancing synergistic activation. It also appears that the -165 bp Egr-1 site may not be critical for the synergism observed between Egr-1, AP-2 and the GR. When the glucocorticoid response element (GRE) within the PNMT promoter was mutated, PNMT promoter activation by Egr-1 and DEX, AP-2 and DEX or all three showed both inhibition and enhancement, even when the GRE was completely eliminated. These observations indicate that induction of PNMT gene transcription may occur either through GR interaction with other transcriptional proteins after binding to its cognate GRE or through direct protein-protein interaction in the absence of GRE binding. While the mechanisms by which Egr-1 and the GR and Egr-1, AP-2 and the GR function cooperatively to stimulate PNMT promoter activity remain to be elucidated, this synergistic stimulation of the PNMT promoter by these factors may provide important in vivo and in vitro regulatory control of the PNMT gene.

Mouse nicotinamide N-methyltransferase gene: molecular cloning, structural characterization, and chromosomal localization

Nicotinamide N-methyltransferase (NNMT) catalyzes the N-methylation of nicotinamide and structurally related compounds. There are large strain-dependent variations in the expression of NNMT activity in mouse liver during growth and development, raising the possibility of developmental regulation of the gene. Therefore, we set out to clone and structurally characterize the mouse NNMT gene, Nnmt. The gene spanned approximately 16 kb and consisted of three exons, 348 bp, 208 bp, and 487 bp in length, with an initial 1228-bp intron and a second intron that was approximately 14 kb in length. The locations of the splice junctions within the gene were highly conserved compared with those in genes for structurally related methyltransferase enzymes. The Nnmt gene contained no canonical TATA box sequences, but an "initiator" (Inr) sequence was located at the site of transcription initiation as determined by 5' rapid amplification of cDNAs ends. A promoter was located within the initial 750 bp of the 5' flanking region of the gene according to studies of the expression of a reporter gene in HepG2 cells. 5'-Flanking region sequences for mouse strains with high and low hepatic NNMT activity differed with regard to a series of nucleotide substitutions, insertions, and deletions, with the most striking difference being a 12-bp insertion/deletion. The Nnmt gene mapped to mouse chromosome 9 in an area of conserved synteny to human chromosome 11q, consistent with the localization of the human NNMT gene to 11q23. Cloning and structural characterization of the mouse Nnmt gene will make it possible to study molecular genetic mechanisms involved in the expression of this important methyltransferase.

Sympathoadrenal system in stress. Interaction with the hypothalamic-pituitary-adrenocortical system

Exposure of an organism to any of a variety of stressors markedly activates the sympathoadrenal and hypothalamic-pituitary-adrenocortical systems. Interactions of these major stress systems occur at several levels in the periphery and the brain. In the present study, we used sham-operated or adrenalectomized cortisol-treated conscious rats to examine glucocorticoid effects on indices of CA release, metabolism, and synthesis, and on CA biosynthetic enzyme activities and gene expression at baseline and during immobilization stress (IMO). Adrenalectomy (ADX) stimulated basal and stress-induced increments in norepinephrine release, reuptake, metabolism, turnover, and biosynthesis. Loss of adrenomedullary hormones after ADX did not appear to contribute to these increments. Cortisol treatment reversed the ADX effects on CA indices and suppressed catecholaminergic responses to IMO in intact rats. These results suggest that endogenous glucocorticoids restrain responses of catecholamine turnover, synthesis, release, reuptake, and metabolism during stress. In contrast, in intact rats, continuous administration of cortisol lasting for 7 days exaggerated the IMO-induced increases in plasma CA levels. Inhibition of DOPA conversion to dopamine elevated plasma DOPA levels in chronically cortisol-treated stressed rats compared to saline-treated ones, suggesting a cortisol-induced increase in tyrosine hydroxylation. Stress increases TH and PNMT activities and mRNA levels in the adrenal medulla. Hypophysectomy reduced adrenal PNMT but not TH mRNA levels in control and IMO rats. Pretreatment of hypophysectomized animals with ACTH fully restored the control and IMO-induced adrenal PNMT mRNA levels and augmented PNMT but not TH mRNA responses in intact rats. Long-term cortisol administration to intact rats also elevated adrenal PNMT but not TH mRNA levels. The results indicate a suppressive effect of endogenous glucocorticoids and a stimulatory effect of chronically elevated glucocorticoid levels on sympathoadrenal activity during stress. The results also suggest that a nonneuronal, nonpituitary factor contributes to TH gene expression during some forms of stress, whereas pituitary-adrenocortical factors play the essential role in the regulation of PNMT gene expression.

Roles of steroid hormones and their receptors in structural organization in the nervous system

Due to their chemical properties, steroid hormones cross the blood-brain barrier where they have profound effects on neuronal development and reorganization both in invertebrates and vertebrates, including humans mediated through their receptors. Steroids play a crucial role in the organizational actions of cellular differentiation representing sexual dimorphism and apoptosis, and in the activational effects of phenotypic changes in association with structural plasticity. Their sites of action are primarily the genes themselves but some are coupled with membrane-bound receptor/ion channels. The effects of steroid hormones on gene transcription are not direct, and other cellular components interfere with their receptors through cross-talk and convergence of the signaling pathways in neurons. These genomic and non-genomic actions account for the divergent effects of steroid hormones on brain function as well as on their structure. This review looks again at and updates the tremendous advances made in recent decades on the study of the role of steroid (gonadal and adrenal) hormones and their receptors on developmental processes and plastic changes in the nervous system.

Investigation of the phenylethanolamine N-methyltransferase gene as a candidate gene for hypertension

Genetic mapping studies have located a gene, Bp1, that accounts for approximately 30% of the genetic variation in the stroke-prone spontaneously hypertensive rat (SHRSP) to a region on chromosome 10 containing the angiotensin-converting enzyme gene. In humans, the gene encoding phenylethanolamine N-methyltransferase (PNMT) was localized near the angiotensin-converting enzyme gene on human chromosome 17. Since most of human chromosome 17 is known to be homologous to rat chromosome 10 and PNMT is known to play a role in blood pressure homeostasis, we reasoned (1) that the rat gene encoding PNMT (Pnmt) may reside on chromosome 10 within the confidence interval containing Bp1 and (2) that Pnmt is a good candidate gene for Bp1. With the use of a somatic cell hybrid panel and genetic mapping techniques, Pnmt mapped within the confidence interval that contains Bp1. To examine further this possibility of Pnmt as a candidate for Bp1, we cloned and characterized Pnmts of the original parental strains, the Wistar-Kyoto rat and SHRSP from the Heidelberg colony. We did not identify any sequence differences between the Wistar-Kyoto rats and SHRSP in the primary structure, in 1077 bp of the 5'-flanking region, or in the 256-bp 3'-end region, making Pnmt an unlikely gene for the genetic basis of salt-loaded hypertension.

Regulation of tyrosine hydroxylase gene expression in depolarized non-transformed bovine adrenal medullary cells: second messenger systems and promoter mechanisms

Activation of the tyrosine hydroxylase (TH) gene in the adrenal medulla during stress is mediated by trans-synaptic mechanisms and may involve cholinergic receptors. Stimulation of nicotinic receptors in adrenal medullary cells induces cell depolarization, influx of Ca2+ ions and increases levels of cAMP. We have shown that both cAMP and membrane depolarization produce an increase in the expression of the TH gene in cultured bovine adrenal medullary cells (BAMC). Others have proposed that transcriptional activation of the TH gene by cAMP is mediated through the sequence homologous to a cAMP responsive element (CRE) located in the proximal region of the TH gene promoter. In the present study we have examined the mechanisms by which membrane depolarization increases the TH gene activity. Treatment of serum-free BAMC cultures with the depolarizing agent, veratridine, increased the extracellular concentration of catecholamines, Met5-enkephalin, and the relative abundance of TH mRNA. Veratridine treatment also increased the levels of mRNAs for the catecholamine biosynthetic enzyme phenylethanolamine N-methyltransferase (PNMT), and proenkephalin A (PEK). Treatment for longer than 3 h was required to increase TH mRNA levels. By contrast, our previous studies indicated that cAMP stimulation for 2 h produces a maximal increase in TH mRNA levels in BAMC. The effects of veratridine and forskolin on TH mRNA levels were additive, further indicating that depolarization and cAMP activate TH gene expression via different pathways. Calmidazolium, an antagonist of calmodulin, had no effect on the veratridine-induced increase in TH mRNA levels. Similarly sphingosine treatment or preincubation with PMA, which reduce protein kinase C (PKC) activity and attenuate the induction of TH mRNA by PMA or the hormone, angiotensin II, did not affect the induction by veratridine. To identify promoter mechanisms of TH gene activation in depolarized cells we transfected BAMC with a plasmid pTHgoodLuc and treated with veratridine for 24 h. pTHgoodLUC contains a luciferase reporter gene linked to a -428/+21 bp fragment of the bovine TH gene promoter (relative to the transcription start site). Veratridine increased the expression of luciferase from the TH promoter 2.5-fold. Deletion of the -194/-54 bp promoter region containing SP-1 and POU/Oct sites reduced veratridine stimulation by 40%. Additional deletion of the -269 to -190 bp promoter segment, including an AP-1 element, further reduced veratridine stimulation to a statistically non-significant level. In conclusion, activation of TH gene expression upon depolarization is not mediated by calmodulin and PKC. Promoter sequences involved in this activation are located upstream from the CRE. Depolarization may activate TH gene transcription by acting on more than one regulatory region.

Brief cortisol exposure elevates adrenal phenylethanolamine N-methyltransferase after a necessary lag period

The present study, using bovine adrenal medullary cells, characterized in detail the time course of regulation of phenylethanolamine N-methyltransferase activity following brief glucocorticoid exposure. Cortisol pulses (10(-4) and 10(-5) M), as short as 15 min, increased phenylethanolamine N-methyltransferase activity measured 2 days following cortisol exposure, with a required lag period of 18 h or more. Phenylethanolamine N-methyltransferase activity was increased 2 days following brief (2 h) exposure to cortisol in concentrations that reach the medulla in vivo (10(-6) to 10(-4) M). Phenylethanolamine N-methyltransferase activity following both continuous and 2 h pulses of 10(-5) M cortisol were reduced by the glucocorticoid receptor antagonist, RU 38486. A 2 h pulse of nicotine (10(-5) M) increased phenylethanolamine N-methyltransferase activity with a lag period of at least 18 h, while combination treatment of nicotine and cortisol (10(-4) M) produced significantly higher increases in phenylethanolamine N-methyltransferase compared to either treatment alone. Therefore, this study provides novel in vitro evidence for the regulation of adrenomedullary phenylethanolamine N-methyltransferase activity, following a necessary lag period, by acute changes in both cortisol and nicotine.

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.

Adrenal phenylethanolamine N-methyltransferase induction in relation to glucocorticoid receptor dynamics: evidence that acute exposure to high cortisol levels is sufficient to induce the enzyme

Glucocorticoids (GCs) are thought to regulate, in a permissive fashion, the basal activity of adrenal medullary phenylethanolamine N-methyltransferase (PNMT). However, it is unclear whether a large short-term increase in GC release, such as occurs during an acute stress response, may also play a role in PNMT regulation. The present study investigated how the GC influence over PNMT activity varies in relation to dynamic changes in the hormone-receptor signal. Using [3H]dexamethasone (DEX) and [3H]RU 28362 as radioligands, we have confirmed the presence of GC receptors in bovine adrenal medullary cells. A concentration-dependent decline in soluble GC receptor sites and an increase in nuclear uptake of [3H]DEX were found in response to GC levels as low as 5 x 10(-8) M. The loss of soluble sites plateaued between 5 x 10(-8) and 10(-6) M cortisol, with further losses occurring at 10(-5) and at 10(-4) M. The functional consequence of GC receptor binding was confirmed by measuring PNMT activity following 3-day exposure to cortisol. The pattern of PNMT induction was similar to that seen with GC receptor occupancy; at cortisol concentrations between 10(-8) and 10(-5) M, PNMT induction was at a plateau, with a further increase in activity at 10(-4) M. The increase in PNMT activity following 3-day exposure to low (10(-7) M) and high (5 x 10(-5), 10(-5) M) cortisol was blocked by the GC receptor antagonist RU 38486, suggesting a GC receptor-mediated event. Finally, a short (2 h) pulse of GC, which mimics the time course of physiological elevation of GC following acute stress, elevated adrenal medullary PNMT activity measured 3 days later. Therefore, our results provide novel evidence that short-term exposure of adrenal medullary cells to high cortisol levels can elevate PNMT activity.

Organization and complete nucleotide sequence of the gene encoding mouse phenylethanolamine N-methyltransferase

Phenylethanolamine N-methyltransferase (PNMT; EC 2.1.1.28) catalyzes the conversion of norepinephrine to epinephrine, the last step of catecholamine biosynthesis. We have previously reported molecular cloning of cDNA encoding human PNMT and chromosomal localization of its gene (Kaneda et al., J. Biol. Chem., 263 (1988) 7672-7677). In this report, we isolated the chromosomal gene encoding mouse PNMT by cross-hybridization with the human PNMT cDNA. Mouse PNMT gene spanned about 1.8 kb and consisted of 3 exons. Primer extension analysis showed two putative transcription initiation sites. Northern blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) revealed the expression of the mouse PNMT mRNA in brain (pons and medulla oblongata) and adrenal gland. Subsequently cDNA encoding mouse PNMT was amplified by RT-PCR and cloned into the plasmid vector. Mouse PMNT gene contained the protein-coding region of 885 bp (295 amino acids) with the predicted molecular weight of 32,627. The deduced amino acid sequence of mouse PNMT revealed the major difference in the N-terminal region, as compared to the human and bovine PNMT sequences. In the 5'-terminal region of the mouse PNMT gene, we found the existence of 23 bp direct repeat sequences, which was not observed in the corresponding regions of the human and bovine PNMT genes. The presence or absence of the direct repeats caused the major difference in the PNMT sequences among species. The typical TATA, GC, and CACCC boxes as well as several sequences homologous to glucocorticoids response elements (GRE) were located in the 5'-flanking region of the mouse PNMT gene.

Genes for human catecholamine-synthesizing enzymes

Catecholamine neurotransmitters--dopamine, noradrenaline (norepinephrine), adrenaline (epinephrine)--are synthesized in catecholaminergic neurons from tyrosine, via dopa, dopamine and noradrenaline, to adrenaline. Four enzymes are involved in the biosynthesis of adrenaline: (1) tyrosine 3-mono-oxygenase (tyrosine hydroxylase, TH); (2) aromatic L-amino acid decarboxylase (AADC, or DOPA decarboxylase, DDC); (3) dopamine beta-mono-oxygenase (dopamine beta-hydroxylase, DBH); and (4) noradrenaline N-methyltransferase (phenylethanolamine N-methyltransferase, PNMT). We cloned full-length complementary DNAs (cDNAs) and genomic DNAs of human catecholamine-synthesizing enzymes (TH, AADC, DBH, PNMT) and determined the nucleotide sequences and the deduced amino acid sequences. We discovered multiple messenger RNAs (mRNAs) of human TH, human DBH, and human PNMT. Four types (types 1, 2, 3, and 4) of human TH mRNAs are produced by alternative mRNA splicing mechanism from a single gene. We found the multiple forms of TH in two species of monkeys, but only a single mRNA corresponding to human TH type 1 in Sunkus murinus and rat, suggesting that the multiplicity of TH mRNA is primate-specific. Total TH mRNA, especially the most abundant type 2 and type 1 mRNAs in the human brain, were found to be reduced during the process of aging. The multiple forms of human TH may give additional regulation to the human enzyme, probably through altered phosphorylation and activation. We have succeeded in producing transgenic mice carrying multiple copies of the human TH gene in brain and adrenal medulla. The level of human TH mRNA in brain was about 50-fold higher than that of endogenous mouse TH mRNA. In situ hybridization demonstrated an enormous region-specific expression of the transgene in substantia nigra and ventral tegmental area. TH immunoreactivity in these regions, Western blot analysis, and TH activity measurements proved definitely increased TH in transgenic mice, though not comparable to the increment of the mRNA. However, catecholamine levels in transgenics were not significantly different from those in non-transgenics. The results suggest complex regulatory mechanisms for human TH gene expression and for the catecholamine levels in transgenic mice. Kohsaka and Uchida in collaboration with us applied genetically engineered (human TH cDNA-transfected) non-neuronal cells to brain tissue transplantation in parkinsonian rat models. We isolated and sequenced a full-length cDNA encoding human AADC.(ABSTRACT TRUNCATED AT 400 WORDS)

Cloning and analysis of the pseudogene for human epinephrine synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT)

1. This gene completely lacks the intervening sequences. 2. This gene is truncated at the 5' end peptide encoding region by 433 base pairs (bp). 3. The 502 bp of this gene containing poly(A) signal are completely identical to the 3' half of mRNA encoding region of functional gene. 4. This gene has a poly(A) tail and is flanked by direct repeat of 6 bp. 5. Here we report for the first time the complete sequence of a human pseudogene for phenylethanolamine N-methyltransferase and this is the first report of cloning of pseudogene for catecholamine biosynthetic enzymes.

Isolation of a rat adrenal cDNA clone encoding phenylethanolamine N-methyltransferase and cold-induced alterations in adrenal PNMT mRNA and protein

Cold stress is known to increase the synthesis and release of catecholamines in the sympathoadrenal system. Previously, we have demonstrated that cold exposure results in a 3- to 4-fold increase in adrenomedullary tyrosine hydroxylase (TH) activity, which is mediated by concomitant alterations in TH mRNA and protein levels. To further investigate the effects of stress on the expression of the catecholamine biosynthetic enzymes, we have isolated a rat cDNA clone encoding the epinephrine-synthesizing enzyme phenylethanolamine N-methyltransferase (PNMT). The cDNA clone is 905 nucleotides in length and contains a single open reading frame corresponding to 270 amino acids. The amino acid sequence predicted from this nearly full-length cDNA is 89% and 86% identical to that of bovine and human PNMT, respectively. Using the rat PNMT cDNA as a hybridization probe, we have measured the effects of cold stress on the relative abundance of adrenomedullary PNMT mRNA. Levels of PNMT protein were also estimated using an immunoblot analysis. As in the case of TH, cold exposure resulted in a rapid and prolonged increase in PNMT mRNA abundance, followed by concomitant increases in PNMT immunoreactivity. However, there appear to be quantitative and qualitative differences in the adaptive response of TH and PNMT to cold stress.

Induction of phenylethanolamine N-methyltransferase mRNA expression by glucocorticoids in cultured bovine adrenal chromaffin cells

The effects of glucocorticoids on the expression of phenylethanolamine N-methyltransferase (PNMT) mRNA and proenkephalin A (ProEnk A) mRNA in cultures of bovine adrenal chromaffin cells were examined. The expression of PNMT mRNA (approx. 1.1 kilobases) was induced in the presence of glucocorticoids. This induction was of high potency with an EC50 in the range of 1-10 nM for dexamethasone, and was blocked by high concentrations of the glucocorticoid antagonist RU-38486. Cortisol, prednisolone and Reichstein substance S (11-deoxy-17-hydroxycorticosterone) were all effective in stimulating PNMT mRNA expression while cortisone, progesterone and beta-estradiol were without effect. These results indicate that the effects are mediated by specific glucocorticoid receptor activation and exhibited a strict structural requirement for the ability of glucocorticoids to induce PNMT mRNA expression. By contrast, glucocorticoids had no significant effect on the expression of ProEnk A mRNA. In summary, this study provides evidence that glucocorticoids act to regulate PNMT (but not ProEnk A) at the transcriptional level. This differential effect of glucocorticoids suggests that different mechanisms govern the expression of mRNAs required for synthesis of the co-stored secretory components, the enkephalins and adrenaline within the chromaffin cells of the adrenal medulla.

Histamine activates proenkephalin A mRNA but not phenylethanolamine N-methyltransferase mRNA expression in cultured bovine adrenal chromaffin cells

The effects of histamine on the regulation of proenkephalin A (ProEnk A) and phenylethanolamine N-methyltransferase (PNMT) mRNA expression were examined in cultures of bovine adrenal chromaffin cells. Prolonged incubation with histamine resulted in a concentration-dependent increase in the levels of ProEnk A mRNA with little effect on the levels of PNMT mRNA. The activation of ProEnK A mRNA by histamine followed a slow time course, reaching 2-3 fold basal levels after 48 h incubation. This activation was antagonized by the H1-antagonist mepyramine but not by the H2-antagonist cimetidine indicating involvement of H1-histamine receptors. The histamine-induced activation of ProEnK mRNA was blocked by the RNA synthesis inhibitor actinomycin D, suggesting that the novo synthesis of ProEnkA mRNA is a requirement for activation. In the presence of the calcium channel blocker D600, the histamine-induced increase in ProEnk A mRNA was greatly reduced, though not abolished. Prolonged incubation with histamine also caused a substantial release of catecholamines and opioid peptides from these cells. These results suggest that the synthesis and release of opioid peptides is controlled by histamine via H1-receptors. The differential effects of histamine on ProEnk A mRNA and PNMT mRNA expression suggest that different regulatory mechanisms are called upon to regulate the synthesis of opioid peptides and adrenaline in response to stimulation of the chromaffin cells.

Isolation and structural characterization of the bovine tyrosine hydroxylase gene

A bovine tyrosine hydroxylase (TH) cDNA probe was used to screen a charon 30 genomic library. Screening of approximately 1 million recombinant phage resulted in the identification of one clone, lambda B1, containing the entire bovine TH gene. Results derived from restriction endonuclease mapping and sequence analysis reveal that the bovine gene contains 13 exons spanning approximately 7 kb of genomic DNA. Determination of the transcription initiation site indicates that the TH gene has a 5' untranslated region of 27 bp. A TATA-box sequence is located between positions-29 and -24 from the transcription initiation site and a cyclic AMP regulatory element (CRE) between-45 and -38. Although the TH gene appears to be glucocorticoid responsive in vitro, no regions bearing identity to the consensus sequence for the glucocorticoid regulatory element (GRE) were detected within approximately 1.5 kb of 5' flanking sequence. A cross-species comparison of the 5' flanking sequences of the bovine, rat, and human TH genes reveals strong sequence and positional conservation of seven sequence elements. An analysis of the nucleotide sequence within these elements reveals similarity to the consensus sequences reported for known cis-acting regulatory elements and transcription factor binding sites, suggesting that they may play a role in the regulation of TH gene expression.

Co-localization of RNAs coding for phenylethanolamine N-methyltransferase and proenkephalin A in bovine and ovine adrenals

A 29-mer oligodeoxyribonucleotide probe, complementary to the coding region of bovine phenylethanolamine N-methyltransferase (PNMT) mRNA was synthesized. Characterization of this probe by Northern blot hybridization showed that it hybridized to a single band in RNA extracted from bovine and ovine adrenal medullae. The molecular size of this hybridized band was approximately 1.0-1.2 kb which is consistent with recently reported data on the molecular weight of bovine PNMT mRNA. In situ hybridization histochemistry was carried out with this probe on bovine and ovine adrenal sections and results compared on adjacent sections with a probe against proenkephalin A (ProEnk A) mRNA synthesized previously. Both showed a similar localization to the outer margin of cells in the adrenal medulla. The results of this study provide strong evidence at the level of mRNA expression that ProEnk A mRNA is expressed preferentially in the adrenaline synthesizing cells within the adrenal medulla. Further, it demonstrates the usefulness of a synthetic oligodeoxyribonucleotide probe for the study of PNMT gene expression.

Developmental expression of proenkephalin A mRNA and phenylethanolamine N-methyltransferase mRNA in foetal sheep adrenal medulla

The ontogenic expression of proenkephalin A (ProEnk A) mRNA and phenylethanolamine N-methyltransferase (PNMT) mRNA was examined in the foetal sheep adrenal medulla by the use of specific oligodeoxyribonucleotide probes. Northern blot analysis of RNA extracts from foetal adrenals demonstrated that ProEnk A mRNA was expressed as early as 60 days of gestation, a time at which the foetal adrenal is not functionally innervated. In situ hybridization on sections of foetal adrenals revealed that at 110-140 days gestation ProEnk A mRNA was expressed in chromaffin cells at the outer margin of the adrenal medulla but at earlier stages of gestation (e.g. 95 days) appeared to be expressed homogeneously throughout the whole of the adrenal medulla. In comparison, PNMT mRNA was expressed preferentially in cells at the outer margin of the adrenal medulla from the earliest stage detectable. Both PNMT mRNA and ProEnk A mRNA co-localized in cells at the outer margin of foetal adrenal of late gestations (110-140 days), a similar pattern to that seen in the adult adrenal medulla. These results indicate that, as with adult animals, in foetuses of late gestation, adrenal enkephalins are co-stored within adrenaline cells. It is likely therefore that enkephalins are co-released from the foetal adrenal with adrenaline in response to intra-uterine stress.

Regulation of phenylethanolamine N-methyltransferase (PNMT) mRNA in the rat adrenal medulla by corticosterone

In the adrenal medulla of adult rat, physiological levels of glucocorticoid hormones are required to maintain the catalytic activity of the epinephrine-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT). The present study was undertaken to determine whether glucocorticoid regulation of PNMT occurs at the level of mRNA coding for PNMT. Adult male Sprague-Dawley rats were hypophysectomized (HPX) and killed after 2 weeks; pellets of corticosterone were implanted for 1, 3 or 7 days prior to killing. Determinations were made of plasma corticosterone levels, adrenal PNMT activity and PNMT mRNA levels by Northern gel analysis. HPX resulted in a decrease in plasma corticosterone to undetectable levels, and decreases in PNMT activity and PNMT mRNA levels to 1 and 18% of the levels observed in sham rats, respectively. Corticosterone replacement produced high prolonged plasma levels of corticosterone which were 10 times those of sham rats, and significantly increased levels of PNMT activity and mRNA. However, corticosterone replacement failed to restore PNMT activity and mRNA levels fully. These results suggest that the maintenance of PNMT mRNA levels is dependent on maintaining corticosterone levels and supports the hypothesis that PNMT gene expression in the adrenal medulla is directly regulated by glucocorticoids produced by the adrenal cortex. However, the results also suggest that in the chronically HPX rat, factors in addition to naturally produced glucocorticoids are required for full restoration of PNMT mRNA levels.

Isolation and nucleotide sequence of a cDNA clone encoding bovine adrenal tyrosine hydroxylase: comparative analysis of tyrosine hydroxylase gene products

Investigations into the structure and mechanisms regulating the expression of the genes involved in catecholamine biosynthesis have led to the isolation of a cDNA coding for bovine adrenal tyrosine hydroxylase (TH). The 1,722 bp cDNA contains the complete coding sequence and 3' untranslated region of the TH mRNA. The nucleotide sequence of the cDNA and the deduced amino acid sequence were compared to those reported for rat and human TH. Bovine TH shares 85% and 84% amino acid sequence identity with that of rat and human TH, respectively. Alignment of the amino acid sequences of rat, bovine, and human TH reveals that 79% of the residues are identical in all three species, indicating a strong evolutionary conservation of enzyme structure. Moreover, three of the four putative phosphorylation sites located in the N-terminal region of TH are conserved in these animal species. There are, however, some interspecies differences in TH gene products. The 3' untranslated region of bovine TH mRNA is 56 and 97 nucleotides shorter than rat and human TH mRNA, respectively. Additionally, the bovine protein is 7 and 6 amino acids smaller than its rat and human homologues. All of the absent amino acid residues of bovine TH are missing from an alanine-rich region in the N-terminal portion of the rat and human proteins (amino acids 51-68). Comparison of the size of bovine and rat TH mRNA and protein by northern blot and immunoblot analyses yielded differences consistent with those predicted from the nucleotide sequence data.

Purification and partial amino acid sequence of bovine adrenal phenylethanolamine N-methyltransferase: a comparison of nucleic acid and protein sequence data

Recently, we have reported the isolation and characterization of a putative genomic DNA clone encoding bovine adrenal phenylethanolamine N-methyltransferase (PNMT) (Batter et al., 1988). However, the lack of primary amino-acid sequence data for this enzyme precluded a definitive proof of the authenticity of this clone. To establish identity, the amino acid sequence of several peptides generated by chemical and enzymatic hydrolysis of purified PNMT was compared to that predicted from the nucleotide sequence of the exons of the putative PNMT gene. Bovine adrenomedullary PNMT was purified by ammonium sulfate precipitation, gel filtration, and ion exchange chromatography. Treatment with 70% formic acid cleaved the protein at a single Asp-Pro bond near the N-terminus. The purified protein was also cleaved at a single methionine residue near the C-terminus by treatment with cyanogen bromide. N-terminal amino acid sequence analysis identified 8 and 10 amino acid residues, respectively, following each of the scissile peptide bonds. Four tryptic peptides, generated by complete enzymatic digestion, were isolated by reverse-phase HPLC and subjected to sequence analysis. Combined, the amino acid sequences of these six peptides represent 20% of the PNMT protein. These amino acid sequences matched exactly the sequences predicted from the exons of the putative PNMT genomic clone.