Dexamethasone enhances serum deprivation-induced necrotic death of rat C6 glioma cells through activation of glucocorticoid receptors

Glucocorticoids have been shown to be neurotoxic and appear to play a role in neuronal cell loss during aging and following neuropathological insults. However, very little is known about the effects of these steroid hormones on glial cells. The effect of the synthetic glucocorticoid dexamethasone (DEX) on glial cell viability was therefore examined by measuring neutral red uptake into rat C6 glioma cells. Serum deprivation markedly reduced cell viability, and this effect was significantly enhanced by DEX. Electrophoretic analysis showed that the cell damage induced by either serum deprivation alone or in combination with DEX was not accompanied by the degradation of DNA into nucleosomic fragments. Electron microscopic studies confirmed that serum deprivation and glucocorticoid treatment caused necrotic cell death. Furthermore, the effect of DEX on cell viability could be mimicked by the glucocorticoid receptor agonist RU28362, and completely prevented by the glucocorticoid receptor antagonist RU38486. These results indicate that dexamethasone can enhance the necrotic death of glioma cells induced by serum deprivation, suggesting that glucocorticoids may be involved in the chronic alteration of brain function arising from neuropathological damage to glial cells.

Vitamin B-6 deficiency and level of dietary protein affect hepatic tyrosine aminotransferase activity in cats

Total activity [pyridoxal 5'-phosphate (PLP) added in the assay] of hepatic tyrosine aminotransferase (TAT) measured in cats at 0300, 0900, 1500 and 2100h was 10.3 +/-1.1, 14.0 +/- 0.7, 9.8 +/- 1.3 and 11.0 +/- 0.7 nkat/g liver, indicating little diurnal variation. Activity after 18 h of food deprivation was 10.0 +/- 0.3 nkat/g liver, also not different from cats that were eating ad libitum. These findings support the idea that cats have only limited changes in the activity of hepatic TAT compared with rats. Total TAT activity was measured in cats fed high protein (550 g/kg) and low protein (180 g/kg) diets for 4 wk. Cats fed a high protein diet had activities significantly higher (about twice) than cats fed the low protein diet. Hepatic TAT activity of vitamin B-6-deficient cats (diet without pyridoxine for 9 wk) was compared with cats given the same diet with 8 mg pyridoxine/kg. Total hepatic TAT activity in deficient cats was significantly (P < 0.05) lower per gram soluble or total protein (but not per gram liver) than control cats; holoenzyme activity and percentage of active enzyme in deficient cats were also significantly lower by 75 and 64%, respectively. The apparent Km of TAT from cats for tyrosine (2.1 mmol/L) was similar to that for rats (1.9 mmol/L), but higher for PLP in cats (0.16 micromol/L) than rats (0.034 micromol/L). Part of the reason for the higher plasma tyrosine in vitamin B-6-deficient cats than rats is the higher Km of TAT for PLP in cats than rats.

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.

Glucocorticoid-dependent action of neural crest factor AP-2: stimulation of phenylethanolamine N-methyltransferase gene expression

AP-2 is a vertebrate transcription factor expressed in neural crest cells and their derivative tissues, including the adrenal medulla, where epinephrine is produced. AP-2 is shown to stimulate expression of the gene encoding the epinephrine biosynthetic enzyme phenylethanolamine N-methyltransferase (PNMT). However, stimulation of the PNMT gene by AP-2 requires glucocorticoids and appears to be mediated through the interaction of AP-2 with activated type II glucocorticoid receptors. Mutation of AP-2 and/or glucocorticoid receptor binding elements within the PNMT promoter disrupts the ability of AP-2 and glucocorticoids to induce PNMT promoter activity. These findings suggest, in the case of PNMT, that AP-2 stimulates gene expression through a novel glucocorticoid-dependent mechanism.

Electrospray ionization mass spectrometric characterization of photocrosslinked DNA-EcoRI DNA methyltransferase complexes

We describe a novel strategy combining photocrosslinking and HPLC-based electrospray ionization mass spectrometry to identify UV crosslinked DNA-protein complexes. Eco RI DNA methyltransferase modifies the second adenine within the recognition sequence GAATTC. Substitution of 5-iodouracil for the thymine adjacent to the target base (GAATTC) does not detectably alter the DNA-protein complex. Irradiation of the 5-iodouracil-substituted DNA-protein complex at various wavelengths was optimized, with a crosslinking yield >60% at 313 nm after 1 min. No protein degradation was observed under these conditions. The crosslinked DNA-protein complex was further analyzed by electrospray ionization mass spectrometry. The total mass is consistent with irradiation-dependent covalent bond formation between one strand of DNA and the protein. These preliminary results support the possibility of identifying picomole quantities of crosslinked peptides by similar strategies.

Adrenergic differentiation potential in PC12 cells: influence of sodium butyrate and dexamethasone

The ability of sodium butyrate and dexamethasone to promote adrenergic differentiation in PC12 cells was examined using the gene encoding the epinephrine biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT), as a marker. Sodium butyrate and dexamethasone independently stimulated expression of PNMT mRNA in PC12 cells, and the combined action of these drugs led to synergistic activation of the PNMT gene. Despite the induction of the PNMT gene, epinephrine is not produced in these cells, in part due to the absence of a corresponding induction in PNMT enzymatic activity. Another contributing factor appears to be a reduction in the precursor catecholamines, norepinephrine and dopamine, in the presence of sodium butyrate. Thus, while sodium butyrate and dexamethasone can induce PNMT gene expression, treatment of PC12 cells with these drugs appears insufficient for full acquisition of the adrenergic phenotype.

Brain specific proteins binding to the 3' UTR of the 5-HT2C receptor mRNA

The 5-HT2C receptor2 is a prominent serotonin receptor that is uniquely expressed in the central nervous system and has been implicated in a variety of psychiatric diseases. While characterizing the 5-HT2C receptor gene, we observed that the mRNA contains a long 3' untranslated region that binds multiple brain proteins. Two proteins, molecular weights 55 and 58 kDa, were of particular interest because they were detected only in brain regions known to express the 5-HT2C receptor abundantly, namely, the hippocampus and cortex. These proteins bind with high affinity to the 5-HT2C receptor mRNA at its extreme 3' end (Kd = 1.8 nM), and binding can be specifically competed by selected regions of the 3' UTR. Furthermore, binding of the 55 and 58 kDa proteins to the mRNA is directionally specific and shows preference for an AU-rich loop containing 6 to 7 nucleotides. These results suggest the possibility that these two brain specific proteins may play a role in the post-transcriptional regulation of the 5-HT2C receptor, and that post-transcriptional control of 5-HT2C receptor expression may be an important regulatory mechanism which has not been previously reported for this serotonin receptor subtype.

Role of Egr-1 in cholinergic stimulation of phenylethanolamine N-methyltransferase promoter

The effects of the cholinergic agonist carbachol on phenylethanolamine N-methyltransferase promoter activity and Egr-1 mRNA expression in PC12-derived RS1 cells were examined to investigate the potential involvement of Egr-1 in the neural regulation of phenylethanolamine N-methyltransferase gene expression. Carbachol stimulated luciferase expression in cells transfected with a rat phenylethanolamine N-methyltransferase promoter-luciferase reporter gene construct and also elevated Egr-1 mRNA levels in untransfected cells. Maximum induction of Egr-1 mRNA by carbachol was rapid (0.5 h), whereas by comparison, peak luciferase activity was delayed (6 h). In addition, carbachol stimulation of both luciferase and Egr-1 mRNA expression could be completely inhibited by atropine but not hexamethonium. Furthermore, bethanechol but not nicotine could mimic the effects of carbachol, indicating that carbachol activation was mediated through muscarinic cholinergic receptors. Finally, carbachol failed to stimulate luciferase expression in cells transfected with a mutant construct, in which the Egr-1 binding element in the phenylethanolamine N-methyl-transferase promoter was mutated. These results suggest that carbachol activates the phenylethanolamine N-methyltransferase promotor through stimulation of Egr-1 expression, and are consistent with the potential involvement of Egr-1 in the cholinergic activation of the phenylethanolamine N-methyltransferase gene.

Neural stimulation of Egr-1 messenger RNA expression in rat adrenal gland: possible relation to phenylethanolamine N-methyltransferase gene regulation

Metrazole, which reflexively activates the splanchnic nerve to the adrenal medulla, was used to investigate the physiological role of Egr-1 in the neural regulation of phenylethanolamine N-methyltransferase (PNMT) gene transcription in the rat adrenal gland. A single dose of this drug (70 mg/kg s.c.) rapidly and transiently induced Egr-1 mRNA, with a maximum 22.0-fold increase at 30 min after treatment, followed by a 3.7-fold increase in PNMT mRNA at 8 hr. In contrast, cocaine (15 mg/kg i.p.), which activates the hypothalamic-pituitary-adrenal axis, increased Egr-1 mRNA only 3-fold at 30 min, although it elevated PNMT mRNA comparably. Consistent with their mechanisms of activation, cocaine increased corticosterone levels 7.7-fold at 30 min, whereas metrazole modestly elevated this endogenous corticosteroid 2.5-fold. The cholinergic agonists nicotine (2 mg/kg l.p.) and muscarine (0.1 mg/kg i.p.) also elevated Egr-1 mRNA, with a peak 12- to 15-fold increase being apparent at 30 min after treatment, followed by a 1.7-to 2.0-fold rise in PNMT mRNA at 8 hr. In vitro, metrazole did not increase Egr-1 mRNA above levels observed with carbachol alone (100 microM) in PC-12-derived RS1 cells pretreated with this cholinergic agonist. Finally, splanchnic denervation partially blocked the metrazole-induced rise in Egr-1 mRNA (50% control), while having no effect on cocaine-induced changes in Egr-1 mRNA. These results provide further support for the involvement of Egr-1 in the neural regulation of PNMT gene expression in the rat adrenal gland.

Expression of phenylethanolamine n-methyltransferase in the embryonic rat heart

Phenylethanolamine N-methyltransferase (PNMT), the final enzyme in the pathway for epinephrine biosynthesis, serves as a marker for tissues and cells producing epinephrine. The present study examines the developmental expression of PNMT in the rat embryo. A transient burst in PNMT mRNA expression begins on embryonic day 9.5 (E9.5), peaks between E10.0 and E11.0, and declines to barely detectable levels by E13.0. Regional localization of PNMT mRNA and enzyme activity demonstrates that PNMT is concentrated in the heart. PNMT has not previously been reported to be expressed at these early stages of development, and its presence in the developing heart suggests that this embryonic tissue may produce epinephrine. Because this catecholamine is known to increase cardiac output and promote the growth of cardiomyocytes, local production of epinephrine by the heart could play an important role in the development of cardiac structure and function.

Evaluation of vocal function in unilateral vocal fold paralysis following thyroplastic surgery

Perceptual, acoustic, and aerodynamic measures of vocal function were examined, pre- and post-treatment, in nine patients who had received thyroplastic (type I) surgery for unilateral vocal fold paralysis. Following thyroplasty, the patients showed significant improvements in the following perceptual and acoustic measures of vocal function: perceived breathiness, maximum phonation time, s/z ratio, vocal shimmer, and signal-to-noise ratio. Significant post-treatment changes were also observed in the following aerodynamic measures of phonation: air pressure, average airflow, laryngeal resistance, and breath group duration. These findings suggest that a combination of perceptual, acoustic, and aerodynamic measures of vocal function may be useful for comparing the relative effectiveness of different treatment procedures (i.e., thyroplasty vs. Teflon injection) in unilateral vocal fold paralysis.

Effects of botulinum toxin type A injections on aerodynamic measures of spasmodic dysphonia

The effects of botulinum toxin type A (BOTOX) injections on aerodynamic measures of phonation were examined in 30 patients with adductor spasmodic dysphonia. Patients received bilateral injections of 2.5 U of botulinum toxin type A in each thyroarytenoid muscle. Measures of air pressure, average airflow, coefficient of variation (CV) of airflow, and laryngeal resistance were obtained before the injections and at 2 and 10 weeks after the injections. These measures were also obtained from 12 normal subjects. Compared with normal subjects, the spasmodic dysphonia patients had significantly higher preinjection values for air pressure, CV of airflow, and laryngeal resistance. At 2 and 10 weeks after the botulinum toxin type A injections, the spasmodic dysphonia patients showed a significant increase in the average airflow values and a significant decrease in the CV of airflow values and the laryngeal resistance values. At 10 weeks after the injections, the values for the three measures began to approach the preinjection values. It is concluded that these aerodynamic measures of phonation can provide useful measures of treatment outcome in adductor spasmodic dysphonia.

Surgical anatomy of the epitympanic space

A clear understanding of the surgical anatomy of the epitympanic space is crucial in modern otologic surgery. The tortuous facial nerve within the tight confines of this region presents important surgical challenges, especially when normal anatomy is obscured by disease. Microdissections of 20 human temporal bones were carried out with particular emphasis on the spatial relations of the facial nerve with various temporal bone landmarks. Measurements were made through a standard transmastoid approach to ensure clinical relevance. A high margin of safety can be achieved by observing consistent landmarks and relations in dealing with the facial nerve. We demonstrated the limitations of the transmastoid approach, particularly in accessing the labyrinthine segment of the facial nerve.

Comparison of botulinum toxin injection procedures in adductor spasmodic dysphonia

This study compares the effects of unilateral and bilateral thyroarytenoid muscle injections of botulinum toxin in 50 patients with adductor spasmodic dysphonia. Patients were randomly assigned to two treatment groups of 25 patients each and a group of 15 normal control subjects was also included. Using a standard electromyographic guidance procedure, one patient group received unilateral thyroarytenoid muscle injections of 15 units of botulinum toxin, while the second patient group received bilateral thyroarytenoid muscle injections of 2.5 units of botulinum toxin on each side. Follow-up data were obtained at 2- and 6-week intervals. Acoustic and perceptual measures of vocal performance included maximum phonation time, fundamental frequency, standard deviation of fundamental frequency, jitter, shimmer, signal/noise ratio, voice break frequency, spasm severity rating, and vocal breathiness rating. Unilateral and bilateral group comparisons at 2-weeks postinjection revealed no significant difference on any of the measures examined. At 6-weeks postinjection, maximum phonation time was significantly lower in the bilateral group. All other measures failed to differentiate the two patient groups. These results suggest that standard unilateral and bilateral botulinum toxin injections provide equivalent degrees of improvement in the symptoms of spasmodic dysphonia. However, bilateral injections appear to be associated with a longer period of excessive phonatory airflow than do unilateral injections.

Hormonal control of rat adrenal phenylethanolamine N-methyltransferase. Enzyme activity, the final critical pathway

To examine whether glucocorticoids control rat adrenal phenylethanolamine N-methyltransferase (PNMT) through gene transcription, the effects of hypophysectomy and acute and chronic glucocorticoid replacement on PNMT mRNA and enzymatic activity were determined. Glucocorticoid depletion through hypophysectomy did not alter PNMT mRNA, whereas PNMT activity declined to approximately 25% of normal. A single dose of ACTH (4 IU SC) rapidly induced PNMT mRNA, with a six-fold peak at 6 hours postinjection. The short-term rise in PNMT mRNA was accompanied by an increase in corticosterone and elevated levels of glucocorticoid receptor mRNA. Ribosomal loading experiments suggested that available PNMT mRNA was fully utilized for protein synthesis. However, PNMT activity did not increase commensurately. Chronic ACTH treatment (4 IU SC daily for 7 days) sustained elevated levels of glucocorticoid receptor mRNA but returned corticosterone to hypophysectomized levels and decreased PNMT mRNA to 50% of normal. Despite the decline in PNMT mRNA and its partial utilization for protein synthesis, PNMT enzymatic activity was fully restored. These findings indicate that glucocorticoids exert marked but complex influences on PNMT gene transcription. In addition, corticosteroids appear to posttranscriptionally regulate PNMT protein expression, underscoring the uncoupling between the expression of PNMT mRNA and active enzyme. Thus, glucocorticoid control of gene transcription and protein synthesis do not fully account for changes in PNMT expression, consistent with the previous observation that glucocorticoid control of PNMT proteolysis is also important in PNMT regulation and the potential for epinephrine biosynthesis.

Effect of neuromuscular activity on the response to botulinum toxin injections in spasmodic dysphonia

Spasmodic dysphonia (SD), a neurologic disorder characterized by involuntary vocal spasms during speech, has been effectively treated by injections of botulinum toxin (BT) into the laryngeal muscles. The aim of the present study was to determine if the therapeutic response to BT is enhanced by immediate and continuous activation of the injected muscles. Twenty SD patients were randomized into two groups following bilateral injections: vocal rest for 30 minutes and continuous vocalization for 30 minutes. Evaluations consisted of voice ratings by expert observers, acoustic measurements using computer analyses, and laryngeal aerodynamic measurements. The findings suggest that vocal rest, rather than vocalization, produces a superior and longer lasting response in SD patients receiving BT injections. It is recommended that SD patients refrain from post-injection vocalization to maximize the therapeutic effects of BT.

Differential activation of the rat phenylethanolamine N-methyltransferase gene by Sp1 and Egr-1

The rat phenylethanolamine N-methyltransferase (PNMT) gene contains overlapping consensus elements for the Sp1 and Egr-1 transcription factors located at -45 bp and -165 bp in the PNMT promoter. In the present study, we show that Sp1 and Egr-1 can specifically bind to these overlapping elements, that this binding appears to be mutually exclusive, and that binding site occupancy is dependent upon the concentration of each factor and its binding affinity for each site. Egr-1 binds to the -165 bp site with relatively high affinity (IC50 = 14 nM) and to the -45 bp site with relatively low affinity (IC50 = 1360 nM), whereas Sp1 binds to both sites with intermediate affinities (IC50 = 210 and 140 nM, respectively). Consistent with the DNA-binding data, Egr-1 stimulates PNMT promoter activity primarily through interaction with the -165 bp site, while Sp1 stimulates PNMT promoter activity by interacting with both the -45 bp and the -165 bp sites. These results show that Sp1 and Egr-1 are capable of differentially activating PNMT gene expression, thereby suggesting that different stimuli may control the activity of the PNMT gene by selectively regulating Sp1 and/or Egr-1.

Role of transcription factor Egr-1 in phorbol ester-induced phenylethanolamine N-methyltransferase gene expression

Transfection of PC12-variant RS1 cells with an Egr-1 expression construct has previously been shown to stimulate phenylethanolamine N-methyltransferase (PNMT) promoter activity, thus suggesting a putative role of Egr-1 as a factor regulating PNMT gene expression. To elucidate the physiological implication of this finding, the effects of phorbol 12-myristate 13-acetate (PMA) on PNMT promoter activity and Egr-1 expression were examined. PMA stimulated luciferase expression in RS1 cells transfected with a rat PNMT promoter-luciferase reporter gene construct, and also elevated both Egr-1 mRNA and Egr-1 protein levels in the untransfected cells. Further study on the concentration dependence of PMA action showed that the stimulation of luciferase expression correlated with the elevation of Egr-1 mRNA level. Finally, the stimulatory action of PMA on luciferase expression was dramatically diminished in the cells transfected with a mutant construct in which the Egr-1 binding site in PNMT promoter was mutated. These findings suggest that PMA-stimulated PNMT gene expression requires the enhancement of Egr-1 expression, thus providing further evidence for the physiological role of Egr-1 in the regulation of PNMT gene expression in the adrenergic cell.

Laryngeal image analysis following botulinum toxin injections in spasmodic dysphonia

The injection of botulinum toxin (BT) into laryngeal muscles has proven to be an effective treatment for spasmodic dysphonia (SD), a neurologic disorder characterized by intermittent vocal spasms during speech. BT treatment has reduced abnormal laryngeal muscle hyperactivity in SD patients, when measured by subjective visual rating scales. This paper utilizes images obtained from endoscopic laryngeal video recordings to quantify changes in pre- and post-injection parameters of 17 patients following bilateral BT injections. A previous study, utilizing perceptual, acoustic, and laryngeal aerodynamic measures, showed significant improvements following treatment with BT. In addition, post-injection vocal rest, rather than vocalization, enhanced therapeutic responses. Results of these measures are compared with data from the image analyses and those parameters that proved to be the most useful are highlighted.

Molecular analysis and test of linkage between the FMR-1 gene and infantile autism in multiplex families

Approximately 2%-5% of autistic children show cytogenetic evidence of the fragile X syndrome. This report tests whether infantile autism in multiplex autism families arises from an unusual manifestion of the fragile X syndrome. This could arise either by expansion of the (CGG)n trinucleotide repeat in FMR-1 or from a mutation elsewhere in the gene. We studied 35 families that met stringent criteria for multiplex autism. Amplification of the trinucleotide repeat and analysis of methylation status were performed in 79 autistic children and in 31 of their unaffected siblings, by Southern blot analysis. No examples of amplified repeats were seen in the autistic or control children or in their parents or grandparents. We next examined the hypothesis that there was a mutation elsewhere in the FMR-1 gene, by linkage analysis in 32 of these families. We tested four different dominant models and a recessive model. Linkage to FMR-1 could be excluded (lod score between -24 and -62) in all models by using probes DXS548, FRAXAC1, and FRAXAC2 and the CGG repeat itself. Tests for heterogeneity in this sample were negative, and the occurrence of positive lod scores in this data set could be attributed to chance. Analysis of the data by the affected-sib method also did not show evidence for linkage of any marker to autism. These results enable us to reject the hypothesis that multiplex autism arises from expansion of the (CGG)n trinucleotide repeat in FMR-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Egr-1 activation of rat adrenal phenylethanolamine N-methyltransferase gene

The immediate early gene transcription factor Egr-1 increases luciferase reporter gene activity 3-4-fold when a rat phenylethanolamine N-methyltransferase (PNMT) promoter-luciferase construct and an Egr-1 expression construct are cotransfected into transformed PC12 cells (RS1). Egr-1 also stimulates endogenous PNMT mRNA expression in the RS1 cells. Furthermore, when transfected RS1 cells are treated with dexamethasone, both luciferase and endogenous PNMT mRNA rise an additional 2-fold although dexamethasone does not independently activate transcription from the PNMT promoter. While both Egr-1 sites (-45 and -165 base pairs) in the PNMT promoter appear necessary for maximum luciferase reporter gene expression, the -165 site appears to be the more important for mediating the Egr-1 response. When the upstream site is deleted or either or both sites are mutated in PNMT-reporter gene constructs, Egr-1-induced luciferase activity from the PNMT promoter is significantly reduced. In addition, the incremental activation by dexamethasone is lost when sequences containing the glucocorticoid response element are deleted or when the Egr-1 sites are mutated. In the transfected RS1 cells, a rise in nuclear Egr-1 protein accompanies the rise in endogenous PNMT mRNA. Similarly, reserpine-treated rats (10 mg/kg, intraperitoneally), which show an 8-fold elevation in adrenal PNMT mRNA at 6 h postdrug administration, also show a marked rise in Egr-1 protein in adrenal medullary cell nuclei. These studies provide the first direct evidence that a transcription factor, Egr-1, can activate PNMT gene expression and identify PNMT as a novel target gene for Egr-1. Finally, the incremental enhancement of the Egr-1 response by glucocorticoids suggests a potential interaction between Egr-1 and another transcription factor, the glucocorticoid receptor.

Neural control of dopamine beta-hydroxylase in vivo: acute and chronic effects

Reserpine treatment was used to examine whether short- and long-term neural stimulation regulates rat adrenal medullary dopamine beta-hydroxylase (DBH, EC 1.14.17.1) through transcriptional activation and to examine the extent of coordinate control of DBH and phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28). A single dose of reserpine (10 mg/kg i.p.) elevates DBH mRNA 1.5-fold by 6 h post-injection. Chronic treatment (10 mg/kg i.p., 4 alternate day injections) continues the rise in DBH mRNA, with a peak of 3.4-fold control values after 2 doses of reserpine and a plateau at this level thereafter. Even though DBH mRNA is elevated 6 h after a single injection of reserpine, DBH activity does not change in parallel. A 1.3-fold rise in activity occurs at 24 h post-injection. In contrast, chronic reserpine treatment concomitantly increases DBH activity and mRNA. As observed for DBH mRNA, enzyme activity peaks and plateaus after 2 injections on alternate days. However, the rise in enzymatic activity is less than the rise in mRNA (2.4-fold versus 3.4-fold). Ribosomal loading experiments demonstrate that the DBH mRNA pool is fully utilized for protein synthesis with an apparent decrease in the number of ribosomes loaded per molecule of mRNA. Western analysis and thermal denaturation studies indicate that an altered form of DBH may be expressed. With a single dose of reserpine, the enzyme shows a decline in specific activity while repeated treatment leads to an enzyme with higher specific activity. In both cases, the protein appears to be more stable. Reserpine treatment also markedly elevates adrenal glucocorticoids. A 1.5-fold increment in glucocorticoid receptor mRNA accompanies the corticosteroid rise, with the receptor mRNA peaking at 6 h and remaining at this level thereafter. The up-regulation of glucocorticoid receptor mRNA expression, together with the presence of a putative glucocorticoid response element in the 5' flanking region of the DBH gene, suggests that neural and hormonal regulatory mechanisms may work in concert to control DBH gene transcription. Finally, by comparison to PNMT, activation of DBH appears to require sustained stimulation of the neural axis, since acute changes in mRNA lead to only minor changes in enzyme expression. Similar to PNMT, continuous neural stimulation increases both DBH mRNA and enzymatic activity. However, the discordance in the magnitude of these indices suggests that other regulatory controls may be important in setting the ultimate limits on DBH expression, glucocorticoids perhaps being one such influence.