摘要:

Abstract:Tyrosine hydroxylase catalyzes the rate‐limiting step in the biosynthesis of the catecholamines dopamine, norepinephrine, and epinephrine. Therefore, the regulation of tyrosine hydroxylase enzyme number and intrinsic enzyme activity represents the central means for controlling the synthesis of these important biogenic amines. An intricate scheme has evolved whereby tyrosine hydroxylase activity is modulated by nearly every documented form of regulation. Beginning with the genomic DNA, evidence exists for the transcriptional regulation of tyrosine hydroxylase mRNA levels, alternative RNA processing, and the regulation of RNA stability. There is also experimental support for the role of both translational control and enzyme stability in establishing steady‐state levels of active tyrosine hydroxylase protein. Finally, mechanisms have been proposed for feedback inhibition of the enzyme by catecholamine products, allosteric modulation of enzyme activity, and phosphorylation‐dependent activation of the enzyme by various different kinase systems. Given the growing literature suggesting that different tissues regulate tyrosine hydroxylase mRNA levels and activity in different ways, regulatory mechanisms provide not only redundancy but also diversity in the control of catecholamine biosynt

ISSN:0022-3042    

DOI:10.1046/j.1471-4159.1996.67020443.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:After a single intraperitoneal injection of the irreversible tryptophan hydroxylase inhibitorp‐chlorophenylalanine (PCPA; 300 mg/kg), there was a rapid down‐regulation of serotonin (5‐HT) transporter mRNA levels in cell bodies. This change was significant at 1 and 2 days after PCPA administration within the ventromedial but not the dorsomedial portion of the dorsal raphe nucleus. Seven days after PCPA treatment, 5‐HT transporter mRNA levels were significantly elevated compared with controls in both regions of the dorsal raphe nucleus. PCPA administration produced no change in the [3H]‐citalopram binding and synaptosomal [3H]5‐HT uptake in terminal regions at 2 and 7 days after treatment but significantly reduced both these parameters by ∼20% in the hippocampus and in cerebral cortex 14 days after PCPA administration. The striatum showed a lower sensitivity to this effect. No significant changes were observed in the levels of [3H]citalopram binding to 5‐HT cell bodies in the dorsal raphe nucleus. In the same animals used for 5‐HT transporter mRNA level measurements, levels of tryptophan hydroxylase mRNA in neurons of the ventromedial and dorsomedial portions of the dorsal raphe nucleus were increased 2 days after PCPA administration and fell to control levels 7 days after injection in the ventromedial region but not in the dorsomedial portion of the dorsal raphe nucleus, where they remained significantly higher than controls. Altogether, these results show that changes in 5‐HT transporter mRNA are not temporally related to changes in 5‐HT transporter protein levels. In addition, our results suggest that the 5‐HT transporter and tryptophan hydroxylase genes are regulated by different mechanisms. We also provide further evidence that dorsal raphe 5‐HT neurons are differentially regulated by drugs, de

ISSN:0022-3042    

DOI:10.1046/j.1471-4159.1996.67020463.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:The nuclear factor 1 (NF‐1) motifs, NF‐1 II/III, in the two 98‐bp repeats of the transcription‐regulatory region of JC virus (JCV), have a critical role in brain‐specific transcription from the JCV early promoter‐enhancer. In this study, the role of these motifs in transactivation of the JCV late promoter‐enhancer (JCVL) was examined in differentiating glial P19 embryonal carcinoma cells. The expression of papovaviral large tumor antigen (T‐Ag) in the glial cells was shown by double immunofluorescence assays. By using site‐directed mutagenesis and in vivo assays, the two wild‐type NF‐1 II/III sites, but not the third site, were found to be essential for the transactivation of JCVLby JCV T‐Ag. In vitro transcription assays confirmed this specific transactivation and the transactivation was abolished by T‐Ag antibody. In electrophoretic mobility shift assays, expression of JCV T‐Ag increased the binding of a factor(s) to the 98‐bp repeat. T‐Ag antibody abolished the increase of binding. Binding assays with oligonucleotides of NF‐1 II/III motifs showed that the increased binding specifically required the wild‐type NF‐1 II/III sequences and confirmed the requirement of T‐Ag. To determine the region of T‐Ag necessary for transactivation of JCVL, the coding sequences were mutated. The amino‐terminal region of JCV Ag in amino acids 1–437 was essentially required for efficient transactivation. These results indicated that transactivation of JCVLand increased binding require a factor(s) found specifically in glial cells, the JCV NF‐1 I

ISSN:0022-3042    

DOI:10.1046/j.1471-4159.1996.67020473.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Heme oxygenase is an essential enzyme in the heme catabolism that produces carbon monoxide (CO). This study was designed to examine the expression of two heme oxygenase isozyme mRNAs in the human brain and to explore the involvement of nitric oxide (NO) and various neuropeptides in the regulation of their expression. Northern blot analysis showed the expression of heme oxygenase‐1 and heme oxygenase‐2 mRNAs in every region of the brain examined, with the highest levels found in the frontal cortex, temporal cortex, occipital cortex, and hypothalamus. In a human glioblastoma cell line, T98G, treatment with any of three types of NO donors—sodium nitroprusside, 3‐morpholinosydnonimine, andS‐nitroso‐l‐glutathione—caused a significant increase in the levels of heme oxygenase‐1 mRNA but not in the levels of heme oxygenase‐2 and heat‐shock protein 70 mRNAs. Sodium nitroprusside increased the levels of heme oxygenase‐1 protein but not the levels of heat‐shock protein 70 in T98G cells. The increase in content of heme oxygenase‐1 mRNA caused by sodium nitroprusside was completely abolished by the treatment with actinomycin D. On the other hand, the levels of heme oxygenase isozyme mRNAs were not noticeably changed in T98G cells following the treatment with 8‐bromo cyclic GMP, sodium nitrite, or various neuropeptides, such as calcitonin gene‐related peptide, endothelin‐1, and corticotropin‐releasing hormone. The present study has shown the expression profiles of heme oxygenase‐1 and ‐2 mRNAs in the human brain and the induction of heme oxygenase‐1 mRNA caused by NO donors in T98G cells. These findings raise a possibility that the CO/heme oxygenase system may function in concert wi

ISSN:0022-3042    

DOI:10.1046/j.1471-4159.1996.67020482.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:ICER (inducible cyclic AMP early repressor), a member of the cyclic AMP response element (CRE) modulator (CREM) family of transcription factors, is a powerful repressor of cyclic AMP‐mediated transactivation. Our studies characterize the regulation of ICER in C6 glioma cells and investigate its role in repressing transcription of the β1‐adrenergic receptor (β1AR) gene. Incubation with isoproterenol (100 nM) results in a rapid induction in levels of mRNA for ICER and its splice variant ICERγ, with maximal induction occurring after 2 h of treatment. Incubation with isoproterenol also increased levels of CREM isoforms within 1 h; this was unexpected given previous reports that these isoforms are not rapidly induced. Increased expression of ICER and CREM was accompanied by induction of two CRE‐binding complexes. The presence of ICER in these two CRE‐binding complexes is demonstrated by their disruption with CREM antibody and by their comigration with recombinant ICER. Because the time course for isoproterenol induction of ICER mRNA and CRE binding corresponds to that for down‐regulation of β1AR mRNA levels in C6 glioma cells, the influence of ICER on β1AR transcription was directly examined. Coexpression of ICER significantly decreased transcriptional activity of a rat β1AR promoter‐luciferase reporter construct that contains a CRE. In contrast, coexpression of ICER did not influence two truncated rat β1AR promoter constructs that lack the CRE site. These data demonstrate that ICER can interact at the β1AR promoter to re

ISSN:0022-3042    

DOI:10.1046/j.1471-4159.1996.67020490.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Protease nexin‐1 (PN‐1) is a potent inhibitor of serine proteases in the extracellular environment. It is abundantly expressed in the nervous system, where it is thought to participate in local injury and repair processes. Although some information has been obtained regarding PN‐1 gene structure, relatively little is known about thecis‐ andtrans‐acting factors that regulate its expression. Elucidation of these factors should provide a better understanding of PN‐1 function during development and wound repair. In this report we describe the characterization of the human PN‐1 promoter and identify regulatory domains and a transactivator mediating its transcriptional activity. The promoter is highly G/C rich proximal to the transcriptional start site. It exhibits tissue specificity and is negatively regulated by a silencer element upstream of position −480. A positive regulatory element was mapped between −199 and −45, which contains multiple putative Sp1 consensus binding sites. Electrophoretic mobility shift analysis confirmed that Sp1 specifically binds this region of the PN‐1 promoter. DNase I foot‐printing revealed six potential Sp1 binding sites between −103 and −56 that were protected by recombinant Sp1. Cotransfection experiments into the Sp1‐deficientDrosophilaSL2 cell line also showed that Sp1 activates PN‐1 promoter activity in a dose‐dependent fashion. Thus, our analysis demonstrates that activation of PN‐1 transcription is regulated by Sp1 through G/C‐richcis‐acting elem

ISSN:0022-3042    

DOI:10.1046/j.1471-4159.1996.67020498.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:C6 glioma cells were used as a model system to study the regulation of EAAC1‐mediated Na+‐dependentl‐[3H]glutamate transport. Although a 30‐min preincubation with forskolin had no effect on transport activity, preincubation with phorbol 12‐myristate 13‐acetate (PMA) increased transport activity two‐ to threefold. PMA caused a time‐dependent and concentration‐dependent increase in EAAC1‐mediatedl‐[3H]glutamate transport activity. A 2‐min preincubation with PMA was sufficient to cause more than a twofold increase in transport activity and the protein synthesis inhibitor cycloheximide had no effect on the increase. These data suggest that this increase is independent of protein synthesis. The EC50value of PMA for stimulation of transport activity was 80 nM. Kinetic analyses demonstrated that the increase in transport activity was due to a 2.5‐fold increase inVmaxwith no change inKm. PMA also increased the transport of the nonmetabolizable analogue,d‐[3H]aspartate to the same extent. In parallel assays, PMA did not, however, increase Na+‐dependent glycine transport activity in C6 glioma. The inactive phorbol ester 4α‐phorbol 12,13‐didecanoate, did not stimulatel‐[3H]glutamate transport activity, and the protein kinase C inhibitor chelerythrine blocked the stimulation caused by PMA. Okadaic acid and cyclosporin A, which are phosphatase inhibitors, had no effect on the stimulation of transport activity caused by PMA. The Ca2+ionophore A23187 did not act synergistically to increase PMA stimulation. In previous studies, PMA caused a rapid increase in amiloride‐sensitive Na+/H+transport activity in C6 glioma. In the present study, pre‐ and coincubation with amiloride had no effect on the stimulation of transport activity caused by PMA. These studies suggest that activation of protein kinase C causes a rapid increase in EAAC1‐mediated transport activity. This rapid increase in Na+‐dependentl‐[3H]‐glutamate transport activity may provide a novel mechanism

ISSN:0022-3042    

DOI:10.1046/j.1471-4159.1996.67020508.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Recent studies have pointed to membrane‐bound guanylyl cyclases (GCs) type A and type B in the rat pineal gland, which augment levels of cyclic GMP (cGMP) in response to atrial natriuretic peptide (ANP), brain‐type natriuretic peptide (BNP), and C‐type natriuretic peptide (CNP). The present report demonstrates for the first time the expression of CNP in the bovine pineal gland. The CNP prohormone transcript (unlike prepro‐ANP) was found by reverse transcriptase (RT)‐PCR in bovine pineal extracts. CNP immunoreactivity (ir) was revealed in a subpopulation of pinealocytes in situ and in nearly all pinealocytes in culture. Electron microscopic immunohistochemical investigations showed the presence of CNP‐ir in cytoplasmic vesicles, providing evidence for the potential secretion of this peptide by pineal cells. Furthermore, the CNP receptor (GC‐B) and GC‐A (receptor for ANP and BNP) were identified by RT‐PCR. Although melatonin secretion was unaffected, natriuretic peptides were able to elevate markedly cGMP production in cultured bovine pinealocytes with a rank order of potency of CNP>BNP = ANP. These findings describe a tissue CNP system in the bovine pineal gland and suggest that CNP may be a local auto‐ or paracrine modulator

ISSN:0022-3042    

DOI:10.1046/j.1471-4159.1996.67020517.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:To study the level of ciliary neurotrophic factor (CNTF) in human nervous tissues, we developed a sensitive enzyme‐linked immunoassay using a specific antibody against human CNTF. This method allowed us to detect as little as 0.3 ng/ml of human CNTF with good linearity and accuracy. Using this method, CNTF levels were determined in human sciatic nerves obtained at autopsy from 21 amyotrophic lateral sclerosis (ALS) patients and 48 subjects who had died of other neurological diseases. CNTF genotypes were also determined. The results indicated that CNTF levels were high in the normal homozygotes and approximately halved in the heterozygote subjects. There was, however, no significant difference in CNTF levels in the sciatic nerves between ALS and other neurological disease patients, indicating that the CNTF level was mainly determined by its genotypes and that the level in the sciatic nerves was not reduced in ALS patient

ISSN:0022-3042    

DOI:10.1046/j.1471-4159.1996.67020525.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Nerve growth factor (NGF) and dibutyryl cyclic AMP (dbcAMP) have synergistic effects on the neurite outgrowth of rat pheochromocytoma PC12 cells. The sites of interaction between NGF and dbcAMP have been studied extensively; however, the role of Ca2+in differentiation induced by the two agents remains unclear. To understand whether intracellular Ca2+is involved in the differentiation induced by the two agents, PC12 cells were treated with NGF, dbcAMP, or NGF plus dbcAMP for 2 days, and then effects on neurite outgrowth, ATP‐induced Ca2+influx, and Ca2+mobilization from intracellular Ca2+pools were examined. NGF or dbcAMP alone enhanced neurite outgrowth and Ca2+accumulation by nonmitochondrial Ca2+pools or the thapsigargin (TG)‐sensitive Ca2+pool. The dbcAMP acted synergistically with NGF to increase neurite outgrowth and to enlarge the TG‐sensitive Ca2+pool. The synergistic effect occurred within the first hour of treatment with dbcAMP plus NGF. On the other hand, dbcAMP abolished NGF's ability to enhance ATP‐induced influx of extracellular Ca2+. Therefore, NGF and dbcAMP induced different effects on Ca2+signaling pathways through two different but interacting pathways. In PC12 cells pretreated with TG to deplete the TG‐sensitive Ca2+pool, the dbcAMP‐ or dbcAMP plus NGF‐mediated neurite outgrowth was significantly inhibited, whereas NGF‐mediated neurite outgrowth was not affected by TG pretreatment. Our results suggest that the intracellular nonmitochondrial Ca2+pools were changed in the differentiation process and were necessary for the synergistic effect of

ISSN:0022-3042    

DOI:10.1046/j.1471-4159.1996.67020530.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY