Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027819 (neuroblastoma)
 27,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

GTP cyclohydrolase I exhibits a positive homotropic cooperative binding to GTP, which raises the possibility of a role for GTP in regulating the enzyme reaction (Hatakeyama, K., Harada, T., Suzuki, S., Watanabe, Y., and Kagamiyama, H. (1989) J. Biol. Chem. 264, 21660-21664). We examined whether or not the intracellular GTP level is within the range of affecting GTP cyclohydrolase I activity, using PC-12 rat pheochromocytoma and IMR-32 human neuroblastoma cells. Since GTP cyclohydrolase I was the rate-limiting enzyme for the biosynthesis of tetrahydrobiopterin in these cell lines, the intracellular activities of this enzyme were reflected in the tetrahydrobiopterin contents. We found that the addition of guanine or guanosine increased GTP but not tetrahydrobiopterin in these cells. On the other hand, three IMP dehydrogenase inhibitors, tiazofurin, 2-amino-1,3,4-thiadiazole, and mycophenolic acid, decreased both GTP and tetrahydrobiopterin in a parallel and dose-dependent manner, and these effects were reversed by the simultaneous addition of guanine or guanosine. There was no evidence suggesting that these inhibitors inhibited other enzymes involved in the biosynthesis and regeneration of tetrahydrobiopterin. Comparing intracellular activities of GTP cyclohydrolase I in the inhibitor-treated cells with its substrate-velocity curve, we estimated that the intracellular concentration of free GTP is 150 microM at which point the activity of GTP cyclohydrolase I is elicited at its maximum velocity. Below this GTP concentration, GTP cyclohydrolase I activity is rapidly decreased. Therefore GTP can be a regulator for tetrahydrobiopterin biosynthesis.
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PMID:IMP dehydrogenase inhibitors reduce intracellular tetrahydrobiopterin levels through reduction of intracellular GTP levels. Indications of the regulation of GTP cyclohydrolase I activity by restriction of GTP availability in the cells. 135 83

Two clonal cell lines (the pheochromocytoma clone PC-12 and the neuroblastoma clone N1E-115) were used to compare direct and indirect drug effects on tyrosine hydroxylase and dopamine turnover. Both clones contain the cofactor of tyrosine hydroxylase, tetrahydrobiopterin, in sufficient concentrations. 2,4-Diamino-6-hydroxy-pyrimidine (DAO-Pyr), an inhibitor of GTP cyclohydrolase, which is the rate-limiting enzyme in tetrahydrobiopterin biosynthesis, lowers DOPA production indicating that cofactor supply is a limiting factor for catecholamine synthesis. DOPA synthesis in the PC-12 cells can be stimulated by incubation with the natural cofactor tetrahydrobiopterin, but also by its possible precursors sepiapterin and dihydrobiopterin or the analogs methyl-tetrahydropterin and dihydropterin. The regulating enzyme for DOPA synthesis, tyrosine hydroxylase, can be inhibited by certain drugs either directly or indirectly by increasing dopamine concentrations in the cytoplasm after release from its vesicular stores. Using the neuroblastoma clone N1E-115 which lacks DOPA decarboxylase and thus contains only low levels of dopamine the site of action of certain drugs could be determined. Drugs affecting the tyrosine hydroxylase directly (alpha-methyl-para-tyrosine, apomorphine) decreased DOPA production in both clones, while drugs acting via interference with the vesicular stores (reserpine, amphetamine, nigericin) were effective only in the PC-12 cells. After total depletion of dopamine by nigericin at high concentrations or long-term incubation with 3-hydroxybenzyl-hydrazine (NSD 1015), DOPA production increased in the PC-12 cells indicating a usually occurring regulation of tyrosine hydroxylase by cytoplasmic dopamine. Dopamine concentration in the cytoplasm was calculated to be in the range of 1 X 10(-6) mol/l.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Evaluation of neurotropic drug actions on tyrosine hydroxylase activity and dopamine metabolism in clonal cell lines. 285 29

We investigated for the first time the effect of lipopolysaccharide and the signal transduction pathway on the biosynthesis of tetrahydrobiopterin [(6R-L-erythro-1',2'-dihydroxypropyl) -2-amino-4-hydroxy-5,6,7,8-tetrahydropteridine], the cofactor for the enzymatic hydroxylation of the aromatic amino acids, in the murine neuroblastoma cell line N1E-115, which synthesizes tetrahydrobiopterin constitutively. Activation of N1E-115 cells with 1 microgram/ml lipopolysaccharide resulted in statistically significant increases in both intracellular tetrahydrobiopterin contents and the activity (Vmax) of GTP cyclohydrolase I, a rate-limiting enzyme in tetrahydrobiopterin de novo biosynthesis. Following simultaneous addition of the inhibitors of protein tyrosine kinases and GTP-binding proteins into serum-free culture media with lipopolysaccharide, we analyzed the transduction pathway of lipopolysaccharide signal toward the tetrahydrobiopterin biosynthetic system in N1E-115 cells. Our data indicate the following conclusions: (a) Protein tyrosine kinase systems are involved in mediating lipopoly-saccharide signal to tetrahydrobiopterin production, and (b) there may be a cross-talk between GTP-binding protein and the protein tyrosine kinase system in mediating lipopolysaccharide signal. These observations suggest that a neuronal cell such as N1E-115, which barely expresses CD14 on its cell surface, responds to lipopolysaccharide like macrophages and monocytes in the absence of soluble CD14.
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PMID:Tetrahydrobiopterin biosynthesis enhanced by lipopolysaccharide stimulation in murine neuroblastoma cell line N1E-115. 893 88

GTP cyclohydrolase I (GTPCH) gene expression was investigated in the human monoamine-containing neuroblastoma cell line SK-N-BE(2)M17. Northern blot analysis revealed a single GTPCH mRNA transcript that was confirmed by RNase protection assay to encode for Type 1 GTPCH; no alternatively spliced forms of GTPCH mRNA were detected with this assay. Incubation with 8Br-cAMP, but not nerve growth factor or leukemia inhibitory factor, produced a rapid increase in GTPCH mRNA and protein levels; protein levels remained elevated during the entire treatment period while mRNA content declined rapidly between 10 and 24 h. Treatment with 8Br-cAMP did not significantly modify the stability of GTPCH mRNA but did increase GTPCH transcription as determined by transient transfection assays of a luciferase reporter construct containing 1171 bp of human GTPCH 5'-flanking sequence. Cis-acting elements required for maximal basal and cAMP-dependent transcription were localized by deletion analysis to the 146 bp proximal promoter. DNase I footprint analysis of the proximal promoter using SK-N-BE(2)M17 nuclear extracts identified two protein binding domains: one an upstream Sp1-like site and the other a combined CRE-Sp1-CCAAT-box element. EMSA and supershift assays demonstrated that the combined CRE-Sp1-CCAAT-box element recruits ATF-2 and NF-Y but not Sp1-4 or Egr-1-3. NF-Y binding was confirmed using pure recombinant human NF-Y protein. Transcription of the human GTPCH gene in human SK-N-BE(2)M17 cells is thus enhanced by cAMP acting through regulatory elements located in the proximal promoter and may involve the transcription factors NF-Y and ATF-2.
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PMID:Characterization of GTP cyclohydrolase I gene expression in the human neuroblastoma SKN-BE(2)M17: enhanced transcription in response to cAMP is conferred by the proximal promoter. 1170 61

Abnormal accumulation of alpha-synuclein in Lewy bodies is a neuropathological hallmark of both sporadic and familial Parkinson's disease (PD). Although mutations in alpha-synuclein have been identified in autosomal dominant PD, the mechanism by which dopaminergic cell death occurs remains unknown. We investigated transcriptional changes in neuroblastoma cell lines transfected with either normal or mutant (A30P or A53T) alpha-synuclein using microarrays, with confirmation of selected genes by quantitative RT-PCR. Gene products whose expression was found to be significantly altered included members of diverse functional groups such as stress response, transcription regulators, apoptosis-inducing molecules, transcription factors and membrane-bound proteins. We also found evidence of altered expression of dihydropteridine reductase, which indirectly regulates the synthesis of dopamine. Because of the importance of dopamine in PD, we investigated the expression of all the known genes in dopamine synthesis. We found co-ordinated downregulation of mRNA for GTP cyclohydrolase, sepiapterin reductase (SR), tyrosine hydroxylase (TH) and aromatic acid decarboxylase by wild-type but not mutant alpha-synuclein. These were confirmed at the protein level for SR and TH. Reduced expression of the orphan nuclear receptor Nurr1 was also noted, suggesting that the co-ordinate regulation of dopamine synthesis is regulated through this transcription factor.
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PMID:Co-ordinate transcriptional regulation of dopamine synthesis genes by alpha-synuclein in human neuroblastoma cell lines. 1271 27

We and others have previously reported that neurons expressing neuronal nitric oxide synthase (nNOS) do not co-express GTP cyclohydrolase I, the enzyme that synthesize its cofactor tetrahydrobiopterin (BH4). BH4 is released from catecholaminergic cells and nNOS-expressing cells are located close to BH4-producing catecholaminergic nerve terminals. We show that BH4 is taken up into the nNOS-expressing human neuroblastoma cells TGW-I-nu in a linear, dose-dependent manner and elevates NO production. Direct exposure to BH4, dihydrobiopterin or biopterin, or coculture with catecholaminergic CATH.a cells increases NO production by TGW-I-nu. Thus, BH4-requiring nNOS cells may obtain BH4 from neighboring catecholaminergic cells or terminals and an intercellular crosstalk may exist between the two cells in vivo.
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PMID:Utilization of exogenous tetrahydrobiopterin in nitric oxide synthesis in human neuroblastoma cell line. 1462 30

Lipopolysaccharide (LPS), an endotoxin released from the outer membranes of Gram-negative bacteria, triggers cells to synthesize and release inflammatory cytokines that may progress to septic shock in vivo. We found that LPS enhances tetrahydrobiopterin (BH4) biosynthesis by inducing the biosynthetic enzyme GTP cyclohydrolase I (GCH) in vitro in the mouse neuroblastoma cell line N1E-115. Furthermore, we observed that gene expression of GCH in the locus coeruleus (LC) in mice was enhanced by peripheral administration of LPS, resulting in increased concentrations of BH4, and norepinephrine, and its metabolite 4-hydroxy-3-methoxyphenylglycol (MHPG). These results suggest that tyrosine hydroxylase (TH) activity is increased by increased content of BH4 due to enhanced mRNA expression of GCH in the LC resulting in the increase in norepinephrine in the LC during endotoxemia. LPS in blood may act as a stressor to increase norepinephrine biosynthesis in the mouse LC.
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PMID:Effect of peripherally administered lipopolysaccharide (LPS) on GTP cyclohydrolase I, tetrahydrobiopterin and norepinephrine in the locus coeruleus in mice. 1751 81