Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0017638 (glioma)
 30,880 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

C6 glioma cells possess endothelin ETA receptor and P2 purinoceptor coupled to two signaling pathways, i.e. phosphoinositide turnover and inhibition of adenylyl cyclase. In this study, the effects of raising cyclic AMP levels on the inositol phospholipid hydrolysis and adenylyl cyclase inhibition caused by endothelin-1 and ATP in C6 glioma cells were examined. Pretreatment with cAMP generating agents (forskolin, isoproterenol and cholera toxin) or dibutyryl cAMP for 10 min-3 h did not affect the inositol phosphate accumulation caused by endothelin and ATP. Long-term (8-24 h) pretreatment with isoproterenol, forskolin, cholera toxin or dibutyryl cAMP resulted in a 40-50% inhibition of endothelin- and ATP-stimulated inositol phosphate accumulation, whereas the EC50 values of endothelin and ATP were not affected. Consistent with the effects on endothelin and ATP, NaF-induced inositol phosphate formation was also inhibited by cAMP generating agents to a similar extent. Permeabilized cells from 24 h isoproterenol-or forskolin-pretreated C6 cells also showed a diminished Ca(2+)-sensitivity of phosphoinositide-specific phospholipase C and also attenuated the potentiation response caused by GTP gamma S. The inhibitory effects on adenylyl cyclase by endothelin, ATP and 2-methylthio-ATP were unaffected by 24 h pretreatment with isoproterenol or forskolin. Long-term treatment with dibutyryl cGMP did not affect the two signaling pathways caused by ATP and endothelin. It is concluded that the phosphoinositide turnover, but not the adenylyl cyclase inhibition caused by endothelin and ATP in C6 cells, was inhibited by protein kinase A-dependent pathway.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of protein kinase A activation on endothelin- and ATP-induced signal transduction. 854 42

(6R)-5,6,7,8-Tetrahydrobiopterin (BH4), which is synthesized intracellularly from GTP, caused a concentration-dependent increase in rat pheochromocytoma (PC12) cell proliferation when added exogenously. Incubation with sepiapterin, which is converted enzymatically to BH4 within cells, also increased PC12 cell proliferation and BH4 levels concomitantly. These sepiapterin effects were mediated by BH4 as inhibition of sepiapterin conversion to BH4 by a sepiapterin reductase inhibitor, N-acetyl-serotonin, blocked the increase in proliferation and the elevation of BH4 levels. 7,8-Dihydrobiopterin (BH2) also increased BH4 levels and PC12 cell proliferation, both of which were reversed by methotrexate, which blocks the conversion of BH2 to BH4 by dihydrofolate reductase. The BH4-induced increase in PC12 cell proliferation was not related to elevated catecholamine or nitric oxide synthesis as inhibitors of tyrosine hydroxylase or nitric oxide synthase did not reduce the BH4 effect. BH4 and its precursors did not alter intracellular cAMP levels, suggesting that this second messenger is not involved in the enhancement of PC12 cell proliferation by BH4. Sepiapterin and BH4 also enhanced the proliferation of SV40-transformed human fibroblasts and rat C6 glioma cells, indicating that the stimulatory effect of BH4 on cell proliferation is not restricted to PC12 cells.
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PMID:Mitogenic effects of tetrahydrobiopterin in PC12 cells. 856

There is increasing evidence that pituitary ATP receptors may play a novel role in modulating pituitary function. This work reports the isolation and expression of a pituitary ATP receptor gene clone from a rat pituitary complementary DNA library. The isolated clone (rpP2U) has a 1125-bp coding sequence flanked by 483 bp of 5' - and 422 bp of 3'-untranslated sequences. The deduced 374-amino acid product shows structural features common to other G protein-coupled receptors, and when stably transfected into a glioma cell line lacking endogenous ATP receptors, is functionally characterized as a P2U purinoceptor. Specifically, the ATP-induced intracellular Ca2+ mobilization in the transfected cells was inhibited by suramin, 2-methylthio-ATP had a modest stimulatory effect on intracellular Ca2+ mobilization, and beta, gamma-methylene ATP and alpha, beta-methylene ATP had no effect. The cloned receptor exhibited the agonist potency and efficacy profile of ATP approximately equal to uridine triphosphate > ADP approximately equal to uridine diphosphate > GTP. Such characteristics very closely mimic the pharmacologically defined P2U purinoceptor of primary rat gonadotropes and mixed sheep pituitary cells, and Southern blot analysis further indicates that there is only one allele in rat genome for the P2U purinoceptor. These findings suggest that the P2U purinoceptor is the predominant G protein-linked ATP receptor found in the pituitary.
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PMID:Molecular cloning and functional characterization of a rat pituitary G protein-coupled adenosine triphosphate (ATP) receptor. 861 22

The G proteins G S and Gi1 appear to be capable of binding to tubulin specifically, and it has been suggested that such binding results in G protein activation via direct transfer of GTP. This study was undertaken to demonstrate that consequences of G protein activation by tubulin, i.e., stimulation or inhibition of adenyl cyclase, were dependent on the G proteins expressed as well as unique aspects of the membrane or cytoskeleton in a given cell type. Membranes from rat C6 glioma cells, which express G s alpha but not G i alpha 1, responded to the addition of tubulin with a stable activation of adenyl cyclase. Conversely, membranes from rat cerebral cortex, which contain both G s and G i 1, responded to exogenous tubulin with a stable inhibition of adenyl cyclase. Unlike C6 membranes, cerebral cortex membranes are richly endowed with tubulin, and antitubulin antibodies immunoprecipitated complexes of tubulin and G i 1 and G s from detergent extracts of these membranes. Nearly 90% of the G s alpha from Triton X-114 extracts coimmunoprecipitated with tubulin, suggesting that these proteins exist as a complex in the synaptic membrane. Such complexes may provide the framework for a G protein-cytoskeleton link that participates in the modulation of cellular signal transduction.
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PMID:Synaptic membrane G proteins are complexed with tubulin in situ. 862 3

The divalent cation selective ionophores A23187 and ionomycin were compared for their effects on the Ca2+ contents, nucleotide contents, and protein synthetic rates of several types of cultured cells. Both ionophores reduced amino acid incorporation by approximately 85% at low concentrations (50-300 nmol/L) in cultured mammalian cells without reducing ATP or GTP contents. At these concentrations A23187 and ionomycin each promoted substantial Ca2+ efflux, whereas at higher concentrations a large influx of the cation was observed. Ca2+ influx occurred at lower ionophore concentrations and to greater extents in C6 glioma and P3X63Ag8 myeloma than in GH3 pituitary cells. The ATP and GTP contents of the cells and their ability to adhere to growth surfaces declined sharply at ionophore concentrations producing increased Ca2+ influx. Prominent reductions of nucleotide contents occurred in EGTA-containing media that were further accentuated by extracellular Ca2+. Ionomycin produced more Ca2+ influx and nucleotide decline than comparable concentrations of A23187. The inhibition of amino acid incorporation and mobilization of cell-associated Ca2+ by ionomycin were readily reversed in GH3 cells by fatty acid-free bovine serum albumin, whereas the effects of A23187 were only partially reversed. Amino acid incorporation was further suppressed by ionophore concentrations depleting nucleotide contents. Mitochondrial uncouplers potentiated Ca2+ accumulation in response to both ionophores. At cytotoxic concentrations Lubrol PX abolished protein synthesis but did not cause Ca2+ influx. Nucleotide depletion at high ionophore concentrations is proposed to result from increased plasmalemmal Ca2+-ATPase activity and dissipation of mitochondrial proton gradients and to cause intracellular Ca2+ accumulation. Increased Ca2+ contents in response to Ca2+ ionophores are proposed as an indicator of ionophore-induced cytotoxicity.
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PMID:Translational suppression by Ca2+ ionophores: reversibility and roles of Ca2+ mobilization, Ca2+ influx, and nucleotide depletion. 873 79

Previous studies of rat cerebral cortex and rat C6 glioma cells have demonstrated that dimeric tubulin is capable of activating the G proteins Gs and Gil via transfer of guanine nucleotide from tubulin to Gs alpha and Gil alpha. To provide further information regarding cytoskeletal modulation of adenylyl cyclase, the present study examined effects of tubulin on the activation of the enzyme in rat striatal membranes. Tubulin, prepared from rat brain by polymerization with the hydrolysis-resistant GTP analog 5'-guanylylimidodiphosphate (GppNHp) caused significant activation of adenylyl cyclase by approximately 130%. Furthermore, tubulin-GppNHp activated SKF 38393-sensitive adenylyl cyclase and potentiated forskolin-stimulated activity of the enzyme. When tubulin, polymerized with the hydrolysis-resistant photoaffinity GTP analog [32p]p3 (4-azidoanilido)-p1-5'-GTP ([32P]AAGTP), was incubated with striatal membranes, AAGTP was transferred from tubulin to Gs alpha as well as Gi alpha with the extents of nucleotide transfers being 7.6 +/- 0.8% and 17.8 +/- 1.4% of AAGTP originally bound to tubulin, respectively. These results indicate that, in rat striatum, the tubulin dimer participates in the stimulatory regulation of adenylyl cyclase by transferring guanine nucleotide to Gs alpha, supporting the hypothesis that tubulin contributes to the regulation of neuronal signal transduction.
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PMID:Tubulin stimulates adenylyl cyclase activity in rat striatal membranes via transfer of guanine nucleotide to Gs protein. 875 Sep 58

GTP gamma S-dependent phospholipase D (PLD) activity time-dependently increased during differentiation of rat C6 glioma cells to astrocytic phenotypes induced by dibutyryl cyclic AMP (dbcAMP)/theophylline. The changes in PLD mRNA level were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) method using the degenerate primers designed based on two conserved amino acid sequences in PLDs of human and yeast. The amplified three DNA fragments (tentatively termed as rPLDa, b, and c) contained the conserved regions present in PLDs of various organisms. RT-PCR using non-degenerate primers showed that rPLDa mRNA increased within 12h following treatment with dbcAMP, reaching a broad plateau and then returned to the initial level at 48h. In contrast, the level of rPLDb mRNA showed a concurrent decrease. rPLDc decreased in a time-dependent manner. These results suggest that the expression of PLD mRNAs are differentially regulated during differentiation in C6 glioma cells.
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PMID:Differential mRNA expression of phospholipase D (PLD) isozymes during cAMP-induced differentiation in C6 glioma cells. 875 90

In C6 glioma cells stably expressing a homogeneous population of the cloned rat mu opioid receptor, the binding affinities of opioid agonists and subsequent activation of G protein were examined. Opioid receptor number in membranes of these cells was high (10-30 pmol/mg protein [3H]diprenorphine binding sites). Opioids were found to bind to the receptor with high affinity [Tyr-D-Ala-Gly-(Me)Phe-Gly-ol (DAMGO) 0.23 nM; sufentanil 0.034 nM; morphine 0.16 nM]. Activation of G protein by opioid agonists was examined by measuring the stimulation of guanosine-5'-O-(3-[35S]thio)triphosphate ([35S]GTP gamma S) binding. Sufentanil increased [35S]GTP gamma S binding by 326% with an EC50 value of 2.39 nM. Agonist stimulation of [35S]GTP gamma S binding was stereoselective, naltrexone-reversible, and pertussis toxin-sensitive. The "intrinsic activity" of opioids at the mu receptor was reflected by the magnitude of agonist-mediated activation of G protein. The rank order of the stimulation of [35S]GTP gamma S binding was etonitazene = sufentanil = DAMGO = PLO17 = fentanyl > morphine > profadol > meperidine > butorphanol = nalbuphine = pentazocine > cyclazocine = nalorphine > levallorphan > naltrexone. High affinity binding of ligands to the mu opioid receptor was reduced by the addition of sodium and guanosine diphosphate at concentrations used in the [35S]GTP gamma S binding assay. Ligand affinity was reduced in a manner correlating with "intrinsic activity". DAMGO, 1229-fold, nalbuphine 35-fold, naltrexone, 3-fold. The results presented show that the stable expression of the rat mu opioid receptor in C6 cells provides an effective tool to examine opioid receptor signal transduction mechanisms and evaluate the activity of novel opioids at the mu receptor.
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PMID:Characterization of opioid agonist efficacy in a C6 glioma cell line expressing the mu opioid receptor. 881 94

Pretreatment of 1321N1 human astrocytoma cells with exogenously added bacterial phospholipase C (PLC) induced an increase in subsequent stimulation of cyclic AMP accumulation by the beta-adrenergic receptor agonist isoproterenol and by the direct adenylyl cyclase activator forskolin, a phenomenon referred to as sensitization. The direct protein kinase C activator phorbol 12-myristate 13-acetate (PMA) induced a similar sensitization. In contrast, in C62B rat glioma cells both PLC and PMA induced a decrease in subsequent cyclic AMP accumulation stimulated by isoproterenol and little or no change in stimulation by forskolin. Although the effects of PMA were completely abolished by pretreating cells overnight with PMA to down-regulate protein kinase C activity, the effects of PLC were inhibited only partially or not inhibited. Pertussis toxin pretreatment did not inhibit the sensitization induced by PLC, whereas sensitization induced by lysophosphatidic acid (previously shown to involve pertussis toxin-sensitive GTP binding proteins) was completely inhibited. Further studies of these phenomena may reveal novel pathways for regulation of the cyclic AMP signalling pathway.
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PMID:Modulation of cyclic AMP accumulation in glial cells by exogenous phospholipase C. 882 10

A GTPase-activating protein (GAP) specific for Galphaz was identified in brain, spleen, retina, platelet, C6 glioma cells, and several other tissues and cells. Gz GAP from bovine brain is a membrane protein that is refractory to solubilization with most detergents but was solubilized with warm Triton X-100 and purified up to 50,000-fold. Activity is associated with at least two separate proteins of Mr approximately 22,000 and 28,000, both of which have similar specific activities. In an assay that measures the rate of hydrolysis of GTP pre-bound to detergent-soluble Galphaz, the GAP accelerates hydrolysis over 200-fold, from 0.014 to 3 min -1 at 15 degrees C, or to >/=20 min-1 at 30 degrees C. It does not alter rates of nucleotide association or dissociation. When co-reconstituted into phospholipid vesicles with trimeric Gz and m2 muscarinic receptor, Gz GAP accelerates agonist-stimulated steady-state GTP hydrolysis as predicted by its effect on the hydrolytic reaction. In the single turnover assay, the Km of the GAP for Galphaz-GTP is 2 nM. Its activity is inhibited by Galphaz-guanosine 5'-O-thiotriphosphate (Galphaz-GTPgammaS) or by Galphaz-GDP/AlF4 with Ki approximately 1.5 nM for both species; Galphaz-GDP does not inhibit. G protein betagamma subunits inhibit Gz GAP activity, apparently by forming a GTP-Galphazbetagamma complex that is a poor GAP substrate. Gz GAP displays little GAP activity toward Galphai1 or Galphao, but its activity with Galphaz is competitively inhibited by both Galphai1 and Galphao at nanomolar concentrations when they are bound to GTPgammaS but not to GDP. Neither phospholipase C-beta1 (a Gq GAP) nor several adenylyl cyclase isoforms display Gz GAP activity.
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PMID:A GTPase-activating protein for the G protein Galphaz. Identification, purification, and mechanism of action. 903 85


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