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)

In their study of prostaglandin E1 (PGE1)-sensitive adenylate cyclase (AC) in rat brain homogenates, Collier and Roy claimed that the activity of this enzyme is inhibited by opiates. They also proposed that opiates exert their analgesic and allied effects by inhibiting AC of neurones that are normally stimulated by E prostaglandins. Studies using neuroblastoma x glioma hybrid cells supported this hypothesis. However, subsequent studies with mammalian brain and rat brain tissue slices yielded conflicting results. PGE1 also inhibits platelet aggregation, probably through activation of platelet AC. Gryglewski et al. showed that morphine inhibits the anti-aggregating effect of PGE1 on ADP- and adrenaline-induced platelet aggregation, and suggested that the inhibition by morphine is mediated through platelet AC activity. We report here our attempts to reproduce the results of Gryglewski et al. and our examination of the effect of morphine on PGE1-sensitive AC activity in platelet lysates and on PGE1-induced accumulation of cyclic AMP in intact platelets. The possible existence of opiate receptors in platelets was also assessed by direct binding studies with 3H-etorphine. In contrast to Gryglewski et al., we could not detect any effect of opiates on the aggregation of human platelets, nor did we find any other evidence supporting the presence of opiate receptors in these cells. Thus we conclude that the presence of opiate receptors in human platelets is unlikely.
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PMID:Do human platelets have opiate receptors? 625 32

The subunit structure of islet-activating protein (IAP), pertussis toxin, has been analyzed to study a possibility that this protein is one of the A-B toxins [Gill, D. M. (1978) in Bacterial Toxins and Cell Membranes (Jeljaszewicz, J., & Wadstrom, T., Eds.) pp 291-332, Academic Press, New York]. Heating IAP with 1% sodium dodecyl sulfate caused its dissociation into five dissimilar subunits named S-1 (with a molecular weight of 28 000), S-2 (23 000), S-3 (22 000), S-4 (11 700), and S-5 (9300), as revealed by polyacrylamide gel electrophoresis; their molar ratio in the native IAP was 1:1:1:2:1. The molecular weight of IAP estimated by equilibrium ultracentrifugation was 117 000 which was not at variance with the value obtained by summing up molecular weights of the constituent subunits. The preparative separation of these IAP subunits was next undertaken; exposure of IAP to 5 M ice-cold urea for 4 days followed by column chromatography with carboxymethyl-Sepharose caused sharp separation of S-1 and S-5, leaving the other subunits as two dimers. These dimers were then dissociated into their constituent subunits, i.e., S-2 and S-4 for one dimer and S-3 and S-4 for the other, after 16-h exposure to 8 M urea; these subunits were obtained individually upon further chromatography on a diethylaminoethyl-Sepharose column. Subunits other than S-1 were adsorbed as a pentamer by a column using haptoglobin as an affinity adsorbent. The same pentamer was obtained by adding S-5 to the mixture of two dimers. Neither this pentamer nor other oligomers (or protomers) exhibited biological activity in vivo. Recombination of S-1 with the pentamer at the 1:1 molar ratio yielded a hexamer which was identical with the native IAP in electrophoretic mobility and biological activity to enhance glucose-induced insulin secretion when injected into rats. In the broken-cell preparation, S-1 was biologically as effective as the native IAP; both catalyzed ADP-ribosylation of a protein in membrane preparations from rat C6 glioma cells. In conclusion, IAP is an oligomeric protein consisting of an A (active) protomer (the biggest subunit) and a B (binding) oligomer which is produced by connecting two dimers by the smallest subunit in a noncovalent manner. Rationale for this terminology is discussed based on the A-B model.
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PMID:Subunit structure of islet-activating protein, pertussis toxin, in conformity with the A-B model. 629 44

Pertussis toxin (islet-activating protein) activates adenylate cyclase in susceptible cells by ADP-ribosylating an inhibitory component of the cyclase system. This toxin, assayed in a cell-free system in the presence of high concentrations of thiol, catalyzed the hydrolysis of NAD to ADP-ribose and nicotinamide. This NAD glycohydrolase activity co-chromatographed on Sephacryl G-200 in 6.5 M urea, pH 3.2, 0.1 M glycine with the ADP-ribosyltransferase activity of the toxin, as monitored by the transfer of [32P]ADP-ribose from [32P]NAD to a 41,000-Da protein in NG108-15 neuroblastoma X glioma hybrid cells. In the absence of thiol, the native holotoxin was enzymatically inactive. Following addition of 250 mM dithiothreitol to the assay, maximal enzymatic activity was evident after a delay of approximately 1 h; with 20 mM thiol, the delay was longer. The Km for NAD with the fully activated enzyme was 25 microM; the Km did not appear to vary with the extent of activation. Thiol was necessary in a cell-free system to demonstrate NAD glycohydrolase activity. When extensively washed membranes were used as a source of 41,000-Da substrate, thiol was necessary to observe ADP-ribosylation in some cases (human erythrocytes) and significantly stimulated activity in others (NG108-15 cells). In contrast to the bacterial toxins choleragen and Escherichia coli heat-labile enterotoxin that ADP-ribosylate stimulatory components of the cyclase system, pertussis toxin did not transfer ADP-ribose to low molecular weight guanidino compounds, such as arginine or agmatine.
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PMID:Activation by thiol of the latent NAD glycohydrolase and ADP-ribosyltransferase activities of Bordetella pertussis toxin (islet-activating protein). 631 27

Adenylate cyclase in NG108-15 (neuroblastoma X glioma hybrid) cells is responsive to both stimulatory and inhibitory ligands. Bordetella pertussis toxin (PT) catalyzes the ADP-ribosylation of a 41,000-Da peptide believed to be a subunit of the putative guanyl nucleotide-binding protein (Gi) involved in cyclase inhibition and abolishes inhibitory effects of opiate agonists. In studying the effects of PT on opiate receptors, we found that [3H]enkephalinamide binding was reduced by approximately 90% in membranes prepared from cells incubated with PT compared to control membranes. Agonist affinity, assessed by enkephalinamide competition for [3H]diprenorphine-binding sites, was markedly reduced in cells incubated with PT. Furthermore, inhibition by guanylylimidodiphosphate of ligand binding to opiate receptors was reduced following treatment with PT. The number of opiate receptors assessed by [3H]diprenorphine binding was unaltered by PT. These data are consistent with the hypothesis that PT-catalyzed ADP-ribosylation impairs the interaction of Gi with the inhibitory receptor-ligand complex, effectively uncoupling the inhibitory receptor from Gi and the cyclase catalytic unit.
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PMID:ADP-ribosylation of adenylate cyclase by pertussis toxin. Effects on inhibitory agonist binding. 631 76

Islet-activating protein (IAP), pertussis toxin, is an oligomeric protein composed of as A protomer and a B oligomer. IAP and its A protomer were equipotent, on a molar basis, in enhancing GTP-dependent adenylate cyclase activity and in causing ADP-ribosylation of the 41,000 Mr protein when directly added to the cell-free membrane preparation from rat C6 glioma cells. Similar actions of IAP observed upon its addition to intact C6 cells were not mimicked by its A protomer, indicating that the A protomer had to be associated with the B oligomer to become accessible to its site of action on the inner surface of the membrane of intact cells. The A protomer, but not IAP, exhibited NAD-glycohydrolase activity in the reaction mixture lacking cellular components but containing dithiothreitol. Their actions on membranes were not accelerated by dithiothreitol, but markedly suppressed by oxidized glutathione. Thus, C6 cell membranes may possess certain "processing" enzyme(s) responsible for releasing the A protomer from the IAP molecule and for reductive cleavage of an intrachain disulfide bond in the released protomer, thereby producing an active peptide which functions to cause ADP-ribosylation of one of the subunits of guanine nucleotide regulatory protein in the receptor-adenylate cyclase system.
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PMID:The A protomer of islet-activating protein, pertussis toxin, as an active peptide catalyzing ADP-ribosylation of a membrane protein. 668 82

Cholera toxin catalyzed the transfer of radioactive label from [adenine-2,8-3H2]NAD+ or ((32P]NAD+ to rat C6 glioma cell membrane and cytosolic proteins. Labeled proteins were resolved by polyacrylamide-NaDodSO4 gel or two-dimensional gel electrophoresis and stained with Coomassie blue, and the gels were subjected to fluorography or autoradiography. Autoradiograms of gels revealed labeled Mr 42000 and 46000-48000 membrane proteins that are putative subunits of the regulatory component (G/F) of the C6 cell hormone-sensitive adenylate cyclase. Cholera toxin also catalyzed the labeling of several cytosolic proteins including a Mr 54000 protein that was observed in autoradiograms of two-dimensional gels to migrate as an acidic satellite relative to Coomassie-stained C6 cell tubulin. Tubulin modified by ADP-ribosylation would undergo an acid shift relative to the stained unmodified tubulin in two-dimensional gels. The data led us to postulate that tubulin undergoes cholera toxin catalyzed ADP-ribosylation. Bovine brain tubulin prepared by three cycles of warm/cold polymerization/depolymerization was incubated with [32P]NAD+, GTP, and cholera toxin and then subjected to two-dimensional gel electrophoresis. Autoradiograms of the gels revealed the presence of [32P]ADP-ribosylated proteins that migrated as acidic satellites relative to the Coomassie-stained brain alpha and beta tubulin. Peptide maps of bovine brain tubulin and the associated [32P]ADP-ribosylated proteins showed a correspondence between the autoradiographic images and the stained peptide fragments. The data demonstrate that cholera toxin catalyzes the ADP-ribosylation of tubulin.
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PMID:Tubulin adenosine diphosphate ribosylation is catalyzed by cholera toxin. 712 51

Islet-activating protein (IAP), one of the pertussis toxins, exerted dual actions on crude membrane preparations from rat C6 glioma cells; an Mr = 41,000 membrane protein was ADP-ribosylated while GTP (and GTP-dependent isoproterenol) activation of membrane adenylate cyclase was enhanced when membranes were incubated with IaP. Both actions of IaP were dependent on the incubation time and the concentrations of NAD and IAP, and were inhibited by nicotinamide; the one action was strictly paralleled by the other in magnitude. Tryptic digestion of the Mr = 41,000 protein was markedly influenced by the presence of guanyl-5'-yl beta-gamma-imidodiphosphate or NaF, the specific ligands of the regulatory component of the adenylate cyclase system. No ADP ribosylation occurred in the membranes prepared from intact C6 cells that had been incubated with IAP, suggesting that the IAP substrate had already been ADP-ribosylated by the intracellular NAD during incubation of the intact cells. Cholera toxin catalyzed ADP ribosylation of other proteins with Mr = 45,000 and 48,000/49,000 (doublet). It is concluded that IAP, added to intact cells or isolated membranes, causes unique modification of the receptor-adenylate cyclase coupling mechanism as a result of ADP ribosylation of the Mr = 41,000 protein which is presumably one of the subunits, other than the cholera toxin substrates, of the guanine nucleotide regulatory component of the cyclase system.
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PMID:ADP ribosylation of the specific membrane protein of C6 cells by islet-activating protein associated with modification of adenylate cyclase activity. 720 Sep 79

The cDNA encoding a novel P2 receptor was isolated from rat aortic smooth muscle cell library and functionally characterized. The cloned P2 receptor exhibits structural features characteristic of the G protein-coupled receptor family and shows 44 and 38% amino acid identity with previously cloned rat P2U and chicken P2Y receptors, respectively. The cloned P2 receptor is functionally coupled to phospholipase C but not to adenylate cyclase in C6 rat glioma cells transfected with the cloned P2 expression vector. The rank order of agonist potency as judged by intracellular Ca2+ mobilization responses is UTP > ADP = 2-methylthioATP > ADP beta S > ATP = ATP gamma S, which is not compatible with any of the previously characterized P2 receptor subtypes. The nonselective P2 antagonists, suramin and reactive blue-2, inhibit nucleotide-induced phospholipase C activation in cells expressing the cloned P2 receptor. The cloned P2 receptor mRNA is abundantly expressed in various rat tissues including lung, stomach, intestine, spleen, mesentery, heart, and, most prominently, aorta. The results indicate that the novel metabotropic P2 receptor has pharmacological characteristics distinct from any of P2 receptor subtypes thus far identified and suggest the existence of a novel regulatory system by extracellular nucleotides of potential significance.
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PMID:Molecular cloning and functional analysis of a novel P2 nucleotide receptor. 759 19

The effect of [H+] on the rate of glycolysis was investigated in glioma C6 and fibroblast BHK-21 cells and in synaptosomes from rat brain. The rates of lactate production at an extracellular pH (pHe) of 6.2, 7.4, and 7.8 were correlated with intracellular [ATP], [ADP], and [P(i)] ([ATP]i, [ADP]i, and [P(i)]i, respectively) and, when relevant, creatine phosphate (PCr) as well as with the levels of several glycolytic intermediates. In C6 cells cytosolic [H+] was measured simultaneously together with [Ca2+], [K+], [Na+], and membrane potentials. In all three systems studied, an increase in [H+]e suppressed whereas a fall enhanced the rate of lactate generation. Changes in pHe produced no simple correlation between the amount of lactate formed and alterations either in the absolute [ATP], [ADP], [P(i)], and [PCr] or their ratios but did correlate with the levels of glycolytic intermediates. Higher [fructose-1,6-bisphosphate] and [glyceraldehyde-3-phosphate] and lower [glucose-6-phosphate] and [fructose-6-phosphate] accompanied faster glycolytic activity. Addition of rotenone markedly enhanced glycolysis at all pHe values studied. The increases were larger at higher [H+] so that the rate of lactate generation was only slightly lower at pH 6.2 than at 7.4 or 7.8. With rotenone present, [ATP] (and where relevant [PCr]) fell and [ADP] and [P(i)] rose under all pHe conditions. Simultaneously [glucose-6-phosphate] and [fructose-6-phosphate] decreased whereas [fructose-1,6-bisphosphate] and [glyceraldehyde-3-phosphate] increased; the levels of the last two were similar at pH 6.2 and 7.4.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The effect of pH on glycolysis and phosphofructokinase activity in cultured cells and synaptosomes. 759 76

The present article investigates chronic opioid regulation of the stimulatory adenylate cyclase-coupled prostaglandin E1 (PGE1) receptor system in neuroblastoma x glioma (NG108-15) hybrid cells. Persistent activation of delta-opioid receptors by morphine (10 mumol/L; 3 days) substantially down-regulates the number of PGE1 binding sites by approximately 30%, without affecting their affinity. Radioligand binding studies performed in the presence of GTP gamma S (100 mumol/L) further revealed that the remaining PGE1 binding sites are still capable of interacting functionally with their associated stimulatory G proteins, Gs. On the postreceptor level, neither changes in the abundance nor in the intrinsic activity of the alpha subunit of Gs (Gs alpha) were found during the state of opioid dependence, as has been verified by western blot and S49 cyc- reconstitution experiments, respectively. Evaluation of the functional interaction between PGE1 receptors and Gs by means of receptor-stimulated, cholera toxin-catalyzed ADP-ribosylation of Gs alpha revealed a significant increase in the ability of PGE1 receptors to activate Gs alpha (3.3-fold increase in EC50; p < 0.05) in cells chronically exposed to morphine. This effect was completely blocked by coincubation of the cells together with the opiate antagonist naloxone (100 mumol/L; 3 days), whereas precipitation of morphine withdrawal by naloxone (100 mumol/L) had no further effect on sensitization in PGE1 receptor/Gs coupling. These findings provide evidence that the stimulatory adenylate cyclase-coupled PGE1 receptor system represents a potential target of chronic delta-opioid receptor activation in NG108-15 hybrid cells. They further suggest that sensitization in stimulatory signal transduction plays a critical role in the generation of opioid dependence.
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PMID:Chronic activation of inhibitory delta-opioid receptors cross-regulates the stimulatory adenylate cyclase-coupled prostaglandin E1 receptor system in neuroblastoma x glioma (NG108-15) hybrid cells. 776 24


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