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)

It has been proposed elsewhere [Meeker, R.B. & Harden, T. K. (1982) Mol. Pharmacol. 22, 310-319] that muscarinic cholinergic receptor-mediated attenuation of cAMP accumulation occurs through activation of phosphodiesterase in 1321N1 human astrocytoma cells. Pertussis toxin, which ADP-ribosylates the guanine nucleotide regulatory protein involved in receptor-mediated inhibition of adenylate cyclase (Ni), has been utilized to further differentiate between the mechanism of cholinergic regulation of cAMP metabolism in 1321N1 cells and the mechanism involving inhibition of adenylate cyclase in other tissues. Muscarinic receptor-mediated regulation of cAMP accumulation in NG108-15 neuroblastoma-glioma cells occurs through inhibition of adenylate cyclase. Pretreatment of these cells with pertussis toxin completely blocked the capacity of carbachol to attenuate cAMP accumulation. In contrast, concentrations of pertussis toxin two to three orders of magnitude higher than those effective in NG108-15 cells had no effect on muscarinic receptor-mediated attentuation of cAMP accumulation in 1321N1 cells. In addition, no effect of pertussis toxin was observed either on the control rate or the carbachol-stimulated rate of cAMP degradation measured directly in intact 1321N1 cells. A 41,000 Mr protein previously proposed to be the alpha subunit of Ni was labeled during incubation of a plasma membrane fraction from 1321N1 cells with [32P]NAD and pertussis toxin. Pertussis toxin is apparently active in 1321N1 cells, since this protein substrate was not labeled in plasma membrane preparations from cells previously incubated with toxin. Functional activity of Ni was demonstrated by the observation that guanosine 5'-[gamma-thio]triphosphate- and GTP-mediated inhibition of forskolin-stimulated adenylate cyclase activity occurred in cell-free preparations from 1321N1 cells. The inhibitory activity of these guanine nucleotides was lost in membrane preparations from pertussis toxin-treated cells. The data suggest that adenylate cyclase is not involved in cholinergic action in 1321N1 cells and, furthermore, Ni is not involved in muscarinic receptor-mediated activation of phosphodiesterase in these cells. Thus, pertussis toxin can be used to differentiate between two mechanisms of cholinergic regulation of cAMP metabolism.
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PMID:Pertussis toxin differentiates between two mechanisms of attenuation of cyclic AMP accumulation by muscarinic cholinergic receptors. 609 Nov 3

The attenuation of cyclic AMP accumulation occurs by different mechanisms in 1321N1 astrocytoma cells and NG108-15 neuroblastoma X glioma cells. In 1321N1 cells, cholinergic agonists reduce cyclic AMP accumulation through a Ca2+-dependent activation of phosphodiesterase; in NG108-15 cells, muscarinic receptor-mediated effects on cyclic AMP metabolism occur through inhibition of adenylate cyclase. The goal of the current study was to determine whether different pharmacological specificities were expressed by the muscarinic receptor populations of these two cell lines. The affinity of muscarinic receptors for [3H]quinuclidinyl benzilate (6 pM), [3H]N-methylscopolamine (50 pM), and atropine (80 pM) was similar in membrane preparations from each cell line. The affinity of the antagonist, pirenzepine, which has been proposed to be a selective ligand for a muscarinic receptor subtype, was 3-fold higher in competition binding assays carried out with membranes of 1321N1 cells, than with NG108-15 cells. The Hill coefficients of pirenzepine competition curves were not significantly different from unity in both cell lines. This selectivity of pirenzepine was also apparent in studies of the competitive inhibition of carbachol-induced attenuation of cyclic AMP accumulation in intact cells. Differences in the relative affinities of agonists were observed in competition binding analyses carried out with membranes in the presence of GTP and absence of Mg2+. The Ki values of bethanechol and carbachol were 5- and 12-fold lower for receptors of NG108-15 cells than those of 1321N1 cells and the Ki of methacholine was 3.5-fold lower for 1321N1 cells than for NG108-15 cells. The affinities of oxotremorine and arecoline were similar between the two cell lines. These differences in agonist affinities between the two cell lines were much smaller in analyses of muscarinic receptor-mediated effects on cyclic AMP metabolism in intact cells. Taken together, these data suggest that muscarinic receptors of differing pharmacological specificities regulate cyclic AMP metabolism by different mechanisms in 1321N1 and NG108-15 cells.
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PMID:Muscarinic cholinergic receptors of two cell lines that regulate cyclic AMP metabolism by different molecular mechanisms. 609 92

[3H]Dihydroergocryptine ([3H]DHE) was shown to bind to sites in membranes from neuroblastoma X glioma hybrid cells (NG 108-15) that had the characteristics expected of alpha-adrenergic receptors. The binding was saturable with 0.3 pmol [3H]DHE bound per mg of protein and of high affinity, with an apparent dissociation constant (KD) of 1.8 nM. The specificity of the binding site for various ligands was more similar to that of alpha 2 receptors than to that of alpha 1. No specific binding of [3H]WB-4101 was found in the membranes derived from NG 108 cells. This finding also indicated that the [3H]DHE binding site in the cell is the alpha 2 receptor. GTP lowered the affinity of agonists for the [3H]DHE binding site, although the nucleotide hardly affected the affinity of antagonists including [3H]DHE.
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PMID:Characterization by [3H]dihydroergocryptine binding of alpha-adrenergic receptors in neuroblastoma X glioma hybrid cells. 611 Jul 4

Specific, GTP hydrolysis catalyzed by membranes prepared from neuroblastoma--glioma (NG108-15) hybrid cells can be measured in the presence of adenosine-5'-[beta, gamma-imido] triphosphate (p[NH]ppA), ATP, and a nucleotide triphosphate-regenerating system. Opiates and opioid peptides stimulate low Km GTP hydrolysis when measured in the presence of Na+ and Mg2+. Opiate stimulation is rapid, stereospecific, and reserved by the antagonist naloxone. Potencies of opiates as stimulators of GTP hydrolysis and as inhibitors of adenylate cyclase are closely correlated. Agents that stimulate adenylate cyclase, including prostaglandin E1, 2-Cl-adenosine, secretin, and NaF, have little or no effect upon the rate of GTP hydrolysis. Opiates have no effect upon either adenylate cyclase or GTPase activity in membranes prepared from C6-BU1 glioma cells, which lack opiate receptors. In view of the pivotal role of GTP in the activation of adenylate cyclase, we conclude that receptor-mediated stimulation of GTP hydrolysis is the mechanism by which opiates and other inhibitory hormones lower adenylate cyclase activity in NG108-15 cell membranes.
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PMID:Opiates inhibit adenylate cyclase by stimulating GTP hydrolysis. 611 72

Opiates and opioid peptides inhibit adenylate cyclase and stimulate specific low Km GTPase activity in membranes from neuroblastoma x glioma NG108-15 hybrid cells. The effects of opiate agonists on both enzymes are mediated by high affinity stereospecific receptors and require Mg2+, GTP, and Na+. In the presence of Mg2+, Na+ inhibits basal GTPase activity; opiates stimulate GTP hydrolysis by antagonizing the Na+-induced inhibition. Activation of GTPase leads, in turn, to inactivation of GTP-stimulated adenylate cyclase activity. The intrinsic activities (or efficacies) of a series of opiates are identical for stimulation of GTPase and inhibition of adenylate cyclase. These results provide a mechanism for the dual requirement for Na+ and GTP in the inhibitory coupling of opiate receptors to the adenylate cyclase system in these cells and may be of general significance to the action of other inhibitory hormones.
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PMID:Modulation of sodium-sensitive GTPase by partial opiate agonists. An explanation for the dual requirement for Na+ and GTP in inhibitory regulation of adenylate cyclase. 612 41

Acute and persistent rabies virus infection of mouse neuroblastoma-rat glioma hybrid cells (NG-108-15) results in a loss of the normal inhibiting function of opiates via the opiate receptor on hormone-stimulated adenylate cyclase activity. Previous studies of these persistently infected cells have shown a decrease in the affinity of the opiate receptors for agonists without any change in the number of these receptors. We now demonstrate that persistently infected cells are unable to couple the opiate receptors to the inhibitory regulatory protein Ni of the adenylate cyclase, as measured by the loss of stimulation of the GTPase activity of this protein. However, the unstimulated basal GTPase activities of the regulatory components Ni and Ns are unchanged in the persistently infected cells. These studies also reveal a disorder of the stimulation of the adenylate cyclase by GTP or fluoride via the stimulating regulatory G/F protein (Ns) in persistently infected cells, whereas direct stimulation of the catalytic subunit of the adenylate cyclase by forskolin remains unchanged. Therefore, there are different points of dysfunction caused by the persistent rabies infection in the signal pathway from the opiate receptor to the adenylate cyclase and from the stimulating Ns protein to the enzyme: (i) opiate receptor binding is reduced by a decrease of agonist affinity (previously published data), (ii) the stimulation of GTPase activity of the inhibiting regulatory component Ni of the adenylate cyclase system is inhibited, and (iii) the signal pathway from the stimulating regulatory component of the adenylate cyclase system to the unchanged activity of the catalytic subunit is defective.
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PMID:Inhibition of opiate receptor-mediated signal transmission by rabies virus in persistently infected NG-108-15 mouse neuroblastoma-rat glioma hybrid cells. 614 55

Guanylate cyclase was activated 3- to 10-fold by hemin in a dose-dependent manner in membranes prepared from homogenates of rat lung, C6 rat glioma cells, or B103 rat neuroblastoma cells. Maximum activation was observed with 50 to 100 microM hemin with higher concentrations being inhibitory. Activation was observed when Mg2+-GTP but not when Mn2+-GTP was used as the substrate. Increased enzyme activity reflected selective activation of the particulate form of guanylate cyclase; hemin inhibited the soluble form of guanylate cyclase 70 to 90% over a wide range of concentrations. Activation was not secondary to proteolysis since a variety of protease inhibitors failed to alter stimulation by hemin. Protophorphyrin IX had little effect on particulate guanylate cyclase activity and sodium borohydride almost completely abolished hemin-dependent activation. These data suggest a requirement for the ferric form of the porphyrin-metal chelate for activation. However, agents which interact with the iron nucleus of porphyrins, such as cyanide, had little effect on the ability of hemin to activate guanylate cyclase. The stimulatory effects of hemin were observed in the presence of detergents such as Lubrol-PX, and highly purified particulate enzyme could be activated to the same extent as enzyme in native membranes. These data suggest that the interaction of porphyrins with particulate guanylate cyclase is complex in nature and different from that with the soluble enzyme.
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PMID:Selective activation of particulate guanylate cyclase by a specific class of porphyrins. 614 94

The guanine nucleotides GDP, GTP, and guanosine-5'-(beta, gamma-imido)triphosphate inhibit binding of opiates and opioid peptides to receptors solubilized from membranes of neuroblastoma X glioma NG108-15 hybrid cells. The inhibition reflects decreased affinity of receptors for opioid ligands. Whereas in membranes, only opioid agonist binding is sensitive to guanine nucleotide inhibition, both agonist and antagonist binding is reduced in the case of soluble receptors. Furthermore, soluble receptors are more sensitive to the effects of guanine nucleotides than are membrane-bound receptors. These observations are consistent with the suggestion that solubilized receptors may be complexes of an opiate binding protein and a guanine nucleotide-sensitive regulatory component.
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PMID:Guanine nucleotides inhibit binding of agonists and antagonists to soluble opiate receptors. 625 76

D-Ala2-Met5-enkephalin, morphine, and noradrenaline inhibit the adenylate cyclase in homogenates of neuroblastoma x glioma hybrid cells in a dose-dependent manner even after the enzyme has been preactivated by cholera toxin. Half-maximal inhibition and extent of inhibition are the same with native or cholera toxin-activated enzyme. The inhibition caused by opioids or noradrenaline are antagonized by naloxone or phentolamine, respectively. The effect of D-Ala2-Met5-enkephalin on cholera toxin-activated enzyme is immediate in onset and rapidly reversed by the addition of naloxone. Guanyl-5'-yl-imidodiphosphate stimulates basal activity but inhibits the enzyme activated by cholera toxin or prostaglandin E1. Stimulation occurs at a concentration of 100 microM or above, inhibition even at 0.1 microM. The inhibitory effect of the non-hydrolysable GTP analog is antagonized by GTP. Guanyl-5'-yl-methylenediphosphonate, another nonhydrolysable GTP analog, inhibits basal as well as cholera toxin-stimulated or prostaglandin E1-stimulated adenylate cyclase. Other guanine derivatives such as GDP, GMP, cyclic GMP, guanyl-5'-yl-phosphoric acid amide and guanosine have no effect under the same conditions. The results may be taken as a piece of evidence for two separate guanyl nucleotide-binding sites accompanying the adenylate cyclase in the hybrid cells and mediating, respectively, stimulation and inhibition of the enzyme by hormones.
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PMID:Opioids, noradrenaline and GTP analogs inhibit cholera toxin activated adenylate cyclase in neuroblastoma x glioma hybrid cells. 625 56

Clonidine and several analogues of clonidine are shown to be useful probes for alpha 2-adrenergic receptors in a comparative study of ligand binding and inhibition of adenylate cyclase. The alpha-adrenergic properties of a new potential probe, N-(4-hydroxyphenacetyl)-4-aminoclonidine hydrochloride, are described. [3H]Clonidine binds to alpha-receptors of NG108-15 neuroblastoma X glioma hybrid cell membranes with Kd values of 1.7 and 33 nM for putative high-affinity and low-affinity sites, respectively. p-Aminoclonidine and hydroxyphenacetyl aminoclonidine displace [3H]clonidine from the high-affinity sites with Kd values of 2.3 and 5.8 nM, respectively. Rat brain alpha 2-receptors also exhibit high affinity toward clonidine, p-aminoclonidine, and hydroxyphenacetyl aminoclonidine, as determined by displacement of specifically bound [3H]clonidine. Clonidine, p-amino-clonidine, and hydroxyphenacetyl aminoclonidine elicit modest inhibition (up to 24%) of NG108-125 adenylate cyclase by interaction with alpha 2-receptors (Kd,app 300, 30, and 130 nM, respectively); these compounds also partially reverse the inhibition elicited by (--)-norepinephrine. Components of the adenylate cyclase assay mixture, particularly ATP, GTP, sodium ions, and a nucleoside-triphosphate-regenerating system, decrease the high-affinity [3H]clonidine binding to NG108-15 membranes; in the presence of these components, alpha-receptors possess only low affinity (Kd 43 nM) for [3H]clonidine. The results are consistent with the concept that certain components required for the receptor-mediated inhibition of adenylate cyclase convert alpha 2-receptors from a high-affinity inactive state to a low-affinity active state.
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PMID:Interaction of clonidine and clonidine analogues with alpha-adrenergic receptors of neuroblastoma X glioma hybrid cells and rat brain: comparison of ligand binding with inhibition of adenylate cyclase. 626 Apr 85


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