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)

Chronic treatment of C6 glioma cells stably expressing the rat delta opioid receptor (C6delta) with full agonists resulted in receptor down-regulation. Chronic [D-Ser2,L-Leu5]enkephalyl-Thr treatment caused a decrease in cell surface as well as a decrease in agonist-stimulated [35S]guanosine-5'-O-(3-thio)triphosphate binding. Treatment with full agonists for 12 hr resulted in a 90% decrease in receptor number that was paralleled by a decrease in the ability of agonist to stimulate [35S]guanosine-5'-O-(3-thio)triphosphate binding and inhibit forskolin-stimulated adenylyl cyclase. Of the remaining receptors, a smaller fraction of receptors (41 +/- 4 vs. 56 +/- 4% in control) exhibited high affinity for agonist as compared to receptors in control membranes. Elimination of functional guanosine triphosphate binding protein (G protein) by Pertussis toxin pretreatment did not alter the ability of agonist to down regulate receptor. We hypothesized that agonist affinity (not efficacy) would be a predictor of an agonist's ability to down-regulate receptor. However, we found that only full agonists were able to down-regulate receptor number, G protein activation and adenylyl cyclase inhibition. Chronic exposure to partial agonist 7-spiroindinooxymorphone, which has a very high affinity for the receptor, as well as morphine, did not cause receptor down-regulation. Taken together, these results suggest that full agonists alter receptor conformation such that the altered conformation is recognized by G protein as well as proteins involved in receptor down-regulation. In addition, down-regulation is independent of agonist-mediated G protein activation and subsequent down-stream signaling.
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PMID:Delta opioid receptor down-regulation is independent of functional G protein yet is dependent on agonist efficacy. 980 89

Hydrogen peroxide has been suggested to play an important role in the pathogenesis of Alzheimer's disease. In the present study, the effects of hydrogen peroxide upon the functional integrity of beta-adrenoceptors have been investigated in C6 glioma cells. Treatment of cells for 24 h with hydrogen peroxide in serum-free medium produced a concentration-dependent cell toxicity, seen both using cell counting and LDH release into medium as end point. There were no large nor consistent changes in either the density of cell surface beta 1, or beta 2-adrenoceptors, measured using the hydrophilic ligand [3H](-)-CGP 12177, nor in either basal, forskolin and isoprenaline-stimulated cAMP responses, following hydrogen peroxide treatment. It is concluded that the decreased adenylyl cyclase activity and responsiveness to Gs stimulation found in post-mortem brain samples from Alzheimer's disease autopsy cases is unlikely to be mediated by hydrogen peroxide.
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PMID:The effect of hydrogen peroxide upon beta-adrenoceptor density and function in C6 rat glioma cells. 1010 Jan 97

Previous studies have established that Ca2+-sensitive adenylyl cyclases, whether endogenously or heterologously expressed, are preferentially regulated by capacitative Ca2+ entry, compared with other means of elevating cytosolic Ca2+ (Chiono, M., Mahey, R., Tate, G., and Cooper, D. M. F. (1995) J. Biol. Chem. 270, 1149-1155; Fagan, K. A., Mahey, R., and Cooper, D. M. F. (1996) J. Biol. Chem. 271, 12438-12444; Fagan, K. A., Mons, N., and Cooper, D. M. F. (1998) J. Biol. Chem. 273, 9297-9305). These findings led to the suggestion that adenylyl cyclases and capacitative Ca2+ entry channels were localized in the same functional domain of the plasma membrane. In the present study, we have asked whether a heterologously expressed Ca2+-permeable channel could regulate the Ca2+-inhibitable adenylyl cyclase of C6-2B glioma cells. The cDNA coding for the rat olfactory cyclic nucleotide-gated channel was inserted into an adenovirus construct to achieve high levels of expression. Electrophysiological measurements confirmed the preservation of the properties of the expressed olfactory channel. Stimulation of the channel with cGMP analogs yielded a robust elevation in cytosolic Ca2+, which was associated with an inhibition of cAMP accumulation, comparable with that elicited by capacitative Ca2+ entry. These findings not only extend the means whereby Ca2+-sensitive adenylyl cyclases may be regulated, they also suggest that in tissues where they co-exist, cyclic nucleotide-gated channels and Ca2+-sensitive adenylyl cyclases may reciprocally modulate each other's activity.
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PMID:Adenovirus-mediated expression of an olfactory cyclic nucleotide-gated channel regulates the endogenous Ca2+-inhibitable adenylyl cyclase in C6-2B glioma cells. 1021 19

Previously it has been shown that persistent activation of the stimulatory adenylyl cyclase pathway with cholera toxin (CT) downregulates the Gs alpha polypeptide (80%) in a cAMP-independent manner in C6 glioma cells (Shah, 1997). This study was conducted to examine the short and long term effects of CT on the regulation of pertussis toxin-sensitive and -insensitive G proteins and their transcripts in C6 glioma cells. Treatment of C6 cells with CT (100 ng/ml) up to 16 h had no effect on either Gi or Gq/11 alpha proteins. However, prolonged exposure (24-48 h) caused increased expression of Gi (20-30%) and Gq/11 alpha proteins (40%). Urea gradient gels, which can separate Gq alpha and G11 alpha proteins, revealed that prolonged CT treatment increased the expression of both of these G proteins. The CT-mediated enhanced expression of Gq alpha and G11 alpha proteins was accompanied by increased mRNA levels of these proteins as determined by RT/PCR. Cyclic-AMP elevating agents like forskolin (10 microM) and db-cAMP (1 mM) mimicked the effect of CT on Gi but not Gq/11 alpha proteins. These studies show long term cAMP-dependent regulation of Gi and cAMP-independent expression of Gq/11 alpha proteins in C6 glioma cells.
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PMID:Cholera toxin mediated regulation of the expression of Gq alpha and G11 alpha GTP binding proteins. 1041 Mar 8

Results from previous studies suggested that chronic treatment of rats or C6 glioma cells with antidepressants augments the coupling between Gs and adenylyl cyclase. As these effects on C6 glioma cells are seen in the absence of presynaptic input, several antidepressant drugs may have a direct "postsynaptic" effect on their target cells. It was hypothesized that the target of antidepressant action was some membrane protein that may regulate coupling between G proteins and adenylyl cyclase. To test this, C6 glioma cells were treated with amitriptyline, desipramine, iprindole, or fluoxetine for 3 days. Chlorpromazine served as a control for these treatments. Membrane proteins were extracted sequentially with Triton X-100 and Triton X-114 from C6 glioma cells. Triton X-100 extracted more G(s alpha) in membranes prepared from antidepressant-treated C6 glioma cells than from control groups. In addition, cell fractionation studies revealed that the amount of G(s alpha) in caveolin-enriched domains was reduced after antidepressant treatment and that adenylyl cyclase comigrated with G(s alpha) in the gradients. These data suggest that some postsynaptic component that increases availability of Gs to activate effector molecules, such as adenylyl cyclase, might be a target of antidepressant treatment.
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PMID:Treatment of C6 glioma cells and rats with antidepressant drugs increases the detergent extraction of G(s alpha) from plasma membrane. 1046 2

Ca(2+)-sensitive adenylyl cyclases may act as early integrators of the two major second messenger-signaling pathways mediated by Ca(2+) and cAMP. Ca(2+) stimulation of adenylyl cyclase type I (ACI) and adenylyl cyclase type VIII (ACVIII) is mediated by calmodulin and the site on these adenylyl cyclases that interacts with calmodulin has been defined. By contrast, the mechanism whereby Ca(2+) inhibits adenylyl cyclase type V (ACV) and adenylyl cyclase type VI (ACVI) is unknown. In this study, Ca(2+), Sr(2+), and Ba(2+) were compared to probe the involvement of E-F hand-like domains in both Ca(2+) stimulation and inhibition of ACVIII and ACVI, respectively. HEK 293 cells transfected with ACVIII cDNA and C6-2B glioma cells (where the endogenous adenylyl cyclases is predominantly ACVI) were used to compare the effects of these three cations in in vitro and in vivo measurements. The in vitro data identified two Ca(2+) regulatory sites for both ACVIII and ACVI. Strikingly different potency series for these cations at mediating high affinity stimulation and inhibition of ACVIII and ACVI, respectively, effectively rule out the possibility that calmodulin or proteins utilizing similar Ca(2+)-binding motifs mediate inhibition of ACVI. On the other hand, the low affinity inhibition that is common to both ACVIII and ACVI showed virtually identical potency profiles for the IIa cation series, indicating a common site of action. Remarkably, whereas Sr(2+) was rather ineffective at regulating these cyclases (particularly ACVI) in vitro, adequate concentrations accumulated in the vicinity of these enzymes as a consequence of capacitative cation entry to partially regulate both of these activities in vivo. This latter finding consolidates earlier observations that Ca(2+)-sensitive adenylyl cyclases detect and respond to capacitative cation entry rather than global cytosolic cation concentrations.
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PMID:Ca(2+), Sr(2+), and Ba(2+) identify distinct regulatory sites on adenylyl cyclase (AC) types VI and VIII and consolidate the apposition of capacitative cation entry channels and Ca(2+)-sensitive ACs. 1070 61

The endogenous Ca(2+)-inhibitable adenylyl cyclase type VI of C6-2B glioma cells is regulated only by capacitative Ca(2+) entry and not by a substantial elevation of [Ca(2+)](i) from either intracellular stores or via ionophore-mediated Ca(2+) entry (Chiono, M., Mahey, R., Tate, G., and Cooper, D. M. F. (1995) J. Biol. Chem. 270, 1149-1155; Fagan, K. A., Mons, N., and Cooper, D. M. F. (1998) J. Biol. Chem. 273, 9297-9305). The present studies explored the role of cholesterol-rich domains in maintaining this functional association. The cholesterol-binding agent, filipin, profoundly inhibited adenylyl cyclase activity. Depletion of plasma membrane cholesterol with methyl-beta-cyclodextrin did not affect forskolin-stimulated adenylyl cyclase activity and did not affect capacitative Ca(2+) entry. However, cholesterol depletion completely ablated the regulation of adenylyl cyclase by capacitative Ca(2+) entry. Repletion of cholesterol restored the sensitivity of adenylyl cyclase to capacitative Ca(2+) entry. Adenylyl cyclase catalytic activity and immunoreactivity were extracted into buoyant caveolar fractions with Triton X-100. The presence of adenylyl cyclase in such structures was eliminated by depletion of plasma membrane cholesterol. Altogether, these data lead us to conclude that adenylyl cyclase must occur in cholesterol-rich domains to be susceptible to regulation by capacitative Ca(2+) entry. These findings are the first indication of regulatory significance for the localization of adenylyl cyclase in caveolae.
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PMID:Regulation of the Ca2+-inhibitable adenylyl cyclase type VI by capacitative Ca2+ entry requires localization in cholesterol-rich domains. 1084 90

Cyclic AMP is a ubiquitous second messenger that coordinates diverse cellular functions. Current methods for measuring cAMP lack both temporal and spatial resolution, leading to the pervasive notion that, unlike Ca(2+), cAMP signals are simple and contain little information. Here we show the development of adenovirus-expressed cyclic nucleotide-gated channels as sensors for cAMP. Homomultimeric channels composed of the olfactory alpha subunit responded rapidly to jumps in cAMP concentration, and their cAMP sensitivity was measured to calibrate the sensor for intracellular measurements. We used these channels to detect cAMP, produced by either heterologously expressed or endogenous adenylyl cyclase, in both single cells and cell populations. After forskolin stimulation, the endogenous adenylyl cyclase in C6-2B glioma cells produced high concentrations of cAMP near the channels, yet the global cAMP concentration remained low. We found that rapid exchange of the bulk cytoplasm in whole-cell patch clamp experiments did not prevent the buildup of significant levels of cAMP near the channels in human embryonic kidney 293 (HEK-293) cells expressing an exogenous adenylyl cyclase. These results can be explained quantitatively by a cell compartment model in which cyclic nucleotide-gated channels colocalize with adenylyl cyclase in microdomains, and diffusion of cAMP between these domains and the bulk cytosol is significantly hindered. In agreement with the model, we measured a slow rate of cAMP diffusion from the whole-cell patch pipette to the channels (90% exchange in 194 s, compared with 22-56 s for substances that monitor exchange with the cytosol). Without a microdomain and restricted diffusional access to the cytosol, we are unable to account for all of the results. It is worth noting that in models of unrestricted diffusion, even in extreme proximity to adenylyl cyclase, cAMP does not reach high enough concentrations to substantially activate PKA or cyclic nucleotide-gated channels, unless the entire cell fills with cAMP. Thus, the microdomains should facilitate rapid and efficient activation of both PKA and cyclic nucleotide-gated channels, and allow for local feedback control of adenylyl cyclase. Localized cAMP signals should also facilitate the differential regulation of cellular targets.
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PMID:Cyclic nucleotide-gated channels colocalize with adenylyl cyclase in regions of restricted cAMP diffusion. 1091 62

Chronic opioid regulation of stimulatory receptor activity was investigated in neuroblastoma x glioma (NG108-15) hybrid cells stably transfected to express the human beta(2)-adrenoceptor (beta(2)-AR). Expressed beta(2)-ARs are functionally coupled to G proteins and display ligand-independent signalling activity, as demonstrated by the ability of an inverse agonist to attenuate basal adenylyl cyclase (AC) activity. Despite the relative increase in basal AC activity due to the development of tolerance/dependence, chronic morphine treatment was found to completely abolish spontaneous beta(2)-AR activity by reducing basal receptor/G protein precoupling. A similar chronic opioid effect was observed in transiently transfected COS-7 cells. These results indicate that during the state of opioid tolerance/dependence basal levels of AC activity are no longer under the control of spontaneously active stimulatory receptors.
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PMID:Opioid tolerance/dependence in neuroblastoma x glioma (NG108-15) hybrid cells is associated with a reduction in spontaneous stimulatory receptor activity. 1109 59

While the cytoskeleton is known to play several roles in the biology of the cell, one role, which has been revealed only recently, is that of a participant in the signal transduction process. Tubulin binds specifically to the alpha subunits of Gs (stimulatory GTP-binding regulatory protein of adenylyl cyclase), Gi1 (inhibitory protein of adenylyl cyclase), and Gq and transactivates those molecules through direct transfer of GTP. The relevance of this transactivation process to G proteins which are normally activated by a neurotransmitter-occupied receptor is the subject of this study. C6 glioma cells, made permeable with saponin, retained tight coupling between Gs and the beta-adrenergic receptor. Although 5-guanylylimidodiphosphate (GppNHp) was incapable of activating Gs (and subsequently, adenylyl cyclase) in the absence of agonist, tubulin with GppNHp bound (tubulin-GppNHp) activated adenylyl cyclase with an EC(50) of 30 nM. Desensitization of beta-adrenergic receptors by isoproterenol exposure had no effect on the ability of tubulin-GppNHp to activate Gs and adenylyl cyclase. When the photoaffinity GTP analog, azidoanilido GTP (AAGTP; P3(4-azidoanilido)-P1-5'-GTP), was added to C6 membranes or permeable C6 cells, it was only weakly incorporated by G alpha s in the absence of isoproterenol. When the same concentration of dimeric tubulin with AAGTP bound was introduced, AAGTP was transferred from tubulin to G alpha s, activating the latter species. Similar 'preferential' activation of G alpha s by tubulin-AAGTP versus the free nucleotide was seen using purified components. Thus, membrane-associated tubulin may serve to activate G alpha s, independent of signals not normally coupled to that protein. Tubulin may act as an agent to link a variety of membrane-associated signalling systems.
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PMID:Tubulin stimulates adenylyl cyclase activity in C6 glioma cells by bypassing the beta-adrenergic receptor: a potential mechanism of G protein activation. 1114 91


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