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)

Desensitization of the responsiveness to hormones or drugs is often mediated by down-regulation of receptors. The stimulatory coupling protein (Ns) of adenylate cyclase has been shown to be involved in the down-regulation of stimulatory beta-adrenergic receptors. Whether the inhibitory coupling protein (Ni) is involved in the down-regulation of receptors that inhibit adenylate cyclase is not known. We wished to determine whether down-regulation of inhibitory muscarinic cholinergic and alpha 2-adrenergic receptors occurs in neuroblastoma X glioma hybrid cells after the ability of Ni to inhibit adenylate cyclase is inactivated by pertussis toxin. After treatment of cells with pertussis toxin, the ability of carbachol or epinephrine to inhibit prostaglandin E1-stimulated cAMP accumulation in intact cells was either completely prevented or markedly attenuated, respectively, indicating functional inactivation of Ni. Furthermore, pertussis toxin treatment of membrane fragments from these cells did not result in labeling of the 41,000-dalton alpha-subunit of Ni with ADP ribose from [32P] NAD, indicating maximal ADP ribosylation of Ni by prior treatment of cells with pertussis toxin. Carbachol treatment of cells resulted in down-regulation of muscarinic cholinergic receptors to 45.7 +/- 12.5% and 52.5 +/- 13.5% of control values for toxin-untreated and toxin-treated cells, respectively. Epinephrine treatment of cells caused homologous desensitization of alpha 2-receptor-mediated inhibition of cAMP accumulation and down-regulation of alpha 2-adrenergic receptors to 42.9 +/- 11.4% and 53.2 +/- 5.3% of control values for toxin-untreated and toxin-treated cells, respectively. Down-regulation of muscarinic cholinergic receptors by carbachol and of alpha 2-adrenergic receptors by epinephrine was not due to the effect of retained agonist and was agonist specific, since it could be prevented by the antagonists atropine and yohimbine, respectively. We conclude that agonist-mediated down-regulation of both the muscarinic cholinergic receptor and the alpha 2-adrenergic receptor does not require functional inhibitory coupling.
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PMID:Agonist-induced down-regulation of muscarinic cholinergic and alpha 2-adrenergic receptors after inactivation of Ni by pertussis toxin. 242 98

In neuronal cells, opioid peptides and opiates inhibit neurotransmitter release, which is a calcium-dependent process. They also inhibit adenylyl cyclase, presumably via the membrane signal-transducing component, Gi, a guanine nucleotide-binding protein (G-protein). No causal relationship between these two events has yet been demonstrated. Besides Gi, membranes of neuronal tissues contain large amounts of Go, a G-protein with unknown function. Both G-proteins are heterotrimers consisting of alpha-, beta- and gamma-subunits; the alpha-subunits can be ADP-ribosylated by an exotoxin from Bordetella pertussis (PT), which modification inhibits receptor-mediated activation of the G-protein. It was recently shown that noradrenaline, dopamine and gamma-aminobutyric acid (GABA) inhibit the voltage-dependent calcium channels in dorsal root and sympathetic ganglia; this inhibition is mimicked by intracellular application of guanine nucleotides and blocked by PT, suggesting the involvement of a G-protein. Here we report an inhibitory effect of the opioid D-Ala2, D-Leu5-enkephalin (DADLE) on the calcium current (ICa) in neuroblastoma X glioma hybrid cells (N X G cells). Pretreatment with PT almost completely abolishes the DADLE effect. The effect is restored by intracellular application of Gi and Go. As the alpha-subunit of Go (with or without beta-gamma complex) is 10 times more potent than Gi, we propose that Go is involved in the functional coupling of opiate receptors to neuronal voltage-dependent calcium channels.
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PMID:The GTP-binding protein, Go, regulates neuronal calcium channels. 243 90

Chronic pertussis toxin treatment (5 days) of NG108-15 neuroblastoma X glioma hybrid cells had no significant effect on basal cyclic AMP levels whereas it effectively blocked the inhibitory action of acute (10 min) exposure of carbachol (10(-4)M) on intracellular cyclic AMP accumulation, stimulated by prostaglandin E1. This action of pertussis toxin was found to be long lasting: exposure of the cells to pertussis toxin (100 ng/ml) for only 24 h followed by a 5-day withdrawal period still was shown effective on day 7 in abolishing the inhibitory action of carbachol on prostaglandin E1-stimulated cyclic AMP production. Chronic exposure (5 days) of NG108-15 cells to carbachol (10(-5)M) causes an increase in basal cyclic AMP levels by 98%, and a desensitization of the muscarinic inhibition of cyclic AMP accumulation, assessed after a 24-h withdrawal period. When carbachol treatment is carried out in the presence of pertussis toxin (100 ng/ml) both of these effects of carbachol are abolished.
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PMID:Chronic exposure to pertussis toxin alters muscarinic receptor-mediated regulation of cyclic AMP metabolism in neuroblastoma x glioma NG108-15 hybrid cells. 245 96

Stimulation of muscarinic cholinergic receptors in SK-N-SH human neuroblastoma cells resulted in a 1.5-4 fold increase in intracellular cAMP levels. This unusual response was sensitive to atropine and pirenzepine but insensitive to pertussis toxin. It was observable regardless of whether basal, PGE1- or forskolin-stimulated cAMP levels were measured. The half-maximal concentration for carbachol-stimulation of cAMP levels (6 microM) was similar to that for the previously determined carbachol-induced stimulation of phosphoinositide turnover in these cells, suggesting that the former is mediated by the latter. These data indicate that cross-talk between the phosphoinositide turnover system and the adenylate cyclase system results in increased cAMP levels in SK-N-SH cells in response to muscarinic receptor stimulation.
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PMID:Muscarinic receptor-mediated increase in cAMP levels in SK-N-SH human neuroblastoma cells. 245 66

Five different pertussis-toxin-sensitive guanine-nucleotide-binding proteins (G proteins) were purified from bovine brain. Immunochemical characterization of alpha subunits identified two G alpha o proteins (G alpha o-I and G alpha o-II), two 41-kDa G alpha i proteins (G alpha i-I and G alpha i-II) and the 40-kDa G alpha i2 protein. Site-directed antisera specific for G alpha o proteins did not differentiate between G alpha o-I and G alpha o-II. However, in situ peptide mapping using polyacrylamide gel electrophoresis revealed distinct cleavage products with different proteases for each of these proteins. Additionally comparison of Rf values demonstrated a slightly faster migration for G alpha o-II than for G alpha o-I, which is the only type of G alpha o protein present in cell membranes of the neuroblastoma/glioma cell line NG 108-15. The importance of these structural differences and possible functional implications are discussed.
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PMID:Purification and characterization of subforms of the guanine-nucleotide-binding proteins G alpha i and G alpha o. 250 13

Each of a range of pharmacological agents which function to increase intracellular levels of cAMP caused a morphological 'differentiation' of neuroblastoma x glioma hybrid, NG108-15, cells grown in tissue culture. Associated with this differentiation, increased incorporation of [32P]ADP-ribose catalysed by pertussis toxin was noted into a band of some 39-40 kDa in membranes derived from these cells. Immunoblotting using two antipeptide antisera which identify different regions of Go alpha demonstrated marked increases in the levels of this polypeptide in membranes of the differentiated cells. However, levels of the beta-subunit did not increase appreciably with differentiation.
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PMID:Elevated levels of the guanine nucleotide binding protein, Go, are associated with differentiation of neuroblastoma x glioma hybrid cells. 253 44

Bordetella pertussis produces a calmodulin-sensitive adenylate cyclase that is associated with the whole bacteria and released into its culture media. Preparations of this enzyme invade animal cells, causing elevations in intracellular cAMP levels. Cell-associated adenylate cyclase accounted for 28% of the total adenylate cyclase activity while 72% was released into the culture supernatant. Over 90% of the cell-associated adenylate cyclase activity was sensitive to trypsin treatment of whole cells, indicating that the catalytic domain of the enzyme is localized on the outer surface of the bacterial cells. Enzyme activity was released from whole cells by treatment with SDS. This activity was resolved as a large form (Mr 215,000) by SDS-polyacrylamide gel electrophoresis. In contrast, the culture supernatant contained only the 45,000-dalton catalytic subunit. Enzyme activity released from spheroplasts by sonication was resolved into a large form (Mr 215,000) and a small form (Mr 45,000). The appearance of the small form with spheroplast formation was probably the result of proteolytic degradation. Antibodies generated against the catalytic subunit purified from culture supernatants cross-reacted with and immunoprecipitated both the large and small forms of adenylate cyclase isolated from bacterial cells. Furthermore, incubation of the cell-associated enzyme with a crude bacterial extract resulted in a time-dependent disappearance of the 215,000-dalton form and a concomitant increase in the amount of the smaller 45,000-dalton form. There was also a parallel increase in the ability of the cell-associated preparation to elevate intracellular cAMP levels in N1E-115 mouse neuroblastoma cells.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Characterization of the bacterial cell associated calmodulin-sensitive adenylate cyclase from Bordetella pertussis. 254 Jul 97

Forskolin and vasoactive intestinal polypeptide (VIP) were shown to increase cyclic AMP accumulation in a human neuroblastoma cell line, SK-N-SH cells. The alpha 2-adrenergic agonist UK 14304 decreased forskolin-stimulated cyclic AMP levels by 40 +/- 2%, with an EC50 of 83 +/- 20 nM. This response was blocked by pretreatment with pertussis toxin (PT) (EC50 = 1 ng/ml) or by the alpha 2-antagonists yohimbine, idazoxan, and phentolamine. Antagonist IC50 values were 0.3 +/- 0.1, 2.2 +/- 0.3, and 1.4 +/- 0.1 microM, respectively. This finding suggests the presence of normal inhibitory coupling of SK-N-SH cell alpha 2-adrenergic receptors to adenylate cyclase via the inhibitory GTP-binding protein species, Gi. Muscarinic receptors in many target cell types are coupled to inhibition of adenylate cyclase. However, in SK-N-SH cells, muscarinic agonists synergistically increased (67-95%) the level of cyclic AMP accumulation elicited by forskolin or VIP. EC50 values for carbamylcholine (CCh) and oxotremorine facilitation of the forskolin response were 1.2 +/- 0.2 and 0.3 +/- 0.1 microM, respectively. Pharmacological studies using the muscarinic receptor subtype-preferring antagonists 4-diphenylacetoxy-N-methylpiperidine, pirenzepine, and AF-DX 116 indicated mediation of this response by the M3 subtype. IC50 values were 14 +/- 1, 16,857 +/- 757, and 148,043 +/- 16,209 nM, respectively. CCh-elicited responses were unaffected by PT pretreatment. Muscarinic agonist binding affinity was indirectly measured by the ability of CCh to compete for [3H]quinuclidinyl benzilate binding sites on SK-N-SH cell membranes.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Alpha 2-adrenergic and muscarinic cholinergic receptors have opposing actions on cyclic AMP levels in SK-N-SH human neuroblastoma cells. 254 24

When SK-N-SH human neuroblastoma cells were exposed to nicotine (NIC) or KCl they showed a dose-dependent transient increase (2- to 4-fold) in intracellular Ca2+ concentration ([Ca2+])i as detected by quin-2 fluorescence, with half maximal effects (EC50) observed at 13 microM and 26 mM, respectively. Tubocurarine and 1-isodihydrohistrionicotoxin potently blocked the NIC-evoked (IC50 congruent to 1 microM and 0.3 microM, respectively), but not the high [K+]o-evoked [Ca2+]i accumulation. The KCl-induced response was inhibited by verapamil and diltiazem (IC50 = 1.4 and 10.9 microM, respectively). Tetrodotoxin (3 microM) and tetraethylammonium (10 microM) had no effect on [Ca2+]i accumulation induced by either agent. Increases in [Ca2+]i could be evoked sequentially by NIC and KCl in the same cells suggesting independent mechanisms of Ca2+ entry. In a Ca2+-free medium, no response to either KCl or NIC was observed. However, when Ca2+ ions were restored, [Ca2+]i accumulation was enhanced to the same extent as cells suspended in a Ca2+-containing buffer. Long-term (18 hr) pretreatment of SK-N-SH cells with pertussis (100 ng/ml) or cholera toxins (10 nM) had no effect on NIC or KCl-induced [Ca2+]i accumulation. Together, these data demonstrate the presence of NIC receptors and voltage-sensitive Ca2+ channels on SK-N-SH neuroblastoma cells, through which [Ca2+]i may be modulated.
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PMID:Calcium influx mediated by nicotinic receptors and voltage sensitive calcium channels in SK-N-SH human neuroblastoma cells. 254 92

According to classical models of drug-receptor interactions, competitive antagonists share with agonists the ability to bind to a common site on the receptor molecule. However, they are different from agonists, as they cannot trigger the "stimulus" that leads to biological responses--i.e., they lack intrinsic activity. For those receptors whose signals are transduced to effector systems by GTP-binding regulatory proteins (G proteins), a mechanistic equivalent of such a stimulus is an increased ability of agonist-bound receptor to accelerate nucleotide exchange and thus GTPase activity on the G-protein molecule. Here we show that for a member of this family of receptors (delta opioid receptors in membranes of NG108-15 neuroblastoma-glioma cells), two types of competitive antagonists can be distinguished. One type has no intrinsic activity, since it neither stimulates nor inhibits the GTPase activity of G proteins and its apparent affinity for the receptor is not altered by pertussis toxin-mediated uncoupling of receptor and G protein. The second type, however, can inhibit GTPase and thus exhibits negative intrinsic activity; its affinity for receptors is increased following uncoupling from G proteins. The existence of antagonists with negative intrinsic activity may be a general feature of several classes of neurotransmitters or hormone receptors and calls for a reevaluation of biological effects produced by competitive antagonists.
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PMID:Antagonists with negative intrinsic activity at delta opioid receptors coupled to GTP-binding proteins. 255 39


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