Cholera toxin impairment of opioid-mediated inhibition of adenylate cyclase in neuroblastoma x glioma hybrid cells is due to a toxin-induced decrease in opioid receptor levels.
Cholera toxin treatment (up to 1 microgram/ml, 16 h) of neuroblastoma x glioma hybrid NG108-15 cells produced a decrease of some 35% in both delta opioid receptor-mediated stimulation of high-affinity GTPase activity and inhibition of forskolin-amplified adenylate cyclase. Coincident with these decreases was a down-regulation of some 35% in the delta opioid receptor population. A similar pattern of a decrease in signalling capacity was noted for the alpha 2B-adrenergic receptor in these cells after cholera toxin treatment. Half-maximal effects of cholera toxin on all of the parameters assayed were noted at concentrations between 2 and 5 ng/ml. Neither levels of Gi2, as assessed by immunoblotting with specific antisera, nor the intrinsic activity of the alpha subunit of the guanine-nucleotide-binding protein which acts as the inhibitory G-protein of the adenylate cyclase in these cells, as assessed by guanosine 5'-[beta gamma-imido]triphosphate (Gpp[NH]p)-mediated inhibition of adenylate cyclase, was lowered by cholera toxin treatment. Furthermore, levels of another pertussis toxin-sensitive G-protein (Go) expressed by these cells was also not lowered by cholera toxin treatment. However, as previously noted in other cells [Milligan, Unson & Wakelam (1989) Biochem. J. 262, 643-649], marked down-regulation of the alpha subunit of the stimulatory G-protein (Gs) of the adenylate cyclase cascade was observed in response to cholera toxin treatment. Previous studies [Klee, Milligan, Simonds & Tocque (1985) Mol. Aspects Cell Regul. 4, 117-129] have shown that cholera toxin treatment can result in a decrease in the maximal effectiveness of agonists which function to inhibit adenylate cyclase. These data have been used as evidence to suggest a functional interaction between Gs and 'Gi'. The results provided herein demonstrate that such effects of the toxin can be explained adequately by a decrease in the number of receptors that function to produce inhibition of adenylate cyclase.
McKenzie
F R
FR
Department of Biochemistry, University of Glasgow, Scotland, U.K.
Milligan
G
G
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000068438:Brimonidine Tartrate; D002772:Cholera Toxin / Q000494:pharmacology*; D005576:Colforsin / Q000494:pharmacology; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D005910:Glioma / Q000201:enzymology*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006822:Hybrid Cells / Q000201:enzymology*; D015151:Immunoblotting; D009447:Neuroblastoma / Q000201:enzymology*; D037342:Pertussis Toxin; D011810:Quinoxalines / Q000494:pharmacology; D011957:Receptors, Opioid / Q000502:physiology*; D017465:Receptors, Opioid, delta; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000316:Adrenergic alpha-Agonists; D011810:Quinoxalines; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D006165:Guanylyl Imidodiphosphate; D000068438:Brimonidine Tartrate; D016308:Enkephalin, Leucine-2-Alanine; D002772:Cholera Toxin; D037342:Pertussis Toxin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins