Biphasic regulation of adenylate cyclase by cholera toxin in neuroblastoma x glioma hybrid cells is due to the activation and subsequent loss of the alpha subunit of the stimulatory GTP binding protein (GS).
Exposure of neuroblastoma x glioma hybrid (NG108-15) cells to low concentrations of cholera toxin produced a stimulation of both basal and forskolin-amplified adenylate cyclase activity in membranes prepared from these cells. Higher concentrations of cholera-toxin reversed this effect. Mn2+ activation of adenylate cyclase indicated that this effect was not due to a modification of the intrinsic activity of this enzyme. Cholera toxin was demonstrated to produce a concentration and time-dependent loss of GS alpha from membranes of these cells. Loss of GS alpha from membranes of these cells was preceded by its ADP-ribosylation. The effects of cholera toxin were specific for GS alpha, as no alterations in levels of the pertussis toxin-sensitive G-proteins Gi2, Gi3 and Go, were noted in parallel. Equally, no alteration in levels of G-protein beta-subunit were produced by the cholera toxin treatment. These experiments demonstrate that cholera toxin-catalysed ADP-ribosylation does not simply maintain an activated population of GS at the plasma membrane and that alterations in levels of GS at the plasma membrane can modify adenylate cyclase activity.
Macleod
K G
KG
Department of Biochemistry, University of Glasgow, Scotland, U.K.
Milligan
G
G
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism*; D002772:Cholera Toxin / Q000494:pharmacology*; D005576:Colforsin / Q000494:pharmacology; D015536:Down-Regulation; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005910:Glioma; D006822:Hybrid Cells; D008969:Molecular Sequence Data; D009447:Neuroblastoma; D014407:Tumor Cells, Cultured
D005576:Colforsin; D000246:Adenosine Diphosphate Ribose; D002772:Cholera Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases