title: Inhibition by cyclic AMP of guanine nucleotide-induced activation of phosphoinositide-specific phospholipase C in human platelets.
abstract: Phosphoinositide-specific phospholipase C (PLC) activity of human platelet membranes was activated by the nonhydrolyzable guanine nucleotide GTP gamma S. This activation did not occur in either membranes prepared from dibutyryl cyclic AMP-pretreated platelets (A-membranes) or those prepared from untreated cells and subsequently incubated with cyclic AMP (cAMP) (B-membranes). This cAMP-mediated inhibition was abolished in the presence of inhibitors of cAMP-dependent protein kinase (A-kinase), suggesting that the inhibition was due to phosphorylation of (a) protein component(s). No significant differences were observed in the basal PLC activity and the extent of pertussis toxin-catalyzed ADP-ribosylation among control membranes and the two types of phosphorylated membranes (A- and B-membranes). GTP-binding activities of Gs, Gi and GTP-binding proteins of lower molecular masses were not altered by the phosphorylation of the membranes. These findings suggest that a GTP-binding protein is involved in the GTP gamma S-mediated activation of PLC and that cAMP (plus A-kinase) inhibits this activation by phosphorylating a membrane protein (probably a 240-kDa protein), rather than the GTP-binding protein or PLC itself. It is likely that this phosphorylation uncouples the GTP-binding protein from PLC.
authors.affiliation: Department of Biochemistry, Gifu University School of Medicine, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yada
authors.forename: S
authors.initials: S
authors.lastname: Nagao
authors.forename: Y
authors.initials: Y
authors.lastname: Okano
authors.forename: Y
authors.initials: Y
authors.lastname: Nozawa
mesh_terms: D000345:Affinity Labels; D001792:Blood Platelets / Q000201:enzymology; D002462:Cell Membrane / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism; D007546:Isoquinolines / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D008970:Molecular Weight; D010750:Phosphoproteins / Q000378:metabolism; D013873:Thionucleotides / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D000345:Affinity Labels; D006150:Guanine Nucleotides; D007295:Inositol Phosphates; D007546:Isoquinolines; D008565:Membrane Proteins; D010750:Phosphoproteins; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C053177:N-(2-(methylamino)ethyl)-5-isoquinolinesulfonamide; D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins