title: Inhibition of cyclic AMP-dependent protein kinase by the polar head group of an insulin-sensitive glycophospholipid.
abstract: A glycophospholipid has been purified from rat liver membranes and shown to copurify with an insulin-sensitive glycophospholipid isolated from H35 hepatoma cells. The polar head group of this glycophospholipid is a phospho-oligosaccharide generated by treatment with phosphatidylinositol-specific phospholipase C from Staphylococcus aureus. It has been proposed that this phospho-oligosaccharide, which is also generated in response to insulin, may play a role in insulin action. Incubation of the catalytic subunit of cyclic AMP-dependent protein kinase with this phospho-oligosaccharide inhibited the activity of the kinase to phosphorylate histone IIA, a purified preparation of phospholipid methyltransferase and kemptide, a phosphate-accepting peptide. Inhibition of kinase activity was dose-dependent and 50% inhibition of histone phosphorylation was demonstrated with a concentration of phospho-oligosaccharide of around 2 microM. This effect was demonstrated in the presence of ATP at concentrations up to 1 mM, indicating that the phospho-oligosaccharide acts at physiological concentrations of ATP and that it does not compete with this nucleotide for the same binding site in the kinase. Inhibition by the phospho-oligosaccharide of kinase activity could be reversed by dilution or dialysis and was not reproduced by up to 50 microM myo-inositol, glucosamine, galactose, myo-inositol 1-phosphate, glucosamine 1-phosphate, galactose 1-phosphate or phosphorylcholine. The inhibitory activity was resistant to mild acid treatment but was labile to treatment with alkali, exposure to nitrous acid or incubation with sodium periodate. The phospho-oligosaccharide had no effect on the phosphorylation of lysine-rich histone by rat brain protein kinase C and on the binding of cyclic AMP to a cyclic AMP-dependent protein kinase. In conclusion, the data in this study suggested that a phospho-oligosaccharide generated from an insulin-sensitive glycophospholipid may play a role in insulin action by modulating cyclic AMP-dependent protein kinase activity.
authors.affiliation: Fundacion Jimenez Diaz, Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Villalba
authors.forename: K L
authors.initials: KL
authors.lastname: Kelly
authors.forename: J M
authors.initials: JM
authors.lastname: Mato
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology; D002417:Cattle; D002462:Cell Membrane / Q000032:analysis; D007295:Inositol Phosphates; D007700:Kinetics; D008099:Liver / Q000502:physiology*; D008114:Liver Neoplasms, Experimental / Q000032:analysis; D008563:Membrane Lipids / Q000494:pharmacology*; D009206:Myocardium / Q000201:enzymology; D009844:Oligosaccharides / Q000302:isolation & purification / Q000494:pharmacology*; D011134:Polysaccharides; D047428:Protein Kinase Inhibitors; D051381:Rats; D010738:Type C Phospholipases
chemical_list: D007295:Inositol Phosphates; D008563:Membrane Lipids; D009844:Oligosaccharides; D011134:Polysaccharides; D047428:Protein Kinase Inhibitors; C028039:inositol phosphate glycan; D010738:Type C Phospholipases