Insulin-Stimulated Hydrolysis of a Novel Glycolipid Generates Modulators of cAMP Phosphodiesterase

Abstract

Insulin action may involve the intracellular generation of low molecular weight substances that modulate certain key enzymes. The production of two substances that regulate the activity of adenosine 3',5'-monophosphate phosphodiesterase was evaluated in cultured myocytes by incorporation of radiolabeled precursors. Insulin caused the rapid hydrolysis of a chemically undefined membrane glycolipid, resulting in the production of two related complex carbohydrates as well as diacylglycerol. Both the glycolipid precursor and the aqueous products were monitored by labeling with radioactive inositol and glucosamine. Depletion of the labeled precursor and the appearance of labeled water-soluble products and diacylglycerol occurred within 30 seconds after hormone treatment and was followed by rapid resynthesis of the precursor. The aqueous products that were radioactively labeled appeared chromatographically and electrophoretically identical to phosphodiesterase modulating activities produced by insulin from the same cells. The purified radiolabeled and bioactive substances had similar chemical properties. Hydrolysis of the glycolipid precursor and subsequent generation of products could be reproduced by incubation of extracted lipids with a phosphatidylinositol-specific phospholipase C. These studies suggest that insulin stimulates an endogenous, selective phospholipase C activity that hydrolyzes a novel glycolipid, resulting in the generation of a complex carbohydrate-phosphate substance containing inositol and glucosamine that may mediate some of the actions of the hormone.

Insulin-like Growth Factors Mediate Heterotrimeric G Protein-dependent ERK1/2 Activation by Transactivating Sphingosine 1-Phosphate Receptors

“…In cultured myocytes, insulin-stimulated processing of the inositol phosphate glycan anchors of membrane proteins requires both regulated proteolysis and pertussis toxin-sensitive G protein-dependent activation of a phosphatidylinositol-specific isoform of phospholipase C (15)(16)(17)(18). In Rat1 fibroblasts, IGF-1-stimulated activation of the ERK1/2 mitogen-activated protein kinase cascade is largely pertussis toxin-sensitive and can be blocked by expressing a G␤␥ subunit sequestrant peptide derived from the C terminus of G proteincoupled receptor kinase 2 (GRK2ct) (19).…”

Asymmetric distribution of the phosphatidylinositol‐linked phospho‐oligosaccharide that mimics insulin action in the plasma membrane

“…1 .27). pase C) from Staphylococcus aureus [I, 2, 61; (b) the presence of inositol monophosphate linked to non-N-acetylated glucosamine [1,2,5,61; (c) the presence of a disaturated diacylglycerol moiety [l , 21. Since the glycosyl-Ptdlns anchor of membrane proteins is localized at the outer surface of the cell, we postulated that the insulin-sensitive glycosyl-PtdIns might also be present at the cell surface.…”

Increased protein synthesis response to insulin in fibroblasts treated with the diacylglycerol kinase inhibitor R59022

“…The signal mechanisms by which insulin exerts these effects are only partly understood; insulin binds to a receptor in the cell plasma membrane and this leads to the generation and release from the membrane of one or more signal molecules [7,8]. Peptide mediators [9], glycophosphoinositides [10,11] and DAG [12] have Correspondence address: J.E. Hesketh, Biochemistry Division, Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB2 9SB, Scotland been implicated in the control of fat and carbohydrate metabolism by insulin while phospholipase C activation, DAG and protein kinase C have been suggested to be involved in the signal mechanism whereby insulin stimulates protein synthesis [13,141. The aim of the present work was to use an inhibitor of DAG kinase to investigate further the role of DAG as a signal in the sequence of events by which insulin stimulates protein synthesis in 3T3 fibroblasts.…”