title: Insulin-stimulated diacylglycerol production results from the hydrolysis of a novel phosphatidylinositol glycan.
abstract: We recently described the insulin-dependent release of a carbohydrate substance from plasma membranes which regulated certain intracellular enzymes (Saltiel, A. R., and Cuatrecasas, P. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 5793-5797). This enzyme-modulating substance appeared to arise from the phosphodiesterase hydrolysis of a novel inositol-containing glycolipid. This is supported by observations that insulin stimulated the rapid generation of [3H]myristate-labeled diacylglycerol in cultured BC3Hl myocytes. Myristoyl diacylglycerol production in these cells was unaffected by epinephrine, although arachidonate-labeled diacylglycerol was rapidly produced in response to stimulation by this alpha-1 adrenergic agent. The production of distinct species of diacylglycerol was apparently due to hormonally specific hydrolysis of different precursors. A novel glycolipid was identified on silica TLC or high pressure liquid chromatography which served as a substrate for the insulin-stimulated phosphodiesterase reaction. This glycolipid was metabolically labeled with radioactive inositol, glucosamine, and myristic acid, suggesting a phosphatidylinositol (PI)-glycan structure. Treatment of this glycolipid with a PI-specific phospholipase C resulted in the generation of two products: an inositol phosphate-glycan which modulated the activity of the low Km cAMP phosphodiesterase and myristoyl diacylglycerol. Insulin caused the rapid hydrolysis of the PI-glycan, which was then apparently resynthesized. These data further suggest that insulin stimulates the activity of a phospholipase C which selectively hydrolyzes a novel PI-glycan, releasing a carbohydrate enzyme modulator as well as a unique species of diacylglycerol.
mesh_terms: D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D004075:Diglycerides / Q000096:biosynthesis*; D005944:Glucosamine / Q000378:metabolism; D005989:Glycerides / Q000096:biosynthesis*; D006868:Hydrolysis; D007294:Inositol / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism; D019814:Myristic Acid; D009227:Myristic Acids / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D004075:Diglycerides; D005989:Glycerides; D007328:Insulin; D009227:Myristic Acids; D010716:Phosphatidylinositols; D019814:Myristic Acid; D007294:Inositol; D010738:Type C Phospholipases; D005944:Glucosamine