Lipid A stimulates phospholipase D activity in rat mesangial cells via a G-protein.
Stimulation of mesangial cells (MC) with the bacterial endotoxin Lipid A activated two enzymes involved in lipid metabolism. First, a phospholipase D hydrolyses phosphatidylethanolamine (PE) to phosphatidic acid (PA), followed by dephosphorylation of PA to 1,2-diacylglycerol (DAG) by PA phosphohydrolase. MC or microsomes from these cells were pre-labelled with [3H]glycerol. A 30-60 s stimulation with 10-100 ng of Lipid A/ml caused a decrease in [3H]glycerol in PE and increased radioactive glycerol in PA. The enzyme responsible for this hydrolysis preferred PE containing unsaturated acyl side chains. DAG was formed from PA within the first 1 min after Lipid A stimulation. Microsomes incubated with 25 mM-NaF to inhibit phospholipase C and to stimulate GTP-binding proteins also caused PE to be converted into PA. The [3H]glycerol and acyl mass of phosphatidylcholine, phosphatidylserine and phosphatidylinositol did not change with either Lipid A or NaF. Addition of guanosine 5'-[gamma-thio]triphosphate to MC microsomes caused the rapid decrease in proportion of PE and increase in PA, followed by an increase in DAG unsaturated acyl mass. These data suggest the concurrent G-protein-dependent activation by Lipid A of a PE-directed phospholipase D and a PA phosphohydrolase.
Harrris
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Neurochemistry Laboratory, Veterans Affairs Medical Center, Seattle, WA 98108.
Bursten
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D000818:Animals; D004075:Diglycerides / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000502:physiology*; D005920:Glomerular Mesangium / Q000201:enzymology*; D005990:Glycerol / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007700:Kinetics; D008050:Lipid A / Q000494:pharmacology*; D013058:Mass Spectrometry; D008861:Microsomes / Q000378:metabolism; D010712:Phosphatidic Acids / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010739:Phospholipase D / Q000378:metabolism*; D051381:Rats; D012969:Sodium Fluoride / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
C011439:1,2-diacylglycerol; D004075:Diglycerides; D008050:Lipid A; D010712:Phosphatidic Acids; D010714:Phosphatidylethanolamines; D010566:Virulence Factors, Bordetella; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D012969:Sodium Fluoride; D010739:Phospholipase D; D019204:GTP-Binding Proteins; D005990:Glycerol