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PubMed1976

[Presence of monogalactosyl diglyceride in the rat nerve sciatic].

We present a pattern of fractionation of total lipids, leading to the isolation of individual glycolipids, MGDG contains as sugars, a high quantity of galactose and a low level of glucose. The study of the fatty acids distribution shows: a) a high level of saturated short chains fatty acids, b) a high level of palmitic acid (C 16:0, 68% of the total).

Animals↗
PubMed1991

Dissociation of protein kinase C activation and sn-1,2-diacylglycerol formation. Comparison of phosphatidylinositol- and phosphatidylcholine-derived diglycerides in alpha-thrombin-stimulated fibroblasts.

Diacylglycerols (DAGs) derived from phosphatidylcholine (PC) hydrolysis have been shown to activate protein kinase C (PKC) in vitro, but it is not known whether this event occurs in response to DAGs generated via agonist-induced PC hydrolysis in intact cells. In this report we have addressed this question directly, using alpha-thrombin stimulation of IIC9 fibroblasts. PKC activation in intact cells was assessed in two ways, by measuring: 1) PKC membrane association as determined by kinase activity and Western blot analysis and 2) the phosphorylation of an endogenous PKC substrate, an 80-kDa protein. Treatment with 500 ng/ml alpha-thrombin has been shown to stimulate both phosphoinositide and PC hydrolysis, whereas treatment with 100 pg/ml alpha-thrombin stimulates only PC breakdown. Using these two conditions, we show that DAG produced from phosphoinositide, but not PC hydrolysis, is associated with the activation of PKC.

Animals↗
PubMed1989

[The role of calcium, diglyceride ester bindings and a synthetic polypeptide in protein kinase C activation].

Protein kinase C, which plays a significant role in the polyphosphoinositide pathway of transmembrane signaling, is activated by a large class of extracellular ligands including neurotransmitters, hormones and growth factors. Diacylglycerols are the intracellular mediators of protein kinase C activation. Tumor promoting phorbol esters mimic the diacylglycerol action in binding to the same site. Active diacylglycerols have the 1.2 sn configuration and saturated short chain or unsaturated long chain fatty acids. Alkyl analogs of diacylglycerols were devoid of activity when an ether bond was present in position 1, whereas activity of the alkyl analog in position 2 was retained. Protein kinase C activation and 3H-TPA binding to the enzyme occurred in the presence of 0.5 mM EGTA. Moreover it has been shown in vivo that full activation of the enzyme was obtained in the intact platelets loaded with an excess of Quin 2, prior to stimulation by phorbol esters. A peptide (residues 499-513) was synthesized which enhanced the affinity of protein kinase C for histone. It is suggested that it may be the receptor site for another peptide of the enzyme (residues 19 to 36) which behaves as a pseudosubstrate.

Animals↗
PubMed1989

Phosphatidylcholine hydrolysis by phospholipase D determines phosphatidate and diglyceride levels in chemotactic peptide-stimulated human neutrophils. Involvement of phosphatidate phosphohydrolase in signal transduction.

Human neutrophils have been labeled in 1-O-alkyl-phosphatidylcholine (alkyl-PC) with 32P by incubation with alkyl-[32P]lysoPC. Upon stimulation with the chemotactic peptide, formylMet-Leu-Phe (fMLP), these 32P-labeled cells produce 1-O-alkyl-[32P]phosphatidic acid (alkyl-[32P]PA) and, in the presence of ethanol, 1-O-alkyl-[32P]phosphatidylethanol (alkyl-[32P]PEt). Because the cellular ATP contains no 32P, alkyl-[32P]PA and alkyl-[32P]PEt must be formed from alkyl-[32P]PC by phospholipase D (PLD)-catalyzed hydrolysis and transphosphatidylation, respectively. Analyses of the sn-1 bonds by selective hydrolysis and mass measurements reveal that the PA and PEt formed during stimulation contain both ester and ether bonds with distributions similar to that in the endogenous PC. Furthermore, in neutrophils labeled in alkyl-[32P]PC, the specific activities of the diradyl-PA and diradyl-PEt formed during stimulation are similar to that of diradyl-PC. These results demonstrate that the fMLP-induced PLD utilizes diradyl-PC as the major substrate. It is further concluded that, at early times (30 s), PA and PEt are both formed almost exclusively by PLD. Following stimulation with fMLP, neutrophils double-labeled in alkyl-PC by incubation with [3H]alkyl-lysoPC and alkyl-[32P]lysoPC generate [3H]alkyl-DG and [32P]orthophosphate [( 32P]PO4) with superimposable kinetics, indicating degradation of PA by a phosphohydrolase. Generation of [3H]alkyl-DG and [32P]PO4 lags behind PA formation and parallels the decline in PA accumulation. In addition, generation of both [3H]alkyl-PA and [3H]alkyl-DG requires extracellular Ca2+ and cytochalasin B. Furthermore, the phosphohydrolase inhibitor, propranolol, decreases both [3H]alkyl-DG and [32P]PO4 while increasing [3H]alkyl-PA and not altering [3H]alkyl-PEt. Moreover, the decreases in DG are accounted for by increases in PA. These results demonstrate that PLD-derived alkyl-PA is degraded by a phosphohydrolase to produce alkyl-DG. DG formed during stimulation contains both ester and ether-linked species and this DG formation is inhibited completely by propranolol. Upon stimulation, alkyl-[32P]PC-labeled neutrophils do not produce [32P]phosphocholine, suggesting that PC is not hydrolyzed by phospholipase C. In addition, PA is formed in amounts sufficient to account for all of the DG formed during stimulation. It is concluded that the DG formed during fMLP stimulation is derived almost exclusively from PC via the PLD/PA phosphohydrolase pathway.

Diglycerides↗
PubMed1985

B cell activation. VI. Effects of exogenous diglyceride and modulators of phospholipid metabolism suggest a central role for diacylglycerol generation in transmembrane signaling by mIg.

Previous evidence indicates that in vitro activators of protein kinase C, such as phorbol myristate acetate (PMA), are able to induce early activation events in murine B cells, including membrane depolarization and increased I-A antigen expression. These same events are induced by specific antigen and anti-receptor antibody. This evidence suggests that protein kinase C activation may be an important intermediary event in mIg-mediated transmembrane signaling. Previously, investigators have suggested that protein kinase C activation is regulated by a novel second messenger, diacylglycerol (DG), and DG is generated by phosphatidylinositol (PI) hydrolysis after receptor-ligand interaction in many systems. In view of this concept, we examined the effects of nonspecific activators and inhibitors of DG production and DG itself on membrane potential and levels of I-A antigen expression in murine B cells. Our results indicate that exposure to DG, or induction of DG production by treatment of B cells with exogenous phospholipase C, results in depolarization and increased I-A antigen expression similar to that induced by anti-receptor antibody and specific antigen. Furthermore, we demonstrate that depolarization and increased I-A expression induced by anti-receptor antibody is blocked under conditions in which DG production is inhibited. As expected, based on its direct activation of protein kinase C, PMA stimulation is unaffected by this inhibition. These results support our earlier hypothesis that occupancy of antigen receptors on B cells is linked to subsequent activation events by PI hydrolysis, DG generation, and protein kinase C activation.

Animals↗
PubMed1986

Effects of phorbol esters, diglyceride, and cholinergic agonists on the subcellular distribution of protein kinase C in intact or digitonin-permeabilized adrenal chromaffin cells.

Phorbol esters which activate protein kinase C increased the percentage of membrane-bound protein kinase C activity in bovine adrenal chromaffin cells from less than 10 to 20-50% within 30 min. Permeabilization of chromaffin cells with digitonin in the absence of Ca2+ and phorbol esters caused virtually 100% of the protein kinase C activity to leave the cells within 1 h, which is consistent with protein kinase C being soluble and cytosolic. However, if cells were incubated for 15-30 min with 12-O-tetradecanoylphorbol-13-acetate (TPA) prior to permeabilization, 50-60% of the protein kinase C activity exited from the cells within 1 h of permeabilization. In cells not incubated with phorbol ester, permeabilization in the presence of 1-10 microM Ca2+ also decreased the rate at which protein kinase C exited from the cells. The slower release of protein kinase C caused by prior incubation of the cells with TPA or because of the presence of micromolar Ca2+ in permeabilized cells was associated with increased membrane-bound protein kinase C. The effects of TPA and permeabilization in the presence of micromolar Ca2+ were approximately additive. Active phorbol esters had different abilities to cause retention of protein kinase C in digitonin-treated cells. Dioctanoylglycerol, which activates protein kinase C in vitro and enhanced Ca2+-dependent secretion from permeabilized chromaffin cells similarly to TPA, also increased membrane-bound protein kinase C in intact cells, but had no effect on the retention of protein kinase C in permeabilized cells in the presence or absence of Ca2+. The different abilities of protein kinase C activators to cause retention of protein kinase C in subsequently permeabilized cells suggest differences in the reversibility of the binding. The mixed nicotinic-muscarinic agonist carbachol and the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium, but not the muscarinic agonist muscarine, caused 3-10% of the total protein kinase C activity to become membrane-bound within 3 min in intact chromaffin cells. Thus, nicotinic stimulation of chromaffin cells may rapidly activate protein kinase C.

Adrenal Medulla↗