Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this study an insulin-sensitive glycophospholipid from rat adipocytes was isolated and partially characterized. A material that activated pyruvate dehydrogenase was extracted from rat adipocyte membrane supernatants. Its release was stimulated by insulin and phosphatidylinositol-specific-phospholipase C and its activity was destroyed by nitrous acid deamination. These findings suggested that insulin might stimulate breakdown of a glycophospholipid containing inositol and glucosamine, as previously reported for some other cell types [Low & Saltiel (1988) Science 239, 268-275]. A lipid that incorporated [3H]glucosamine, [3H]galactose, [3H]inositol, and [3H]myristate and whose turnover was stimulated by insulin was subsequently isolated from intact adipocytes by sequential t.l.c. using an acidic solvent system followed by a basic solvent system. The effects of insulin on turnover of the lipid in these cells were transient, with maximal effects at 1 min, and there was a typical concentration-response curve to insulin (0.07 nM-7 nM), with effects being detected over the physiological range of insulin concentrations. In contrast with studies in other cells, there was appreciable turnover of the sugar labels. The majority of the [3H]glucosamine and [3H]galactose labels were cycled through to triacylglycerol in the adipocyte. However, of that recovered in the glycophospholipid band, a major proportion (less than 40%) was recovered as the native label. Digestion of the purified molecule with phosphatidylinositol-specific phospholipase C generated a material that activated both pyruvate dehydrogenase and low-Km cyclic AMP phosphodiesterase. Impairment in insulin-stimulated breakdown of the molecule in adipocytes of streptozotocin-diabetic rats was found, consistent with the impaired insulin activation of pyruvate dehydrogenase and glucose utilization seen in this model. These findings suggest that insulin stimulates breakdown of this glycophospholipid by stimulating an insulin-sensitive phospholipase in adipocytes. This compound may serve a function as a precursor for intracellular insulin mediators.
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PMID:Isolation of insulin-sensitive phosphatidylinositol-glycan from rat adipocytes. Its impaired breakdown in the streptozotocin-diabetic rat. 217 62

This study investigated the extent to which a purified phosphatidylinositol-specific and a commercial non-specific phospholipase C mimicked acute insulin action in rat adipocytes. The enzymes mimicked insulin stimulation of pyruvate dehydrogenase (PDH) and breakdown of a glycophospholipid proposed as a precursor for an intracellular mediator of insulin action, but were much less effective in stimulating glucose transport and utilization. These observations corroborate recent suggestions that insulin may activate a phospholipase C to generate a mediator that can account for insulin activation of PDH from a mediator precursor with a phosphatidylinositol anchor. This mediator precursor is probably an outer membrane component since effects were obtained with intact cells. It is unlikely that this mechanism accounts fully for insulin action since phosphatidylinositol-specific and commercial phospholipase C stimulation of glucose transport was significantly less than that elicited by insulin.
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PMID:Phospholipase C mimics insulin action on pyruvate dehydrogenase and insulin mediator generation but not glucose transport or utilization. 217 4

Some of the acute actions of insulin may be mediated by the intracellular generation of a chemical substance that modulates certain enzymes. Such a substance has been identified which is released from liver plasma membranes after exposure to insulin. This substance was purified on sequential ion exchange, reverse phase, and gel permeations columns. The purified substance modulated the activities of cAMP phosphodiesterase, adenylate cyclase, and pyruvate dehydrogenase. The activities that modulated each of these enzymes exhibited singular chromatographic behavior and sensitivity to a variety of chemical reagents. Each activity was also produced by treatment of membranes with a phosphatidylinositol-specific phospholipase C. These results suggested that each of the enzyme-modulating activities was due to a single complex carbohydrate substance which contained inositol, phosphate, glucosamine, and other monosaccharides. The actions of this substance on these three enzymes mimicked those of insulin, suggesting that the release of this enzyme modulator might play a role in mediating some of the actions of the hormone.
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PMID:Insulin generates an enzyme modulator from hepatic plasma membranes: regulation of adenosine 3',5'-monophosphate phosphodiesterase, pyruvate dehydrogenase, and adenylate cyclase. 302 92

The polar head group that was released by treating an insulin-sensitive glycophospholipid with a phosphatidylinositol-specific phospholipase C (PI-PLC) stimulated pyruvate dehydrogenase (PDH) in both subcellular and whole cell assays. Stimulation of PDH activity in the subcellular assay was detected after gel filtration chromatography of the polar head group. This stimulation was not due to the presence of contaminating calcium and magnesium. The PDH-stimulating activity was proportional to the amount of polar head group added to the assay. The effect of the polar head group on PDH in the subcellular assay was blocked by sodium fluoride, suggesting that the polar head group activated the PDH phosphatase. In the whole cell assay, the polar head group stimulated PDH activity to an equal or greater extent as a physiological concentration of insulin. The effect of the polar head group was detected at 5 min, peaked at 10 min, and declined thereafter. In contrast, insulin stimulated PDH activity more slowly, but consistently. The PDH-stimulating activity eluted after bacitracin but ahead of ATP during gel filtration chromatography, and it was destroyed by exposure to NH4OH or alkaline phosphatase and by boiling in water. These data support the proposal that an early step in insulin action is the release of insulinomimetic polar head group from the insulin-sensitive glycophospholipid.
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PMID:The insulinomimetic effects of the polar head group of an insulin-sensitive glycophospholipid on pyruvate dehydrogenase in both subcellular and whole cell assays. 327 39

We have previously demonstrated that insulin stimulates glycerolipid synthesis and phospholipid hydrolysis in BC3H-1 myocytes, resulting in the generation of membrane diacylglycerol, a known cellular mediator. This led us to the original proposal that diacylglycerol may contribute to the mediation of insulin action, especially stimulation of glucose transport. The fact that agents such as phenylephrine and phorbol esters, which increase or act as membrane diacylglycerols, are fully active in stimulating glucose transport in this tissue lent further support to this proposal. In this paper, we demonstrate that the diacylglycerol analogues PMA (4 beta-phorbol 12-myristate 13-acetate) and mezerein (both possessing 12 beta- and 13 alpha-O-linked substituents as well as a 4 beta-hydroxyl group) each increase the Vmax of the glucose transporter as does insulin. Diacylglycerol generated by the addition of phospholipase C also stimulates glucose uptake to a maximum which is equal and nonadditive to that of insulin, while addition of the narrowly active phosphatidylinositol-specific phospholipase C which generates the putative phosphoinositol-glycan mediator of Saltiel et al. (Saltiel, A., Fox, J., She Lin, P., and Cutrecasas, P. (1986) Science 233, 967-972) stimulates pyruvate dehydrogenase in these cells without any effect on glucose uptake. Pretreatment of the myocytes with PMA resulted in desensitization of subsequent glucose uptake to stimulation by phenylephrine, but had no effect on stimulation of glucose uptake by phospholipase C or by insulin, indicating that PMA pretreatment primarily desensitizes agonist-induced polyphosphoinositide hydrolysis which, as we have previously shown, is not involved in the insulin-induced generation of diacylglycerol. This was confirmed by the absence of intracellular Ca2+ mobilization during insulin administration, as measured by the sensitive fluorescent probe fura-2 in attached monolayer BC3H-1 myocytes. Furthermore, we have shown that insulin-generated diacylglycerol satisfies several criteria for a mediator of insulin action, including the demonstration that insulin-stimulated endogenous diacylglycerol generation is antecedent to glucose transport and has an identical insulin dose-response curve and moreover that the magnitude and time course of subsequent stimulation of glucose transport is reproduced by the addition of the simple exogenous diacylglyerol, dioctanoylglycerol, in the complete absence of the hormone. These results establish a central role for insulin-induced glycerolipid metabolism in mediating insulin-stimulated glucose transport in BC3H-1 myocytes.
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PMID:Insulin-induced glycerolipid mediators and the stimulation of glucose transport in BC3H-1 myocytes. 328 20

Exposure to phospholipase C increased the incorporation of [32P]Pi into phosphatidate, CMP-phosphatidate and phosphatidylinositol in rat adipose tissue and isolated adipocytes. A similar effect was observed in response to insulin and oxytocin. Theophylline, 3-isobutyl-1-methylxanthine and adenosine deaminase decreased [32P]Pi incorporation, and adenosine and N6-phenylisopropyladenosine reversed these effects. As with insulin, exposure of adipose tissue to phospholipase C stimulated oxidation of glucose, pyruvate and leucine and activated pyruvate dehydrogenase. Oxytocin and adenosine also mimicked the effects of insulin on leucine oxidation and pyruvate dehydrogenase. However, only insulin stimulated glycogen synthase activity, indicating that the regulation of synthase may be achieved by intracellular events distinct from those regulating changes in phospholipid metabolism, sugar transport and mitochondrial enzyme activities. It is postulated that exposure to phospholipase C forms diacylglycerol, which is phosphorylated to yield phosphatidate. The increased labelling of CMP-phosphatidate and phosphatidylinositol results from the conversion of phosphatidate into these lipids. The correlation between the effects of phospholipase C on phosphatidate synthesis and changes in adipose-tissue metabolism suggests the possibility that increased phosphatidate may directly or indirectly produce changes in membrane transport and enzyme activities. The pattern of phospholipid labelling produced by insulin, adenosine and oxytocin suggests that these stimuli may also increase phosphatidate synthesis, and, if so, changes in phospholipid metabolism could account for some of the metabolic actions of these stimuli.
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PMID:Phosphatidic acid and phosphatidylinositol labelling in adipose tissue. Relationship to the metabolic effects of insulin and insulin-like agents. 641 Oct 68

To profile changes in gene expression in response to ischemic postconditioning, isolated rat hearts were subjected to 30 min of regional ischemia followed by 120 min of reperfusion with or without postconditioning. At the end of reperfusion, cardiac RNA was assayed by DNA microarrays (31,000 format), verified by quantitative real-time polymerase chain reaction (QRT-PCR). Postconditioning significantly up-regulated 50 genes and down-regulated 58 different genes, including pyruvate dehydrogenase, 60 kDa heat shock protein 1, lipoprotein lipase, gamma-sarcoglycan, and phospholipase C. Gene ontology analysis revealed that most of the altered genes belong to the cellular metabolic processes cluster. Many of the genes have not previously been suspected to be involved in the mechanism of postconditioning.
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PMID:Ischemic postconditioning alters the gene expression pattern of the ischemic heart. 2441 79