Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Tumor necrosis factor (TNF) is a proinflammatory polypeptide that is able to induce a great diversity of cellular responses via modulating the expression of a number of different genes. One major pathway by which TNF receptors communicate signals from the membrane to the cell nucleus involves protein kinase C (PKC). In the present study, we have addressed the molecular mechanism of TNF-induced PKC activation. To this, membrane lipids of the human histiocytic cell line U937 were labeled by incubation with various radioactive precursors, and TNF-induced changes in phospholipid, neutral lipid, and water-soluble metabolites were analyzed by thin layer chromatography. TNF treatment of U937 cells resulted in a rapid and transient increase of 1'2'diacylglycerol (DAG), a well-known activator of PKC. The increase in DAG was detectable as early as 15 s after TNF treatment and peaked at 60 s. DAG increments were most pronounced (approximately 360% of basal levels) when cells were preincubated with [14C]lysophosphatidylcholine, which was predominantly incorporated into the phosphatidylcholine (PC) pool of the plasma-membranes. Further extensive examination of changes in metabolically labeled phospholipids indicated that TNF-stimulated hydrolysis of PC is accompanied by the generation of phosphorylcholine and DAG. These results suggest the operation of a PC-specific phospholipase C. Since no changes in phosphatidic acid (PA) and choline were observed and the production of DAG by TNF could not be blocked by either propranolol or ethanol, a combined activation of phospholipase D and PA-phosphohydrolase in DAG production appears unlikely. TNF-stimulated DAG production as well as PKC activation could be blocked by the phospholipase inhibitor p-bromophenacylbromide (BPB). Since BPB did not inactivate PKC directly, these findings underscore that TNF activates PKC via formation of DAG. TNF stimulation of DAG production could be inhibited by preincubation of cells with a monoclonal anti-TNF receptor (p55-60) antibody, indicating that activation of a PC-specific phospholipase C is a TNF receptor-mediated event.
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PMID:Tumor necrosis factor induces rapid production of 1'2'diacylglycerol by a phosphatidylcholine-specific phospholipase C. 165 88

Following addition TNF-alpha to variety of cells the diversity of action has been observed. TNF-alpha induced rapid elevation of intercellular Ca2+ level in all studied cells. This suggests TNF receptor is coupled to phospholipase C.
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PMID:The effect of tumor necrosis factor (TNF-alpha) on calcium (Ca2+) level. 166 6

The human p55 tumor necrosis factor (TNF) receptor (TR55) initiates at least two independent signaling cascades. The acidic sphingomyelinase (A-SMase) pathway involves a phosphatidylcholine-specific phospholipase C, an endosomal A-SMase, and controls expression of multiple TNF-responsive genes through induction of transcription factors such as NF-kappaB. The neutral sphingomyelinase (N-SMase) pathway comprises a membrane-bound N-SMase, proline-directed protein kinases, as well as phospholipase A2 and appears critical for the inflammatory responses induced by TNF. While the domain of TR55 that induces A-SMase is probably identical to the death domain, the exact location and extent of a putative N-SMase activation domain are still unknown. Structure-function analysis of TR55 deletion mutants revealed a novel region of 11 amino acids at position 309-319 that is both necessary and sufficient for activation of N-SMase. The N-SMase activation domain is distinct from the death domain and incapable of induction of A-SMase, NF-kappaB, and cytotoxicity. Taken together, our results suggest that a functionally independent region of TR55 is responsible for selectively initiating the N-SMase pathway that couples to an important inflammatory signaling cascade.
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PMID:A novel cytoplasmic domain of the p55 tumor necrosis factor receptor initiates the neutral sphingomyelinase pathway. 866 14

Tumor necrosis factor (TNF) is a pleiotropic mediator of inflammation that has been implicated in the pathogenesis of devastating clinical syndromes including septic shock. We have investigated the role of a TNF-responsive phosphatidylcholine-specific phospholipase C (PC-PLC) for the cytotoxic and proinflammatory activity of TNF. We show here that the cytotoxicity signaled for by the so-called "death domain" of the p55 TNF receptor is associated with the activation of PC-PLC. The xanthogenate tricyclodecan-9-yl (D609), a specific and selective inhibitor of PC-PLC, blocked the cytotoxic action of TNF on L929 and Wehi164 cells. In vivo, D609 prevented both adhesion molecule expression in the pulmonary vasculature and the accompanying leukocyte infiltration in TNF-treated mice. More strikingly, D609 protects BALB/c mice from lethal shock induced either by TNF, lipopolysaccharide, or staphylococcal enterotoxin B. Together these findings imply PC-PLC as an important mediator of the pathogenic action of TNF, suggesting that PC-PLC may serve as a novel target for anti-inflammatory TNF antagonists.
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PMID:Function of the p55 tumor necrosis factor receptor "death domain" mediated by phosphatidylcholine-specific phospholipase C. 876 Aug 26

The effect of recombinant human tumor necrosis factor-alpha (TNF) on voltage-gated membrane currents of cultured neurons derived from embryonic rat cerebral cortex was studied using the whole-cell patch-clamp technique. Treatment of neurons with TNF resulted in an increase in outward potassium current density, dependent upon the concentration of TNF and the incubation time, without affecting other membrane currents such as barium and N-methyl-D-aspartate (NMDA). Long exposures (12-48 hr) to TNF (10-100 ng/ml) increased transient outward potassium current (A-current) density without affecting the parameters of activation and inactivation of the current. Prolonged exposures to TNF diminished its increasing effect on the A-current. Since the increase of A-current density induced by TNF is inhibited by both the anti-TNF receptor antibody and cycloheximide treatment, the effect of TNF might be mediated through receptors and by de novo synthesis of the channel protein itself and/or modulating proteins associated with the channel activities. Results indicate that phosphatidylcholine-specific phospholipase C and protein kinase C, but not ceramide, are involved in the signal transduction. In toxicological experiments, TNF had no neurotoxicity. Moreover, a 12 hr pretreatment of TNF protected neurons against NMDA-induced neurotoxicity. This protective effect of TNF was cancelled by 4-aminopyridine, an A-current blocker, suggesting that the increase of A-current densities induced by TNF contributes to the neuroprotection.
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PMID:Tumor necrosis factor enhancement of transient outward potassium currents in cultured rat cortical neurons. 945 13

The present studies were carried out to evaluate the mechanisms by which PTH/PTHrP receptor (PTHR) activation influences cell viability. In 293 cells expressing recombinant PTHRs, PTH treatment markedly reduced the number of viable cells. This effect was associated with a marked apoptotic response including DNA fragmentation and the appearance of apoptotic nuclei. Similar effects were evidenced in response to serum withdrawal or to the addition of tumor necrosis factor (TNFalpha). Addition of caspase inhibitors or overexpression of bcl-2 partially abrogated apoptosis induced by serum withdrawal. Caspase inhibitors also protected cells from PTH-induced apoptosis, but overexpression of bcl-2 did not. The effects of PTH on cell number and apoptosis were neither mimicked by activators of the cAMP pathway (forskolin, isoproterenol) nor blocked by an inhibitor (H-89). However, elevation of Ca(i)2+ by addition of thapsigargin induced rapid apoptosis, and suppression of Ca(i)2+ by overexpression of the calcium- binding protein, calbindin D28k, inhibited PTH-induced apoptosis. The protein kinase C inhibitor GF 109203X partially inhibited PTH-induced apoptosis. Regulator of G protein signaling 4 (RGS4) (an inhibitor of the activity of the alpha-subunit of Gq) suppressed apoptotic signaling by the PTHR, whereas the C-terminal fragment of GRK2 (an inhibitor of the activity of the beta(gamma)-subunits of G proteins) was without effect. Chemical mutagenesis allowed selection of a series of 293 cell lines resistant to the apoptotic actions of PTH; a subset of these were also resistant to TNFalpha. These results suggest that 1) apoptosis produced by PTHR and TNF receptor signaling involve converging pathways; and 2) Gq-mediated phospholipase C/Ca2+ signaling, rather than Gs-mediated cAMP signaling, is required for the apoptotic effects of PTHR activation.
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PMID:Apoptosis mediated by activation of the G protein-coupled receptor for parathyroid hormone (PTH)/PTH-related protein (PTHrP). 1067 97

A fundamental property of animal cells is the ability to regulate their own cell volume. Even under hypotonic stress imposed by either decreased extracellular or increased intracellular osmolarity, the cells can re-adjust their volume after transient osmotic swelling by a mechanism known as regulatory volume decrease (RVD). In most cell types, RVD is accomplished mainly by KCl efflux induced by parallel activation of K+ and Cl- channels. We have studied the molecular mechanism of RVD in a human epithelial cell line (Intestine 407). Osmotic swelling results in a significant increase in the cytosolic Ca2+ concentration and thereby activates intermediate-conductance Ca2+-dependent K+ (IK) channels. Osmotic swelling also induces ATP release from the cells to the extracellular compartment. Released ATP stimulates purinergic ATP (P2Y2) receptors, thereby inducing phospholipase C-mediated Ca2+ mobilization. Thus, RVD is facilitated by stimulation of P2Y2 receptors due to augmentation of IK channels. In contrast, stimulation of another G protein-coupled Ca2+-sensing receptor (CaR) enhances the activity of volume-sensitive outwardly rectifying Cl- channels, thereby facilitating RVD. Therefore, it is possible that Ca2+ efflux stimulated by swelling-induced and P2Y2 receptor-mediated intracellular Ca2+ mobilization activates the CaR, thereby secondarily upregulating the volume-regulatory Cl- conductance. On the other hand, the initial process towards apoptotic cell death is coupled to normotonic cell shrinkage, called apoptotic volume decrease (AVD). Stimulation of death receptors, such as TNF receptor and Fas, induces AVD and thereafter biochemical apoptotic events in human lymphoid (U937), human epithelial (HeLa), mouse neuroblastoma x rat glioma hybrid (NG108-15) and rat phaeochromocytoma (PC12) cells. In those cells exhibiting AVD, facilitation of RVD is always observed. Both AVD induction and RVD facilitation as well as succeeding apoptotic events can be abolished by prior treatment with a blocker of volume-regulatory K+ or Cl- channels, suggesting that AVD is caused by normotonic activation of ion channels that are normally involved in RVD under hypotonic conditions. Therefore, it is likely that G protein-coupled receptors involved in RVD regulation and death receptors triggering AVD may share common downstream signals which should give us key clues to the detailed mechanisms of volume regulation and survival of animal cells. In this Topical Review, we look at the physiological ionic mechanisms of cell volume regulation and cell death-associated volume changes from the facet of receptor-mediated cellular processes.
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PMID:Receptor-mediated control of regulatory volume decrease (RVD) and apoptotic volume decrease (AVD). 1128 21

Tumor necrosis factor (TNF), via its receptor 2 (TNFR2), induces Etk (or Bmx) activation and Etk-dependent endothelial cell (EC) migration and tube formation. Because TNF receptor 2 lacks an intrinsic kinase activity, we examined the kinase(s) mediating TNF-induced Etk activation. TNF induces a coordinated phosphorylation of vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2) and Etk, which is blocked by VEGFR2-specific inhibitors. In response to TNF, Etk and VEGFR2 form a complex resulting in a reciprocal activation between the two kinases. Subsequently, the downstream phosphatidylinositol 3-kinase (PI3K)-Akt signaling (but not signaling through phospholipase C-gamma) was initiated and directly led to TNF-induced EC migration, which was significantly inhibited by VEGFR2-, PI3K-, or Akt-specific inhibitors. Phosphorylation of VEGFR2 at Tyr-801 and Tyr-1175, the critical sites for VEGF-induced PI3K-Akt signaling, was not involved in TNF-mediated Akt activation. However, TNF induces phosphorylation of Etk at Tyr-566, directly mediating the recruitment of the p85 subunit of PI3K. Furthermore, TNF- but not VEGF-induced activation of VEGFR2, Akt, and EC migration are blunted in EC genetically deficient with Etk. Taken together, our data demonstrated that TNF induces transactivation between Etk and VEGFR2, and Etk directly activates PI3K-Akt angiogenic signaling independent of VEGF-induced VEGFR2-PI3K-Akt signaling pathway.
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PMID:Etk/Bmx transactivates vascular endothelial growth factor 2 and recruits phosphatidylinositol 3-kinase to mediate the tumor necrosis factor-induced angiogenic pathway. 1453 77

Endotoxin (LPS)-induced cardiac failure is associated with an up-regulation of RGS16 protein expression and repression of phospholipase C activity in vivo. Since the release of pro-inflammatory cytokines plays an important role in mediating LPS-induced myocardial dysfunction, we examined the effect of recombinant cytokines on the expression of RGS16 protein in neonatal cardiac myocytes. Myocytes in culture were treated with 50 ng/ml recombinant tumor necrosis factor alpha (TNFalpha), 2 ng/ml interleukin 1beta (IL-1beta), interleukin 6 (IL-6), interferon gamma (IFNgamma) or diluent (NaCl) for 24 h. Before stimulation with LPS (4 micro g/ml for 24 h) cells were treated with 200 ng/ml interleukin 1-receptor antagonist (IL-1ra), 500 ng/ml soluble TNF receptor (sTNFr), or NaCl for 1 h. Isolated membrane proteins were used for Western blot analysis. Cell-associated and secreted IL-1beta and TNFalpha protein content were determined in myocyte protein homogenates and cell culture supernatants by ELISA immunoblotting 3, 6, 24, 48 and 72 h after treatment with LPS. IL-1beta (1.75-fold) and TNFalpha (1.62-fold) but not IL-6 and IFNgamma induced RGS16 protein expression. LPS stimulated intracellular IL-1beta expression within 6 h (847.1+/-172.9 pg/3x10(6) cells) followed by an increase in extracellular secretion up to 70.8+/-8.1 pg/3x10(6) cells after 48 h. In contrast, intracellular protein concentrations of TNFalpha were almost not detectable (0.03+/-0.01 pg/3x10(6) cells), but extracellular secretion was induced by LPS with a maximum at 6 h (653.9+/-36.3 pg/3x10(6) cells). The LPS-induced increase in RGS16 (1.6-fold) was blunted by IL-1ra but not by TNFalpha scavenging. Interestingly, both, the IL-1beta- and TNFalpha-effect could be blocked by IL-1ra, indicating that also the TNFalpha-induced RGS16 expression is mediated by IL-1. We therefore conclude that LPS induces RGS16 protein expression by activation of the cytokine IL-1beta in cardiac myocytes. Our data substantiate the role of IL-1beta as an important mediator in LPS-induced cardiac failure.
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PMID:Interleukin-1beta mediates endotoxin- and tumor necrosis factor alpha-induced RGS16 protein expression in cultured cardiac myocytes. 1456 49

The clinical application of adriamycin, an exceptionally good chemotherapeutic agent, is limited by its dose-related cardiomyopathy. Our recent study showed that tumor necrosis factor-alpha (TNF-alpha) receptors mediated cytoprotective signaling against adriamycin-induced mitochondrial injury and cardiomyocyte apoptosis. In the present study, we investigated the potential targets of TNF receptor-mediated cytoprotective signaling by global genome microarray analysis using wild-type and TNF receptor-deficient mice. Microarray analysis revealed that adriamycin treatment induced the down-regulation of several mitochondrial functions and energy production-related genes in double TNF receptor-deficient mice, notably, phospholipase C-delta1, a protein involved in fatty acid metabolism and calcium regulation. The role of phospholipase C-delta1 in TNF receptor-mediated cardioprotection against adriamycin-induced injury was evaluated by measuring changes in cardiac function using high-frequency ultrasound biomicroscopy. Selective inhibition of phospholipase C activity in wild-type mice by its inhibitor, U73122, exacerbated adriamycin-induced cardiac dysfunction. Inhibition of phospholipase C-delta1 resulted in the significant decrease of left ventricular ejection fraction and fractional shortening, and the decreased levels were similar to those observed in adriamycin-treated double TNF receptor-deficient mice. The data derived from the global genome analysis identified phospholipase C-delta1 as an important target for TNF receptors and revealed the critical role of TNF receptor signaling in the protection against adriamycin-induced cardiotoxicity.
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PMID:Phospholipase C-delta1 is a critical target for tumor necrosis factor receptor-mediated protection against adriamycin-induced cardiac injury. 1661 58


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