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)

Previously, we identified peptides that stimulate phosphoinositide hydrolysis in several leukocyte cell lines from mixtures of random hexapeptide sequences. Moreover, the peptides activate phospholipase C via a pertussis toxin-sensitive G protein-coupled receptor. We now investigate the structure-activity relationship of the peptides with the goal of improving the activity of the peptides, as well as the biologic function of the peptides. Substitution of the L-methionine at the C terminus of peptides with D-methionine markedly increased the effectiveness of the peptides. The half-maximal effective concentrations of MKYMPm-NH2 and WKYMVm-NH2 for stimulation of phosphoinositide hydrolysis in U266 cells were 30 and 0.5 nM, respectively. By BIAcore analysis we confirmed the existence of a receptor for WKYMVm-NH2. Furthermore, the intracellular calcium concentration increase induced by WKYMVm-NH2 was not inhibited by several chemoattractants (FMLP, IL-8, platelet-activating factor, C5a, granulocyte-macrophage CSF, and granulocyte CSF) suggests that WKYMVm-NH2 has a unique cell surface receptor on leukocytes. WKYMVm-NH2 stimulated the phosphoinositide hydrolysis in U937, HL60, and U266 cells, as well as in human neutrophils. Moreover, WKYMVm-NH2 is more effective than FMLP in the production of superoxide in human neutrophils. The data suggest that WKYMVm-NH2 may have the ability to activate the microbicidal functions of human neutrophils.
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PMID:A peptide with unique receptor specificity: stimulation of phosphoinositide hydrolysis and induction of superoxide generation in human neutrophils. 902 31

In rat neutrophils, formyl-Met-Leu-Phe (fMLP)-induced phosphate formation was inhibited by abruquinone A (IC50 value about 32.7 +/- 6.4 microM) as well as by a putative phospholipase C inhibitor, [6-[[17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole- 2,5-dione (U73122) (IC50 value about 11.3 +/- 1.2 microM). The reduction in inositol phosphate levels appeared to reflect inhibition of phospholipase C activity because the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) catalyzed by a soluble fraction from neutrophils was also inhibited by abruquinone A (IC50 value about 31.4 +/- 5.6 microM) over the same range of concentrations. Although abruquinone A alone induced Ca2+ and Mn2+ influx into neutrophils in Ca(2+)-containing medium, abruquinone A, like U73122, inhibited Ca2+ release (IC50 value about 23.5 +/- 0.5 microM) from internal stores in Ca(2+)-free medium. These results indicate that abruquinone A inhibits the activity of phosphoinositide-specific phospholipase C in neutrophils.
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PMID:Inhibition by abruquinone A of phosphoinositide-specific phospholipase C activation in rat neutrophils. 903 Sep 8

Relationships between phospholipases are poorly understood, but phosphatidic acid (PA) and diglycerides (DGs), produced by phospholipase D (PLD) and phosphatidate phosphohydrolase actions, might function as second messengers coupling cell stimulation to cellular responses. This study investigates the role of PLD-mediated PA and DG formation in inducing phospholipase A2 (PLA2) activity in intact human neutrophils (PMNs) and in PMNs permeabilized with Staphylococcus aureus alpha-toxin. PMNs were labelled with [3H]arachidonic acid (AA) to assess AA release and metabolism and diacylglycerol formation, or with [3H]1-O-hexadecyl-2-lyso-glycerophosphatidylcholine for the determination of platelet-activating factor (PAF), PA and alkylacylglycerol production. In intact PMNs primed with tumour necrosis factor alpha before stimulation with N-formyl-Met-Leu-Phe, AA release and metabolism and PAF formation increased in parallel with enhanced PA and DG formation, and inhibition of PA and DG production led to a decrease in both AA release and PAF accumulation. In alpha-toxin-permeabilized PMNs, AA release and PAF production result from the specific activation of cytosolic PLA2 (cPLA2). In this system, PA and DG formation were always present when cPLA2 activation occurred; blocking PA and DG production inhibited AA release and PAF accumulation. Adding either PA or DG back to permeabilized cells (with endogenous PA and DG formation blocked) led to a partial restoration of AA release and PAF formation; a combination of PA and DGs reconstituted full cPLA2 activity. These results strongly suggest that products of PLD participate in activating cPLA2 in PMNs.
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PMID:Induction of cytosolic phospholipase A2 activity by phosphatidic acid and diglycerides in permeabilized human neutrophils: interrelationship between phospholipases D and A2. 906 50

1. The possible mechanisms of the inhibitory effect of ethyl 2-(3-hydroxyanilino)-4-oxo-4,5-dihydrofuran-3-carboxylate (HAJ11) on the respiratory burst of rat neutrophils in vitro was investigated. 2. HAJ11 caused a reversible and a concentration-dependent inhibition of formyl-Met-Leu-Phe (fMLP)-induced superoxide anion (O2.-) generation (IC50 4.9 +/- 0.7 microM) and O2 consumption (IC50 4.9 +/- 1.5 microM). Concanavalin A (Con A)- and NaF-induced O2.- generation were also suppressed by HAJ11. However, HAL11 was a weak inhibitor of the phorbol 12-myristate 13-acetate (PMA)-induced responses. 3. HAJ11 did not scavenge the /2.- generation in the xanthine-xanthine oxidase system and dihydroxyfumaric acid (DHF) autoxidation. 4. HAJ11 showed no activity on fMLP-induced inositol phosphates formation and [Ca2+]i elevation in intact neutrophils. In addition, HAJ11 had no effect on neutrophil cytosolic phospholipase C (PLC) activity. 5. HAJ11 reduced fMLP-induced phosphatidic acid (PA) (IC50 29.1 +/- 6.5 microM) and phosphatidylethanol (PE+) (IC50 22.6 +/- 1.9 microM) formation in a concentration-dependent manner. HAJ11 also reduced protein tyrosine phosphorylation in neutrophils stimulated by fMLP. 6. HAJ11 was a weak inhibitor of neutrophil cytosolic protein kinase C (PKC) activity, and had a negligible effect on brain PKC. Cellular cyclic nucleotides levels were not altered by HAJ11. In addition, HAJ11 did not affect protein kinase A (PKA) activity. 7. HAJ11 had not effect on the O2.- generation of PMA-activated and arachidonic acid (AA)-activated NADPH oxidase preparations. 8. Taken together these results indicate that the inhibition of respiratory burst by HAJ11 probably mainly occurs through inhibition of protein tyrosine phosphorylation and phospholipase D (PLD) activity.
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PMID:Inhibition by HAJ11 of respiratory burst in neutrophils and the involvement of protein tyrosine phosphorylation and phospholipase D activation. 911 3

The involvement of the small GTP-binding protein ADP-ribosylation factor (ARF) in guanosine 5'-[gamma-thio]triphosphate (GTP[S])-dependent activation of phospholipase D (PLD) in HL-60 cells has been well established in vitro. In this study, we tested the effect of brefeldin A, which prevents ARF activation by inhibiting guanine-nucleotide-exchange activity, on PLD stimulation by receptor agonists (formyl-Met-Leu-Phe and ATP) and by the phorbol ester phorbol 12-myristate 13-acetate (PMA) in differentiated HL-60 cells. However, brefeldin A did not affect the activation of PLD at a time (1 h) when it eliminated the activity of the trans-Golgi enzyme galactosyltransferase. It also did not inhibit PLD activity in Golgi-enriched membranes treated with GTP[S] with or without ARF in vitro. However, longer times of brefeldin A treatment (>6 h), progressively and completely inhibited the activation of PLD by formyl-Met-Leu-Phe and partly inhibited (approximately 50%) the activation by PMA. In contrast, long-term brefeldin A treatment did not inhibit the effect of GTP[S] on PLD in permeabilized HL-60 cells. Long-term brefeldin A treatment completely inhibited inositol phosphate production in response to formyl-Met-Leu-Phe and ATP, indicating that it affected inositolphospholipid-specific phospholipase C activity. These data indicate that the rapid inhibitory effect of brefeldin A on Golgi function is not associated with inhibition of receptor-mediated or PMA-mediated PLD activation in HL-60 cells. However, longer-term effects, presumably arising from the disruption of the Golgi, lead to a total inhibition of agonist activation of PLD and inositolphospholipid-specific phospholipase C. In summary, these results do not support a role for brefeldin-A-sensitive ARF in agonist regulation of PLD in HL-60 cells.
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PMID:Effects of brefeldin A on phosphatidylcholine phospholipase D and inositolphospholipid metabolism in HL-60 cells. 939 31

Phospholipids of isolated rat hepatocytes were labelled by preincubation with either 2 microM -methyl-14C-S-adenosylmethionine (AdoMet) or 2 microM [methyl-14C]methionine. Subsequent addition of phospholipase C to the suspension removed 95% of the radioactivity from phospholipids methylated by [methyl-14C]AdoMet within a few minutes, but was without effect on phospholipids methylated by [methyl-14C]methionine radioactivity from the latter could, nevertheless, be removed by phospholipase C after permeabilization of the cells with digitonin. The results clearly show that the methyl group of exogenous AdoMet, contrary to that of methionine, is transferred on to phospholipids located on the external face of the plasma membrane. Accordingly, pretreatment of isolated hepatocytes with trypsin prevented the methylation of phospholipids from exogenous AdoMet by 60-80%, whereas it was almost without effect when exogenous methionine was the methyl donor. Our data corroborate previous work [Bontemps and Van den Berghe (1997) Biochem. J. 327, 383-389], which indicated that AdoMet methylates hepatocyte phospholipids without penetrating the cells.
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PMID:Novel evidence for an ecto-phospholipid methyltransferase in isolated rat hepatocytes. 946 82

Formylated peptides (e.g. n-formyl-Met-Leu-Phe (fMLP)) and platelet-activating factor (PAF) mediate chemotactic and cytotoxic responses in leukocytes through receptors coupled to G proteins that activate phospholipase C (PLC). In RBL-2H3 cells, fMLP utilizes a pertussis toxin (ptx)-sensitive G protein to activate PLC, whereas PAF utilizes a ptx-insensitive G protein. Here we demonstrate that fMLP, but not PAF, enhanced intracellular cAMP levels via a ptx-sensitive mechanism. Protein kinase A (PKA) inhibition by H-89 enhanced inositol phosphate formation stimulated by fMLP but not PAF. Furthermore, a membrane-permeable cAMP analog 8-(4-chlorophenylthio)-cAMP (cpt-cAMP) inhibited phosphoinositide hydrolysis and secretion stimulated by fMLP but not PAF. Both cpt-cAMP and fMLP stimulated PLCbeta3 phosphorylation in intact RBL cells. The purified catalytic subunit of PKA phosphorylated PLCbeta3 immunoprecipitated from RBL cell lysate. Pretreatment of intact cells with cpt-cAMP and fMLP, but not PAF, resulted in an inhibition of subsequent PLCbeta3 phosphorylation by PKA in vitro. These data demonstrate that fMLP receptor, which couples to a ptx-sensitive G protein, activates both PLC and cAMP production. The resulting PKA activation phosphorylates PLCbeta3 and appears to block the ability of Gbetagamma to activate PLC. Thus, both fMLP and PAF generate stimulatory signals for PLCbeta3, but only fMLP produces a PKA-dependent inhibitory signal. This suggests a novel mechanism for the bidirectional regulation of receptors which activate PLC by ptx-sensitive G proteins.
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PMID:Differential regulation of formyl peptide and platelet-activating factor receptors. Role of phospholipase Cbeta3 phosphorylation by protein kinase A. 955 82

The amyloid precursor protein (APP) can be cleaved by a beta-secretase to generate a beta-amyloid peptide, which has been implicated in the pathogenesis of Alzheimer's disease. However, APP can also be cleaved by an alpha-secretase to form a non-amyloidogenic secreted form of APP (APP-S). APP-S secretion can be physiologically regulated. This study examined the glutamatergic regulation of APP in the human neuronal Ntera 2 (NT2N) cell line. Metabotropic glutamate receptor subtypes 1alpha/beta and 5alpha were identified in the NT2N neurons by reverse transcription-polymerase chain reaction. Stimulation of these phosphatidylinositol-linked receptors with glutamate or specific receptor agonists resulted in a dose- and time-dependent increase in the secretion of the amyloid precursor protein (APP-S), measured by the immunoprecipitation of APP-S from the medium of [35S]methionine-labeled NT2N neurons. The glutamate-induced APP-S secretion was maximal at 30 min and at a concentration of 1 mM glutamate. Glutamate-induced APP-S secretion required activation of phospholipase C, which resulted in inositol 1, 4,5-trisphosphate production, as shown by the rapid glutamate-induced accumulation of inositol 1,4,5-trisphosphate. Glutamate also caused an increase in intracellular Ca2+. The protein kinase C activator phorbol 12-myristate 13-acetate, a phorbol ester, as well as 1-oleoyl-2-acetoyl-3-glycerol, a cell-permeable diacylglycerol analog, also stimulated APP-S secretion. These findings suggest that APP-S secretion from NT2N neurons can be regulated by the activation of phosphatidylinositol-linked metabotropic glutamate receptor signaling pathway.
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PMID:Regulation of amyloid precursor protein secretion by glutamate receptors in human Ntera 2 neurons. 959 52

The resting K+ conductance (GK,r) of locust jumping muscle and its modulation by two neuropeptides, proctolin (Arg-Tyr-Leu-Pro-Thr) and YGGFMRFamide (Tyr-Gly-Gly-Phe-Met-Arg-Phe-NH2), were investigated using the two-electrode voltage clamp. At a physiological [K+]o of 10 mM, GK,r accounts for approximately 90% of the membrane resting conductance, and the resting membrane potential differs by </=1 mV from EK (mean: -74 mV). There is a K+ conductance that slowly activates on hyperpolarization (GK,H) and that seems to be largely located in the transverse tubules. Steady-state activation of GK,H was analyzed by tail current measurements. GK,H is activated partially at EK but accounts for probably </=50% of total resting K+ conductance. Raising [K+]o caused a large increase in GK,r and in maximal steady state GK,H without shifting the voltage sensitivity of GK,H. YGGFMRFamide and proctolin reduce GK,H, mainly affecting the maximal steady-state conductance. The voltage-insensitive component of the resting K+ conductance is also reduced. The conductance suppressed by the peptides exhibited an outwardly rectifying instantaneous current/voltage-characteristic that is quite similar to that of GK,H. The actions of the two peptides appeared to be identical, but proctolin was by some two orders of magnitude more potent than YGGFMRFamide. The effects of both peptides are mediated by G proteins. They are mimicked by phorbol esters but do not seem to be initiated by either branch of the phospholipase C-dependent intracellular pathways. The properties of the resting K+ conductance in locust muscle and other invertebrate muscles are compared. The biological significance of peptide-induced reduction in resting K+ conductance is discussed in view of the known property of proctolin to support tonic force as opposed to FMRFamide-peptides that support quick leg movements.
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PMID:Resting membrane properties of locust muscle and their modulation I. Actions of the neuropeptides YGGFMRFamide and proctolin. 970 68

The mechanism by which substance P depolarizes cholinergic interneurons in the rat striatum was studied using whole-cell recording techniques. In all cases the effects of substance P were mimicked by the neurokinin1 receptor agonist [Sar9, Met(O2)11] substance P and were antagonized by the neurokinin1 receptor antagonist SR140333. [Sar9, Met(O2)11] substance P was found to depolarize cholinergic interneurons by the induction of a calcium-activated inward current at -60 mV. This inward current was irreversibly potentiated by photolysis of caged GTPgammaS within neurons implicating the involvement of a G-protein. The [Sar9, Met(O2)11] substance P-induced inward current was inhibited by the phospholipase C inhibitor U-73122, and by the inclusion of the inositol-1,4,5-triphosphate receptor antagonist heparin in the electrode solution. These findings suggest that neurokinin1 receptors depolarize cholinergic interneurons in the rat striatum primarily through a phosphoinositide signalling pathway.
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PMID:Characterization of the mechanism of action of tachykinins in rat striatal cholinergic interneurons. 975 31


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