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)

Production of [3H]1,2-dipalmitoylglycerol ([3H]DAG) from 1-palmitoyl-2-[9,10-3H]palmitoyl-sn-glycero-3-phosphocholine and [3H]phosphorylcholine from 1,2-dipalmitoyl-sn-glycero-3-[Me-3H]phosphocholine was studied using sonicated rat platelets. The formation of [3H]DAG and [3H]phosphorylcholine occurred at a comparable rate. [3H]Phosphorylcholine formation was dependent on the concentration of the substrate, platelet sonicates and calcium in the incubation medium. The [3H]phosphorylcholine formation increased in presence of 0.01% deoxycholate and 0.01% Triton X-100. The phosphatidylcholine-phospholipase C (PC-PLC) in the platelet sonicates was recovered in both the supernatant and particulate fractions obtained after ultracentrifugation at 105,000 x g for 1 h. The PC-PLC activity in both fractions was inhibited by 2 mM EDTA. In the presence of 0.01% deoxycholate and 0.01% Triton X-100 the activity in the particulate fraction increased compared to the activity in the supernatant, which was inhibited by 0.01% Triton X-100. The pH optima for PC-PLC in both fractions was between pH 7.2 and 7.6. PC-PLC activity was also found in rabbit and human platelet sonicates, but the activity was significantly lower than in rat platelet sonicates. There was no evidence to suggest presence of phosphatidylcholine-specific phospholipase D activity in rat sonicated platelets. This data, therefore, provides direct evidence for the presence of PC-PLC activity in rat platelets.
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PMID:Evidence for phosphatidylcholine hydrolysis by phospholipase C in rat platelets. 157 68

We developed a monoclonal antibody specific to phosphatidic acid (PA). Using this antibody, a novel method to quantify trace amounts of PA was achieved. With the method, PA can be measured in the range of 20-500 pmol. We applied this method to quantify changes in PA levels in Balb/c 3T3 cells stimulated by platelet-derived growth factor. PA contents were very low in quiescent cells and dramatically increased with time up to 15 min. On the other hand, a biphasic diacylglycerol (DG) increase was found. The early phase showed a transient small peak of DG at 30 s followed by a decrease to 1 min. In the second phase, DG accumulated gradually but very markedly up to 15 min. Treatment with propranolol, a PA phosphohydrolase inhibitor, enhanced the accumulation of PA and inhibited the formation of DG in the second phase. However, R59022, a DG kinase inhibitor, did not influence the accumulation of DG or PA, suggesting that platelet-derived growth factor stimulates mainly phospholipase D-catalyzed hydrolysis of phospholipids rather than phospholipase C-catalyzed hydrolysis in the second phase. PA, even after contaminating lyso-PA was removed, could stimulate DNA synthesis, although lyso-PA was 25 times more potent. Moreover, phospholipase D was found to be a much stronger mitogen than phospholipase C. Phospholipase D treatment caused a biphasic accumulation of PA. PA levels reached a maximum at 1 h, and then decreased between 1 and 2 h; finally, there was a gradual elevation up to 10 h. In this case, there was no significant DG accumulation. On the other hand, phospholipase C treatment induced only DG accumulation without any significant change in PA. These results indicate that PA accumulation, rather than an increase in DG, correlates well with mitogenesis.
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PMID:Phosphatidic acid that accumulates in platelet-derived growth factor-stimulated Balb/c 3T3 cells is a potential mitogenic signal. 159 41

Stimulation of phospholipase D (PLD) by cell surface receptors has been observed in many cell types. We have investigated the mechanism of activation of this enzyme in undifferentiated HL60 cells. GTP analogues and Ca2+ (buffered in the nanomolar to micromolar range) were introduced into HL60 cells in the presence of the permeabilizing agent, streptolysin O. We report that guanosine 5'-[gamma-thio]triphosphate (GTP[S]) is a potent activator of phospholipase D when Ca2+ is available at micromolar levels. Phorbol 12-myristate 13-acetate or Ca2+ alone can also stimulate PLD, but to a limited extent. The activation of PLD by GTP[S] can be partially dissociated from GTP[S]-stimulated phosphoinositide-specific phospholipase C, suggesting that a G-protein may be directly involved in regulating PLD. However, maximal activation of PLD only occurs under conditions that are permissive to phospholipase C stimulation. We conclude that PLD activation is under dual control, i.e. protein kinase C- as well as G-protein-mediated regulation. Synergistic activation occurs when both pathways are simultaneously stimulated. We conclude that full activation of PLD requires protein kinase C, increased Ca2+ and a GTP-binding protein. Evidence for cytosolic components that may also be involved in obtaining full activation of PLD is also presented.
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PMID:Synergistic activation of phospholipase D by protein kinase C- and G-protein-mediated pathways in streptolysin O-permeabilized HL60 cells. 159 36

Phosphoinositide-specific phospholipase C (PLC) catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) to inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DG), which act as second messengers. Substantial evidence has strongly suggested that a putative G-protein (s), Gp, regulates PLC activity in human platelets. Recently, the molecular mechanism of PLC activity regulation was clarified as to two types of enzymes, PLC-gamma and PLC-beta. In this chapter, the regulatory mechanisms of the PLCs via a Gp or tyrosine kinase is summarized, and the involvement of some G-protein in the regulation of other phospholipases, phosphatidylcholine-specific PLC, phospholipase A2 and phospholipase D, is also discussed.
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PMID:[Role of GTP-binding proteins in phospholipid metabolism in human platelets]. 161 75

We investigated the effect of bacterial lipopolysaccharide (LPS) on phospholipid (PL) turnover in human monocytic leukaemia U937 cells. Cells were pre-labelled with [3H]choline, [14C]ethanolamine and [3H]inositol for 24 h. By monitoring the radiolabel association with cellular PL, the data indicated that LPS (10 micrograms/ml) drastically altered the catabolism of choline-containing PL; it induced their breakdown by 50% within 20 min. The reutilization of choline or its phosphates for PL synthesis was also suggested as a result of regaining radiolabel in the next 40 min. Choline-containing PL then underwent a second degradation after 60 min; 50% decline in radiolabel was detected at 120 min. In contrast, LPS did not induce the breakdown of phosphatidylethanolamine and phosphatidylinositol through phospholipase C/phospholipase D (PLC/PLD). No significant redistribution of the radiolabel in PL was detected in any cases during chasing. The data clearly indicate that LPS stimulates phosphatidylcholine breakdown, implying that the liberation of phosphatidic acid or diacylglycerol via PLC/PLD reaction may be relevant to the initiation of LPS-induced monocytic activation.
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PMID:Bacterial lipopolysaccharide induces phosphatidylcholine breakdown in human leukaemia monocytic U937 cells. 162 16

Interleukin-2 (IL-2) plays a central role in the immune system by regulating the proliferation and differentiation of T lymphocytes. However, the molecular mechanism of the signal transduction through the IL-2 receptor is poorly understood. We have studied the role of phosphatidic acid (PA) on IL-2 signal transduction using cloned T lymphocytes. IL-2 stimulated a transient increase in the PA concentration in resting CTLL-2 cells prelabeled with [3H]palmitic acid. This effect was detected as early as 1 min after IL-2 addition and peaked at 5 min. IL-2 similarly increased phospholipase D activity in intact CTLL-2 cells, as inferred by phosphatidylethanol production. By contrast, IL-2 did not affect [3H]palmitic acid-labeled diacylglycerol levels. Furthermore, exogenous addition of several natural or synthetic PA to T cells mimicked IL-2 activity. Thus, PA were able to induce DNA synthesis on CTLL-2 cells, although this effect was only 10%-20% of that observed with IL-2. PA showed a synergistic effect with low doses of IL-2. In addition, PA was able to induce c-myc RNA transcription in CTLL-2 cells as well as IL-2 receptor (CD25) expression on the cell membrane with equal potency as saturating doses of IL-2. It is likely that IL-2-induced PA accumulation is a consequence of phospholipase D activation. This hypothesis is further supported by the fact that the addition of exogenous phospholipase D but not phosphatidylinositol-specific phospholipase C also reproduced the IL-2 or PA effects mentioned above. In summary, our results suggest a role of phospholipase D activation and PA formation as second messengers of IL-2 activity.
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PMID:Regulation of interleukin-2 responses by phosphatidic acid. 162 28

The content and molecular species composition of 1,2-diacylglycerol (DAG) in rat sciatic nerve was determined and compared with the molecular species profiles for glycerophospholipid classes in order to gain information concerning the metabolic pathways of DAG formation. The level of DAG in freshly dissected epineurium-free nerve (44 +/- 2 pmol/mg wet weight) was 10-40% of that in other tissues and cultured cells. The predominant DAG molecular species were 18:0/20:4 (30%) and 16:0/18:1 (17%). In comparison with phospholipid molecular species patterns, DAG was characterized by a substantial but lower proportion of the 18:0/20:4 species than was found in phosphoinositides, and a significant fraction of saturated species such as those found in phosphatidylcholine. In nerve from diabetic rats, both the content and arachidonoyl-containing molecular species of DAG were reduced. These species were also decreased in individual glycerophospholipids, except for phosphatidylinositol. The distribution of molecular species in phosphatidic acid (PA) did not resemble that of any other phospholipid. A large rise in DAG content occurred when nerve was incubated in vitro. Molecular species analysis indicated that phosphoinositides were the main source, especially during the initial period. This process was virtually abolished in a Ca(2+)-free medium and probably reflects a response to tissue injury. Evidence was obtained for the isomerization of DAG to 1,3-diacylglycerol during incubation. PA content and molecular species composition of incubated nerve did not change. However, inclusion of propranolol, a PA phosphatase inhibitor, caused a 40% accumulation of PA within 10 min, suggesting that formation of this phospholipid is continuous. These findings support the conclusion that DAG is principally derived from phosphoinositides by phospholipase C hydrolysis, but a minor fraction could be derived from phosphatidylcholine either by the action of phospholipase C or via phospholipase D and PA phosphatase. The metabolic origins of PA appear to be diverse.
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PMID:Diacylglycerol composition and metabolism in peripheral nerve. 163 7

Lysophosphatidic acid (LPA) is a simple phospholipid that possesses hormone- and growth-factor-like properties. LPA initiates its action by inducing GTP-dependent phosphoinositide hydrolysis and inhibiting adenylate cyclase [van Corven, Groenink, Jalink, Eichholtz & Moolenaar (1989) Cell 59, 45-54]. Here we show that LPA stimulates rapid breakdown of phosphatidylcholine (PC) in Rat-1 fibroblasts. LPA-induced PC breakdown occurs through activation of phospholipase D (PLD), as measured by the formation of free choline and phosphatidic acid and by transphosphatidylation in the presence of butan-1-ol. LPA also stimulates generation of diacylglycerol, but there is no detectable formation of phosphocholine, suggesting that a PC-specific phospholipase C (PLC) is not involved. The response to LPA was compared with that to endothelin, a potent inducer of phospholipid hydrolysis but a poor mitogen for Rat-1 cells. Our results indicate that: (1) LPA is less efficient than endothelin in inducing phosphoinositide and PC breakdown; (2) LPA-induced PLD activation is short-lived, levelling off after 2 min, whereas the endothelin-stimulated increase in PLD activity persists for at least 1 h; (3) the effect of LPA on PLD, like that of endothelin, is blocked by long-term pretreatment of the cells with phorbol ester, suggesting that PLD activation occurs through a protein kinase C-dependent mechanism. Furthermore, our results support the notion that there is no simple causal relationship between the degree of agonist-induced phospholipid hydrolysis and the magnitude of the mitogenic response.
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PMID:The biologically active phospholipid, lysophosphatidic acid, induces phosphatidylcholine breakdown in fibroblasts via activation of phospholipase D. Comparison with the response to endothelin. 163 5

Human preimplantation embryos and endometrium secrete platelet-activating factor (PAF). The mechanism of phosphatidylcholine (PC) degradation stimulated by PAF was investigated in endometrial explants prelabeled with [methyl-3H]choline or preincubated with [3H]butan-1-ol. Analysis of the water-soluble metabolites of PAF-induced PC hydrolysis in secretory endometrium demonstrated that the stimulated generation of [3H]choline ([3H]Cho) precedes that of [3H]choline phosphate ([3H]ChoP) and [3H]glycerophosphocholine ([3H]GPC). Within 30 sec there was a rapid rise in PAF-induced [3H]Cho generation and by 2 min this had increased to 59.9% +/- 10.6% (p less than 0.02), with no effect upon [3H]ChoP and [3H]GPC during this period. Both [3H]GPC and [3H]ChoP, however, were increased at a later time point. The slower [3H]ChoP generation may suggest that PC-specific phospholipase C activation as well as delayed [3H]GPC rise may be due to PC-specific phospholipase A2 and lysophospholipase activation. Phospholipase D activity was confirmed by the incorporation of high-specific-activity [3H]butan-1-ol into [3H]phosphatidylbutanol ([3H]PBut). The rapid generation of [3H]PBut, which paralleled the rise in intracellular [3H]Cho, strongly suggests that PC breakdown is catalyzed by the phospholipase D pathway. It is proposed that PAF induces PC hydrolysis as a consequence of an early phospholipase D-catalyzed breakdown of PC in human secretory endometrium. This may be an alternative source for prostaglandin synthesis and an important pathway essential for long-term activation of local cellular events at the time of implantation.
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PMID:Platelet-activating factor mediates phosphatidylcholine hydrolysis by phospholipase D in human endometrium. 163 48

The activation of phospholipase D by platelet-activating factor (PAF) in the human promonocytic cell line U937 has been investigated. In cells prelabeled with [3H]palmitic acid, addition of PAF or phorbol 12-myristate 13-acetate (PMA) induced the synthesis of [3H]phosphatidylethanol, indicating phospholipase D activation. When U937 cells were preincubated for 5 min with PMA, and then stimulated with PAF, formation of phosphatidylethanol was greatly enhanced. In contrast, under the same experimental conditions PMA treatment blocked completely the PAF-induced inositol phosphates formation in cells prelabeled with [3H]inositol. Thus, PMA treatment demonstrates that phospholipase D activation can occur independently from phosphoinositide-specific phospholipase C activation during PAF stimulation in U937 cells. On the other hand, the data herein presented suggest that influx of external calcium is required for phospholipase D activation by PAF, as assessed by complete inhibition of the enzyme activity by chelation of extracellular calcium or by treatment with the calcium channel blocker verapamil. Based on these findings, a hypothetical model for phospholipase D activation is discussed.
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PMID:Platelet-activating factor synergizes with phorbol myristate acetate in activating phospholipase D in the human promonocytic cell line U937. Evidence for different mechanisms of activation. 165 58


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