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

---

Query: EC:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Extracellular ATP and UTP caused increases in the concentration of cytoplasmic free calcium ([Ca2+]i) and the intracellular level of inositol 1,4,5-trisphosphate (IP3), a second messenger for calcium mobilization, prior to the release of prostacyclin (PGI2) from cultured bovine pulmonary artery endothelial (BPAE) cells. The agonist specificity and dose-dependence were similar for nucleotide-mediated increases in IP3 levels, [Ca2+]i and PGI2 release. An increase in [Ca2+]; and PGI2 release was observed after addition of ionomycin, a calcium ionophore, to BPAE cells incubated in a calcium-free medium. The addition of ATP to the ionomycin-treated cells caused no further increase in [Ca2+]i or PGI2 release. The inability of ATP to cause an increase in [Ca2+]i or PGI2 release in ionomycin-treated cells was apparently due to the ionomycin-dependent depletion of intracellular calcium stores since the subsequent addition of extracellular calcium caused a significant increase in both [Ca2+]i and PGI2 release. Introduction of BAPTA, a calcium buffer, into BPAE cells inhibited ATP-mediated increases in [Ca2+]i and PGI2 release, further evidence that PGI2 release is dependent upon an increase in [Ca2+]i. The increase in [Ca2+]i elicited by ATP apparently caused the activation of a calmodulin-dependent phospholipase A2 since trifluoperazine, an inhibitor of calmodulin, and quinacrine, an inhibitor of phospholipase A2, prevented the stimulation of PGI2 release by ATP. Furthermore, ATP caused the specific hydrolysis of [14C]arachidonyl-labeled phosphatidylcholine and the generation of free arachidonic acid, the rate-limiting substrate for PGI2 synthesis, prior to the release of PGI2 from BPAE cells. These findings suggest that the increase in PGI2 release elicited by ATP and UTP is at least partially dependent upon a phospholipase C-mediated increase in [Ca2+]i and the subsequent activation of a phosphatidylcholine-specific phospholipase A2. ATP analogs modified in the adenine base or phosphate moiety caused PGI2 release with a rank order of agonist potency of adenosine 5'-O-(2-thiodiphosphate) (ADP beta S) greater than 2-methylthioATP (2-MeSATP) greater than ATP, whereas alpha, beta methyleneATP and beta, gamma methyleneATP had no effect on PGI2 release.
...
PMID:Mechanisms by which extracellular ATP and UTP stimulate the release of prostacyclin from bovine pulmonary artery endothelial cells. 131 59

ATP promoted biphasic effects on both basal and fMLP-stimulated arachidonic acid (AA) release in neutrophil-like HL60 cells: stimulation in the micromolar range (EC50 = 3.2 +/- 0.9 microM) and inhibition at higher concentrations (EC50 = 90 +/- 11 microM). ATP also inhibited UTP- and platelet activating factor-stimulated AA release. Only stimulatory effects of ATP on basal or fMLP-stimulated phospholipase C were observed. The inhibitory effect of ATP on AA release was not due to reacylation of released AA, chelation of extracellular Ca2+, cell permeabilization, or changes in the rise of [Ca2+]i induced by agonist. The inhibition was rapid, being detected within 5-15 s. The inhibitory effect of ATP on fMLP-stimulated AA release could be desensitized by pretreatment of the cells with 2 mM ATP, but not 20 microM ATP, the concentration that resulted in maximal release of AA and inositol phosphates. The inhibition by ATP was neither dependent on generation of adenosine by ATP hydrolysis nor the result of direct interaction of ATP with P1 purinergic receptors. Among other nucleotides tested (CTP, GTP, ITP, TTP, XTP, adenosine 5'-(beta,gamma-methylene)triphosphate (AMP-PCP), adenyl-5'-yl imidodiphosphate (AMP-P(NH)P), ADP, adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), and UTP), only UTP and ATP gamma S displayed biphasic effects with potencies and efficacies almost identical to those of ATP. The other nucleotides only exhibited stimulatory effects (EC50 = 60-300 microM). The results are consistent with a model of dual regulation of AA release by two distinct subtypes of P2U receptors in HL60 cells.
...
PMID:Dual regulation of arachidonic acid release by P2U purinergic receptors in dibutyryl cyclic AMP-differentiated HL60 cells. 131 16

Macrophages express two distinct types of nucleotide (P2 purinergic) receptors for extracellular ATP: one type induces a Ca(2+)-mobilizing response via the activation of phosphatidylinositol-phospholipase C (PI-PLC) while the second type induces the rapid formation of nonselective pores which are permeated by ions and small (< 1 kDa) organic molecules. We have confirmed the presence of these two ATP receptor types in the BAC1.2F5 murine macrophage cell line and have identified 3'-O-(4-benzoyl)benzoyl-ATP (BzATP) as a selective and potent agonist for the so-called P2z or pore-forming ATP receptor type. Several lines of evidence indicated that occupation of these P2z receptors is also accompanied by a rapid and large increase in the activity of a phosphatidylcholine-selective phospholipase D (PLD) effector enzyme. In cells metabolically labeled with [3H]oleic acid or [3H]glycerol and stimulated in the presence of ethanol, ATP and BzATP induced a severalfold increase in the rate and extent of [3H]phosphatidylethanol (PEt) accumulation. These responses were stimulated only by ATP, BzATP, and ATP gamma S (adenosine 5'-O-(3-thiotriphosphate) with the rank order of potency: BzATP >> ATP > ATP gamma A; there was no response to other adenine nucleotides or to non-adenine nucleotides. Significantly, the ability of P2z receptor agonists to stimulate this PLD activity was not dependent on the presence of extracellular [Ca2+] or elevation of cytosolic [Ca2+]. The inability of ionomycin, gramicidin, digitonin, UTP, platelet-activating factor, or phorbol ester to quantitatively mimic these nucleotide effects suggested that activation of this PLD by P2z receptor agonists was not a secondary response due to: 1) enhanced Ca2+ influx; 2) membrane depolarization; 3) nonselective permeabilization of the plasma membrane; 4) stimulation of Ca(2+)-mobilizing ATP receptors; 5) stimulation of a primary PI-PLC pathway; or 6) activation of protein kinase C. These findings suggest that activation of a novel PLD-based signaling pathway may play an important role in the modulation of macrophage function by pore-forming P2z receptors for extracellular ATP.
...
PMID:A novel pathway for the activation of phospholipase D by P2z purinergic receptors in BAC1.2F5 macrophages. 133 Oct 96

Cultured aortic fibroblasts express high affinity Et-1 binding sites that poorly discriminate between Et-1 and Et-3. Both endothelins activate phospholipase C hence indicating the presence of ETB receptors. Fibroblasts respond to bradykinin by large activations of phospholipase C and increases in [Ca2+]i in a manner that was abolished by D-Arg, [Hyp3,Thi5,8,D-Phe7]-bradykinin, thus indicating the presence of B2 kinin receptors. Finally, ATP, UTP and ADP increases [Ca2+]i in aortic fibroblasts via a nucleotide receptor that has a higher affinity for ATP and UTP (3 microM) than for ADP (50 microM) and that is distinct from P2x and P2y purinoceptors.
...
PMID:High reactivity of aortic fibroblasts to vasoactive agents: endothelins, bradykinin and nucleotides. 141 43

We have investigated the characteristics of the receptor for ATP on neuronal cells and the involvement of phospholipase C and phospholipase D in the effector mechanisms, using PC12 rat phaeochromocytoma cells in culture. We show that the cells respond, with generation of total inositol phosphates, to ATP and adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) but not to 2-methylthioadenosine5'-triphosphate (2MeSATP), beta,gamma-methylene ATP, or adenosine 5'-O-(2-thiodiphosphate) (ADP beta S). The largest response to ATP gamma S was mainly independent of extracellular calcium, had an EC50 of 7.93 +/- 0.76 microM, and was competitively inhibited by the nonspecific antagonist suramin. The pyrimidine nucleotide UTP also elicited a response in these cells. Measurement of [3H]inositol triphosphate showed a rapid rise to maximum (10-15 sec) in response to both ATP gamma S and UTP but no response to 2MeSATP. Cells prelabeled with 32Pi and stimulated in the presence of 50 mM butanol responded to ATP gamma S, ATP, and UTP with enhanced formation of [32P]phosphatidylbutanol as well as [32P]phosphatidic acid, indicating that agonist-stimulated phosphatidic acid occurs by both phospholipase D and phospholipase C activity. The stimulation of phospholipase D was inhibited by the presence of a protein kinase C inhibitor, Ro 31-8220. The dose-response curve for the stimulation by ATP gamma S of phospholipase C was shifted to the right by the presence of UTP, indicating that both compounds act on the same receptors. The data provide the first evidence for the existence of a nucleotide receptor on neuronal cells (insensitive to both purines and pyrimidines) and show that this receptor is linked to both phospholipase C and phospholipase D.
...
PMID:Neuronal "nucleotide" receptor linked to phospholipase C and phospholipase D? Stimulation of PC12 cells by ATP analogues and UTP. 154 77

Stimulation of phagocytic cells with micromolar concentrations of extracellular ATP primes the production of toxic oxygen metabolites in response to chemoattractants and independently activates a secretory response in vitro. It is hypothesized that extracellular ATP derived from platelet storage granules and damaged endothelium at sites of localized tissue damage or infection may potentiate the pro-inflammatory effects of phagocytic cells in vivo. ATP-dependent functional responses in the phagocyte appear to be due to stimulation of putative P2 purinoreceptors that are coupled to the activation of a phospholipase C via a pertussis toxin-sensitive G-protein. The existence in nature of at least four subtypes of P2 purinoreceptors has been proposed based on the rank order of potency of nucleotide analogs of ATP studied in a variety of cell types. However, no studies involving the structural identification and characterization of the putative receptors have been reported. We have used the Xenopus oocyte expression system to demonstrate acquired adenosine 5'-(thio) triphosphate (ATP gamma S) responsiveness in oocytes injected with mRNA from the promyelocytic leukemia cell line HL60 by measuring the accelerated efflux of intracellular calcium. Two peaks of ATP gamma S responsiveness (Peak I and Peak II) were detected in sucrose gradient fractionated RNA that corresponded to transcript sizes of 4 and 6 kilobases and that were distinct from a third peak previously shown to be enriched in formyl peptide chemoattractant receptor activity. Peak I and Peak II RNA endowed receptor activity in the oocyte that was pharmacologically indistinguishable: ADP and AMP were inactive whereas UTP and ITP exhibited activity that was similar in potency to that of ATP gamma S. Both Peak I and Peak II ATP gamma S-dependent activity was inhibited by pertussis toxin. These data strongly support the concept of phagocytic cell receptors for extracellular nucleotide triphosphates whose ligand specificity is distinct from all other previously described P2 purinoreceptor subtypes, with the exception of the P2 receptor described in Ehrlich ascites tumor cells, by virtue of the ineffectiveness of ADP as a stimulus. These receptors are most likely composed of a single polypeptide chain that can be expressed in the Xenopus oocyte in a functional form regulated by a pertussis toxin-sensitive G-protein.
...
PMID:Characterization of phagocyte P2 nucleotide receptors expressed in Xenopus oocytes. 169 46

Extracellular ATP and UTP produced a rapid accumulation of inositol phosphates in human airway epithelial cells (CF/T43). The order of agonist potencies for a series of nucleotide analogues differed markedly from that of the classically described P2x- or P2y-purinergic receptors. UTP was the most potent agonist and was fully efficacious; ATP and adenosine-5'-O-(3-thiotriphosphate) were also full agonists. In contrast, 2-methylthio-ATP, adenosine-5'-O-(2-thiodiphosphate) and alpha,beta-methylene-ATP were without effect. ADP and UDP had little or no effect at concentrations as high as 100 microM, and deoxyribose and dideoxyribose compounds were inactive. The effects of ATP and UTP were not additive, whereas bradykinin- or histamine-stimulated inositol phosphate production was additive with the effects of ATP or UTP. Preincubation of cells with either UTP or ATP resulted in a parallel loss of responsiveness to both agonists. Desensitization was specific for the response to nucleotides, because no ATP- or UTP-induced effect on the response to histamine or bradykinin was observed. Pertussis toxin treatment of CF/T43 cells produced a 30-40% decrease in the response to ATP or UTP, which correlated with the ADP-ribosylation of 41- and 43-kDa proteins. Bradykinin and histamine responses were not modified by pertussis toxin. Guanine nucleotides had little effect on the inositol phosphate response in intact CF/T43 cells at concentrations below 100 microM. However, in streptolysin-O-permeabilized cells GTP-gamma S produced a concentration-dependence activation of inositol phosphate formation. UTP or ATP had little effect in permeabilized cells in the absence of guanine nucleotides but markedly increased inositol phosphate formation in the presence of guanine nucleotides. Taken together, these results suggest that UTP and ATP activate a 5'-nucleotide receptor on CF/T43 cells that is distinct from the classically defined P2x- and P2y-purinergic receptors. Activation of phospholipase C by this receptor involves, at least in part, a guanine nucleotide-binding regulatory protein.
...
PMID:Evidence that UTP and ATP regulate phospholipase C through a common extracellular 5'-nucleotide receptor in human airway epithelial cells. 194 36

Undifferentiated and differentiated HL-60 leukemic cells possess nucleotide receptors which functionally couple to phospholipase C via pertussis toxin-sensitive guanine nucleotide-binding proteins (G-proteins). We investigated the role of extracellular nucleotides in the regulation of beta-glucuronidase release in HL-60 cells. In dibutyryl cyclic AMP (Bt2cAMP)-differentiated HL-60 cells, the chemotactic peptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe), the phosphorothioate analogue of ATP, adenosine 5'-O-[3-thio]triphosphate (ATP[gamma S]), and UTP increased cytosolic Ca2+ from 100 nM up to 1.2 microM with EC50 values of 4 nM, 1 microM and 100 nM, respectively. In these cells, ATP[gamma S] induced exocytosis with an EC50 of 4 microM and an effectiveness amounting to 50-70% of that of fMet-Leu-Phe. ATP, ITP, UTP, CTP, and uridine 5'-O-[2-thio]diphosphate activated exocytosis as well. Phorbol myristate acetate (PMA) induced exocytosis with an EC50 of 115 ng/ml and an effectiveness similar to that of ATP[gamma S]. Cytochalasin B (CB) differently potentiated exocytosis induced by ATP[gamma S], fMet-Leu-Phe and PMA. Treatment of Bt2cAMP-differentiated HL-60 cells with pertussis toxin (500 ng/ml) for 24 h resulted in ADP-ribosylation of more than 97.5% of the G-proteins. Under these conditions, pertussis toxin almost completely inhibited the increase in cytosolic Ca2+ and beta-glucuronidase release induced by fMet-Leu-Phe but only partially inhibited the effects of ATP[gamma S] and UTP. fMet-Leu-Phe at a non-stimulatory concentration (1 nM) potentiated ATP[gamma S]-induced beta-glucuronidase release in the presence but not in the absence of CB. In contrast, ATP[gamma S] and fMet-Leu-Phe synergistically activated superoxide formation in the absence of CB. PMA potentiated superoxide formation induced by ATP[gamma S] or fMet-Leu-Phe and did not affect exocytosis induced by ATP[gamma S] or fMet-Leu-Phe. In undifferentiated HL-60 cells, fMet-Leu-Phe, ATP[gamma S], UTP and PMA did not induce beta-glucuronidase release. fMet-Leu-Phe did not increase cytosolic Ca2+ in undifferentiated HL-60 cells, whereas ATP[gamma S] and UTP were similarly potent and effective as in Bt2cAMP-differentiated cells. In differentiated HL-60 cells, fMet-Leu-Phe induced aggregation, and ATP[gamma S] induced a transient shape change. Our results show (I) that exocytosis in HL-60 cells does not obligatorily depend on CB. (II) Purine and pyrimidine nucleotides activate exocytosis via pertussis toxin-sensitive and -insensitive signal transduction pathways.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:Nucleotide-, chemotactic peptide- and phorbol ester-induced exocytosis in HL-60 leukemic cells. 196 23

We have previously determined that human neutrophils and monocytes, as well as neutrophil/monocyte progenitor cells, express a subtype of P2-purinergic receptors (for ATP) which activate the inositol phospholipid signalling system. In the present study, membranes prepared from HL-60 promyelocytic leukemia cells were used to examine the mechanism by which these ATP receptors activate phosphatidylinositol-specific phospholipase C (PI-PLC) under defined in vitro conditions. Micromolar concentrations of the receptor agonists ATP, UTP, and ATP gamma S stimulated the GTP-dependent formation of inositol bisphosphate (IP2) and inositol trisphosphate (IP3) in washed membranes prepared from undifferentiated HL-60 cells prelabeled with [3H]inositol. The stimulatory effects of these nucleotides on PI-PLC appeared to be mediated through a GTP binding protein since minimal inositol polyphosphate accumulation was observed in the absence of guanine nucleotides. The increased inositol polyphosphate formation triggered by these nucleotide receptor agonists did not result from inhibition of GTP breakdown. Neither was it a consequence of increased [3H]polyphosphatidylinositol levels resulting from enhanced activity of membrane-associated PI- or PIP-kinases. Instead, the stimulated phospholipase activity was apparently receptor-mediated. The rank order of potency observed in these in vitro membrane assays (ATP = UTP greater than ATP gamma S much greater than TTP greater than CTP much greater than beta, gamma-CH-ATP) was similar to that observed with intact HL-60 cells. This order of potency appears to distinguish the P2-purinergic receptors expressed by human phagocytic leukocytes from the P2 gamma-purinergic receptors which activate PI-PLC in turkey erythrocyte membranes.
...
PMID:P2-purinergic receptors activate a guanine nucleotide-dependent phospholipase C in membranes from HL-60 cells. 216 87

Myeloid differentiated human leukaemia (HL-60) cells contain a soluble phospholipase C that hydrolysed phosphatidylinositol 4.5-bisphosphate and was markedly stimulated by the metabolically stable GTP analogue guanosine 5'-[gamma-thio]triphosphate (GTP[S]). Half-maximal and maximal (up to 5-fold) stimulation of inositol phosphate formation by GTP[S] occurred at 1.5 microM and 30 microM respectively. Other nucleotides (GTP, GDP, GMP, guanosine 5'-[beta-thio]diphosphate. ATP, adenosine 5'-[gamma-thio]triphosphate, UTP) did not affect phospholipase C activity, GTP[S] stimulation of inositol phosphate accumulation was inhibited by excess GDP, but not by ADP. The effect of GTP[S] on inositol phosphate formation was absolutely dependent on and markedly stimulated by free Ca2+ (median effective concn. approximately 100 nM). Analysis of inositol phosphates by anion-exchange chromatography revealed InsP3 as the major product of GTP[S]-stimulated phospholipase C activity. In the absence of GTP[S], specific phospholipase C activity was markedly decreased when tested at high protein concentrations, whereas GTP[S] stimulation of the enzyme was markedly enhanced under these conditions. As both basal and GTP[S]-stimulated inositol phosphate formation were linear with time whether studied at low or high protein concentration, these results suggest that (a) phospholipase C is under an inhibitory constraint and (b) GTP[S] relieves this inhibition, most likely by activating a soluble GTP-binding protein.
...
PMID:Guanosine 5'-[gamma-thio]triphosphate-stimulated hydrolysis of phosphatidylinositol 4,5-bisphosphate in HL-60 granulocytes. Evidence that the guanine nucleotide acts by relieving phospholipase C from an inhibitory constraint. 217 6


1 2 3 4 5 6 7 8 9 10 Next >>

---