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)

The cholinergic agonist carbachol induced the release of arachidonic acid in the 1321N1 astrocytoma cell line, and this was blocked by atropine, suggesting the involvement of muscarinic receptors. To assess the mechanisms of signalling involved in the response to carbachol, a set of compounds characterized by eliciting responses through different mechanisms was tested. A combination of 4beta-phorbol 12beta-myristate 13alpha-acetate and thapsigargin, an inhibitor of endomembrane Ca2+-ATPase that induces a prolonged elevation of cytosolic Ca2+ concentration, induced an optimal response, suggesting at first glance that both protein kinase C (PKC) and Ca2+ mobilization were involved in the response. This was consistent with the observation that carbachol elicited Ca2+ mobilization and PKC-dependent phosphorylation of cytosolic phospholipase A2 (cPLA2; phosphatide sn-2-acylhydrolase, EC 3.1.1.4) as measured by a decrease in electrophoretic mobility. Nevertheless, the release of arachidonate induced by carbachol was unaltered in media containing decreased concentrations of Ca2+ or in the presence of neomycin, a potent inhibitor of phospholipase C which blocks phosphoinositide turnover and Ca2+ mobilization. Guanosine 5'-[gamma-thio]triphosphate added to the cell-free homogenate induced both [3H]arachidonate release and cPLA2 translocation to the cell membrane fraction in the absence of Ca2+, thus suggesting the existence of an alternative mechanism of cPLA2 translocation dependent on G-proteins and independent of Ca2+ mobilization. From the combination of experiments utilizing biochemical and immunological tools the involvement of cPLA2 was ascertained. In summary, these data indicate the existence in the astrocytoma cell line 1321N1 of a pathway involving the cPLA2 which couples the release of arachidonate to the occupancy of receptors for a neurotransmitter, requires PKC activity and G-proteins and might operate in the absence of Ca2+ mobilization.
...
PMID:Cytosolic phospholipase A2 is coupled to muscarinic receptors in the human astrocytoma cell line 1321N1: characterization of the transducing mechanism. 917 94

A family of G protein-coupled P2Y receptors that are activated by adenine and uridine nucleotides has been identified recently. Degenerate primers based on conserved sequences in these P2Y receptors were used to amplify turkey DNA, which was used to isolate the complete coding sequence of a cDNA that encodes a novel G protein-coupled receptor. Stable expression of this avian cDNA in 1321N1 human astrocytoma cells resulted in the conveyance of marked inositol phosphate responses to various nucleotides. Although this cloned avian receptor exhibited its highest homology to the previously cloned mammalian P2Y4 receptor, its pharmacological selectivity was not consistent with the avian receptor's being a species homologue of the P2Y4 receptor. That is, whereas the P2Y4 receptor is selectively activated by UTP and is not activated by ATP or Ap4A, the novel avian receptor was potently activated by ATP and Ap4A as well as by UTP. Taken together, these results describe the identification of an avian phospholipase C-coupled P2Y receptor that, like the mammalian P2Y2 receptor, is activated by both adenine and uridine nucleotides.
...
PMID:Molecular cloning and expression of an avian G protein-coupled P2Y receptor. 941 2

IL-1 beta is one of the cytokines known to affect astroglial cells in normal brain development, brain injury and neurodegenerative diseases. IL-1 beta causes astrocytes to become more reactive, alter the expression and release of molecules and in some cases to proliferate. We have investigated the mitogenic effect and signal transduction pathway induced by IL-1 beta in U373 cells, a human astrocytoma cell-line. Recombinant human IL-1 beta induced mitogenesis of U373 cells in a dose-dependent fashion as assessed by tritiated thymidine incorporation. The following signal transduction mechanisms, reported to be induced in other systems by IL-1 beta, were investigated in U373 cells: (1) activation of phosphatidylcholine-specific phospholipase C as assayed by incorporation of tritiated choline into cellular phospholipids, (2) production of diacylglycerol, a lipid second messenger, (3) activation of sphingomyelinase, and (4) activation of mitogen-activated protein kinase (MAPK). Of these, IL-1 beta activated only MAPK. In cultured rat astrocytes, IL-1 beta caused activation of MAPK without inducing proliferation.
...
PMID:Interleukin-1 beta stimulates mitogen-activated protein kinase in U373 astrocytoma cells without the production of lipid second messengers. 947 19

The compartmentation of inositol phospholipids was examined by using a combination of radiolabelling approaches in intact and permeabilized 1321N1 astrocytoma cells. A 'chase' protocol was developed with whole cells in which phosphoinositide (PI) pools were labelled to steady state with [3H]inositol and the cellular [3H]inositol pool was then diluted selectively with non-radioactive inositol. In these cells muscarinic-receptor-stimulated phospholipase C (PLC) hydrolysed [3H]PI at approx. 1-2%/min. However, after the chase procedure the relative specific radioactivity of [3H]Ins(1,3,4)P3, a rapidly metabolized and sensitive marker of PLC activity, decreased only after more than 5 min and over a time course similar to that during which the labelling of each [3H]PtdIns, [3H]PtdInsP and [3H]PtdInsP2 declined by at least 50%. These results demonstrate a large receptor-responsive [3H]PI pool that is accessed by stimulated PLC without apparent metabolic compartmentation, despite its probable distribution between different membrane fractions. Support for this was obtained in intact cells by using an acute [3H]inositol labelling method in which increases in the specific radioactivity of [3H]inositol phosphates stimulated by carbachol occurred only in parallel with similar increases in the labelling of the bulk of cellular [3H]PI. In [3H]inositol-prelabelled cells permeabilized to deplete cytosolic proteins, carbachol and guanosine 5'-[gamma-thio]triphosphate stimulated the endogenous PLC to degrade only approx. 5% of [3H]PI. This was increased to approx. 30% in the presence of exogenous PtdIns transfer protein, which, at a concentration approx. 5-10% of that in 1321N1 cell cytosol, was sufficient to support PLC activity comparable with that observed in response to carbachol in whole cells. These and earlier results in 1321N1 cells suggest a model of integrated PI pools involving an obligatory role for lipid transport. Given the multifunctional capacity of PI in cellular signalling mechanisms, this model has important implications, particularly for the hypothesis that the ability of Li+ ions to influence these selectively might account for its therapeutic actions.
...
PMID:Evidence for a model of integrated inositol phospholipid pools implies an essential role for lipid transport in the maintenance of receptor-mediated phospholipase C activity in 1321N1 cells. 949 70

The Gq/phospholipase C-linked human P2Y2 receptor was tagged at its amino terminus with the hemagglutinin A (HA) epitope sequence (P2Y2-HA) and stably expressed in 1321N1 human astrocytoma cells. Neither the pharmacological selectivity nor the signaling properties of the receptor were altered by the presence of the epitope. An enzyme-linked immunosorbent assay was developed to quantify cell surface levels of P2Y2-HA receptors using an anti-HA antibody. Incubation of cells with P2Y2 receptor agonists resulted in a concentration of agonist- and time-dependent decrease in cell surface immunoreactivity. Methodology for indirect immunofluorescence confocal microscopy was developed and applied to demonstrate that the agonist-promoted decreases in cell surface immunoreactivity paralleled increases in intracellular immunoreactivity. Agonist-induced internalization of P2Y2 receptors was demonstrated directly by prelabeling P2Y2-HA receptors with antibody before agonist challenge and then quantifying the movement of receptors from a cell surface to intracellular localization in the presence of agonist. Removal of agonist from the medium resulted in recovery of cell surface immunoreactivity to control levels within approximately 1 hr. Incubation of P2Y2-HA receptor-expressing cells with P2Y2 receptor agonists also resulted in receptor-specific desensitization of nucleotide-promoted inositol phosphate accumulation. This loss of responsiveness occurred more rapidly and to a greater extent than did the agonist-promoted loss of surface receptors. Inhibition of receptor internalization by reduction of temperature to 16 degrees had no effect on the capacity of nucleotides to induce P2Y2 receptor-specific desensitization. These results illustrate that the P2Y2 receptor undergoes agonist-promoted movement to an intracellular compartment. This receptor internalization is not required for agonist-induced desensitization.
...
PMID:Agonist-induced internalization of the P2Y2 receptor. 973 Sep 7

Recent evidence supporting a role for phosphoinositides in the endocytosis of phospholipase C-coupled receptors has prompted an investigation of whether there exists a similar requirement for the internalization of adenylyl cyclase-linked receptors. When 1321N1 astrocytoma cells, which possess both muscarinic cholinergic receptors (mAChRs) that couple to phospholipase C and beta-adrenergic receptors (beta(2)-ARs) linked to adenylyl cyclase, were pretreated with wortmannin (WT) at a concentration known to inhibit phosphatidylinositol 4-kinase activity, the labeling of both phosphatidylinositol 4-phosphate and phosphatidylinositol 4, 5-bisphosphate (PIP(2)) was reduced. Stimulation of phosphoinositide breakdown by activation of mAChRs in WT-pretreated cells led to a further depletion of PIP(2). As previously demonstrated for SH-SY5Y neuroblastoma, inclusion of WT inhibited the endocytosis of mAChRs in 1321N1 cells by >85%. In contrast, the internalization of beta(2)-ARs was only partially ( approximately 30%) prevented. However, when the concentration of PIP(2) was further reduced by exposure of WT-pretreated 1321N1 cells to a muscarinic agonist, the endocytosis of beta(2)-ARs was substantially inhibited (>70%). Lower concentrations of WT (100 nM) that were sufficient to fully inhibit phosphatidylinositol 3-kinase activity had no effect on either phosphoinositide synthesis or receptor endocytosis. The results indicate that the agonist-induced endocytosis of an adenylyl cyclase-linked receptor such as the beta(2)-AR, like that of the phospholipase C-coupled mAChR, is dependent on the synthesis of phosphoinositides and, in particular, that of PIP(2).
...
PMID:Inhibition of beta(2)-adrenergic and muscarinic cholinergic receptor endocytosis after depletion of phosphatidylinositol bisphosphate. 1041 68

Thromboxane A2 (TXA2) receptor expression with its signaling was investigated in 1321N1 human astrocytoma cells differentiated with dibutyryl cyclic AMP (dbcAMP). The cells cultured in 0.5% fetal calf serum containing 0.5 mM dbcAMP for 3 days showed the star-shaped morphology, accompanied with the reduction of a TXA2 mimetic U46619-induced phosphoinositide hydrolysis and Ca2+ mobilization. Immunoblotting analysis revealed that human astrocytoma cells expressed phospholipase C (PLC)-beta1 and -beta3, but not PLC-beta2. The contents of PLC-beta1 and beta3 were not changed by the differentiation. The alpha subunit of Gq/ll bound to TXA2-receptor was reduced by the differentiation, determined by immunoblotting after immunoprecipitation with an anti-TXA2-receptor antibody. Scatchard analysis of the binding of [3H]SQ29548, a TXA2 receptor antagonist, to the membranes revealed that the maximum binding site was reduced by the differentiation. The expression of TXA2 receptor mRNA also was reduced by the differentiation, determined by reverse-transcribed-polymerase chain reaction. Although placental type of TXA2 receptor mRNA expression increased after the differentiation, endothelial type of TXA2 receptor mRNA expression slightly decreased. The results suggest that 1321N1 human astrocytoma cells differentiated with dbcAMP show impaired TXA2 receptor-mediated phosphoinositide hydrolysis and Ca2+ mobilization, due to the decrease in TXA2 receptor number.
...
PMID:Decrease in thromboxane A2 receptor expression by differentiation with dibutyryl cyclic AMP in 1321N1 human astrocytoma cells. 1048 87

We recently cloned and expressed a novel P2Y receptor (tp2y receptor) from a turkey cDNA library. Expression of this receptor in 1321N1 human astrocytoma cells confers nucleotide-dependent stimulation of phospholipase C activity; however, as we demonstrate here, it also confers nucleotide-dependent inhibition of adenylyl cyclase. Both the phospholipase C and adenylyl cyclase responses were promoted by receptor agonists over a similar range of concentrations. Moreover, not only did UTP and ATP activate the avian receptor but ITP, GTP, xanthosine 5'-triphosphate, and CTP were also agonists, with EC(50) values ranging between 0.1 and 1 microM. Similar potencies, rank-order, and selectivity of nucleotide agonists were also demonstrated for intracellular Ca(2+) mobilization measured during a 30-s stimulation under constant superfusion conditions. This observation indicates that receptor activation by nucleoside 5'-triphosphates is not produced by interconversion of these nucleotides into ATP or UTP. Pretreatment of cells with pertussis toxin completely abolished the inhibitory effect of nucleotide agonists on adenylyl cyclase, whereas the activation of phospholipase C was only partially inhibited. These results demonstrate that the avian P2Y receptor is a nucleoside triphosphate receptor of broad agonist selectivity that interacts with both pertussis toxin-insensitive and -sensitive G proteins to activate phospholipase C and to inhibit adenylyl cyclase. This is the first cloned P2Y receptor that is clearly Gi/adenylyl cyclase-linked.
...
PMID:A molecularly identified P2Y receptor simultaneously activates phospholipase C and inhibits adenylyl cyclase and is nonselectively activated by all nucleoside triphosphates. 1072 29

Thromboxane A2 (TXA2) receptor-mediated signal transduction was investigated in 1321N1 human astrocytoma cells. 9,11-Epithio-11,12-methano-TXA2 (STA2), a TXA2 receptor agonist, induced Ca2+ mobilization and phosphoinositide hydrolysis in a concentration-dependent manner. These responses were inhibited by treatment with U73122, an inhibitor of phosphatidylinositol-specific phospholipase C, or by culturing in 0.5% fetal calf serum containing 0.5 mM dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP) for 2 days. However, the dbcAMP treatment augmented the TXA2 receptor-mediated phosphorylation of mitogen-activated protein kinase (MAPK). These results were confirmed by a functional MAPK assay measuring the incorporation of 32P into the MAPK substrate peptide. The TXA2 receptor-mediated MAPK activation was inhibited by SQ29548, a TXA2 receptor antagonist, and GF109203X, an inhibitor of protein kinase C. Although U73122 did not inhibit or only slightly inhibited the activation of MAPK, D-609, an inhibitor of phosphatidylcholine-specific phospholipase C, potently attenuated the activation in a concentration-dependent manner. Furthermore, STA2 accelerated the release of [3H]choline metabolites from the cells prelabeled with [3H]choline chloride. This release was inhibited by treatment with D-609. These results suggest that phosphatidylcholine-specific phospholipase C and protein kinase C, but not phosphatidylinositol-specific phospholipase C, are involved in TXA2 receptor-mediated MAPK activation in 1321N1 human astrocytoma cells.
...
PMID:Involvement of phosphatidylcholine-specific phospholipase C in thromboxane A2-induced activation of mitogen-activated protein kinase in astrocytoma cells. 1080 Sep 62

1. The human P2Y(11) (hP2Y(11)) receptor was stably expressed in two cell lines, 1321N1 human astrocytoma cells (1321N1-hP2Y(11)) and Chinese hamster ovary cells (CHO-hP2Y(11)), and its coupling to phospholipase C and adenylyl cyclase was assessed. 2. In 1321N1-hP2Y(11) cells, ATP promoted inositol phosphate (IP) accumulation with low microM potency (EC(50)=8.5+/-0.1 microM), whereas it was 15 fold less potent (130+/-10 microM) in evoking cyclic AMP production. 3. In CHO-hP2Y(11) cells, ATP promoted IP accumulation with slightly higher potency (EC(50)=3.6+/-1.3 microM) than in 1321N1-hP2Y(11) cells, but it was still 15 fold less potent in promoting cyclic AMP accumulation (EC(50)=62.4+/-15.6 microM) than for IP accumulation. Comparable differences in potencies for promoting the two second messenger responses were observed with other adenosine nucleotide analogues. 4. In 1321N1-hP2Y(11) and CHO-hP2Y(11) cells, down regulation of PKC by chronic treatment with phorbol ester decreased ATP-promoted cyclic AMP accumulation by 60--80% (P<0.001) with no change in its potency. Likewise, chelation of intracellular Ca(2+) decreased ATP-promoted cyclic AMP accumulation by approximately 45% in 1321N1-hP2Y(11) cells, whereas chelation had no effect on either the efficacy or potency of ATP in CHO-hP2Y(11) cells. 5. We conclude that coupling of hP2Y(11) receptors to adenylyl cyclase in these cell lines is much weaker than coupling to phospholipase C, and that activation of PKC and intracellular Ca(2+) mobilization as consequences of inositol lipid hydrolysis potentiates the capacity of ATP to increase cyclic AMP accumulation in both 1321N1-hP2Y(11) and CHO-hP2Y(11) cells.
...
PMID:Differential coupling of the human P2Y(11) receptor to phospholipase C and adenylyl cyclase. 1115 92


<< Previous 1 2 3 4 5 6 7 8 Next >>

---