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)

Proton magnetic resonance imaging (MRI) and 31P magnetic resonance spectroscopy (MRS) have been used to study the response of the rat liver in situ to bromobenzene, a classic hepatotoxicant. A localized region of high proton signal intensity was seen in the perihilar region of the liver 24 hr after injection of a sublethal dose of bromobenzene. The signal intensity of the entire liver was increased at 48 hr with a gradual return approaching control values by 120 hr. These results are consistent with acute hepatic edema followed by repair of the damaged tissue. In vivo 31P MRS studies of the same rat livers were performed under conditions whereby localized, quantitative spectra could be obtained without surgical intervention. Initial concentrations of the major endogenous phosphorus-containing metabolites within the livers of control rats were 2.97 +/- 0.43 mM for the phosphomonoesters (PME), 2.92 +/- 0.56 mM for inorganic phosphate, 11.3 +/- 1.0 mM for phosphodiesters (PDE), 4.09 +/- 0.54 mM for ATP, and 0.56 +/- 0.50 mM for ADP and the intracellular pH was 7.39 +/- 0.14 (mean +/- SD, n = 10). Bromobenzene was found to cause statistically significant (p less than 0.05) changes in several of these metabolites: a decrease in hepatic ATP levels (20% at 24 hr; 27% at 48 hr), a decrease in PDE levels (15% at 24 hr; 18% at 48 hr), and an increase in the PME (63% at 24 hr; 84% at 48 hr). Both the proton MRI and the 31P MRS changes have an onset of 15-20 hr and maximum effect at 25-60 hr, but the MRS changes returned to normal well before the MRI changes. The decreased ATP levels indicate deleterious effects of bromobenzene on the bioenergetic status of the liver in situ, while the increase in PME, due to a selective increase in phosphocholine, suggests the activation of a phosphatidylcholine-specific phospholipase C in response to tissue damage. Trolox C, a potent inhibitor of lipid peroxidation, prevented the bromobenzene-induced hepatic edema (i.e., the increase in proton MRI signal intensity) and the bioenergetic deterioration (i.e., the decrease in ATP levels). However, the bromobenzene-induced increase in PME levels was not prevented by Trolox C. These results indicate that the process of lipid peroxidation plays a significant role in the hepatotoxicity of bromobenzene within the intact animal.
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PMID:The response of the rat liver in situ to bromobenzene--in vivo proton magnetic resonance imaging and 31P magnetic resonance spectroscopy studies. 194 10

ADP-ribosyltransferase from Clostridium botulinum type C strain was found to induce an increase of inositol phosphates (IPs) formation in murine thymocytes membranes. Incubation of electropermeabilized murine thymocytes with the enzyme also caused an increase of IPs formation in the cells. This increase of IPs formation in the enzyme-treated membranes and electropermeabilized cells was dependent on the amount of both NAD and the enzyme, suggesting that the stimulation of phosphoinositide-specific phospholipase C (PLC) was related to ADP-ribosylation of membrane proteins by the enzyme. On the other hand, in calf and murine thymocytes two proteins with the same molecular weight of 21,000 were found to be ADP-ribosylated by the botulinum ADP-ribosyltransferase. A minor ADP-ribosylation substrate was shown by two-dimensional polyacrylamide gel electrophoresis to be G21k, a low-molecular-weight GTP-binding protein (G protein) suggested previously by us to be involved in PLC regulation [Wang, P. et al. (1987) J. Biochem. 102, 1275-1287; (1988) 103, 137-142; and (1989) 105, 461-466], and the other major ADP-ribosylation substrate was identified as a rho A protein. Under the experimental conditions of the IPs formation study, ADP-ribosylation of both G21k and rho A proteins by botulinum ADP-ribosyltransferase in membranes and permeabilized cells was observed. These results suggest that botulinum ADP-ribosyltransferase-induced PLC stimulation in thymocytes is closely correlated with ADP-ribosylation of the low-molecular-weight G proteins.
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PMID:Low-molecular-weight GTP-binding proteins serving as ADP-ribosylation substrate for ADP-ribosyltransferase from Clostridium botulinum and their relation to phosphoinositides metabolism in thymocytes. 196 61

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)
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PMID:Nucleotide-, chemotactic peptide- and phorbol ester-induced exocytosis in HL-60 leukemic cells. 196 23

The effect of the vasodilatory peptide bradykinin on the regulation of phosphoinositide metabolism in endothelial cells was investigated. Activation of phosphoinositide metabolism by bradykinin in the endothelium of the bovine pulmonary artery was not blocked by pertussis toxin, which ADP-ribosylates a membrane protein of molecular mass 40 kDa, but botulinum toxin, which ADP-ribosylates a membrane protein of molecular mass 24 kDa, fully blocked bradykinin-stimulated phosphoinositide metabolism. The effect of bradykinin was potentiated by guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S), an activator of GTP-binding proteins, and inhibited by guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S), an inhibitor of GTP-binding proteins. Activation of phosphoinositide metabolism by bradykinin was fully blocked by a B2-receptor antagonist, whereas a B1-receptor antagonist did not affect bradykinin action. It is concluded that the B2-receptor in endothelial cells is coupled to phospholipase C via a GTP-binding protein, which is a substrate for botulinum toxin.
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PMID:Regulation by bradykinin of phosphoinositide metabolism in the endothelial cells of the pulmonary artery. 196 71

Guanine nucleotide binding proteins (G proteins) are regulatory molecules that couple membrane receptors to effector systems such as adenylate cyclase and phospholipase C. The alpha subunits of G proteins bind to guanosine 5'-diphosphate (GDP) in the unstimulated state and guanosine 5' triphosphate (GTP) in the active state. Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide), a specific inhibitor of inosine monophosphate (IMP) dehydrogenase, decreases guanylate synthesis from IMP in HL-60 promyelocytic leukemia cells and depletes intracellular guanine nucleotide pools. This study demonstrates that treatment of HL-60 cells with tiazofurin is associated with a fourfold increase in membrane binding sites for the nonhydrolyzable analogue GDP beta S. This increase in binding sites was associated with a 3.2-fold decrease in GDP beta S binding affinity. Similar findings were obtained with GTP gamma S. These effects of tiazofurin treatment on guanine nucleotide binding were also associated with decreased adenosine diphosphate-ribosylation of specific G protein substrates by cholera and pertussis toxin. The results further demonstrate that tiazofurin treatment results in inhibition of G protein-mediated transmembrane signaling mechanisms. In this regard, stimulation of adenylate cyclase by prostaglandin E2 was inhibited by over 50% in tiazofurin-treated cells. Furthermore, tiazofurin treatment resulted in inhibition of N-formylmethionylleucylphenylalanine-induced stimulation of phospholipase C. Taken together, these results indicate that tiazofurin acts at least in part by inhibiting the ability of G proteins to function as transducers of intracellular signals.
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PMID:Effects of tiazofurin on guanine nucleotide binding regulatory proteins in HL-60 cells. 196 38

G proteins are membrane-bound molecules involved in coupling of surface receptors with signal transduction effector systems in multiple cell types including T lymphocytes. Given that mature T cells which lack antigen receptors (CDl-Ti) are refractory to stimulation through CD2 or other accessory molecules, T cell receptor components likely play a critical role in coupling surface receptors with signal transduction effectors. It has recently been proposed that modulation of T cell receptor components with MAbs results in a physical loss or functional inactivation of G protein(s). In view of the importance of the T cell activation process, we herein examined G proteins in untreated or antibody-modulated Jurkat T cells as well as in genetic variants lacking either CD3-Ti or CD2 surface receptors. 43- and 41-kDa G protein alpha chains are ADP ribosylated with cholera (CTX) and pertussis (PTX) toxins, respectively, in wild type and receptor minus cell populations. In the wild type Jurkat cell line as well as in CD3- and CD2- variants, AlF4- can activate the G protein(s) presumably associated with phospholipase C to generate polyphosphoinositide turnover as well as an increase in cytoplasmic free calcium ions. Furthermore, G protein(s) linked to adenylylcyclase, a pathway which inhibits T lymphocyte activation, can be directly activated with CTX in the absence of CD3-Ti or CD2 on the membrane. Importantly, AlF4- can also induce polyphosphoinositide turnover in Jurkat cells whose T cell receptor proteins have been modulated with anti-CD3 MAb. These data provide functional and biochemical evidence that at least certain G proteins are intact in the absence of surface expression of CD3-Ti or CD2 molecules and imply that CD3-Ti desensitization is not singularly due to G protein loss.
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PMID:Characterization of functional GTP binding proteins in Jurkat T cell mutants lacking either CD3-Ti or CD2 surface receptors. 197 60

The association of G-proteins with the T-cell-specific receptor structures CD3 and CD2 was investigated. High-affinity GTPase activity in membrane preparations of the human leukemic T-cell line Jurkat could be induced by the monoclonal antibodies OKT3 (anti-CD3) and OKT11 (anti-CD2). When combining maximally active concentrations of OKT3 and OKT11, no additive effect was seen on GTPase activity. In mutant Jurkat cells lacking the CD3 complex but with an intact CD2 receptor, neither OKT3 nor OKT11 could stimulate GTPase activity. Activation of CD3 and CD2 by monoclonal antibodies also stimulated phospholipase C activity as measured by breakdown of membrane phosphoinositides in wild-type but not in mutant Jurkat cells. Neither GTPase nor phospholipase C activation was sensitive to pretreatment with doses of pertussis toxin (PTX) that caused ADP ribosylation of a sensitive G-protein. Our data show that the CD3 complex and the CD2 receptor may activate a common PTX-insensitive G-protein. The CD2 receptor appears to stimulate the G-protein by interacting with the CD3 complex. The data are compatible with, but do not prove, that this G-protein is involved in the activation of phospholipase C by the two receptors.
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PMID:Stimulation of the T-cell receptors CD3 and CD2 with OKT3 and OKT11 antibodies activates a common pertussis toxin-insensitive G-protein. 198 60

ATP and ADP, in concentrations ranging from 1-100 microM, increased the release of [3H]choline and [3H]phosphorylcholine (P-choline) from bovine aortic endothelial cells (BAEC) prelabelled with [3H]choline. This action was detectable within 5 minutes and was maintained for at least 40 minutes. ATP and ADP were equiactive, and their action was mimicked by their phosphorothioate analogs (ATP gamma S and ADP beta S) and adenosine 5'-(beta, gamma imido) triphosphate (APPNP), but not by AMP, adenosine, and adenosine 5'-(alpha, beta methylene)triphosphate (APCPP): these results are consistent with the involvement of P2Y receptors. ATP also induced an intracellular accumulation of [3H]choline: the intracellular level of [3H]choline was increased 30 seconds after ATP addition and remained elevated for a least 20 minutes. The action of ATP on the release of choline metabolites was reproduced by bradykinin (1 microM), the tumor promoter phorbol 12-myristate 13-acetate (PMA, 50 nM), and the calcium ionophore A23187 (0.5 microM). Down-regulation of protein kinase C, following a 24-hour exposure of endothelial cells to PMA, abolished the effects of PMA and ATP on the release of choline and P-choline, whereas the response to A23187 was maintained. These results suggest that in aortic endothelial cells, ATP produces a sustained activation of a phospholipase D hydrolyzing phosphatidylcholine. The resulting accumulation of phosphatidic acid might have an important role in the modulation of endothelial cell function by adenine nucleotides. Stimulation of phospholipase D appears to involve protein kinase C, activated following the release of diacylglycerol from phosphatidylinositol bisphosphate by a phospholipase C coupled to the P2Y receptors (Pirotton et al., 1987a).
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PMID:Adenine nucleotides modulate phosphatidylcholine metabolism in aortic endothelial cells. 210 83

We have previously characterized a hormonally regulated soluble form of phospholipase A2 (PLA2) in the cultured renal mesangial cell which is similar and possibly identical to the major form in rat kidney. In an attempt to further characterize the mechanisms of regulation of this enzyme we have used epidermal growth factor (EGF), which does not activate polyphosphoinositide-specific phospholipase C in these cells. EGF-enhanced PLA2 activity as assayed by the ability of the soluble extracts of cells to cleave arachidonic acid from the sn-2 position of phosphatidylcholine and phosphatidylethanolamine. This represents a direct demonstration of EGF-induced PLA2 activation which is preserved in a cell-free extract. Phorbol myristate acetate (PMA), as well as 1-oleoyl-2-acetylglycerol, also enhanced PLA2 activity. By contrast, the calcium ionophore A23187 had no effect on extract PLA2 activity. The EGF- and PMA-induced enhanced activity was recovered following fractionation by Mono-Q anion exchange chromatography. The peak of activity comigrated for both agonists, suggesting that both EGF and PMA stimulated the same form of the enzyme. Down-regulation of protein kinase C by pretreatment with PMA resulted in loss of the PMA-induced, but not the EGF-induced, enhancement in PLA2 activity. 8-Bromo-cAMP had no effect upon the PLA2 activity, and did not modulate the EGF effect. Pertussis toxin induced G protein ADP-ribosylation but had no effect upon PLA2 activity, and did not alter the EGF effect. In summary, EGF results in a stable modification of PLA2 activity in glomerular mesangial cells. This enhanced activity is independent of polyphosphoinositide hydrolysis, insensitive to protein kinase C down-regulation, and is not affected by cAMP or pertussis toxin pretreatment of the cells.
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PMID:Epidermal growth factor enhances glomerular mesangial cell soluble phospholipase A2 activity. 210 62

Guanine nucleotide-binding regulatory proteins, or G proteins, mediate the interaction of agonist receptors on the platelet surface with phospholipase C and adenylyl cyclase. To better understand this process, we have used several approaches to identify which G proteins are present in platelets, normal human megakaryocytes, and human erythroleukemia (HEL) cells, a leukemic cell line with megakaryocytic features. Because platelet and HEL cell responses to thrombin are inhibited by pertussis toxin, we have focused upon the members of the Gi family, whose alpha subunits can be ADP-ribosylated by that toxin. Western blots with antisera specific for Gi alpha demonstrated the presence in both platelets and HEL cells of the three best-described forms of this protein: Gi alpha 1, Gi alpha 2, and Gi alpha 3. Based upon immunoprecipitation studies with [35S]-methionine-labeled HEL cells, their relative abundance appears to be Gi alpha 2 much greater than Gi alpha 3 greater than Gi alpha 1. A HEL cell cDNA library screened with the Gi alpha antisera produced clones encoding Gi alpha 2 and Gi alpha 3 that had sequences similar to those reported from other sources. Gi alpha-specific probes created from these cDNA clones confirmed the presence of mRNA encoding Gi alpha 2 and Gi alpha 3 in both platelets (by Northern blotting) and megakaryocytes (by in situ hybridization). Thus the pertussis toxin substrates that have previously been detected in platelets and HEL cells are shown to be members of the Gi alpha family, all of which are candidates for interaction with receptors for thrombin and other agonists.
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PMID:Identification of the pertussis toxin-sensitive G proteins in platelets, megakaryocytes, and human erythroleukemia cells. 211 27


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