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)

When loaded alongside GTP-gamma-S into ATP-permeabilized cells, neomycin, at concentrations below 1 mM, inhibits GTP-gamma-S-induced histamine secretion and phosphatidic acid formation (Cockcroft, S., and B. D. Gomperts, 1985. Nature (Lond.). 314: 534-536; Aridor, M., L. M. Traub, and R. Sagi-Eisenberg. 1990. J. Cell Biol. 111:909-917). However, at higher concentrations internally applied neomycin induces histamine secretion in a process that is: (a) dose dependent; (b) dependent on the internal application of GTP; (c) independent of phosphoinositide breakdown; and (d) inhibited by pertussis toxin (PtX) treatment. These results indicate that neomycin can stimulate histamine secretion in a mechanism that bypasses phospholipase C (PLC) activation and yet involves a PtX-sensitive GTP-binding protein (G protein). Unlike its dual effects, when internally applied, neomycin induces histamine secretion from intact mast cells in a dose-dependent manner. Half-maximal and maximal effects are obtained at 0.5 and 1 mM neomycin, respectively. This process is rapid (approximately 30 s), is independent of external Ca2+, and is associated with phosphatidic acid formation, implying that neomycin can activate histamine secretion by a mechanism similar to that utilized by other basic secretagogues of mast cells. Neomycin stimulates fourfold the GTPase activity of cholate-solubilized rat brain membranes in a PtX-inhibitable manner. In addition neomycin, as well as the basic secretagogues of mast cells, compound 48/80, and mastoparan, significantly reduce (by approximately 80%) the ADP ribosylation of PtX substrates present in rat brain membranes. Taken together these data suggest that neomycin can stimulate secretion from mast cells by directly activating G proteins that play a role in stimulus-secretion coupling. When internally applied, neomycin presumably stimulates secretion by activating a G protein that is located downstream to PLC. This G protein serves as a substrate for PtX.
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PMID:Neomycin is a potent secretagogue of mast cells that directly activates a GTP-binding protein involved in exocytosis. 170 86

The localization of several GTP-binding regulatory proteins in teh apical membrane of intestinal epithelial cells has prompted us to investigate a possible role for G-proteins as modulators of apical Cl- channels. In membrane vesicles isolated from rat small intestine or human HT29-cl.19A colon carcinoma cells, the entrapment of guanosine 5'-O-(3-thiophosphate (GTP gamma S) led to a large increase in Cl- conductance, as evidenced by an increased 125I- uptake and faster SPQ quenching. The enhancement was observed in the presence, but not in the absence of the K+ ionophore valinomycin, indicating that the increased Cl- permeability is not secondary to the opening of K+ channels. The effect of GTP gamma S was counteracted by guanosine 5'-O-(2-thiophosphate (GDP beta S) and appeared to be independent of cytosolic messengers, including ATP, cAMP, and Ca2+, suggesting that protein phosphorylation and/or phospholipase C activation is not involved. Patch clamp analysis of apical membrane patches of HT29-cl.19A colonocytes revealed a GTP gamma S-activated, inwardly rectifying, anion-selective channel with a unitary conductance of 20 +/- 4 pS. No spontaneous channel openings were observed in the absence of GTP gamma S, while the open time probability (Po) increases dramatically to 0.81 +/- 0.09 upon addition with GTP gamma S. Since the electrophysiological characteristics and regulatory properties of this channel are markedly different from those of the more widely studied cAMP/protein kinase A-operated channel, we propose the existence of a separate Cl(-)-selective ion channel in the apical border of intestinal epithelial cells. Our results suggest an alternative regulatory pathway in transepithelial salt transport and a possible site for anomalous channel regulation as observed in cystic fibrosis patients.
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PMID:G-proteins mediate intestinal chloride channel activation. 170 25

A major part of the present understanding of the molecular basis of signal transduction has been gained from in vitro studies using classical biochemical methods. In this study, we used 31P NMR spectroscopy to investigate the response of live M2R mouse melanoma cells to stimulation by melanocyte-stimulating hormone (MSH; melanotropin). In the presence of 3-isobutyl-1-methylxanthine and a synergistic dose of forskolin (1.67 microM), MSH induced a transient (approximately 60-min) rise in the cellular concentration of 3',5'-cyclic adenosine monophosphate (cAMP), which coincided in time with an equivalent decrease (approximately 40%) in ATP. However, no detectable change in phosphocreatine concentration was observed. Concomitantly, MSH induced a striking and unexpected increase in the concentration of three phosphomonoester (PME) metabolites (approximately 2-fold increase in total PME signal area); one signal has been assigned to phosphoethanolamine. The levels of the PMEs remained high for 2-4 hr and declined slowly (approximately 10 hr) to basal level, following perfusion with fresh culture medium. The increase in PME was also observed after stimulation with MSH alone. In contrast, stimulation with a high dose of forskolin (50 microM) and isobutylmethylxanthine (0.2 mM), although effective in stimulating the production of cAMP, did not induce the PME response. Evaluation of the cells' energetics indicated that the enhanced production of phosphoethanolamine is probably not due to ethanolamine phosphorylation. Therefore, it is likely to result from hydrolysis of phosphatidylethanolamine by a specific phospholipase C. The response of the PMEs appears to be regulated by a cAMP-independent process, suggesting the existence of an alternative transduction pathway controlled by MSH.
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PMID:Stimulation of cAMP and phosphomonoester production by melanotropin in melanoma cells: 31P NMR studies. 170 40

Extracellular ATP initiates a variety of changes in the parotid acinar cell. The initial effect appears to be the entry of Ca2+ (and perhaps Na+), and a series of ion transport events result from the subsequent elevation of [Ca2+]i. Agonists of phospholipase C-linked receptors elevate [Ca2+]i by a different pathway, involving the generation of inositol polyphosphate compounds, but share in the subsequent initiation of the ion transport events. Although the maintenance of the physiological changes may depend on specific inositol polyphosphate intermediates, the critical initiating factor is the elevation of [Ca2+]i. Fluid secretion by the parotid gland is triggered by the action of neurotransmitters, which alter the membrane permeability of the acinar cell. The similarities between the two receptor-mediated activation pathways suggests that ATP may act as a neurotransmitter and play a role in the control of fluid secretion. Basing our analysis on the purinoceptor characteristics outlined by Gordon, we suggest that the parotid receptor belongs to the P2Z class, which is highly sensitive to ATP4-. Basing his analysis on the earlier report by Gallacher of the effects of ATP on mouse parotid cells, Gordon placed the parotid purinoceptor in a different P2 subclass (P2Y). However, our findings of an increased potency of ATP in the absence of Mg2+, as well as the potency order of different nucleotides, indicate that the P2Z class is a more appropriate category.
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PMID:Elevation of [Ca2+]i and the activation of ion channels and fluxes by extracellular ATP and phospholipase C-linked agonists in rat parotid acinar cells. 170 2

Thrombin induced an increase in [Ca2+]i in mouse mastocytoma P-815 cells. This increase was markedly reduced by prior exposure to pertussis toxin (PT) but not by removal of extracellular Ca2+, suggesting that thrombin stimulates phospholipase C via a PT-sensitive GTP-binding protein. ATP also induced an increase in [Ca2+]i. This increase was insensitive to PT but completely suppressed on removal of extracellular Ca2+, suggesting that ATP stimulates Ca2+ influx in a PT-insensitive manner. Iloprost, a stable prostacyclin analogue, increased the cellular cAMP level and dose-dependently inhibited the thrombin-induced increase in [Ca2+]i, whereas the ATP-induced increase in [Ca2+]i was markedly enhanced by iloprost. Cyclic AMP analogues, dibutyryl cAMP and 8-bromo cAMP, also inhibited the increase in [Ca2+]i induced by thrombin and promoted that by ATP, indicating that the inhibitory and stimulatory effects of iloprost are mediated by cAMP. These results suggest that the prostacyclin receptor differentially regulates two distinct Ca2+ mobilizing systems via cAMP in mastocytoma cells.
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PMID:Differential regulation of thrombin- or ATP-induced mobilization of intracellular Ca2+ by prostacyclin receptor in mouse mastocytoma cells. 170 39

Although most studies of protein phosphorylation have focused on intracellular protein kinases, evidence for protein kinase activity on the surface of several types of cells has been described. Evidence was recently provided for the existence of ecto-protein kinase activity on the surface of human neutrophils. Evidence for three distinct ecto-protein kinase activities was detected, one that phosphorylates endogenous surface proteins, one that phosphorylates exogenous substrates in a cAMP-independent manner and is released in the presence of substrate, and a low level of activity of one that phosphorylates exogenous Kemptide in a cAMP-dependent manner. To begin to elucidate its role in neutrophil function, we have characterized several properties of the releasable ecto-protein kinase activity on human neutrophils. This enzyme activity was inhibited by impermeant stilbene disulfonic acids, which are known to alter neutrophil function, as well as by impermeant sulfhydryl reactive agents. Enzyme activity was detectable at physiologic concentrations of Mg2+, but was higher in the presence of Mn2+. Protein kinase activity was strongly inhibited by heparin, whereas trifluoperazine, cAMP, and cGMP had little effect on kinase activity. Protein kinase activity was selectively removed from the cell surface by incubation with the ecto-kinase substrates casein and phosvitin, but the enzyme was not released by phosphatidylinositol-specific phospholipase C. Repeated exposure of neutrophils to substrate depleted ecto-protein kinase activity from the cell surface, but activity was rapidly restored by incubation in buffer lacking substrate. The released protein kinase had a Km for ATP of approximately 0.5 microM and a pH maximum between 7.0 and 7.5. At least four ecto-protein kinase substrates were detected in serum; vitronectin was identified as one of these substrates by immunoprecipitation studies. Although the exact role of ecto-protein kinase activity in neutrophil function remains undefined, the identification of vitronectin as a serum substrate suggests that it interacts with a physiologically important substrate.
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PMID:Characterization of human neutrophil ecto-protein kinase activity released by kinase substrates. 171 14

The role of lipid-bound second messengers in the regulation of neurotransmitter secretion is an important but poorly understood subject. Both bovine adrenal chromaffin cells and rat phoeochromocytoma (PC12) cells, two widely studied models of neuronal function, respond to bradykinin by generating phosphatidic acid (PA). This putative second messenger may be produced by two receptor-linked pathways: sequential action of phospholipase C (PLC) and diacylglycerol kinase (DAG kinase), or directly by phospholipase D (PLD). Here we show that bradykinin stimulation of chromaffin cells prelabelled (24 h) with 32Pi leads to production of [32P]PA which is not affected by 50 mM butanol. However, bradykinin stimulation of PC12 cells leads to [32P]PA formation, all of which is converted to phosphatidylbutanol in the presence of butanol. When chromaffin cells prelabelled with [3H]choline were stimulated with bradykinin there was no enhancement of formation of water soluble products of phosphatidylcholine hydrolysis. When chromaffin cells were permeabilised with pneumolysin and incubated in the presence of [gamma-32P]ATP, the formation of [32P]PA was still stimulated by bradykinin. These results show that, although both neuronal models synthesize PA in response to bradykinin, they do so by quite different routes: PLC/DAG kinase for chromaffin cells and PLD for PC12 cells. The observation that neither bradykinin nor tetradecanoyl phorbol acetate stimulate PLD in chromaffin cells suggests that these cells lack PLD activity. The conservation of PA formation, albeit by different routes, may indicate an essential role of PA in the regulation of cellular events by bradykinin.
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PMID:Lack of phospholipase D activity in chromaffin cells: bradykinin-stimulated phosphatidic acid formation involves phospholipase C in chromaffin cells but phospholipase D in PC12 cells. 171 14

Addition of ethanol (17 to 340 mM) to cultured rat hepatocytes stimulated the breakdown of phosphatidylcholine phospholipases D and C as measured by an increase in the rate of release of choline and phosphocholine into the medium. The effects of ethanol were mimicked by propanol, dimethylsulfoxide and to a lesser extent methanol. The magnitude of the stimulation seen with ethanol was equivalent to and additive to that produced by glucagon vasopressin, norepinephrine, A23187 or PMA. In contrast, ethanol (340 mM) stimulated PI-specific phospholipase C activity by less than 20%. An equivalent stimulation of PC-specific phospholipase D and C was seen with as little as 20 mM ethanol and a 100% increase was seen with 340 mM ethanol. Ethanol did not significantly affect the ability of vasopressin, norepinephrine, ATP or A23187 to stimulate PI-specific phospholipase C. It is concluded that while ethanol is only a weak stimulator of PI-specific phospholipase C, it is a potent stimulator of phosphatidylcholine breakdown in rat hepatocytes.
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PMID:Ethanol is a potent stimulator of phosphatidylcholine breakdown in cultured rat hepatocytes. 173 64

The mechanism of arachidonic acid (AA)-induced LH release was characterized using sheep pituitary cells in primary culture permeabilized with Staphylococcal alpha-toxin. In intact cells, exogenous AA evoked release of LH in a manner which was partially dependent on extracellular Ca2+. At similar concentrations, AA also caused cell permeabilization as monitored by efflux of [3H]2-deoxyglucose metabolites. In alpha-toxin-permeabilized cells where cytosolic Ca2+ was clamped at resting levels, AA retained its ability to cause LH release. Unlike the stimulation of exocytosis produced by Ca2+, phorbol ester or cyclic AMP, AA-evoked release was independent of ATP and was not inhibited by pretreatment with N-ethyl maleimide. These findings indicated that exogenous AA does not cause LH release by Ca2+ influx or mobilization or by activating protein kinase C. The results suggest that LH release induced by exogenous AA is probably due to its detergent-like properties, and does not represent true exocytosis.
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PMID:Arachidonic acid-induced LH release is ATP-independent and insensitive to N-ethyl maleimide. 173 62

The phospholipid bilayer of the plasma membrane plays an important role in forming a functional barrier against leakage of ions and other cell constituents. We have examined the effect of an exogenously added phospholipase C (PLC) on phospholipid degradation in isolated rat myocardial cells subjected to hypothermia (5 degrees C) and hypothermia followed by rewarming to 37 degrees C. The activity of PLC was measured as glycerol output to the incubation medium since the combined action of PLC and endogenous lipases will result in glycerol production. Addition of PLC resulted in a significantly higher output of glycerol in rewarmed myocytes than in myocytes kept constantly at 5 degrees C and 37 degrees C. Rewarmed cells also showed the highest leakage of lactate dehydrogenase (LDH), but there was no additional effect of PLC on LDH leakage. Normal levels of cellular ATP were maintained in all myocyte groups. These results show that rewarming from hypothermia may cause structural derangements in the phospholipid bilayer of the sarcolemma which in turn could favor attack by endogenous phospholipases.
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PMID:Membrane phospholipid metabolism of rat myocardial cells during hypothermia and rewarming. 181 80


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