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)

In WRK1 cells vasopressin stimulates Ins(1,4,5)P3 accumulation and mobilizes intracellular calcium. These two phenomena are transient and exhibit similar time-courses. Experiments performed on intact cells or membrane preparations demonstrate that calcium may also stimulate an accumulation of inositol phosphates. This suggests a possible positive feedback regulation of the primary accumulation of Ins(1,4,5)P3 induced by vasopressin. In order to test such a possibility we studied the vasopressin-induced Ins(1,4,5)P3 accumulation, where intracellular calcium mobilization is artificially suppressed by incubating the cells with EGTA in the presence of ionomycin. Under these conditions the accumulation of Ins(1,4,5)P3 induced by 1 microM vasopressin is inhibited by around 50% when measured 5 s after stimulation. This inhibition is not due to an alteration of the VIa vasopressin receptor binding properties, a reduction of the amount of substrate available for the phospholipase C, a stimulation of the Ins(1,4,5)P3 5-phosphatase or an activation of the Ins(1,4,5,)P3 kinase. It is more likely the consequence of the suppression of calcium wave generated by Ins(1,4,5)P3 which may in its turn stimulate a phospholipase C. Different arguments favour this hypothesis: (1) calcium at an intracellular physiological concentration (0.1-1 microM) is able to stimulate a phospholipase C; (2) artificially increasing the [Ca2+]i inside the WRK1 cell induces an accumulation of Ins(1,4,5)P3; and (3) the time-course of the inhibition of Ins(1,4,5)P3 accumulation induced by an EGTA/ionomycin treatment correlates well with that of the calcium mobilization. Altogether these results suggest that Ins(1,4,5)P3 accumulation in WRK1 cells may result from two distinct mechanisms: a direct vasopressin receptor-mediated PLC activation which is independent of calcium and a calcium-mediated PLC activation related to the intracellular calcium mobilization.
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PMID:Positive feedback regulation of phospholipase C by vasopressin-induced calcium mobilization in WRK1 cells. 217 21

Adherence, chemotaxis, phagocytosis, and responses to cytokines are mediated by distinct classes of cell surface receptors in human neutrophils. Intracellular signaling by these different receptors is a subject of active investigation. Observation of single neutrophils adherent to surfaces reveals the presence of spontaneous oscillations of cytosolic-free calcium, [Ca2+]i, generated by mechanisms that are presently unknown. Chemoattractant receptor activation via a specific G-regulatory protein activates a plasma membrane phospholipase C and generates diacylglycerol and inositol(1,4,5)triphosphate. DG activates C kinase(s). Ins(1,4,5)P3 releases Ca2+ from a specific intracellular organelle, the calciosome. Calciosomes resemble sarcoplasmic reticulum: they contain a Ca2(+)-ATPase and a high capacity/low affinity calcium-binding, calsequestrin-like protein. Chemoattractant receptor stimulation of calcium influx across the plasma membrane in phagocytes correlates strongly with the conversion of Ins(1,3,4,5)P3 to Ins(1,3,4,5)P4 by a Ca2(+)-calmodulin-sensitive kinase. The transduction system of phagocytosis receptors also generates DG and Ins(1,4,5)P3 and elicits [Ca2+]i elevations. The Ca2+ signal is an important regulator of secretion (granule exocytosis, superoxide production), whereas C kinase(s)/and other unknown mediators appear to be more important for the control of movement. Several mechanisms that could account for the specificity of cell signaling by different receptors are discussed.
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PMID:Receptors and intracellular signaling in human neutrophils. 217 32

This article reviews literature up to mid-1988 covering recent developments pertaining to agonist-induced Ca2+ signaling in various cell types. A large amount of experimental evidence supports a mechanism involving specific guanine nucleotide-binding proteins (G-proteins) as transducing factors between occupancy of a wide variety of receptors by many different agonists and activation of polyphosphoinositide specific phospholipase C enzymes. Although many different G-proteins and phospholipase C enzymes have been purified and cloned, successful reconstitution of the components has not been achieved. Hence, many questions concerning the specificity of coupling between particular receptors to a particular G-protein and phospholipase C subtype remain unresolved. Phospholipase C subtypes isolated from the membrane and soluble fractions of the cell are directly activated by Ca2+ and, preferentially, hydrolyse phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol 4-phosphate (PIP). The role of the G-protein is to stimulate inositol lipid breakdown at free Ca2+ concentrations (0.1-0.2 microM) typical of unstimulated cells. Overwhelming evidence supports the concept that Ins 1,4,5-P3, the product of PIP2 hydrolysis, is responsible for the initial agonist-induced Ca2+ transient by mobilization of Ca2+ from a specialized intracellular store. An Ins 1,4,5-P3 receptor has been purified that may correspond to the postulated Ins 1,4,5-P3 gated Ca2+ channel. Despite a growing understanding of the complexities of the metabolism of Ins 1,4,5-P3 and a successful purification of many enzymes involved, including the ATP-dependent 3-kinase that converts Ins 1,4,5-P3 to Ins 1,3,4,5-P4, the role of Ins 1,3,4,5-P4 as a putative second messenger remains enigmatic. Multiple forms of protein kinase C have been described and the role is well established for a 1,2-diacylglycerol, the second product of PIP2 hydrolysis, as its physiological activator. Although protein kinase C has been shown to phosphorylate and modulate the activity of several proteins involved in the Ca2+ signaling pathway and Ca2+ transport, the physiological significance of the protein kinase C in agonist-stimulated cell function requires further elucidation. The extension of measurements of hormone-induced Ca2+ changes to single cells has shown that the occurrence of Ca2+ oscillations is a common phenomena. Elucidation of the biochemical mechanisms causing this oscillatory response and its physiological significance represents an important challenge for future studies.
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PMID:Signal transduction mechanisms involved in hormonal Ca2+ fluxes. 219 Aug 6

1,25-dihydroxycholecalciferol (1,25(OH)2D3) rapidly affects calcium (Ca2+) transport in several cell systems, suggesting physiological actions independent of genomic activation. To test this hypothesis, we studied immediate to early effects (0.5-300 sec) of 1,25(OH)2D3 on cytosolic Ca2+ [Ca2+]i in single osteogenic sarcoma ROS 17/2.8 cells loaded with fura-2. An acute rise in [Ca2+]i was observed in 40% of the cells following addition of 1,25(OH)2D3, with a threshold concentration of 10(-11) M. In most cases, the [Ca2+]i rise was transient, with return to baseline within 1 min; less frequently a more prolonged effect was observed, with variable recovery times. 25-hydroxycholecalciferol (25(OH)D3) reproduced the effect of 1,25(OH)2D3 on [Ca2+]i, with equal potency and similar responses, whereas 24,25-dihydroxycholecalciferol, 1 alpha-hydroxycholecalciferol, and 22 oxa-1,25(OH)2D3 were not effective. 1,25(OH)2D3 also increased [Ca2+]i in ROS 24/1 cells, which are defective of receptors for the vitamin D metabolites. At high doses (10(-8)-10(-7) M) of 1,25(OH)2D3 the [Ca2+]i rise in ROS 17/2.8 cells was due to both influx of extracellular Ca2+ and release of Ca2+ from intracellular stores, as the effect was only partially inhibited by Ca2(+)-channel blockade by nifedipine. At low doses (10(-9)-10(-10) M), the effect was entirely dependent on extracellular Ca2+. 1,25(OH)2D3 also increased the production of inositol 1,4,5 trisphosphate (Ins(1, 4, 5)P3) and diacylglycerol, at a threshold dose of 10(-9) M, indicating activation of phospholipase C (PLC). In two thirds of the cells studied, a second addition of 1,25(OH)2D3 within 5 min to cells prestimulated with equimolar doses of the vitamin D metabolite resulted in a [Ca2+]i transient of higher amplitude than the first, a phenomenon occurring at all doses of the hormone, and associated with production of Ins(1, 4, 5)P3. This response amplification was not produced by 25(OH)D3, and pretreatment with 1 alpha(OH)D3 did not significantly enhance 1,25(OH)2D3-induced production of Ins(1, 4, 5)P3. In conclusion, activation of the Ca2+ message system by vitamin D metabolites is a rapid, nongenomic effect; 1,25(OH)2D3 specifically activates both PLC and dihydropyridine-sensitive Ca2+ channels, and "primes" the cells to respond with an enhanced [Ca2+]i rise to a subsequent homologous stimulation; the presence of both the 1 alpha and 25 hydroxyl groups is necessary to express the full hormonal action of vitamin D on [Ca2+]i.
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PMID:Nongenomic activation of the calcium message system by vitamin D metabolites in osteoblast-like cells. 222 14

Skeletal muscle triads are possessing the whole set of enzymes of the phosphatidylinositol (PI)-linked signal generating pathway, PI-kinase, PI(4)P-kinase, and PI(4,5)P2-phospholipase C (PLC). The activities of these enzymes are comparable to those found in other cell types for which a functional role of the PI-pathway in intracellular signal transduction has been established. For skeletal muscle an unequivocal function and an initiating signal for Ins(1,4,5)P3-liberation is still unknown. However, the observed Ca-dependency of PLC activity suggests that here Ins(1,4,5)P3 production is a consequence rather than a cause of increasing cytosolic Ca2+. Recently, the glycolytic enzyme aldolase, whose activity can be modulated by inositol polyphosphates, has been localized in the triadic structure. The enzyme which has a high affinity to Ins(1,4)P2, Ins(1,4,5)P3 and Ins(1,3,4,5)P4, seems to be compartmentalized to the junctional foot structure from which it is released upon binding of these molecules. This phenomenon could reflect a capability for regulation of the glycolytic flux even for aldolase, especially if a non steady-state situation in the junctional gap is considered. Meanwhile we have accumulated evidence for the operation of a partial glycolytic sequence in the junctional region established by the enzymes aldolase, glyceraldehyde-3-P (GAP) dehydrogenase and phosphoglycerate kinase. This system is able to produce ATP upon oxidation of GAP and could be, because of the inositol polyphosphate-sensing abilities of aldolase, a target for the membrane associated PI-pathway. The ATP production is however transient which indicates the coupling to an ATP hydrolyzing reaction.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Relation of phosphatidylinositol metabolism to glycolytic pathway in skeletal muscle membranes. 228 42

Stimulation of P2-purinergic receptors by ATP resulted in activation of phosphorylase, which was associated with marked production of inositol trisphosphate (Ins-P3), in rat hepatocytes. ATP also inhibited forskolin-induced accumulation of cAMP in the presence of a phosphodiesterase inhibitor. On the contrary, adenosine or AMP never inhibited the cAMP accumulation, but increased hepatocyte cAMP; the stimulation was antagonized by a methylxanthine. Thus, P1-purinergic receptors are linked to adenylate cyclase in a stimulatory fashion in hepatocytes. Various kinds of purine nucleotides stimulating P2-receptors can be divided into two groups on the basis of their relative abilities to stimulate Ins-P3 production and to inhibit cAMP accumulation; the first group including adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), ADP, 5-adenylyl imidodiphosphate, GTP, and guanosine 5'-O-(3-thiotriphosphate) has an efficacy similar to that of ATP, and the second group of nucleotides including alpha, beta-methyleneadenosine 5'-triphosphate, beta, gamma-methyleneadenosine 5'-triphosphate (App(CH)2)p), and GDP exerts considerable inhibitory effects on cAMP accumulation, but only slight effects on inositol lipid metabolism. Treatment of hepatocytes with islet-activating protein, pertussis toxin, blocked the nucleotide-induced inhibition of cAMP accumulation, but exerted only a small effect on Ins-P3 production. In membranes prepared from hepatocytes, forskolin-stimulated adenylate cyclase was inhibited by GTP. This GTP-induced inhibition of the enzyme was susceptible to islet-activating protein and dependent on the concentration of ATP (or its derivatives, ATP gamma S or App(CH2)p). It is concluded that there are two types of P2-purinergic receptors: one is linked to adenylate cyclase via an inhibitory guanine nucleotide regulatory protein (Gi) and the other is linked to phospholipase C.
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PMID:P2-purinergic receptors are coupled to two signal transduction systems leading to inhibition of cAMP generation and to production of inositol trisphosphate in rat hepatocytes. 244 92

Cultured pituitary cells prelabeled with myo-[2-3H] inositol were permeabilized by ATP4-, exposed to guanine nucleotides and resealed by Mg2+. Addition of guanosine 5'-0-(3-thio triphosphate) (GTP gamma S) to permeabilized cells, or gonadotropin releasing hormone (GnRH) to resealed cells, resulted in enhanced phospholipase C activity as determined by [3H] inositol phosphate (Ins-P) production. The effect was not additive, but the combined effect was partially inhibited by guanosine 5'-0-(2-thiodiphosphate) (GDP beta S) or by neomycin. Surprisingly, addition of GDP beta S (100-600 microM) on its own resulted in a dose-related increase in [3H]Ins-P accumulation. Several nucleoside triphosphates stimulated phospholipase C activity in permeabilized pituitary cells with the following order: UTP greater than GTP gamma S greater than ATP greater than CTP. The stimulatory effect of UTP, ATP and CTP, but not GTP gamma S or GDP beta S, could also be demonstrated in normal pituitary cells suggesting a receptor-activated mechanism. GTP and GTP gamma S decreased the affinity of GnRH binding to pituitary membranes and stimulated LH secretion in permeabilized cells. These results suggest the existence of at least two G-proteins (stimulatory and inhibitory) which are involved in phospholipase C activation and GnRH action in pituitary cells.
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PMID:Effect of guanine nucleotides on phospholipase C activity in permeabilized pituitary cells: possible involvement of an inhibitory GTP-binding protein. 249 87

The involvement of inositol lipid metabolism in agonist-mediated Ca2+ signaling by Ins 1,4,5-P3 has become firmly established. Recent advances have led to a better understanding of the proteins associated with signal transduction in the plasma membrane. A number of specific receptors (G proteins, phospholipases and inositol lipid kinases) have now been purified and characterized. An Ins 1,4,5-P3 receptor has also been purified which is presumably involved in mediating Ca2+ efflux from intracellular stores. The morphological site of the hormone-sensitive Ca2+ pool has been tentatively identified as discrete, specialized intracellular structures (calciosomes), but further studies are required to demonstrate that these contain Ins 1,4,5-P3-gated Ca2+ channels and their possible functional relationship to the plasma membrane. Receptor occupancy by Ca2+ mobilizing agonists also stimulates Ca2+ entry into the cell, but the mechanism for activation of voltage insensitive Ca2+ channels and the possible involvement of Ins 1,4,5-P3, Ins 1,3,4,5-P4 and/or G proteins in this process has not been established. The Ca2+ signaling pathway is subject to multisite feedback regulation by Ca2+ itself and by a diacylglycerol-mediated activation of protein kinase C. Potential sites for Ca2+ interaction are displacement of Ins 1,4,5-P3 from its receptor by a Ca2+-dependent mechanism, promotion of Ins 1,3,4,5-P4 formation by the Ca2+/calmodulin-regulated Ins 1,4,5-P3 3-kinase, and efflux of Ca2+ from the cell or sequestration into intracellular Ca2+ stores by Ca2+/calmodulin-regulated Ca2+-ATPases. Protein kinase C activation potentially affects the rate of generation of Ins 1,4,5-P3 by negative feedback to the receptor-G protein-phospholipase C transduction system and possibly also the rate of Ins 1,4,5-P3 degradation by activation of an inositol polyphosphate 5-phosphomonoesterase. It may also attenuate the Ca2+ transient directly by increasing the activity of Ca2+-ATPases associated with the plasma membrane and the endoplasmic reticulum. Cell-to-cell heterogeneity in the relative control strengths of these different mechanisms may explain the differences in the Ca2+ signal in different tissues and even in different cells within a population. The ability of Ca2+ and protein kinase C to provide negative feedback at various points in the signal transduction pathway suggests that a complex mechanism involving multiple feedback loops is likely to regulate the generation of Ca2+ oscillations seen in some cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Hormone effects on cellular Ca2+ fluxes. 249 41

As previously described, WRK1 plasma membrane possesses a vasopressin-sensitive phospholipase C [G. Guillon et al., 1986, FEBS Lett. 196, 155-159]. In the present study, we examined the sensitivity of this enzyme to guanylnucleotides. GTP gamma S induces a time- and dose-dependent stimulation of Ins(1,4,5)P3 and Ins(1,4)P2 accumulation. No accumulation of InsP1, Ins(1,3,4)P3 or Ins(1,3,4,5)P4 occurred under similar conditions. Gpp(NH)p produced the same effect but was less potent. GTP and a nonhydrolyzable analogue of ATP, App(NH)p, were without effect. Calcium also stimulated the phospholipase C activity in a time- and dose-dependent manner. In the absence of calcium, the activity of GTP gamma S was considerably reduced. Physiological calcium concentrations (between 10(-8) and 10(-7) M), allowed maximal GTP gamma S stimulation of phospholipase C activity. In this system, the presence of vasopressin alone did not generate inositol phosphate accumulation. However, this hormone: (i) reduced the lag-time observed during GTP gamma S stimulation, (ii) increased the sensitivity of phospholipase C to GTP and to GTP gamma S, and (iii) did not modify the stimulation of phospholipase C induced by maximal doses of GTP gamma S. Unlike sodium fluoride, GTP gamma S elicited an irreversible activation of phospholipase C. Calcium, GTP gamma S and sodium fluoride stimulated the phospholipase C activity via mechanisms sharing a common step, since their maximal effects were not additive. Cholera toxin treatment, known to produce complete ADP-ribosylation of 'alpha s' subunits, partially reduced the basal and the maximal GTP gamma S-mediated stimulation of phospholipase C activity as well as that caused by vasopressin. This inhibition was not mimicked by treatment with either forskolin or pertussis toxin.
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PMID:Properties of membranous phospholipase C from WRK1 cell: sensitivity to guanylnucleotides and bacterial toxins. 253 43

Conditions have been established for the incorporation of [3H]inositol ([3H]Ins) into the phosphoinositides of cultured bovine adrenal zona fasciculata/reticularis (ZFR) cells. Stimulation of these prelabelled cells with angiotensin II (10(-11)-10(-7) M AII) resulted in the dose-dependent (max. 16-fold at 10(-7) M AII), time-dependent formation of water-soluble radiolabelled products which show the same chemical and chromatographic properties as [3H]InsP, [3H]InsP2 and [3H]InsP3 standards. The results of the time-course studies of the changes in these products are consistent with the view that AII rapidly (less than 15 s) induces the activation of a polyphosphoinositide-specific phospholipase C. The action of this phospholipase on the polyphosphoinositides is sustained throughout 15 min of stimulation. The dose dependency of this response correlates closely with cortisol output and is reduced (to 52%, P less than 0.00005), but not abolished, in the absence of extracellular Ca2+. To our knowledge these results are the first clear demonstration that AII stimulates a polyphosphoinositide-specific phospholipase C in bovine ZFR cells.
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PMID:Angiotensin II-stimulated cortisol secretion is mediated by a hormone-sensitive phospholipase C in bovine adrenal fasciculata/reticularis cells. 254 75


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