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)

Guanine nucleotides have been shown to stimulate phosphoinositide breakdown in brain membranes, but no potentiation of such an effect by agonist was demonstrated. We have studied the effect of carbachol and histamine on guanosine 5'-[gamma-thio]triphosphate (GTP[S]) stimulation of inositol phosphates formation in [3H]inositol-labelled rat brain cortical membranes. In this preparation, GTP[S] enhancement of phosphoinositide hydrolysis required the presence of MgATP and low Ca2+ concentration (100 nM). Carbachol potentiation of the GTP[S] effect was only observed when 1 mM-deoxycholate was also added. Under these conditions, stimulated production of [3H]inositol phosphates was linear for at least 15 min, and [3H]inositol bisphosphate [( 3H]IP2) accounted for approx. 80%, whereas the amount of [3H]inositol trisphosphate [( 3H]IP3) was very low. Stimulation by GTP[S] was concentration-dependent (half-maximal effect at 0.86 microM), and its maximal effect (815% over basal) was increased by 1 mM-carbachol (1.9-fold) and -histamine (1.7-fold). Both agonists decreased the slope index of the GTP[S] concentration/effect curve to values lower than unity, suggesting the appearance of some heterogeneity in the population of guanine-nucleotide-binding proteins (G-proteins) involved. The carbachol and histamine effects were also concentration-dependent, and were inhibited by atropine and mepyramine respectively. Fluoroaluminate stimulated phosphoinositide hydrolysis to a higher extent than GTP[S] plus carbachol, and these stimulations were not additive, indicating that the same polyphosphoinositide phospholipase C-coupled G-protein mediates both effects.
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PMID:Carbachol and histamine stimulation of guanine-nucleotide-dependent phosphoinositide hydrolysis in rat brain cortical membranes. 254 64

Ca2+ dependent polyphosphoinositide phospholipase C (PLC) activity in cardiac sarcolemma hydrolyzed both endogenous and exogenous phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) with an associated increase in inositol bisphosphate (IP2). Dialyzed cytosol and certain fractions of cytosol isolated by anion exchange or gel filtration chromatography activated sarcolemmal PLC activity by approx. 100%. The PLC activator eluted with an apparent molecular weight of 160 Kdal on a Sephacryl 300 column and was destroyed by heat or trypsin treatment. Exogenous 3H-PIP2 was not hydrolyzed by cytosolic fractions containing sarcolemmal PLC activator. These studies demonstrate that the polyphosphoinositide PLC in cardiac sarcolemma is regulated by a cytosolic protein.
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PMID:A cytosolic protein activator of cardiac sarcolemmal phosphoinositide phospholipase C. 254 98

We demonstrated previously that alpha-1 adrenergic catecholamines modulate cardiac automaticity in a manner that is dependent upon the function of a pertussis toxin sensitive guanine nucleotide binding protein (G protein). Furthermore, we demonstrated that alpha-1 adrenergic receptor stimulation promotes the accumulation of inositol monophosphate (IP1). In the present study we used high-pressure liquid chromatography to resolve individual inositol phosphate isomers formed in norepinephrine-stimulated cultured rat ventricular myocytes. Norepinephrine stimulated a rapid, transient increase in 1,4,5-inositol trisphosphate (1,4,5-IP3) which was followed by slower, sustained increases in 1,3,4-IP3, inositol bisphosphate (IP2) and IP1. IP1 was composed of two major isomers with retention times characteristic of 1-IP1 and 4-IP1. 4-IP1 was the predominant IP1 isomer formed during stimulation with norepinephrine suggesting that the polyphosphoinositides rather than phosphatidylinositol are the principal targets of norepinephrine-stimulated phospholipase C activity in the heart. This was confirmed in studies performed on myocyte membranes which demonstrated proportionately greater IP2 and IP3 (relative to IP1) accumulation in response to norepinephrine. G protein regulation of alpha-1 adrenergic-dependent inositol phospholipid hydrolysis also was examined. In myocyte membranes, guanosine-5'-0-(3-thiotriphosphate) induced the accumulation of IP2 and IP3 and was required for the stimulatory effect of norepinephrine. This response was not impaired after pretreatment with pertussis toxin. These results indicate that the myocyte alpha-1 adrenergic receptor is coupled to a polyphosphoinositide-specific phospholipase C by a pertussis toxin insensitive G protein and suggest that under certain conditions IP3 may serve an important role in alpha-1 adrenergic modulation of cardiac function.
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PMID:Alpha-1 adrenergic stimulation of 1,4,5-inositol trisphosphate formation in ventricular myocytes. 255 Jun 17

Recent evidence suggests that guanyl nucleotide binding (G) proteins are involved in receptor-mediated bone resorption and in osteoblastic function, but the nature of the G protein coupled to effectors that are involved in these skeletal effects is unknown. The purposes of this study were to determine (1) whether a G protein mediates activation of phosphoinositide-specific phospholipase C in UMR-106 rat osteosarcoma cells, and (2) whether parathyroid hormone (PTH) and a PTH-like protein (PLP) associated with humoral hypercalcemia of malignancy promote GTP-dependent PIP2 hydrolysis. Addition of GTP (10(-4) M) or guanosine 5'-0-(3-thiotriphosphate, GTP gamma S, 10(-5) M) to membranes prepared from UMR-106 cells labeled with [3H]myo-inositol increased both [3H]inositol trisphosphate (IP3) and [3H]inositol bisphosphate (IP2) formation. The increases in [3H]IP2 and [3H]IP3 produced by GTP were 8.6- and 4.3-fold, respectively. GTP gamma S produced a 17.6- and 11.9-fold increase in [3H]IP2 and [3H]IP3, respectively. The stimulatory effects of GTP and GTP gamma S were dose dependent (GTP ED50 = 3.9 x 10(-6) M; GTP gamma S ED50 = 2.5 x 10(-7) M) and progressive over 10 minutes and required the presence of Mg2+.GTP (10(-4) M) and GTP gamma S (10(-5) M) decreased membrane [3H]phosphoinositides concomitantly with increased [3H]IP2 and [3H]IP3. The GDP analog guanosine 5'-O-(2-thiodiphosphate, GDP beta S) alone did not alter [3H]IP2 or [3H]IP3 production but at 10(-4) M blocks the stimulatory effects of GTP and GTP gamma S. NaF (3 x 10(-2)M) produced a 2.8- and 2.0-fold stimulation of [3H]IP2 and [3H]IP3, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:G protein-dependent activation of a phosphoinositide-specific phospholipase C in UMR-106 osteosarcoma cell membranes. 255 86

The light-stimulated production of inositol triphosphate (IP3), via hydrolysis of phosphatidylinositol bisphosphate (PIP2), can be demonstrated in an in vitro preparation of isolated distal segments of squid photoreceptors. The retina is labeled with [3H]inositol (Szuts, E. Z., Wood, S. F., Reid, M. S., and Fein, A. (1986) Biochem. J. 240, 929-932), and the rhodopsin-containing distal segments are isolated in artificial cytosol. Within 2 s after a flash, IP3 levels increase 200% (corresponding to an intracellular increase of approximately 5 microM), and the lipid precursor PIP2 decreases by 50%. Inositol bisphosphate (IP2) levels increase later, as a breakdown product of IP3. IP3 response is light-dependent, saturating when 0.5% of the rhodopsin is photoactivated. Guanosine-5'-O-(3-thiotriphosphate (GTP gamma S) binding demonstrates that the plasma membrane of most of the photoreceptor distal segments is intact or only transiently permeable. Membrane permeabilization enhances light-activated GTP gamma S binding but abolishes the light-activated IP3 production. Receptor-mediated production of IP3 is believed to be the result of a receptor-G-protein-phospholipase C cascade (i.e. Cockcroft, S., and Gomperts, B. D. (1985) Nature 314, 534-536). To test for G-proteins, we incubated the photoreceptors in AlF4- (an activator of G-proteins) in the dark. IP3 and IP2 were produced with a corresponding decrease in PIP2. Incubation with GTP or GTP gamma S, in hypotonic buffer, which causes transient leakiness, increased dark levels by IP3 by 50%. Addition of GTP in isotonic buffer enhanced the light-induced increase of IP3. These results localize the light-stimulated phospholipase C activity to the distal segments and suggest that a G-protein couples rhodopsin to phospholipase C.
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PMID:Inositol trisphosphate production in squid photoreceptors. Activation by light, aluminum fluoride, and guanine nucleotides. 266 14

Several monoclonal antibodies directed against a number of T cell surface molecules are used to elucidate the role of these molecules (cell surface molecules) in T cell activation. The activation of T cells via these molecules are both antigen-dependent (CD3/TcR complex) and antigen-independent. Irrespective of their antigen dependency, these monoclonal antibodies activate T cells by a classical signal transduction pathway, in which the binding of monoclonal antibodies to their cell surface receptors leads to activation of phospholipase C resulting in the depolarization of plasma membrane, hydrolysis of IP2 and IP3 and DAG, the 'second messengers'. IP3 leads to mobilization of intracellular calcium to contribute to an increase in [Ca++]i, whereas DAG causes activation and translocation of PKC and an increasing apparent affinity for Ca++. The role of IP4 in the mobilization of intracellular calcium is emerging. In addition, influx of extracellular calcium also contributes to increase in [Ca++]i. The increase in [Ca++]i following activation via some T cell surface antigen is predominantly due to intracellular mobilization of Ca++ (e.g. CD3/TcR complex), whereas activation via other T cell surface antigen, the increase in [Ca++]i is almost entirely due to an influx of extracellular calcium (e.g. CD5 antigen). All these molecules activate autocrine system of T cell growth, namely IL-2 production, IL-2 receptor expression and T cell proliferation.
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PMID:Mechanisms of transmembrane signalling in human T cell activation. 269 33

In addition to stimulation of cyclic AMP, parathyroid hormone (PTH) may influence cellular events by utilizing other pathways of hormone action, such as the generation of inositol phosphates (IPs). We sought to examine this potential action of PTH by assessing the formation of inositol phosphates in PTH-sensitive ROS 17/2.8 cells. The polyphosphoinositides were labeled by growing the cells with [3H]inositol following which cell homogenates were prepared. The nonhydrolyzable guanine nucleotide, GTP gamma S, and calcium ion, alone and together, stimulated all three IPs, IP1, IP2, and IP3. IP1 formation was linear over 30 minutes but IP2 and IP3 accumulated more rapidly peaking by 5 minutes for all agonist conditions. The proportion of total P as IP3 was enhanced when the cells were grown with retinoic acid (1 microM) or when the assay was conducted at pH 4.5. In addition, the lower pH was associated with much more enzyme activity. PTH agonists, bPTH-(1-84) and bPTH-(1-34), both caused a small but significant stimulation of IP3 formation. When bPTH-(1-84), and the analog bPTH-(3-34)amide, that inhibits PTH-mediated adenylate cyclase activity were present together, there was additive stimulation of IP3 formation compared with that with either agent alone. The results demonstrate that inositol phosphate formation can be stimulated directly in a membrane preparation of ROS cells by GTP gamma S, calcium ion, and PTH and that the enzyme mediating this activity, phospholipase C, is regulated by a guanine nucleotide binding protein.
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PMID:Stimulation of inositol phosphate formation in ROS 17/2.8 cell membranes by guanine nucleotide, calcium, and parathyroid hormone. 276 77

Rabbit platelets were labelled with [3H]inositol and a membrane fraction was isolated in the presence of ATP, MgCl2 and EGTA. Incubation of samples for 10 min with 0.1 microM-Ca2+free released [3H]inositol phosphates equivalent to about 2.0% of the membrane [3H]phosphoinositides. Addition of 10 microM-guanosine 5'-[gamma-thio]triphosphate (GTP[S]) caused an additional formation of [3H]inositol phosphates equivalent to 6.6% of the [3H]phosphoinositides. A half-maximal effect was observed with 0.4 microM-GTP[S]. The [3H]inositol phosphates that accumulated consisted of 10% [3H]inositol monophosphate, 88% [3H]inositol bisphosphate ([3H]IP2) and 2% [3H]inositol trisphosphate ([3H]IP3). Omission of ATP and MgCl2 led to depletion of membrane [3H]polyphosphoinositides and marked decreases in the formation of [3H]inositol phosphates. Thrombin (2 units/ml) or GTP (4-100 microM) alone weakly stimulated [3H]IP2 formation, but together they acted synergistically to exert an effect comparable with that of 10 microM-GTP[S]. The action of thrombin was also potentiated by 0.1 microM-GTP[S]. Guanosine 5'-[beta-thio]diphosphate not only inhibited the effects of GTP[S], GTP and GTP with thrombin, but also blocked the action of thrombin alone, suggesting that this depended on residual GTP. Incubation with either GTP[S] or thrombin and GTP decreased membrane [3H]phosphatidylinositol 4-phosphate ([H]PIP) and prevented an increase in [3H]phosphatidylinositol 4,5-bisphosphate ([3H]PIP2) observed in controls. Addition of unlabelled IP3 to trap [3H]IP3 before it was degraded to [3H]IP2 showed that only about 20% of the additional [3H]inositol phosphates that accumulated with GTP[S] or thrombin and GTP were derived from the action of phospholipase C on [3H]PIP2. The results provide further evidence that guanine-nucleotide-binding protein mediates signal transduction between the thrombin receptor and phospholipase C, and suggest that PIP may be a major substrate of this enzyme in the platelet.
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PMID:Activation of phospholipase C associated with isolated rabbit platelet membranes by guanosine 5'-[gamma-thio]triphosphate and by thrombin in the presence of GTP. 282 Mar 81

Inositol phospholipids play a crucial role in the intracellular signal transduction in most cell types. Activation of an enzyme called phospholipase C or PIP2-phosphodiesterase (PIP2-PDE) leads to the production of two second messenger molecules, diacylglycerol (DG) and inositol 1,4,5-triphosphate (IP3). DG activates a kinase called protein kinase C, whereas IP3 mediates the release of Ca2+ from intracellular storage sites. The measurement of IP3 and its degradation products, inositol diphosphate (IP2) and inositol monophosphate (IP1) provides a way of assessing the extent to which this complex system has been activated. In the central nervous system (CNS) most of the studies on the neurotransmitter stimulated formation of inositol phosphates (IPs) have been performed on brain slices, a mixture of mainly neurons and glial cells. The recent development of pure neuronal cultures provides a means of determining which of these responses were of neuronal origin. The purpose of this review is to summarize the results obtained in neurons in primary culture together with a brief appraisal of the possible function of this second messenger system in neurons.
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PMID:Putative role of inositol phospholipid metabolism in neurons. 282 May 14

In human thyroid slices prelabeled with myo-[2-3H]inositol, thyrotropin (TSH, 3-30 mU/ml) stimulated IP3, IP2 and IP1 generation over a prolonged time course. The cAMP response was much more sensitive to TSH, peaking between 1 and 5 mU/ml. Forskolin (10(-5) M) and isoproterenol had no effect on basal IP levels, while carbamylcholine (10(-5) M, 10(-4) M) also increased IP accumulation. These data suggest that in the human thyroid, TSH activates a phospholipase C generating IP3 and diacylglycerol independently of the well-known adenylate cyclase stimulation. They validate in the human model a dual mode of action of the hormone previously proposed on the basis of indirect observations.
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PMID:Dual activation by thyrotropin of the phospholipase C and cyclic AMP cascades in human thyroid. 282 Aug 16


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