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)

Changes in the intracellular free calcium ([Ca2+]i) of cultured normal human epidermal keratinocytes (NHEK) were investigated in order to determine whether the adenylate cyclase cAMP (AC) system and phospholipase C activating system are involved in increasing [Ca2+]i. NHEK were obtained from neonatal foreskin and grown in serum-free medium (K-GM) supplemented with 2% bovine pituitary extract. [Ca2+]i was measured by fluorescence ratio imaging microscopy using Fura-2 as the indicator. In the case of the AC system, transient increases in [Ca2+]i were observed in response to stimulation with epinephrine, norepinephrine, isoproterenol and salbutamol. Methoxamine, clonidine and dobutamine did not induce any [Ca2+]i increase. The [Ca2+]i increase evoked by epinephrine was inhibited by pretreatment with propranolol, but not by prazosin or yohimbine, indicating that epinephrine-induced [Ca2+]i elevation via beta 2-adrenergic stimulation. Similar changes were observed when NHEK were stimulated with histamine, adenosine, GTP gamma S, forskolin and dibutyryl cAMP respectively. The absence of extracellular Ca2+ had no effect on the epinephrine-induced [Ca2+]i increase. It appears that activated protein kinase A, based on cAMP accumulation via stimulatory GTP binding protein, elicited the release of Ca2+ from intracellular stores. On the other hand, when drugs known to activate phospholipase C in a wide variety of cell types were tested, a transient increase in [Ca2+]i was demonstrated in response to the addition of thrombin, bradykinin and substance P. This reaction was not affected by the presence of EGTA, suggesting that these drugs raise [Ca2+]i via phosphatidylinositol breakdown. Vasopressin, angiotensin II, serotonin and acetylcholine did not induce any increase in [Ca2+]i. On the basis of these studies, it was concluded that NHEK possess the mechanism which increase [Ca2+]i via AC system and phospholipase C activating system. It seems probable that this rise in [Ca2+]i initiates a calcium-dependent cellular response, such as activation of calcium/calmodulin dependent kinase, and subsequently regulates the proliferation and differentiation of human epidermal keratinocytes.
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PMID:[Changes in the intracellular free calcium of cultured human epidermal keratinocytes]. 171 97

Substance P (SP) stimulates polyphosphoinositide breakdown in the rat anterior pituitary through an NK-1 receptor. In the present study we present evidence that the coupling between the SP-NK1 receptor complex and polyphosphoinositide-specific phospholipase C (PI-PLC) in rat anterior pituitary membranes may involve a mechanism consistent with a GTP-binding protein. The formation of inositol phosphates from [3H]myo-inositol-labelled anterior pituitary membranes induced by SP was potentiated by GTP and non-hydrolysable guanine nucleotides. The stimulatory effects of SP alone and SP plus GTP could be blocked by addition of GDP-beta-S (guanosine 5-O-(thiodiphosphate] in excess. Basal and SP plus guanine nucleotide-induced inositol phosphate formation were stimulated by fluoride, whereas the effect of SP alone was inhibited. Pretreatment of anterior pituitary membranes with sodium deoxycholate attenuated the inositol phosphate response elicited by GTP and GTP-gamma-S, whereas basal and SP-stimulated inositol phosphate production showed a peak at 1 mg sodium deoxycholate/ml. SP, fluoride and guanine nucleotide stimulatory effects on hydrolysis of polyphosphoinositide (PPI) were unaffected by pretreatment of anterior pituitary cells with cholera or pertussis toxin for 12h. Treatment of anterior pituitary membranes with cholera and pertussis toxin yielded [32P]ADP-ribosylation of two proteins with molecular masses of 45 and 41 kDa respectively. We conclude that SP coupling to PI-PLC through the NK1 receptor in the rat anterior pituitary involves a GTP-binding mechanism distinct from the G-proteins associated with adenylate cyclase, Gs and Gi.
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PMID:Substance P stimulation of polyphosphoinositide hydrolysis in rat anterior pituitary membranes involves a GTP-dependent mechanism. 171 80

The effects of substance P (SP) on inositol trisphosphate (IP3) accumulation, myosin light chain (MLC) phosphorylation, cAMP formation and contraction were studied in iris sphincter smooth muscle of different mammalian species. SP receptor density was also examined in membrane fractions from this tissue. The data obtained can be summarized as follows. (1) In the iris sphincters of rabbit, bovine and pig, SP receptors are coupled to the phospholipase C system, whereas in dog, cat and human these receptors are coupled to the adenylate cyclase system. (2) In those species which employ the phospholipase C system, SP induced IP3 accumulation, MLC phosphorylation and contraction in a dose-dependent manner; in contrast, in those species in which SP induced the formation of cAMP we found the neuropeptide to cause muscle relaxation. The findings on cAMP formation in intact tissue were confirmed in iris sphincter membranes. Both the effect of SP on IP3 accumulation in rabbit and bovine sphincters and its effect on cAMP formation in the dog were blocked by the SP antagonist, (D-Pro2, D-Trp7, 9)-SP. (3) The density of SP receptors in rabbit, bovine and dog were found to be 227, 110.9 and 13.6 fmol mg-1 protein, respectively, and the Kd values were 1.9, 1.8 and 1.3 nM, respectively. (4) Of the neuropeptides investigated SP, neurokinin A and neurokinin B had significant stimulatory effects on IP3 accumulation and on contraction in the rabbit iris sphincter; however, neither neurokinin Y nor the calcitonin gene-related peptide (CGRP) had any effect on these responses. In addition, none of the neuropeptides studied had any effect on IP3 or on contraction in the dog iris sphincter. While it is possible that SP may have dual actions, with the predominant action dependent on the species, the data presented could suggest the presence of two SP receptor subtypes, one coupled to phospholipase C and the other to adenylate cyclase. The results of this investigation indicate major species differences in biochemical and functional responsiveness to SP and in SP receptor density in the iris sphincter of the mammalian eye, and support a modulatory role for the neuropeptide in muscle response in this tissue.
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PMID:Species differences in the effects of substance P on inositol trisphosphate accumulation and cyclic AMP formation, and on contraction in isolated iris sphincter of the mammalian eye: differences in receptor density. 172 88

It is reported that a defect in dopamine-1 (DA-1) receptor adenylate cyclase coupling in the proximal convoluted tubule in the spontaneously hypertensive rat may contribute to the diminished natriuretic response to DA-1 receptor agonists. Since the tubular DA-1 receptor is also coupled to phospholipase C, and both of these cellular signaling processes are involved in DA-1 receptor-mediated diuresis and natriuresis, it is important to know whether a similar defect is also present in DA-1 receptor-coupled phospholipase C pathway. The present study was therefore designed to determine the functional status of DA-1 receptor-phospholipase C coupling system of adult spontaneously hypertensive rats using a renal cortical slice preparation. In addition, the renal response to exogenously administered dopamine (1 microgram/kg/min i.v.) was also determined. We found that basal phospholipase C activity was significantly higher in hypertensive rats than in age-matched Wistar-Kyoto rats (7.36 +/- 0.32% versus 5.61 +/- 0.27%, p less than 0.05). However, compared with the normotensive controls, dopamine-induced increases in phospholipase C activity were significantly attenuated in the preparations of hypertensive rats in a concentration-dependent manner (13 +/- 6% versus 38 +/- 6% for 1 mM dopamine, p less than 0.05; 49 +/- 6% versus 71 +/- 9% for 3 mM dopamine, p less than 0.05; 50 +/- 16% versus 106 +/- 22%, p less than 0.05 for 10 mM dopamine).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Diminished phospholipase C activation by dopamine in spontaneously hypertensive rats. 173 Apr 34

The polypeptide hormone erythropoietin (Ep) is a growth factor whose actions on the erythroid progenitor cell induce proliferation and differentiation. The signal transduction system activated by Ep to mediate these cellular processes remains largely uncharacterized despite many years of research devoted to its elucidation. It is clear that an Ep receptor-mediated activation of adenylate cyclase or guanylate cyclase does not occur, although cAMP and cGMP may play modulatory roles. The role of calcium in the action of Ep is less clear. Although the presence of extracellular calcium seems to be an absolute requirement for Ep-induced proliferation, the positive changes induced by Ep in intracellular calcium occur with a time course suggestive of influx through ion channels opening within the cell membrane rather than release of intracellular stores by inositol trisphosphate. There is good evidence for the involvement of phospholipases A2 and C in the actions of Ep, including an early rise in lipoxygenase metabolites of arachidonic acid. Activation of phospholipase C can also result in the activation of protein kinase C in response to Ep. We present a model for the signal transduction pathway of Ep that is consistent with current knowledge and provides a framework for the coordinate actions of several intracellular mechanisms in the mediation of Ep-induced proliferation.
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PMID:Signal transduction in erythropoiesis. 175 62

The blood coagulation factor, human thrombin has been shown to have chemotactic and mitogenic effects on mononuclear phagocytic inflammatory cells. In the present study, we have used the U937 human monocytic cell line to explore the signal transduction mechanisms utilised by thrombin in these cells. In U937 cells differentiated into a macrophage-like phenotype, thrombin stimulated the formation of inositol trisphosphate (IP3) and the mobilisation of intracellular Ca2+ [( Ca2+]i) via a mechanism which was partially sensitive to pertussis toxin. Thrombin failed, however, to evoke thromboxane (Tx) B2 synthesis in the differentiated cells. In contrast, the chemotactic peptide N-formyl-L-methionylleucyl-L-phenylalanine (FMLP) stimulated TxB2 synthesis under conditions where it evoked increases in IP3 formation and [Ca2+]i mobilisation, via a pertussis toxin-sensitive mechanism, comparable in extent to those mediated by thrombin. Thrombin also failed to cause inhibitory guanine nucleotide binding protein (Gi)-mediated inhibition of adenylate cyclase activity in U937 cell membranes. These results indicate that U937 cells express receptors for thrombin which are in part coupled via a pertussis toxin-sensitive guanine nucleotide binding protein to phospholipase C activation, the formation of IP3 and the mobilisation of [Ca2+]i. However, the failure of thrombin to stimulate TxB2 synthesis or cause Gi-mediated inhibition of adenylate cyclase in U937 cells contrasts with its effects in human platelets and other thrombin-responsive cells. These results suggest that the thrombin receptor or receptor-effector coupling mechanism(s) in mononuclear cells is functionally distinct from the thrombin receptor or receptor-effector coupling mechanism(s) present in other thrombin-responsive cells.
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PMID:Thrombin signalling in U937 human monocytic cells is coupled to inositol phosphate formation but not to thromboxane B2 synthesis nor to inhibition of adenylate cyclase: distinct differences in thrombin signalling between U937 cells and platelets. 180 Jan 26

Human decidual tissue synthesizes and secretes a protein that is identical to pituitary prolactin in its chemical, biological and immunological properties. Nevertheless, the factors that regulate the synthesis and release of prolactin from the decidual tissues appear to be different to those regulating the synthesis and release of pituitary prolactin. Studies from our laboratory over the past few years indicate that the synthesis and release of decidual prolactin are regulated, at least in part, by factors released by placenta, fetal membranes and decidua. The placenta releases a 23.5 KMr protein [decidual prolactin-releasing factor (PRL-RF)] that stimulates a rapid release of prolactin within the first few minutes of exposure and a sustained, prolonged, increase in the synthesis and release of prolactin beginning 6-8 h after exposure. The acute release of prolactin in response to PRL-RF is inhibited by decidual prolactin release-inhibitory factor (PRL-IF), a 35-45 K Mr protein that is released by the decidua. The secondary increase in the synthesis and release of prolactin in response to PRF-RF is blocked by lipocortin I, which is synthesized by both the placenta and decidua. IGF-I, insulin and relaxin also stimulate the synthesis and release of prolactin. However, the stimulation in response to these factors does not occur until 24-48 h after exposure. The cellular mechanisms involved in the release of decidual prolactin are as yet unknown. However, recent studies implicate activation of adenylate cyclase, phospholipase C-mediated phosphoinositide hydrolysis and phospholipase A2-mediated arachidonic acid release in the regulation of prolactin release. The finding that the synthesis and release of decidual prolactin are regulated, at least in part, by PRL-RF, IGF-I, insulin, relaxin and lipocortin I strongly suggests that there is novel feedback regulation between the placenta, fetal membranes, and decidua in the regulation of the synthesis and release of decidual prolactin.
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PMID:Regulation of the synthesis and release of decidual prolactin by placental and autocrine/paracrine factors. 183 Dec 61

The phospholipase C-mediated hydrolysis of phosphatidylcholine has been shown recently to be activated by a number of agonists. Muscarinic receptors, which trigger various signal transduction mechanisms including inhibition of adenylate cyclase through Gi, have been shown to be potent stimulants of this novel phospholipid degradative pathway. We demonstrate here, by exogenous addition of Bacillus cereus phosphatidylcholine-hydrolyzing phospholipase C, that phosphatidylcholine breakdown mimics the ability of carbachol to inhibit adenylate cyclase. This effect is sensitive to pertussis toxin and is entirely dependent on the presence of protein kinase C. This kinase is also required for the inhibition by carbachol of adenylate cyclase. These results suggest that the activation of phosphatidylcholine breakdown by phospholipase C may play an important role linking or favoring the coupling muscarinic receptors to Gi. Results presented here also show that phospholipase C-mediated hydrolysis of phosphoinositides by exogenous addition of Bacillus thuringiensis phosphoinositide-hydrolyzing phospholipase C does not affect adenylate cyclase, despite the fact that protein kinase C is translocated to an extent similar to that produced by the hydrolysis of phosphatidylcholine. According to the results shown here, both phospholipases also differ in their ability to down-regulate protein kinase C as well as to phosphorylate p80 and to transmodulate the binding of epidermal growth factor, two well established effects of protein kinase C in Swiss 3T3 fibroblasts. This emphasizes the complexity, from a functional point of view, of protein kinase C activation "in vivo."
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PMID:Mechanism of inhibition of adenylate cyclase by phospholipase C-catalyzed hydrolysis of phosphatidylcholine. Involvement of a pertussis toxin-sensitive G protein and protein kinase C. 184 88

Thrombin is believed to activate platelets via cell surface receptors coupled to G proteins. In order to better understand this process, we have examined the interaction of thrombin with HEL cells, a leukemic cell line that has served as a useful model for studies of platelet structure and function. In HEL cells, as in platelets, thrombin stimulated inositol trisphosphate (IP3) formation and suppressed cAMP synthesis. Both events were inhibited by pertussis toxin with 50% inhibition occurring at a toxin concentration that ADP-ribosylated 50% of the Gi alpha subunits present in HEL cells. IP3 formation was also stimulated by a second serine protease, trypsin. The trypsin response was identical to the thrombin response in time course, magnitude, and pertussis toxin sensitivity, suggesting that a similar mechanism is involved. Agonist-induced changes in the cytosolic-free Ca2+ concentration were used to test this hypothesis. Both proteases caused a transient increase in intracellular calcium [Ca2+]i that could be inhibited with D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone thrombin. Exposure to either protease desensitized HEL cells against subsequent increases in [Ca2+]i and IP3 caused by the other, although responses to other agonists were retained. This loss of responsiveness persisted despite repeated washing of the cells and the addition of hirudin. Complete recovery occurred after 20 h and could be prevented with cycloheximide. These observations suggest that 1) HEL cell thrombin receptors, like those on platelets, are coupled to phospholipase C and adenylylcyclase by pertussis toxin-sensitive G proteins, 2) the G proteins involved are equally accessible to pertussis toxin in situ, 3) when access is limited to the outside of the cell the response mechanisms for thrombin and trypsin are similar, if not identical, despite the broader substrate specificity of trypsin, 4) both proteases cause persistent changes that may involve proteolysis of their receptors or associated proteins, and 5) desensitization of the thrombin response occurs at a step no later than the activation of phospholipase C and requires protein synthesis for recovery.
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PMID:Receptor and G protein-mediated responses to thrombin in HEL cells. 184 99

Prostaglandin E2 (PGE2, 5 ng/ml to 5 micrograms/ml) induced a dose-dependent increase in cAMP accumulation, inositol phosphates (IPs) accumulation, and cytoplasmic free Ca2+ ([Ca2+]i) in a clonal osteoblast-like cell line, MOB 3-4. In contrast, prostaglandin F2 alpha (PGF2 alpha, 5 ng/ml to 5 micrograms/ml) stimulated increases in IPs accumulation and [Ca2+]i without stimulating an increase in cAMP accumulation. Both PGE2 (greater than 0.5 micrograms/ml) and PGF2 alpha (greater than or equal to 5 micrograms/ml) increased cytoplasmic pH (pHi) from approximately 7.15 to 7.35 in BCECF-loaded cells. A tumor promotor, phorbol 12-myristate 13-acetate (PMA, 0.1-100 nM) also increased pHi without effect on phosphoinositide hydrolysis. Both PGE2-(5 micrograms/ml) and PMA- (100 nM) induced cytoplasmic alkalinization was inhibited by removal of extracellular Na+, or by pretreatment of the cells with amiloride (0.5 mM), an inhibitor of Na+/H+ exchange, or H-7 (100 microM), a nonspecific inhibitor of protein kinase C. Thus, MOB 3-4 cells appeared to possess PGE2 receptors and PGF2 alpha receptors: the former are coupled to adenylate cyclase and phospholipase C, and the latter are predominantly coupled to phospholipase C. Also the cells appeared to possess an amiloride-sensitive Na+/H+ exchange activity, which increases pHi in response to PGE2 and PGF2 alpha, as well as to PMA. Long-term (48 hr) exposure of the cells to PGE2 at a high concentration (5 micrograms/ml), but not to PGF2 alpha and PMA, decreased DNA synthesis in the serum-deficient medium. Thus, cytoplasmic alkalinization appeared insufficient for cell replication. At least in MOB 3-4 cells, the inhibitory effect of PGE2 on DNA synthesis may be due to the cAMP messenger system.
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PMID:Effects of prostaglandin E2 and F2 alpha on cytoplasmic pH in a clonal osteoblast-like cell line, MOB 3-4. 184 35


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