Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Degranulation of eosinophils and release of toxic granule proteins play key roles in allergic diseases such as bronchial asthma. However, the intracellular signaling mechanisms that trigger eosinophil degranulation remain unclear. In this study, we investigated protein tyrosine kinase (PTK) involvement in the degranulation of human blood eosinophils induced by immobilized Ig. Eosinophils stimulated with Sepharose beads coated with secretory IgA (slgA) or IgG showed rapid increases in the tyrosine phosphorylation of intracellular proteins with molecular masses of 50 to 56, 73, 78, 100, and 105 kDa. The Ig-induced phosphorylation response was not affected by pertussis toxin, a known inhibitor of Ig-dependent eosinophil activation. The tyrosine kinase inhibitors genistein and herbimycin A inhibited both the tyrosine phosphorylation and degranulation responses of eosinophils induced by sIgA- or IgG-coated beads. In contrast, eosinophil degranulation induced by PMA was not affected by genistein. Treatment of eosinophils with the protein phosphatase inhibitor pervanadate induced the phosphorylation of a similar set of intracellular proteins as well as cellular degranulation. Pervanadate also stimulated an increase in phosphoinositide hydrolysis, which was consistent with the activation of a phospholipase C-gamma isoform by this stimulus. Genistein pretreatment blocked the Ig-induced phospholipase C activation, providing evidence for PTK involvement in this reaction. These findings indicate that a PTK-dependent signaling pathway plays an important role in triggering the degranulation responses of human eosinophils to immobilized sIgA and IgG.
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PMID:Tyrosine phosphorylation is required for eosinophil degranulation induced by immobilized immunoglobulins. 760 11

1. A pharmacological characterization of tyrosine kinase inhibitors (TKI) belonging to two distinct groups (competitors at the ATP-binding site and the substrate-binding site, respectively) was performed, based on their effects on the contractility of rat mesenteric arteries. 2. Both the ATP-site competitors (genistein and its inactive analogue, daidzein) and the substrate-site competitors (tyrphostins A-23, A-47 and the inactive analogue, A-1) reversibly inhibited noradrenaline (NA, (10 microM)) and KCl (125 mM) induced contractions, concentration-dependently. Genistein was slightly but significantly more potent than daidzein; the tyrphostins were all less potent than genistein, and there were no significant differences between the individual potencies. The tyrosine kinase substrate-site inhibitor bis-tyrphostin had no inhibitory effect. 3. Genistein, daidzein, A-23 and A-47 each suppressed the contraction induced by Ca2+ (1 microM) in alpha-toxin permeabilized arteries. A-1 and bis-tyrphostin had little or no effect on contraction of the permeabilized arteries. 4. Genistein was significantly more potent than daidzein with respect to inhibition of the contraction induced by 200 nM Ca2+ in the presence of NA (100 microM) and GTP (3 microM). The effect of A-23, A-47, A-1 and bis-tyrphostin was similar in permeabilized arteries activated with Ca2+ (200 nM) + NA (100 microM) + GTP (3 microM) and permeabilized arteries activated with 1 microM Ca2+. 5. Genistein (30 microM) reduced the fura-2 measured intracellular calcium activity ([Ca2+]j) in arteries stimulated with NA but had no effect on [Ca2+]i in arteries stimulated with KCl (125 mM).6. The potent effect of the TKIs in this study is consistent with a role for tyrosine kinases in the mechanisms which regulate both cytoplasmic Ca2+ levels and the effect of Ca2+ on the contractile apparatus in smooth muscle cells in resistance arteries. However, the results must be interpreted cautiously because the enzyme inhibitors may have a poor specificity in intact tissues and because the presumed inactive analogues had potent effects.
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PMID:Effects of tyrosine kinase inhibitors on the contractility of rat mesenteric resistance arteries. 762 Jul 18

Genistein, a potent tyrosine kinase inhibitor, inhibits contraction of several types of smooth muscle, suggesting that protein tyrosine phosphorylation may be an important regulatory mechanism for smooth muscle contraction. We suspected that one site between activation of smooth muscle and contraction which might be modulated by protein tyrosine phosphorylation involved mechanisms for control of Ca2+ sensitivity. Since smooth muscle permeabilized with staphylococcal alpha-toxin permits direct assessment of agonist-induced Ca2+ sensitivity, we studied the effects of genistein on potential coupling between tyrosine phosphorylation and Ca2+ sensitivity in permeabilized ileal smooth muscle. Results show that contraction of intact preparations with carbachol is markedly and reversibly inhibited by 40% at 4 micrograms genistein/ml and by 60% at 20 micrograms genistein/ml. Permeabilized preparations that are contracted with a submaximal [Ca2+] in the presence of GTP relax when genistein is added to the medium. Genistein also reversibly inhibits contractions induced in permeabilized muscle with either a submaximal or maximal [Ca2+] in the presence of GTP, as well as receptor-coupled activation of Ca2+ sensitization with 10 microM carbachol/10 microM GTP. Activation of permeabilized preparations at pCa 4.6 in the presence of 100 microM GTP promotes time-dependent tyrosine phosphorylation of several substrates. Both phosphorylation and force are inhibited by genistein. However, relatively high levels of myosin light chain phosphorylation persist during genistein-induced inhibition of Ca2+ sensitivity. In contrast, genistein has no effect on Ca(2+)-activated contraction in Triton-skinned preparations in either the presence or the absence of GTP. This shows that it does not directly inhibit actin-myosin interaction and suggests that its target(s) may be a cytosolic or membrane-bound regulatory protein(s) that is leached from the preparations during Triton-skinning. Taken together, these new data suggest that (a) tyrosine phosphorylation of one or more substrates may be coupled to mechanisms which regulate Ca2+ sensitivity and (b) the inhibitory effects of genistein are probably due to inhibition of agonist-induced Ca2+ sensitivity.
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PMID:Modulation of Ca2+ sensitivity in smooth muscle by genistein and protein tyrosine phosphorylation. 762 29

Stimulation of aldosterone synthesis in bovine adrenal zona glomerulosa (ZGB) cells by angiotensin II (AngII) is believed to be mediated by the phospholipase C (PLC) pathway that results in the increase of cytosolic free calcium concentration and in the activation of protein kinase C (PKC). However, the cell proliferation and contraction associated with AngII action are known to be mediated in part by protein tyrosine kinases (PTK). To assess the potential role of PTK in the stimulatory effect of AngII on adrenal steroidogenesis, the actions of a series of PTK inhibitors on this metabolic pathway were examined in isolated ZGB cells. Tyrphostin 23 (TP23) caused a dose-dependent inhibition of AngII-stimulated aldosterone production with an IC50 of 15 microM and reached complete inhibition at 100 microM. Genistein (GS) was more potent with an IC50 of 35 nM and complete inhibition at 10 microM. The stimulation of aldosterone production by the calcium-mobilizing agent thapsigargin (Thaps) was also dose-dependently inhibited by TP and GS with the same potency. A specific PKC inhibitor, calphostin C (0.1 microM) caused only a 51.7% inhibition of AngII-stimulated aldosterone production. In the same way, a specific Ca2+/calmodulin-dependent protein kinase inhibitor, KN-62 (1 microM), reduced aldosterone production stimulated by AngII by 64%. As expected, thapsigargin-stimulated aldosterone biosynthesis was not affected by calphostin C, but was completely inhibited by KN-62. These results demonstrate for the first time that protein tyrosine kinase activity is part of the angiotensin II signalling pathway in bovine zona glomerulosa cells. The activation of this PTK occurs subsequently to the mobilization of intracellular calcium. This calcium-dependent protein tyrosine kinase pathway is essential for the steroidogenic response to AngII in bovine zona glomerulosa cells.
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PMID:A role for protein tyrosine kinase in the steroidogenic pathway of angiotensin II in bovine zona glomerulosa cells. 763 15

Our previous study revealed that the intracellular killing of Staphylococcus aureus by human monocytes after cross-linking Fc gamma receptor I (Fc gamma RI) or Fc gamma RII is a phospholipase C (PLC)-dependent process. The aim of the present study was to investigate whether protein tyrosine kinase (PTK) activity plays a role in the Fc gamma R-mediated intracellular killing of bacteria and activation of PLC in these cells. The results showed that phagocytosis of bacteria by monocytes was not affected by the PTK inhibitors genistein and tyrphostin-47. The intracellular killing of S. aureus by monocytes after cross-linking Fc gamma RII or Fc gamma RII with anti-Fc gamma R monoclonal antibody and a bridging antibody or with human immunoglobulin G (IgG) was inhibited by these compounds in a dose-dependent fashion. The production of O2- by monocytes after stimulation with IgG or IgG-opsonized S. aureus was almost completely blocked by the PTK inhibitor. These results indicate that inhibition of PTK impairs the oxygen-dependent bactericidal mechanisms of monocytes. Genistein and tyrphostin-47, which do not affect the enzymatic activity of purified PLC, prevented activation of PLC after cross-linking Fc gamma RI or Fc gamma RII, measured as an increase in the intracellular inositol 1,4,5-trisphosphate concentration. Cross-linking Fc gamma RI or Fc gamma RII induced rapid tyrosine phosphorylation of several proteins in monocytes, one of which was identified as PLC-gamma 1, and the phosphorylation could be completely blocked by PTK inhibitors, leading to the conclusion that activation of PLC after cross-linking Fc gamma R in monocytes is regulated by PTK activity. Together, these results demonstrate that PTK activity is essential for the activation of PLC which is involved in the Fc gamma R-mediated intracellular killing of S. aureus by human monocytes.
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PMID:Protein tyrosine kinase activity is essential for Fc gamma receptor-mediated intracellular killing of Staphylococcus aureus by human monocytes. 792 87

Genistein, a potent inhibitor for protein tyrosine kinase, remarkably inhibited the stimulatory action of N6-(L-2-phenylisopropyl)adenosine (PIA), an A1-adenosine receptor agonist, on thyrotropin (TSH)-induced phospholipase C activation in FRTL-5 thyroid cells. This drug also suppressed both the A1-receptor-mediated inhibition of cAMP accumulation in the cells and binding of [3H]8-cyclopentyl-1,3-dipropylxanthine, a specific antagonist for A1-receptor, to the cell membranes in a competitive manner. Adenosine-induced cAMP accumulation through A2-receptor in pertussis toxin-treated cells was also competitively antagonized by genistein. We conclude that genistein is also a competitive antagonist for P1-purinergic receptors.
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PMID:Genistein, an inhibitor of protein tyrosine kinase, is also a competitive antagonist for P1-purinergic (adenosine) receptor in FRTL-5 thyroid cells. 794 96

Gap junction-mediated intercellular communication (GJC) may play an important role in cell proliferation and transformation since GJC is inhibited by growth factors, oncogenes, tumor promoters, and carcinogens. We have studied inhibition of GJC by platelet-derived growth factor-BB (PDGF) in the mouse fibroblast cell line C3H/10T1/2 and have sought to determine whether PDGF-induced inhibition of GJC is mediated by the PDGF receptor tyrosine kinase (RTK). PDGF-mediated inhibition of GJC was rapid and transient, with maximal inhibition occurring 40 min after PDGF addition and GJC returning to control levels after 70 min. The effect of PDGF on GJC was concentration-dependent, with maximal inhibition of 90% or greater occurring at 10 ng/ml PDGF. Stimulation of RTK activity, as determined by antiphosphotyrosine immunoblot analysis of PDGF receptor and the receptor substrates phospholipase C-gamma I (PLC-gamma I) and guanosine triphosphatase activating protein (GAP), was also concentration-dependent. Inhibition of GJC required a greater concentration of PDGF than did stimulation of RTK activity. The tyrosine kinase inhibitor genistein blocked PDGF-induced RTK activity, as measured by PDGF receptor, PLC-gamma I, and GAP tyrosine phosphorylation, in a concentration-dependent manner but did not affect PDGF-mediated inhibition of GJC. Genistein alone had no effect on GJC or PDGF receptor expression. PDGF treatment in the presence or absence of genistein resulted in phosphorylation of the connexin 43 protein on nontyrosine residues. These results suggest that inhibition of GJC by ligand-activated PDGF receptor is dissociable from the RTK activity responsible for PDGF, PLC-gamma I, and GAP phosphorylation.
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PMID:Dissociation of PDGF receptor tyrosine kinase activity from PDGF-mediated inhibition of gap junctional communication. 812 67

Cd2+ provokes inositol trisphosphate production and releases stored Ca2+, apparently by binding to a zinc site in the external domain of an orphan receptor. One microM Cd2+ evokes an immediate spike in cytosolic free Ca2+, which is similar to that evoked by bradykinin. Platelet-derived growth factor (PDGF) also increases free Ca2+ in human dermal fibroblasts, but there is a distinct lag before free Ca2+ rises in response to PDGF. Genistein, which selectively inhibits tyrosine kinases, markedly inhibited Ca2+ mobilization evoked by PDGF. Calcium mobilization triggered by cadmium or bradykinin was relatively insensitive to genistein. The PDGF receptor is known to be a tyrosine kinase, which phosphorylates and thereby activates phospholipase C gamma, whereas a G protein couples the bradykinin receptor to another phospholipase C isoform. These findings support the hypothesis that the orphan receptor triggered by cadmium is coupled to phospholipase C via a G protein.
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PMID:Genistein inhibits calcium release by platelet-derived growth factor but not bradykinin or cadmium in human fibroblasts. 824 30

Although several previous studies have indicated a role for tyrosine phosphorylated proteins in platelet function, their precise function and relationship to other biochemical processes remains elusive. In the present study genistein, an inhibitor of tyrosine kinase activity, was used to address this latter question. Genistein inhibited aggregation of washed human platelets in response to the thromboxane analogue U46619, to the phorbol ester phorbol myristate acetate, and to the calcium ionophore A23187. Only in the case of U46619, however, did the concentration of genistein required (IC50 of 10 micrograms/ml) correlate to that reported to inhibit tyrosine kinases. Likewise, genistein also inhibited U46619-induced serotonin secretion, elevation of cytosolic calcium, [32P]-phosphatidic acid production (an index of phospholipase C activity) and the phosphorylation of pleckstrin (an index of protein kinase C activity) at similar concentrations (IC50 of 4-9 micrograms/ml). U46619 caused the phosphorylation of a phosphoprotein which was insensitive to KOH digestion and therefore presumably a phosphotyrosine. This phosphorylation was also inhibited by genistein (IC50 of 3 micrograms/ml. However genistein also inhibited [3H]-U46619 binding to platelets with an IC50 of 3 micrograms/ml. These data suggest that the inhibitory effects of genistein on platelet activation occurs as a result of antagonism of the thromboxane receptor.
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PMID:The effects of genistein on platelet function are due to thromboxane receptor antagonism rather than inhibition of tyrosine kinase. 832 74

Genistein, a tyrosine kinase inhibitor, had no or only slight inhibitory effects on platelet aggregation or serotonin release induced by thrombin, while intracellular Ca2+ concentration ([Ca2+]i) elevation was substantially attenuated. It also inhibited the cyclooxygenase pathway, but this effect was not directly related to the suppressive effect of genistein on [Ca2+]i elevation. In order to clarify the mechanism by which genistein suppresses Ca2+ mobilization, its effect was examined on inositol phospholipid metabolism. The production of inositol-1,4,5-trisphosphate was inhibited by genistein in a dose-dependent manner, while 47 kDa protein phosphorylation or phosphatidic acid formation was not affected, suggesting that genistein does not inhibit phospholipase C activity. Pretreatment of unstimulated platelets with genistein increased the amount of phosphatidylinositol-4-monophosphate [PI(4)P], while that of phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2] was reduced. Thrombin stimulation of genistein-pretreated cells intensified this tendency, i.e. a further increase in the amount of PI(4)P and a decrease in the amount of PI(4,5)P2 in an inversely proportional manner. Taken together, these findings imply that genistein acted at the step of PI(4)P 5-kinase which produces PI(4,5)P2 from PI(4)P. Protein tyrosine phosphorylation induced by thrombin was not affected by genistein, suggesting that the inhibitory effect of genistein on polyphosphoinositides was unrelated to tyrosine kinase inhibition.
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PMID:Effects of genistein, a tyrosine kinase inhibitor, on platelet functions. Genistein attenuates thrombin-induced Ca2+ mobilization in human platelets by affecting polyphosphoinositide turnover. 839 81


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