Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We previously reported that p72syk, a non-receptor tyrosine kinase, was activated maximally at 10 s after thrombin or thromboxane A2 stimulation, even in platelets that were not allowed to aggregate [Taniguchi et al. (1993) J. Biol. Chem. 268, 2277-2279; Maeda et al. (1993) Biochem. Biophys. Res. Commun. 197, 62-67]. Then, the change in the shape of porcine platelets induced by the thromboxane A2 analogue, STA2, and the role of protein-tyrosine kinases including p72syk in this response were evaluated, using the shape-change parameter. We show that p72syk activation is correlated with the disc-sphere change in a time- and dose-dependent manner following stimulation by STA2. Tyrphostin B44, a potent protein-tyrosine kinase inhibitor, reduced the thromboxane A2-evoked p72syk activation and the disc-sphere change in a dose-dependent manner. Furthermore, the translocation of p72syk to the cytoskeleton-rich fraction and an increase in the tyrosine phosphorylation of an about 120 kDa protein were observed during the disc-sphere change induced by STA2. These lines of evidence suggest that the activation of protein-tyrosine kinases such as p72syk may be involved in the disc-sphere change response in thromboxane A2-stimulated porcine platelets.
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PMID:Possible involvement of protein-tyrosine kinases such as p72syk in the disc-sphere change response of porcine platelets. 749 Feb 61

Thrombin stimulation induces a dramatic increase in the activity of p72syk in platelets. We have found that activated p72syk, which is phosphorylated on tyrosine residue(s), translocates from the Triton X-100-soluble fraction to the Triton X-100-insoluble, cytoskeleton-rich fraction after thrombin stimulation. In addition, the redistribution of p72syk from the 100,000 x g Triton X-soluble fraction and the membrane skeleton was found to correlate with an increased level of p72syk in the cytoskeleton. Furthermore, the early phase of p72syk translocation (within 60 s) was significantly inhibited with cytochalasin D, whereas the late phase of p72syk translocation (after 90 s) was completely inhibited with RGDS tetrapeptide treatment. These results suggest that translocation of the activated p72syk to the cytoskeleton correlates with different phases of the platelet activation process through actin polymerization and glycoprotein IIb/IIIa-fibrinogen-mediated aggregation of platelets and, hence, may have a regulatory role in tyrosine phosphorylation of platelets.
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PMID:Translocation of p72syk to the cytoskeleton in thrombin-stimulated platelets. 780 2

We previously demonstrated that thrombin-induced activation of p72syk was independent of intracellular Ca2+ elevation in platelets. However, our previous studies also demonstrated that activation of platelets by ionophore A23187 results in a dramatic increase in tyrosine phosphorylation of several cellular proteins. In the present study, we investigated the effect of Ca2+ elevation on the activity of p72syk. When washed porcine platelets were stimulated with ionophore A23187 and the activity of p72syk was assessed by means of an immunoprecipitation kinase assay, A23187 caused a time- and dose-dependent increase in the specific activity of p72syk. In addition, pretreatment of platelets with both aspirin and ADP scavengers or chelation of extracellular Ca2+ by EGTA had no effect on the A23187-induced activation of p72syk. These results indicate that A23187-induced activation of p72syk is independent of the formation of endoperoxide/thromboxane A2, released ADP and extracellular Ca2+, suggesting the existence of a novel pathway for activation of p72syk. Furthermore, evidence is presented which indicates a synergistic effect of A23187 and thrombin on the activation of p72syk, and an inhibitory effect of pretreatment with phorbol 12-myristate 13-acetate, a protein kinase C activator, on the activation of p72syk induced by either A23187 or thrombin.
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PMID:Intracellular calcium dependent activation of p72syk in platelets. 788 62

We have previously reported that a non-receptor-type protein-tyrosine kinase p72syk, exists in both membrane and cytosolic fractions in porcine platelets and is activated after thrombin stimulation. To facilitate the understanding of the function of p72syk, we have investigated the topological features, kinase activities and the interaction with another signal-transducing molecule, namely phosphatidylinositol 3-kinase, during platelet activation. Membrane and cytosolic fractions were separated from thrombin-treated porcine platelets, and the amount of p72syk was quantified by the immunoblot technique or the kinase activity of each fraction was determined by an immunoprecipitation kinase assay. After stimulation by thrombin, cytosolic p72syk rapidly translocated to the membrane fraction within 10 s and there was also a significant increase in the amount of p72syk in the cytoskeletal fraction. The autophosphorylation activity of membrane-associated p72syk significantly increased approximately tenfold and reached a maximum at 10 s; the activity subsequently decreased to almost the basal level within 120 s. For similar time courses, association of p72syk with phosphatidylinositol 3-kinase and tyrosine phosphorylation of p72syk were observed. These results suggest that translocation, activation, and association of p72syk with transducing molecules such as phosphatidylinositol 3-kinase, events which occur during platelet activation, may participate in early signal-transduction events.
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PMID:Translocation, activation and association of protein-tyrosine kinase (p72syk) with phosphatidylinositol 3-kinase are early events during platelet activation. 792 45

Thrombin dramatically activated p72syk in a time- and dose- dependent fashion in extracts of resting porcine platelets in the presence of EDTA. Separation analysis using Sephacryl S-300 column chromatography has demonstrated that p72syk may exist as large (complex) and small (monomer) forms in resting platelets, and activation of p72syk was only observed in the fraction of large form. Pretreatment with ATP scavenger, GDP beta S and protein phosphatase inhibitors had no effect on this activation. Furthermore, washed immuno-precipitates of large form p72syk were also activated by thrombin or fibrinogen. These results suggest that p72syk may associate with thrombin receptor or other agonist receptors and there may be a novel activation mechanism of non-receptor type protein-tyrosine kinase, which does not require the modification by other protein kinases, protein phosphatases and GTP binding proteins.
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PMID:Activation of p72syk by thrombin in a cell-free system. 816 76

Activation of platelets by thrombin results in a dramatic increase in tyrosine phosphorylation on multiple cellular proteins (Ferrell, J. E., and Martin, G. S. (1988) Mol. Cell. Biol. 8, 3603-3610; Golden, A., and Brugge, J. S. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 901-905; Nakamura, S., and Yamamura, H. (1989) J. Biol. Chem. 264, 7089-7091). However, none of the responsible protein-tyrosine kinase has been reported so far. We report here that p72syk, one of the non-receptor-type protein-tyrosine kinases, is activated following thrombin stimulation in blood platelets. Washed porcine platelets were stimulated by thrombin, and the activation of p72syk was assessed in an immunoprecipitation kinase assay. The activity of p72syk increased within 5 s, reached a maximum at 10 s, and decreased to a basal level within 60 s after 0.5 unit/ml thrombin stimulation. The amount of immunoprecipitated p72syk was not altered throughout the time course. This activation was greatly enhanced in a dose-dependent manner and was completely canceled by the pretreatment of platelet suspension with hirudin, a specific antagonist of thrombin. In the Ca(2+)-depleted condition both extra- and intracellularly, the activation of p72syk was still persistent; in contrast, the deactivation process was completely abrogated even at 120 s after thrombin stimulation. In addition, the replenishment of Ca2+ resulted in a similar deactivation pattern as seen in the Ca(2+)-rich condition. Furthermore, this deactivation was also canceled by the pretreatment of platelets with W7, a calmodulin antagonist, as well as ML9, a myosin-light-chain kinase inhibitor. These results indicate that p72syk can be a responsible enzyme to the protein-tyrosine phosphorylation events following the platelet activation by thrombin and may be negatively regulated by Ca2+ in a calmodulin-dependent manner, inter alia myosin light-chain kinase, in thrombin-stimulated platelets.
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PMID:Protein-tyrosine kinase p72syk is activated by thrombin and is negatively regulated through Ca2+ mobilization in platelets. 842

Both thrombin and thrombin receptor agonist peptide (TRAP) activated p72syk and p60c-src with similar magnitudes. Both thrombin and TRAP induced translocation of p60c-src and p54/58lyn to cytoskeleton in an aggregation-dependent manner. Thrombin also induced cytoskeletal association of p72syk, but independent of platelet aggregation. Furthermore, p72syk associated with cytoskeleton underwent marked proteolysis, which was partially dependent upon calpain activation. In contrast, TRAP, even at concentrations as high as 100 mu M, did not induce p72syk translocation to cytoskeleton. Our findings suggest that cytoskeletal translocation of p72syk induced by thrombin is governed by a mechanism distinct from those of p60c-src and p54/58lyn translocation. It is also suggested that p72syk translocation induced by thrombin requires additional signal(s) other than that mediated by the recently-cloned thrombin receptor that couples with GTP-binding proteins and interacts with TRAP.
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PMID:Differential mobilization of tyrosine kinases in human platelets stimulated with thrombin or thrombin receptor agonist peptide. 878 Jul 38

The binding of collagen to platelet glycoprotein VI (GPVI) leads to the subsequent activation of phospholipase Cgamma2 through a pathway that is dependent on the Fc receptor gamma (FcR gamma) chain and the tyrosine kinase p72syk. We have investigated the role of platelet Src-family kinases in this signalling pathway. The selective Src-family kinase inhibitor PP1 prevented collagen-stimulated increases in whole-cell tyrosine phosphorylation and tyrosine phosphorylation of the FcR gamma chain and p72syk. A similar set of observations was made for a collagen-related peptide (CRP), which binds to GPVI but not to the integrin alpha2beta1 (GPIa/IIa). These effects were seen at a concentration of PP1 that inhibited platelet aggregation, dense granule release and Ca2+ mobilization induced by CRP, but not aggregation and Ca2+ mobilization mediated by the G-protein-coupled receptor agonist thrombin. After stimulation by CRP or collagen, the Src-family kinases p59fyn and p53/56lyn became associated with several tyrosine-phosphorylated proteins including the FcR gamma chain. This was not true of the other platelet Src-family kinases. The association between the FcR gamma chain and p59fyn was also seen under basal conditions, and was stable only in the weak detergent Brij96 but not in Nonidet P40, suggesting a non-SH2-dependent interaction. These results provide strong evidence for the involvement of p59fyn and p53/56lyn in signalling via GPVI, with p59fyn possibly acting upstream of FcR gamma chain phosphorylation.
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PMID:Evidence for the involvement of p59fyn and p53/56lyn in collagen receptor signalling in human platelets. 993 17

ATP binding cassette transporter A1 (ABCA1) is involved in regulation of intracellular lipid trafficking and export of cholesterol from cells to high density lipoproteins. ABCA1 defects cause Tangier disease, a disorder characterized by absence of high density lipoprotein and thrombocytopenia. In the present study we have demonstrated that ABCA1 is expressed in human platelets and that fibrinogen binding and CD62 surface expression in response to collagen and low concentrations of thrombin, but not to ADP, are defective in platelets from Tangier patients and ABCA1-deficient animals. The expression of platelet membrane receptors such as GPVI, alpha2beta1 integrin, and GPIIb/IIIa, the collagen-induced changes in phosphatidylserine and cholesterol distribution, and the collagen-induced signal transduction examined by phosphorylation of LAT and p72syk and by intracellular Ca2+ mobilization were unaltered in Tangier platelets. The electron microscopy of Tangier platelets revealed reduced numbers of dense bodies and the presence of giant granules typically encountered in platelets from Chediak-Higashi syndrome. Further studies demonstrated impaired release of dense body content in platelets from Tangier patients and ABCA1-deficient animals. In addition, Tangier platelets were characterized by defective surface exposure of dense body and lysosomal markers (CD63, LAMP-1, LAMP-2, CD68) during collagen- and thrombin-induced stimulation and by abnormally high lysosomal pH. We conclude that intact ABCA1 function is necessary for proper maturation of dense bodies in platelets. The impaired release of the content of dense bodies may explain the defective activation of Tangier platelets by collagen and low concentrations of thrombin, but not by ADP.
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PMID:Impaired platelet activation in familial high density lipoprotein deficiency (Tangier disease). 1516 65