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

Platelets are required for certain experimental metastases. Several lines of animal tumor cells aggregate platelets in vitro and in vivo. Previous studies with one of these lines, an SV40-transformed 3T3 mouse fibroblast (SV3T3) have revealed that the platelet-aggregating material is an extractable membrane-associated sialolipoprotein which requires divalent cation, complement, and a heat-stable plasma component for activity. Little information is available on the interaction of human tumors with platelets. We now report on the ability of two human adenocarcinomas of the colon (LoVo and HCT-8) and an anaplastic mouse tumor (Hut-20) to aggregate platelets by a different mechanism, the generation of thrombin. These spontaneous cell lines aggregate human or rabbit platelet-rich plasma after a 1- to 2-min lag period. This is often followed by a visible clot. Unlike SV3T3 cells, aggregation by LoVo, HCT-8, and Hut-20 cells is not inhibited by neuraminidase, trypsin, or cobra venom factor. These three cell lines markedly shorten the recalcification time of citrated plasma, whereas SV3T3 cells do not. Phospholipase A2 treatment inhibits the shortening of the recalcification time for the three tumors; this parallels its inhibitory effect on platelet aggregation. LoVo, HCT-8, and Hut-20 cells generate thrombin via the "tissue factor" coagulation pathway (using coagulation factor-deficient substrates). Dansylarginine-N-(3-ethyl-1,5-pentanediyl)amide, a highly specific, potent antithrombin antagonist, inhibits LoVo-, HCT-8-, and Hut-20-induced platelet aggregation at 4 to 15 microM, whereas its effect on SV3T3 cells is negligible. If platelets are required for certain human tumor metastases, dansylarginine-N-(3-ethyl-1, 5-pentanediyl)amide, or other antithrombin agents, may prove to be valuable therapeutic agents.
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PMID:Inhibition of the platelet-aggregating activity of two human adenocarcinomas of the colon and an anaplastic murine tumor with a specific thrombin inhibitor, dansylarginine N-(3-ethyl-1,5-pentanediyl)amide. 730 74

Phospholipase A2 (Naja mocambique) catalyzed release of epoxyeicosatrienoic acids (EETs) and 20-hydroxyeicosatetraenoic acid (20-HETE) from phospholipids of isolated human platelets. The amount of EETs released by phospholipase A2 measured by gas chromatography/mass spectrometry (GC/MS) was 4.3 +/- 0.9 pmol/10(6) platelets. No EETs were detected when phospholipase A2 was omitted from the incubations. The relative abundance of EET isomers (14,15-EET, 11,12-EET, 8,9-EET, and 5,6-EET) from human platelets was 5.4:4.5:3.7:1, respectively, as established by a new method based on particle-beam liquid chromatography/mass spectrometry (LC/MS). Fractionation of platelet phospholipids by normal-phase high-performance liquid chromatography followed by hydrolysis and GC/MS analyses indicated that the amount of EETs was highest in fractions containing phosphatidylinositol and phosphatidylserine (142 and 61 pmol/nmol of phosphorus, respectively) while low in phosphatidylcholine and phosphatidylethanolamine (19 and 11 pmol/nmol of phosphorus, respectively). The majority of EETs associated with phosphatidylcholine was found in fractions containing 1-O-alkylphosphatidylcholine. Human platelet phospholipids also released 20-HETE on phospholipase treatment (9.7 +/- 1.6 fmol/10(5) cells) and at least three other HETEs, one of which was tentatively identified as 16-HETE. Activation of human platelets by thrombin or platelet-activating factor released 5 to 7 fmol EET/10(6) cells. Receptor-mediated hydrolysis of phospholipids containing EETs and 20-HETE may play a role in stimulus-response coupling in platelets.
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PMID:Identification of arachidonate P-450 metabolites in human platelet phospholipids. 772 44

ADP and thrombin are two of the most important agonists of platelet aggregation--a cellular response that is critical for maintaining normal hemostasis. However, aberrant platelet aggregation induced by these agonists plays a central role in the pathogenesis of cardiovascular and cerebrovascular diseases. Agonist-induced primary or secondary activation of phospholipases leads to generation of the second messengers that participate in biochemical reactions essential to a number of platelet responses elicited by ADP and thrombin. Phospholipase A2 (PLA2) has been linked to cardiovascular diseases. However, the mechanism(s) of activation of PLA2 in platelets stimulated by ADP and thrombin has remained less well defined and much less appreciated. The purpose of this review is to examine and compare the molecular mechanisms of activation of PLA2 in platelets stimulated by ADP and thrombin.
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PMID:Phospholipase A2: its role in ADP- and thrombin-induced platelet activation mechanisms. 978 76

Cytosolic Phospholipase A(2) (cPLA(2)) has been implicated in receptor-mediated release of arachidonic acid from membrane phospholipids, the limiting step in prostacyclin and other eicosanoid production. Its activity is controlled by Ca(++) levels and enzymatically regulated phosphorylation. The purpose of this study was to assess the importance of phosphorylation of cPLA(2) in human umbilical vein endothelial cells and to identify the kinases involved. Inhibitors were used to study the pathways leading to phosphorylation and activation of mitogen activated protein kinases (MAP-kinases) and cPLA(2), as well as release of arachidonic acid and prostacyclin production after stimulation with different agonists. We have found that agonists that release arachidonic acid, including histamine, thrombin, AlF(4)(-), and pervanadate, all activate the MAP kinases ERK, p38 and JNK and cause phosphorylation of cPLA(2). Agonist specific differences in the signal transduction pathways included variable contribution of tyrosine phosphorylation, protein kinase C and ERK activity, and different effects of pertussis toxin. Treatment with PD98059 (inhibitor of ERK-activation) or SB203580 (inhibitor of p38) caused partial decrease in arachidonic acid release and cPLA(2) activity. In contrast the nonspecific protein kinase inhibitor staurosporin completely inhibited cPLA(2) activity. We conclude that in endothelial cells arachidonic acid release is largely mediated by cPLA(2) through agonist-specific pathways. The MAP kinases ERK and p38 both have demonstrable but not major effect on agonist stimulated arachidonic acid release and the data suggest that an additional unidentified kinase also has a role.
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PMID:Involvement of MAP kinases in the control of cPLA(2) and arachidonic acid release in endothelial cells. 1136

Composition of Indian Russell's viper (Daboia russelii russelii) venom, a medically important snake and member of "Big Four" snakes of India was done by gel filtration chromatography followed by tandem mass spectrometry. The MS/MS analyses of tryptic digested gel filtration peaks divulged the presence of 63 different proteins belonging to 12 families. Phospholipase A2 (PLA2), serine proteases, metalloproteases, cysteine-rich secretory proteins, l-amino acid oxidase, C-type lectin-like proteins, kunitz-type serine protease inhibitor, disintegrin, nucleotidase, phosphodiesterase, vascular endothelial growth factor and vascular nerve growth factor families were identified. PLA2 enzymes with isoforms of N-, S- and H-type based on their first N-terminal amino acid residue were observed. The venom is also found to be rich in RVV-X, RVV-V and thrombin-like enzymes. Homologues of disintegrins with RGD and RTS motifs were also observed. The high percentage of PLA2 and proteases in the venom proteome could be responsible for the observed coagulopathy, haemorrhage and edema which can be correlated with the clinical manifestations of Russell's viper envenomation. This is the first proteomic analysis of Indian D. russelii venom which might assist in understanding the pathophysiological effects of viper envenomation. Such study will also be important for developing more effective antivenom for viper bite management.
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PMID:Unveiling the complexities of Daboia russelii venom, a medically important snake of India, by tandem mass spectrometry. 2616 Apr 95


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