UNIPROT:P00750 - FACTA Search

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Query: UNIPROT:P00750 (PLA)
16,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The vascular endothelium is a rich source of plasminogen activator (PA) and thus of blood vessel-associated fibrinolytic activity. Cultured bovine aortic endothelial cells were employed to determine if components of the coagulation system interact with the endothelium to modify expression of this activity. The addition of thrombin to these cultures led to a rapid decline in intracellular PA activity, with as little as 3 ng/ml, or 0.1 nM thrombin causing a 50% decrease within 30 min. Thrombin inactivated with diisopropylflurophosphate or hirudin did not elicit the response. Although control cultures secreted high levels of PA, no PA activity could be detected in the media surrounding the thrombin-treated cells. This loss of activity did not appear to result from direct inactivation of PA by thrombin. These observations indicate that the fibrinolytic potential of cultured endothelial cells is rapidly suppressed by trace amounts of thrombin. The generation of thrombin at sites of vascular injury may have a similar effect on the endothelium.
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PMID:Effect of thrombin on the fibrinolytic activity of cultured bovine endothelial cells. 44 60

Extracapillary glomerulonephritis are associated with fibrin deposition in the urinary space of the glomerulus. Such deposits were correlated with the severity of the disease and with a poor renal outcome. Fibrin formation involves an activation of the coagulation cascade either through the intrinsic pathway, Hageman factor being activated by the altered glomerular basement membrane, either by the extrinsic pathway, infiltrating monocytes and glomerular cells exhibiting a procoagulant activity i.e. thromboplastin or tissue factor. Treatments with heparin or warfarin were shown to decrease the severity of experimental glomerular diseases. A similar beneficial effect was obtained with a monocyte-depleting serum and more recently with a treatment by a tissue type plasminogen activator. Glomerular cells also produce a fibrinolytic activity which could be too low or uneffective on extracapillary fibrin deposits if they contain high amounts of plasminogen activator inhibitors. Thrombin has procoagulant activity, antifibrinolytic activity and has cellular chemotactic and proliferative effects. It could play a major role in the pathogenesis of crescent formation.
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PMID:[Role of hemostasis in the formation of crescents in extracapillary glomerulonephritis]. 129 84

Plasmin inhibited the biosynthesis of tissue-type plasminogen activator (tPA) antigen by human umbilical vein endothelial cells (HUVEC) in a dose-dependent manner. The amount of tPA antigen found in the 24-h conditioned medium of cells treated with 100 nM plasmin for 1 h was 20-30% of that in the control group. However, in contrast to tPA, such treatment led to a 3-fold increase in plasminogen activator inhibitor (PAI) activity, whereas the amount of PAI type 1 antigen was unchanged. The effects of plasmin on HUVEC were binding- and catalytic activity-dependent and were specifically blocked by epsilon-aminocaproic acid. Microplasmin, which has no kringle domains, was less effective in reducing tPA antigen biosynthesis or enhancing PAI activity in HUVEC. Kringle domains of plasmin affected neither tPA antigen nor PAI activity of the cells. Other proteases including chymotrypsin, trypsin, and collagenase at comparable concentrations did not have a significant effect on the biosynthesis of tPA antigen or PAI activity of HUVEC. Thrombin stimulated the biosynthesis of tPA and PAI-1 antigens by HUVEC. Thrombin also stimulated an increase in the protein kinase activity in HUVEC, whereas plasmin inhibited the protein kinase activity of the cells. It is possible that plasmin regulates the biosynthesis of tPA in HUVEC through the signal transduction pathway involving protein kinase.
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PMID:Plasmin and the regulation of tissue-type plasminogen activator biosynthesis in human endothelial cells. 138 68

Cross-linked hybrid oligomers of fibrinogen and fibrin are found in plasma from fibrinaemic patients and normal individuals as well as in preparations of purified human fibrinogen. The present study was undertaken to see if such hybrid oligomers have the same stimulatory effect on tissue plasminogen activator (t-PA) conversion of plasminogen as do polymeric and monomeric fibrin. Hybrid oligomeric fibrin(ogen) material was provided by subjecting purified human fibrinogen to gel filtration in urea-containing buffer at pH 5.6. Well separated fractions of hybrid oligomeric material and monomeric fibrinogen were thus obtained. Some of this material was converted to soluble polymeric or monomeric fibrin using insolubilized thrombin. Hybrid polymeric fibrin, polymeric fibrin or monomeric fibrin were then added to citrated, normal plasma to 2.5 or 5 per cent of the plasma fibrinogen concentration. The added material was kept in solution by plasma fibrinogen. The "COA-SET Fibrin Monomer Test" (Kabi,Stocholm,Sweden), based on the ability of fibrin monomers to enhance t-PA mediated plasminogen-plasmin conversion, was used to compare the potential stimulatory effect of the preparations above. The results led to the following conclusions: 1) Cross-linked, soluble fibrin(ogen) hybrid polymers in a concentration of 5 per cent of plasma fibrinogen concentration (w/w) do not stimulate t-PA. 2) Thrombin conversion of the fibrin-fibrinogen hybrid material resulted in an increase in the rate of t-PA mediated plasminogen conversion, corresponding to the one observed with equivalent (w/w) amounts of fibrin monomers. Compared on a mole to mole basis, fibrin oligomers are more powerful than fibrin monomers as stimulators of t-PA activity.
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PMID:Soluble, cross-linked fibrin(ogen) hybrid oligomers do not stimulate t-PA conversion of plasminogen. 141 94

We have previously shown that alpha-thrombin exerted a mitogenic effect on human glomerular epithelial cells and stimulated the synthesis of urokinase-type (u-PA) and tissue-type plasminogen activator (t-PA) and of their inhibitor, plasminogen activator inhibitor 1 (PAI-1). In the present study, we investigate the signal transduction mechanisms of thrombin in these cultured cells. Thrombin induced an increase in intracellular free calcium concentrations ([Ca2+]i) in a dose-dependent manner, a plateau being reached at 1 U/ml thrombin. A 60% inhibition of this effect was produced by 300 nM nicardipine, a dihydroperidine agent, or by 4 mM EGTA, indicating that increase in [Ca2+]i was due in part to extracellular Ca2+ entry through L-type voltage-sensitive calcium channels. Thrombin also induced an increase in inositol trisphosphate (IP3), suggesting that phospholipase C activation and phosphatidylinositides breakdown were stimulated. Interestingly thrombin-stimulated cell proliferation measured by 3H thymidine incorporation was inhibited by 300 nM nicardipine, and restored by addition of 10(-8) M ionomycin, indicating that calcium entry was critical for the mitogenic signal of thrombin. Conversely, nicardipine did not modify thrombin-stimulated synthesis of u-PA, t-PA, and PAI-1. Both thrombin-stimulated cell proliferation and protein synthesis required protein kinase C activation since these effects were blocked by 10 microM H7, an inhibitor of protein kinases, and by desensitization of protein kinase C by phorbol ester pretreatment of the cells. Interestingly, DFP-inactivated thrombin which binds the thrombin receptor and gamma-thrombin, which has some enzymatic activity but does not bind to thrombin receptor, had no effect when used alone. Simultaneous addition of these two thrombin derivatives had no effect on [Ca2+]i, and 3H thymidine incorporation but stimulated u-PA, t-PA, and PAI-1 synthesis although to a lesser extent than alpha-thrombin. This effect also required protein kinase C activation to occur, presumably by a pathway distinct from phosphoinositoside turnover since it was not associated with IP3 generation. In conclusion, multiple signalling pathways can be activated by alpha-thrombin in glomerular epithelial cells: 1) Ca2+ influx through a dihydroperidine-sensitive calcium channel, which seems critical for mitogenesis; 2) protein kinase C activation by phosphoinositide breakdown, which stimulates both mitogenesis and synthesis of u-PA, t-PA, and PAI-1; 3) protein kinase C activation by other phospholipid breakdown can stimulate u-PA, t-PA, and PAI-1 synthesis but not mitogenesis.
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PMID:Thrombin signal transduction mechanisms in human glomerular epithelial cells. 153 79

In the present study we investigated several factors of hemostasis and fibrinolysis during the normal pregnancy in 52 women. Whereas the Thrombin-Time did not show any change, the increase of the Hepato-Quick and the decrease of the Partial Thromboplastin-Time was significant. During pregnancy we observed a significant increase of the activity of fibrinogen, factor XII and prekallikrein as well as of the von-Willebrand-factor-antigen (VIIIR:Ag). The activity of factor II and X remained constantly. The increased activity of factors of hemostasis was accompanied by an increase of activity and concentration of antithrombin-III. In contrast to the activity of the hemostatic system we could not find any significant alteration of the fibrinolytic system. The cause must be searched in the observed increase of plasminogen-activator-inhibitor (PAI)--likly in combination with a decrease of the tissue-type plasminogen activator (t-PA). Our data indicate, that the highest risk for thrombosis already might exist in week 24 of pregnancy, because a distinct increase of hemostatic activity is combined with a nearly unchanged fibrinolytic activity.
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PMID:[Changes in the blood coagulation and fibrinolysis system in the course of normal pregnancy]. 162 53

Adenosine 3',5'-cyclic monophosphate (cAMP) elevation in cultured rat mesangial cells causes urokinase-dependent adhesion loss, stress-fiber fragmentation, and shape change. Thrombin cleaves single-chain urokinase (scu-PA), causing its inactivation, but not two-chain u-PA [tcu-plasminogen activator (PA)] or tissue-type PA. We tested the ability of thrombin to inhibit the effects of cAMP elevation in mesangial cells and inactivate cell-associated scu-PA. In an assay of trypsin-sensitive adhesion, 65.9% of control cells and 5.5% of cells treated with isoproterenol + methylisobutylxanthine (IM) remained adherent. In the presence of 0.01, 0.1, 1.0, and 10.0 unit/ml thrombin, 20.9, 46.6, 50.4, and 53.3%, respectively, of IM-treated cells remained attached. Thrombin also inhibited stress-fiber fragmentation and shape change. The effects of thrombin were blocked by hirudin or antithrombin III plus heparin. Direct zymography in gels containing gelatin and plasminogen revealed loss of a closely spaced pair of PA bands with thrombin treatment (1.0 unit/ml). Hirudin blocked the loss. alpha-Thrombin inactivated by diisopropyl fluorophosphate neither inhibited shape change nor caused loss of the PA bands; however, gamma-thrombin was nearly as active as native alpha-thrombin in both regards. Pretreatment of the cells with as little as 1.0 unit/ml thrombin for 1.0 min caused marked inhibition of shape change and near total loss of the slower migrating u-PA band (of the doublet). The faster migrating band was inhibited less. The results indicate that the slower migrating band represents scu-PA; the nature of the faster migrating band is less certain. Thrombin reversed the adhesion loss and shape change caused by 8-(4-chlorophenylthio)-cAMP and MIX. Thus physiological concentrations of thrombin rapidly inactivate mesangial cell scu-PA and inhibit and reverse cAMP-stimulated adhesion loss and shape change.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Regulation of mesangial cell adhesion and shape by thrombin. 165 8

Thrombin promotes the formation of arterial thrombi by converting fibrinogen to fibrin and by causing platelets to aggregate. We have examined the combined effects of plasminogen activators and inhibitors of platelet aggregation on the lysis of platelet-rich fibrin clots formed by alpha-thrombin in citrated platelet-rich plasma. The extent of platelet aggregation and clot formation were measured by recording light transmission in an aggregometer. Immediately after the formation of platelet-rich fibrin clots, addition of 2,000 U/ml streptokinase or 50 micrograms/ml recombinant tissue-type plasminogen activator alone resulted in the degradation of polymerized fibrin and the release of trapped platelet aggregates without causing significant platelet deaggregation. Preincubation of the platelet-rich plasma with 20 microM indomethacin for 1 min before thrombin stimulation or simultaneous addition of prostaglandin E1 (10 microM) with the plasminogen activators after thrombin stimulation resulted in spontaneous platelet deaggregation. Because platelet aggregation is, in part, mediated by the binding of Arg-Gly-Asp-containing adhesive proteins to activated platelets, the effect of Arg-Gly-Asp peptides on platelet deaggregation was examined. By itself, Gly-Arg-Gly-Asp-Ser-Pro specifically caused dose- and time-dependent deaggregation of platelet aggregates formed by ADP or by thrombin in the presence of 1 mM Gly-Pro-Arg-Pro, but had no effect on the dissociation of thrombin-induced platelet-rich fibrin clots. In combination with streptokinase or recombinant tissue-type plasminogen activator, Gly-Arg-Gly-Asp-Ser-Pro enhanced the rate of lysis of platelet-rich fibrin clots. The control Gly-Arg-Gly-Glu-Ser-Pro peptide was completely ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Rapid dissociation of platelet-rich fibrin clots in vitro by a combination of plasminogen activators and antiplatelet agents. 176 85

Coronary thrombolysis is the treatment of choice for patients with acute Q wave myocardial infarcts who have no contraindication to such therapy. However, the time required for thrombolysis to occur and the possibility of reocclusion of the infarct-related artery following thrombolytic therapy are problems. The time required for thrombolysis to occur with currently available agents ranges from 40 to 60 minutes and the frequency of reocclusion of the infarct-related artery after tissue-type plasminogen activator is 10 to 20%. We review experimental studies and clinical evaluations in which attempts have been made to develop adjunctive therapies that when coupled with available thrombolytic interventions might shorten the time to thrombolysis and delay or prevent reocclusion. From the studies done to date, it appears that a combination of thromboxane synthesis inhibitor and receptor antagonist with a serotonin receptor antagonist and heparin shortens the time to thrombolysis and delays or prevents coronary artery reocclusion in experimental canine models with copper coil-induced coronary artery thrombi. A monoclonal antibody to the platelet glycoprotein IIb/IIIa receptor given with tissue plasminogen activator and heparin also shortens the time to thrombolysis and delays or prevents reocclusion in experimental canine models. A mutant tissue plasminogen activator with a glycosylation defect and prolonged systemic clearance delays coronary artery reocclusion following lysis of three-hours coronary thrombi, induced by a copper coil. Thrombin inhibitors, including heparin, and synthetic inhibitors, given with tissue plasminogen activator and aspirin, appear to shorten the time to thrombolysis and delay or prevent coronary artery reocclusion in experimental canine models.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Thrombolytic therapy: enhancement by platelet and platelet-derived mediator antagonists. 180 65

Human glomerular epithelial cells (GECs) in culture synthesize single-chain, urokinase-type plasminogen activator (SC-uPA), tissue-type plasminogen activator (t-PA), and plasminogen activator inhibitor 1 (PAI-1) and possess specific membrane-binding sites for u-PA. Using purified 125I-alpha thrombin, we demonstrate here the presence of two populations of specific binding sites for thrombin on GECs (1.Kd = 4.3 +/- 1.0 x 10(-10) M, 5.4 +/- 1.4 x 10(4) M sites per cell, 2. Kd = 1.6 +/- 0.5 x 10(-8) M, 7.9 +/- 1.8 x 10(5) sites per cell). Purified human alpha thrombin promoted the proliferation of GECs and induced a time- and dose-dependent increase of SC-uPA, t-PA, and PAI-1 antigens released by GECs. Thrombin-mediated increase in antigen was paralleled by an increase in the levels of corresponding u-PA and PAI-1 messenger RNA. In contrast, thrombin decreased u-PA activity in conditioned medium. This discrepancy between u-PA antigen and u-PA activity was explained by a limited proteolysis of SC-uPA by thrombin, leading to a two-chain form detected by immunoblotting and that could not be activated by plasmin. Thrombin also decreased the number of u-PA binding sites on GECs (p less than 0.05) without changing receptor affinity. Hirudin inhibited the binding and the cellular effects of thrombin, whereas thrombin inactivated by diisopropylfluorophosphate had no effect, indicating that both membrane binding and catalytic activity of thrombin were required. We conclude that thrombin, through specific membrane receptors, stimulates proliferation of GECs and decreases the fibrinolytic activity of GECs both at the cell surface and in the conditioned medium. These results suggest that thrombin could be involved in the pathogenesis of extracapillary proliferation and persistency of fibrin deposits in crescentic glomerulonephritis.
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PMID:Thrombin increases proliferation and decreases fibrinolytic activity of kidney glomerular epithelial cells. 184 34

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