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)

Considerable progress has been made recently in understanding the mechanisms and significance of coagulation activation in human malignancy. Neoplastic cells may activate coagulation reactions directly, that is through contact with coagulation factors; or indirectly by formation of cytokines capable of activating certain host cells such as macrophages or endothelial cells. Data suggest that at least two autoregulatory pathways involving components of coagulation and fibrinolysis pathways exist. In one of these, tumour cell procoagulants lead to generation of thrombin in the tumour periphery. Thrombin is a mitogen that may also contribute to tumour stoma formation. Alternatively, tumour cells may express urokinase responsible for generation of cell surface-related proteolysis that may facilitate tumour cell proliferation, invasion and metastasis. An appreciation of these diverse mechanisms may permit rational design of clinical trials of agents capable of interrupting relevant pathways.
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PMID:Clotting factors in tumour tissue: implications for cancer therapy. 210 90

A 77-kDa complex of thrombin and a protein secreted by activated platelets had little if any thrombin amidolytic activity, indicating that the secreted protein is an inhibitor. The molecular weight of the inhibitor before reaction with thrombin was approximately 50,000. The apparent second-order rate constant for complex formation was estimated to be 1.3 x 10(6) M-1 s-1 (mean of four measurements); it was not affected by heparin or heparinase. These properties distinguish this inhibitor from other protease inhibitors secreted by platelets. The inhibitor reacted with trypsin and possibly with urokinase but not with factor Xa.
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PMID:Characteristics of a thrombin inhibitor secreted by activated platelets. 210 89

The effect of fibrin-targeting of urokinase-type plasminogen activator (u-PA) on its fibrinolytic potency was studied using recombinant fusion proteins of u-PA with the NH2-terminal region of tissue-type plasminogen activator (t-PA/u-PA) and chemical complexes of u-PA with F(ab')2 fragments of a fibrin specific monoclonal antibody (u-PA/MA-15C5-F(ab')2). Two chain derivatives of a low Mr variant of u-PA comprising amino acids Leu144-Leu411 (tcu-PA-32k), obtained by cleavage of recombinant single-chain u-PA (rscu-PA-32k) with thrombin (rtcu-PA-32k/T) or plasmin (rtcu-PA-32k/P) were investigated. The plasmin-derived two chain u-PA moieties, rtcu-PA-32k/P, rt-PA/tcu-PA-32k/P and rtcu-PA-32k/MA-15C5-F(ab')2/P had high specific activities in amidolytic and fibrin plate assays (130,000 and 150,000 IU/mg u-PA, 43,000 and 71,000 IU/mg u-PA and 32,000 and 56,000 IU/mg u-PA respectively). The thrombin-derived two chain u-PA moieties had a very low amidolytic activity, corresponding to less than or equal to 1 percent of that of their plasmin-derived counterparts. On fibrin plates, however, rtcu-PA-32k/T had a negligible activity, whereas rt-PA/tcu-PA-32k/T and rtcu-PA-32k/MA-15C5-F(ab')2/T had specific activities of 12,000 and 25,000 IU/mg u-PA respectively. The catalytic efficiency for plasminogen activation of rtcu-PA-32k/MA-15C5-F(ab')2/T is 4,000-fold lower than that of rtcu-PA-32k/MA-15C5-F(ab')2/P, but its concentration required for 50 percent lysis in 2 hours of a 125I-fibrin labeled plasma clot in human plasma (C50) is only 25-fold higher. The catalytic efficiency of rt-PA/tcu-PA-32k/T is 1,600-fold lower and the C50 100-fold higher than that of rt-PA/tcu-PA-32k/P. The catalytic efficiency and the fibrinolytic potential of rtcu-PA-32k/T are negligible as compared to that of rtcu-PA-32k/P. These observations may be explained by conversion of the thrombin derived two chain u-PA moieties to their plasmin-derived analogues at the fibrin surface. This conversion appears to be most efficient for the antibody conjugate which has a high fibrin-affinity, less efficient for the t-PA/u-PA chimera which has only moderate fibrin-affinity, and negligible for the unconjugated u-PA moiety which has no fibrin-affinity. These findings illustrate the importance of plasmin-mediated positive feedback mechanisms in u-PA mediated clot lysis.
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PMID:Effect of fibrin-targeting on clot lysis with urokinase-type plasminogen activator. 210 93

The effects of thrombin, interleukin-1 (IL-1), tumor necrosis factor (TNF) and gamma-interferon (gamma-IFN) on the release of plasminogen activator (PA) and inhibitor (PAI) were studied using cultivated human glomerular epithelial cells (GECs). Species of PAs and PAI secreted from the GECs were urokinase-type PA (u-PA) and tissue-type PA (t-PA), while the major species was a single chain u-PA in the amount of 28.6 +/- 2.34 ng/10(5) cells for 24 hours (N = 4, mean +/- SD), and PAI-1. The addition of increased concentrations of thrombin (0.1 to 31.6 U/ml) into confluent cultures enhanced the GECs to release u-PA, t-PA and PAI-1 in a dose- and time-dependent manner. The incubation of the GECs with 10 U/ml thrombin resulted in about a fourfold increase in the concentration of u-PA, threefold in t-PA and twofold in PAI-1. All thrombin effects, however, were suppressed by the simultaneous addition of cycloheximide, indicating that the enhancing effects of thrombin were due to an increase in the production of PAs and PAI-1, via protein synthesis. These thrombin effects appeared to be dependent upon the enzymatically active site of thrombin because DFP-thrombin had no effect. In the conditioned medium which was under continuous thrombin stimulation for 24 hours, no u-PA activity was detectable, even after the plasmin treatment, because a single chain u-PA was degraded by the thrombin. The stimulation of cultured GECs with thrombin only for the first three hours in 24 hour cultivation showed an apparent increase in the antigenic amount of u-PA. IL-1 enhanced the release of t-PA and PAI-1, and TNF did that of u-PA and t-PA, while gamma-IFN showed no significant effects. These findings indicate that the GECs participate in the regulation of extracapillary fibrinolysis in the glomerular microenvironment, as being modulated by thrombin and two cytokines, IL-1 and TNF.
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PMID:Secretion of plasminogen activator and its inhibitor by glomerular epithelial cells. 211 68

The mechanism of coagulation activation in renal cell carcinoma was investigated using immunohistochemical techniques applied to fresh frozen sections of resected primary tumors. Tissue factor antigen was detected in the endothelium of vascular channels within the tumors. Fibrinogen and factor V were distributed diffusely in the perivascular tumor connective tissue. Fibrin was readily detected in a linear pattern along the edges of nodules of viable tumor indicating that thrombin had formed from the interaction of coagulation factors demonstrated previously in renal cell carcinoma tissue. Tissue plasminogen activator was detected in the endothelium of blood vessels in the vicinity of the tumor and urokinase in areas of necrosis but neither were associated with viable tumor cells. These results indicate that thrombin is formed locally in renal cell carcinoma tissue that transforms fibrinogen to fibrin. There also appears to be a net deficit in fibrinolysis in situ in this tumor. We postulate that these conditions might contribute to stabilization and progression of renal cell carcinoma and that clinical trials of antithrombotic agents are justified in this tumor type.
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PMID:Fibrinogen-fibrin transformation in situ in renal cell carcinoma. 211 16

Increasing attention is being paid to alterations of the hemostatic balance in tumors, in general, and brain tumors, in particular. Apparently divergent results, showing excess fibrinolysis (i.e., increased plasminogen activator activity) or its inhibition (i.e., increased inhibitor activity), have been reported. The 9L rat brain tumor is a gliosarcoma and a model used to study treatment paradigms for human gliomas. To study the roles of fibrin and fibrinolysis in this brain tumor model, we used these features to investigate the nature of the plasminogen activator (PA) and thrombin inhibitors in normal rat brain and in the 9L rat brain tumor, growing both in vitro and in vivo in rat brain. The results indicate that cells cultured from the tumor in vitro express PA inhibitory activity which is both of the protease nexin I and PA inhibitor 1 types. However, the serpin PA inhibitory activity in extracts of both the normal brain and tumor is of the protease nexin I/PA inhibitor 3 type. This activity is higher in the tumor than in the surrounding "normal" tissue. In addition, we present evidence for a novel thrombin inhibitor which (a) is present only in the tumor growing in rat brain and undetectable either in the normal brain tissue or in vitro, (b) is in a latent, but sodium dodecyl sulfate-activatable, state, and (c) does not bind urokinase. In current studies, investigators are exploring the roles of these molecules and the target serine proteases they inhibit in the pathogenesis of gliomas.
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PMID:Serpin inhibitors of urokinase and thrombin in normal rat brain and the 9L brain tumor: evidence for elevated expression of protease nexin I-like inhibitor and a novel sodium dodecyl sulfate-activated tumor antithrombin. 211 23

A problem after successful thrombolytic therapy of acute myocardial infarction is the early occurrence of re-occlusions. An incidence between 10 and 30% is reported. All efforts made so far to reduce the re-occlusion rate using a variety of agents have been disappointing. In a pilot study 20 patients with acute myocardial infarction were treated, in whom a successful lytic therapy with urokinase or rt-PA was documented by means of coronary angiography 90 min after the beginning of treatment. Subsequently the patients were heparinised (thrombin time greater than 30 s), and in addition the selective serotonin-2 receptor-blocking agent ketanserin was given intravenously (4 mg/h). After 24 h the occurrence of early reocclusions was investigated by control angiography. None of the 20 patients showed reocclusions. The degree of stenosis in the infarcted vessel was 72% immediately after lytic therapy, and 68% after 24 h. These preliminary results may suggest a possible reduction in the re-occlusion rate after thrombolytic therapy with a combination of heparin and ketanserin.
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PMID:Prevention of an early re-occlusion after thrombolytic therapy of acute myocardial infarction by ketanserin. 213 77

Recombinant human single-chain urokinase-type plasminogen activator (suc-PA) (SM0: wild type) and its variants resistant to plasmin and/or thrombin (SM1: Lys135 to Gln; SM3: Phe157 to Asp; and SM4: Lys135 to Gln and Phe157 to Asp) have been constructed by site-directed mutagenesis with the aim of producing more efficient thrombolytic agents [Miyake, T. et al. (1988) J. Biochem. 104, 643-647]. In the present study, we characterized the recombinant variant scu-PAs expressed in Escherichia coli. They appeared to have structural integrity because their heat-stabilities, immunological reactivities, and circular dichroism spectra were essentially identical to those of each other and of native scu-PA (nscu-PA). In the presence of thrombin, SM3 and SM4 showed efficient clot lysis by all of the assays used, compared with SM0, SM1, and nscu-PA. While in the absence of thrombin, when measured by a fibrin plate method in a purified system, SM3 and SM4 had lower specific activities than SM0, SM1, and nscu-PA, because of their catalytic constants for conversion to the two-chain form (tcu-PA) by plasmin are lower. However, SM4 lysed clots as efficiently as SM0 in plasma by retaining the single-chain form, whereas SM0 was partly converted to the two-chain form.
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PMID:Characterization of thrombin- and plasmin-resistant mutants of recombinant human single chain urokinase-type plasminogen activator. 214 58

Components of coagulation and fibrinolysis reactions were identified in situ by immunohistochemical staining in fresh frozen sections of small cell carcinoma of the lung tissue. Tumor cells stained positively for tissue factor, a protein that is capable of activating the extrinsic pathway of coagulation (the components of which have been seen within small cell carcinoma of the lung [SCCL] tissue), and for proteins C and S antigens. Fibrin was seen in a focal distribution at the host-tumor interface, indicating that thrombin had acted upon the fibrinogen found throughout the tumor stroma. Staining with a neoepitope-specific antibody, which does not discriminate between fibrinogen fragment D and fibrin fragment D-dimer, was similar to that of the fibrin antibody. High molecular weight urokinase-type and tissue-type plasminogen activators were seen in vascular endothelium, but neither existed within the tumor. Low molecular weight urokinase was found in rare isolated foci of tumor cells primarily adjacent to areas of necrosis. Plasminogen activator inhibitor-3 occurred in tumor cell cytoplasmic blebs and in necrotic tumor cells, but plasminogen activator inhibitors 1 and 2 were not seen. Our data suggest a mechanism for thrombin generation and fibrin formation within SCCL tissues that could support cell proliferation, stroma formation, and preservation. These features could be conductive to perpetuation of this tumor and conceivably could form the basis of the beneficial effects of antithrombotic therapy seen in SCCL.
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PMID:Abnormal regulation of coagulation/fibrinolysis in small cell carcinoma of the lung. 215 29

Senile plaques, often surrounded by abnormally grown neurites, are characteristic of Alzheimer's diseased brain. The core of the plaque is mainly composed of amyloid beta protein (beta-AP), two of whose three precursors (APP) have serine proteinase inhibitor regions (APPI). APPI derivatives containing 60, 72 or 88 amino-acid fragments (APPI-60, APPI-72 and APPI-88, respectively) of the longest APP were produced in COS-1 cell culture medium, with the APPI cDNA ligated to the signal sequence of tissue plasminogen activator. The secreted APPIs were purified by sequential acetone precipitation followed by affinity chromatography using immobilized trypsin. These three APPIs and O-glycosylation-site-mutated APPI showed similar inhibitory activity against trypsin, chymotrypsin and plasmin. The purified APPI-72 was found to inhibit trypsin (Ki = 1.1 x 10(-10) M) and chymotrypsin (Ki = 5.8 x 10(-9) M) most strongly, and to inhibit leukocyte elastase (Ki = 7.9 x 10(-7) M) and several blood coagulation proteinases (Ki = 0.46-12 x 10(-7) M), but not urokinase or thrombin. The observed inhibition pattern was quite different from that of protease nexin I, one of serine proteinase inhibitors possessing neurite outgrowth activity. This suggests that the physiological roles of APPI are different from those of protease nexin I, and that APPI could not cause aberrant growth of neurite into the plaque. The presence of APPI having strong inhibitory activity in the brain might lead to the formation of amyloid deposits by preventing complete degradation of APPs.
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PMID:Enzyme specificity of proteinase inhibitor region in amyloid precursor protein of Alzheimer's disease: different properties compared with protease nexin I. 218 Apr 85


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