Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.73 (urokinase-type plasminogen activator)
 10,685 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombin cleaves single-chain urokinase-type plasminogen activator (scu-PA) into a two-chain form (tcu-PA/T), which is virtually inactive in plasminogen activator assays. Little is known about the physiological importance of tcu-PA/T. To examine the occurrence of tcu-PA/T in vivo, we developed a sensitive and specific bioimmunoassay (BIA) for the assessment of tcu-PA/T in human body fluids. In this BIA, urokinase antigen was immuno-immobilized in microtiter plates and treated with cathepsin C, a specific activator of tcu-PA/T, after which plasminogen activator activity was measured. The occurrence of tcu-PA/T was examined in the plasma of 27 healthy individuals and of 17 sepsis patients, and in the synovial fluid of 16 rheumatoid arthritis patients. In addition, the concentration of urokinase antigen and scu-PA were measured in all three groups. In the plasma of the healthy individuals no measurable amounts of tcu-PA/T could be found(< detection limit of 0.2 ng/ml). In the plasma of almost all sepsis patients tcu-PA/T could be detected (median value 0.4 ng/ml). The amount of tcu-PA/T was 12% of the amount of scu-PA and accounted for about 9% of urokinase antigen. In the synovial fluid of all rheumatoid arthritis patients tcu-PA/T could be measured (median value 5.4 ng/ml) at a concentration which was twofold higher than the concentration found for scu-PA. In this group tcu-PA/T contributed to about 47% of the urokinase antigen. From these data we conclude that inactivation of scu-PA by thrombin can take place in vivo under pathological conditions which involve the production of large amounts of thrombin. This way thrombin may regulate fibrinolysis and extracellular proteolysis. The BIA for tcu-PA/T can be of use for further research on the physiological role of tcu-PA/T.
 ...
PMID:A sensitive bioimmunoassay for thrombin-cleaved two-chain urokinase-type plasminogen activator in human body fluids. 882 85

It is increasingly realised that fibrin deposition and fibrin lysis are major factors in vascular pathology. In addition to thrombotic occlusion fibrin is a component of atherosclerotic lesions, but the increased interest in components of the haemostatic system was mainly triggered by clinical use of fribrinolytic agents, and the problems of re-stenosis following angioplasty. This review focuses on the main components of the fibrinolytic system--tissue plasminogen activator (tPA), urokinase (uPA) and plasminogen activator inhibitor (PAI-1)--and on thrombin. These factors are not only involved in fluid phase clotting and clot lysis; they react specifically with cells and matrix components. During the last 5 years, the main period under review, there have been numerous studies on their interactions with endothelial and smooth muscle cells in culture, in whole tissues and in vivo, and with arterial extracellular matrix of which a major component is fibrin. Plasminogen activators bind to cell surface receptors, influence cell migration and release active thrombin from fibrin. Thrombin emerges as a pluripotent factor which modulates many aspects of endothelial and smooth muscle cell behaviour, including release and synthesis of fibrinolytic components, and stimulation of cell proliferation.
 ...
PMID:Haemostatic factors and atherogenesis. 883 Sep 27

Barley serpin BSZx is a potent inhibitor of trypsin and chymotrypsin at overlapping reactive sites (Dahl, S.W., Rasmussen, S.K. and Hejgaard, J. (1996) J. Biol. Chem., in press). We have now investigated the interactions of BSZx with a range of serine proteinases from human plasma, pancreas and leukocytes, a fungal trypsin and three subtilisins. Thrombin, plasma kallikrein, factor VIIa/tissue factor and factor Xa were inhibited by BSZx at heparin independent association rates (k(ass)) of 4.5 X 10(3)-1.3 x 10(5) M(-1) s(-1) at 22 degrees C. Only factor Xa turned a significant fraction of BSZx over as substrate. Complexes of these proteinase with BSZx resisted boiling in SDS, and amino acid sequencing showed that cleavage in the reactive center loop only occurred after P1 Arg. Activated protein C and leukocyte elastase were slowly inhibited by BSZx (k(ass)=1-2 x 10(2) M(-1) s(-1)) whereas factor XIIa, urokinase and tissue type plasminogen activator, plasmin and pancreas kallikrein and elastase were not or only weakly affected. The inhibition pattern with mammalian proteinases reveal a specificity of BSZx similar to that of antithrombin III. Trypsin from Fusarium was not inhibited while interaction with subtilisin Carlsberg and Novo was rapid but most BSZx was cleaved as a substrate. Identification of a monoclonal antibody specific for native BSZx indicate that complex formation and loop cleavage result in similar conformational changes.
 ...
PMID:Inhibition of coagulation factors by recombinant barley serpin BSZx. 884 56

Tryptase is a serine protease secreted by mast cells that is able to activate other cells. In the present studies we have tested whether these responses could be mediated by thrombin receptors or PAR-2, two G-protein-coupled receptors that are activated by proteolysis. When added to a peptide corresponding to the N terminus of PAR-2, tryptase cleaved the peptide at the activating site, but at higher concentrations it also cleaved downstream, as did trypsin, a known activator of PAR-2. Thrombin, factor Xa, plasmin, urokinase, plasma kallikrein, and tissue kallikrein had no effect. Tryptase also cleaved the analogous thrombin receptor peptide at the activating site but less efficiently. When added to COS-1 cells expressing either receptor, tryptase stimulated phosphoinositide hydrolysis. With PAR-2, this response was half-maximal at 1 nM tryptase and could be inhibited by the tryptase inhibitor, APC366, or by antibodies to tryptase and PAR-2. When added to human endothelial cells, which normally express PAR-2 and thrombin receptors, or keratinocytes, which express only PAR-2, tryptase caused an increase in cytosolic Ca2+. However, when added to platelets or CHRF-288 cells, which express thrombin receptors but not PAR-2, tryptase caused neither aggregation nor increased Ca2+. These results show that 1) tryptase has the potential to activate both PAR-2 and thrombin receptors; 2) for PAR-2, this potential is realized, although cleavage at secondary sites may limit activation, particularly at higher tryptase concentrations; and 3) in contrast, although tryptase clearly activates thrombin receptors in COS-1 cells, it does not appear to cleave endogenous thrombin receptors in platelets or CHRF-288 cells. These distinctions correlate with the observed differences in the rate of cleavage of the PAR-2 and thrombin receptor peptides by tryptase. Tryptase is the first protease other than trypsin that has been shown to activate human PAR-2. Its presence within mast cell granules places it in tissues where PAR-2 is expressed but trypsin is unlikely to reach.
 ...
PMID:Interactions of mast cell tryptase with thrombin receptors and PAR-2. 902 Jan 12

Protease nexin 1 (PN1) is a serine protease inhibitor (SERPIN) that acts as a suicide substrate for thrombin (Th) and urokinase-type plasminogen activator (uPA). PN1 forms 1:1 stoichiometric complexes with these proteases, which are then rapidly bound, internalized, and degraded. The low density lipoprotein receptor-related protein (LRP) is the receptor responsible for the internalization of protease-PN1 complexes. However, we found that the LRP is not significantly involved in the initial cell surface binding of thrombin-PN1, leading us to investigate what cellular component was responsible for this initial interaction. Since Th-PN1 complexes retain a high-affinity for heparin after complex formation, unlike several of the other SERPINs, we tested the possibility that cell surface heparins were involved in initial complex binding. Soluble heparin was found to be a potent inhibitor of the binding of Th-PN1 to the cell surface and greatly facilitated the dissociation of Th-PN1 complexes pre-bound in the absence of soluble heparin. To ascertain the role of cell surface heparins, further studies were done using complexes of thrombin and PN1(K7E), a variant of PN1 in which the heparin binding site was rendered non-functional. When added at equal initial concentrations of complexes, Th-PN1(K7E) was catabolized 5- to 10-fold less efficiently than Th-PN1, a direct result of the greatly diminished initial binding of the Th-PN1(K7E) complexes. These data demonstrate the sizable contribution of cell surface heparins to Thrombin-PN1 complex binding and support a model in which these heparins act to concentrate the complexes at the cell surface facilitating their subsequent LRP-dependent endocytosis.
 ...
PMID:The efficient catabolism of thrombin-protease nexin 1 complexes is a synergistic mechanism that requires both the LDL receptor-related protein and cell surface heparins. 936 Sep 77

There is increasing evidence suggesting that members of the serine protease family, including thrombin, chymotrypsin, urokinase plasminogen activator, and kallikrein, may play a role in normal development and/or pathology of the nervous system. Serine proteases and their cognate inhibitors have been shown to be increased in the neural parenchyma and cerebrospinal fluid following injury to the blood brain barrier. Zymogen precursors of thrombin and thrombin-like proteases as well as their receptors have also been localized in several distinct regions of the developing or adult brain. Thrombin-like proteases have been shown to exert deleterious effects, including neurite retraction and death, on different neuronal and non-neuronal cell populations in vitro. These effects appear to be mediated through cell surface receptors and can be prevented or reversed with specific serine protease inhibitors (serpins). Furthermore, we have recently shown that treatment with protease nexin-1 (a serpin that inhibits thrombin-like proteases) promotes the survival and growth of spinal motoneurons during the period of programmed cell death and following injury. Taken together, these observations suggest that thrombin-like proteases play a deleterious role, whereas serpins promote the development and maintenance of neuronal cells. Thus, changes in the balance between serine proteases and their cognate inhibitors may lead to pathological states similar to those associated with some neurodegenerative diseases such as Alzheimer's disease. The present review summarizes the current state of research involving such serine proteases and speculates on the possible role of these thrombin-like proteases in the development, plasticity and pathology of the nervous system.
 ...
PMID:The role of thrombin-like (serine) proteases in the development, plasticity and pathology of the nervous system. 937 52

Tumour cells may express urokinase type plasminogen activator (u-PA). This may influence the invasive properties of the cells but has seldom been implicated in production of a systemic bleeding state. Two patients are described in whom severe bleeding occurred in association with disseminated malignancies. Thrombin generation was little disturbed and platelet numbers were insufficient to account for the bleeding. Florid plasmin generation was evident in the circulation and the fibrinolytic inhibitor tranexamic acid controlled the bleeding well. Free active u-PA was demonstrated in the circulation and u-PA antigen on the malignant cells which invaded the marrow of one of the patients. Tumour cell u-PA may occasionally be responsible for a bleeding state.
 ...
PMID:Tumour cell u-PA as a cause of fibrinolytic bleeding in metastatic disease. 940 Oct 67

Thrombin cleaves single-chain urokinase-type plasminogen activator (scu-PA) into a virtually inactive two-chain form (tcu-PA/T), a process which may contribute to the maintenance of a fresh blood clot. We have examined the inactivation of scu-PA by thrombin in a plasma milieu to get more insight in the physiological relevance of this phenomenon. Citrated pooled normal plasma was treated with thrombin in the absence and presence of thrombomodulin. After an incubation period of 30 min the concentrations of scu-PA and tcu-PA/T were measured using specific bioimmunoassays. The inactivation of scu-PA in citrated plasma was found to be stimulated fourfold by thrombomodulin. Kinetic experiments showed that the inactivation of scu-PA by thrombin in the absence and presence of thrombomodulin occurred rapidly and declined within 1 min as a result of rapid inhibition by antithrombin III (ATIII) and other possible inhibitors. Calcium had no direct effect on the inactivation of scu-PA by exogenously added thrombin in the absence and presence of thrombomodulin. However, recalcification of plasma induced significant inactivation of scu-PA in plasma as a result of endogenous thrombin generation through the contact activation system. This calcium-induced inactivation of scu-PA was completely abolished in the presence of thrombomodulin, most likely as a result of activation of protein C by the complex formed between thrombomodulin and endogenously generated thrombin. Thrombomodulin thus appeared to play a dual role both by stimulating the inactivation of scu-PA by thrombin, and by inhibiting calcium-induced inactivation of scu-PA in plasma. In the plasma from a patient heterozygous for protein C deficiency, thrombomodulin could not prevent calcium-induced generation of tcu-PA/T, whereas the stimulating effect of thrombomodulin predominated instead. This result implied that disturbance of the protein C pathway may lead to the inactivation of substantial amounts of scu-PA in plasma under (patho)physiological circumstances and may provide an additional explanation for the association found between thromboembolism and deficiencies in the protein C pathway. This study shows that the amount of scu-PA that is inactivated in plasma depends mainly on the generation of thrombin and on thrombomodulin. We conclude that the inhibition of scu-PA-induced fibrinolysis appears to be regulated by activation of the coagulation system, providing a link between coagulation and fibrinolysis.
 ...
PMID:The inactivation of single-chain urokinase-type plasminogen activator by thrombin in a plasma milieu: effect of thrombomodulin. 971 90

Endothelial cells form a multifunctional cell lining that covers all of the inner surface of blood vessels and regulates several important physiological and pathological reactions. These include inflammation/immune reaction, blood vessel tonus, hemostasis/thrombosis, angiogenesis and so on. Thus, abnormalities of endothelial function may play crucial roles in the development of angitis syndrome, thrombosis/embolism, bleeding disseminated intravascular coagulation (DIC), and neovascularization in some pathological states including tumor growth and diabetic retinopathy. Research on endothelial cells now forms a new frontier termed 'Endotheliology'. Recent advances of the functional and structural aspects of endothelial cells are reviewed here mainly from the viewpoint of endothelial regulation of coagulation and the fibrinolytic system. First we show that the natural endothelial membrane protein thrombomodulin is localized not only on apical endothelial surface but also in caveolae. Since it has been reported that such factors involved in coagulation/fibrinolysis as tissue factor, tissue factor pathway inhibitor (TFPI), thrombin receptor and urokinase receptor are also localized in the caveolae, this membrane structure may act as a special component to regulate coagulation/fibrinolysis on the endothelial membrane surface. Next we demonstrate the signaling pathway of the thrombin receptor. Thrombin cleaves the N-terminus of the receptor as a substrate, exposing a new N-terminus. This newly exposed N-terminus acts as a ligand and activates platelets, endothelial cells and vascular smooth-muscle cells. We have identified that the signal from the thrombin receptor activates NF-kappaB through the activation of protein C kinase, tyrosine kinase and MAP kinase, and results in proliferation of the cells. We have also shown that the receptor is over-expressed on platelets from diabetes patients.
 ...
PMID:Biology of endothelium. 981 71

Serine proteases exert a variety of functions in the body; food digestion, regulation of other proteins and modification of extracellular matrix. Cumulative evidence has shown the importance of serine proteases in the nervous system as well. It has been shown that three serine proteases, thrombin, plasminogen activators and neuropsin, have functional roles in neural plasticity. Most of the actions of thrombin are thought to be mediated by its specific receptors. Thrombin reverses neurite outgrowth of serum-deprived neuroblastoma cells, and induces protective and apoptotic effects on neurons and glial cells depending on concentration and time. Tissue-type and urokinase-type plasminogen activators (tPA and uPA) distribute broadly in the brain. tPA and uPA exert a variety of functions during development. These proteases also function in long-term potentiation and kindling formation. Furthermore, tPA is essential to excitotoxic neuronal cell death. Neuropsin is a serine protease expressed in the limbic system of the brain. Kindling induced neuropsin mRNA and protein expression and anti-neuropsin antibody ameliorates kindling epilepsy. The possible roles of these proteases in neural plasticity are reviewed here.
 ...
PMID:Plasticity-related serine proteases in the brain (review). 1008 14


<< Previous 1 2 3 4 5 6 7 8 Next >>