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)

We examined changes in fibrinolytic parameters in male patients with diabetes mellitus (DM) and controls. DM patients were divided into three groups: patients without retinopathy, patients with simple retinopathy, and patients with proliferative retinopathy. Plasma levels of t-PA (tissue plasminogen activator) and t-PA-PAI-1 (plasminogen activator inhibitor-1) complex increased with increase in age, but those of PAI-1 (total and free) did not change in controls. On the other hand plasma levels of PAI-1 decreased with increase in age in DM patients. Plasma levels of t-PA, t-PA-PAI-1 complex, free and total PAI-1 increased with increase in body mass index in controls, but no significant changes were shown in these parameters in DM patients. When compared with controls, plasma levels of t-PA, t-PA-PAI-1 complex and PAI-1 were lower in DM patients. Plasma levels of UK (urokinase) and Lp(a) were higher in DM patients. ELT (euglobulin clot lysis time) was significantly shorter in DM patients than in controls. Patients without retinopathy showed increased fibrinolytic activities compared with those with retinopathy due to the increased levels of t-PA in plasma. These results seem to indicate that blood vessels release larger amounts of t-PA at the early stage of DM, then release being impaired at its advance stage. It is also suggested that the regulatory control mechanisms of fibrinolytic activity associated with mechanisms of fibrinolytic activity associated with change in age and body mass index are different between patients with DM and normal people.
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PMID:Changes in fibrinolytic parameters in male patients with type 2 (non-insulin-dependent) diabetes mellitus. 823 67

One of the mechanisms by which endothelial cells (ECs) regulate fibrinolysis is through the regulated assembly of proteins such as plasminogen, tissue plasminogen activator (tPA) and urokinase (uPA) on their membrane surface. Receptors for many of these fibrinolytic factors have been isolated and characterized. A unique 45 kD plasminogen receptor present on ECs derived from vein vasculature has been identified and resolved into two plasminogen binding components. One component consists of the unique 45 kD plasminogen receptor (pI = 6.3) whereas the other component (pI = 5.1) is identified as the cytoskeletal protein, actin. Immunofluorescent studies of isolated ECs confirm the presence of actin on their extracellular surface. This observation is consistent with a number of other recent reports of actin externally localized on other cell types. In vitro studies using purified actin confirm that plasminogen binds to actin both saturably and with relatively high affinity. Competition studies with lysine indicated that the binding was largely kringle-dependent, and when binding of tPA to actin was assessed, it also bound to actin with 70-80% of binding inhibited by lysine. Lipoprotein (a), which shows homology with plasminogen, also interacted with actin. Addition of plasminogen and low-density lipoproteins inhibited Lp(a) binding to actin in a dose-dependent fashion. Moreover, in competition with tPA, partial inhibition of plasminogen binding to actin was also observed. In experiments using anti-actin antibodies added in excess to cultured ECs, binding of plasminogen was inhibited by 45%, tPA binding was inhibited by 46% and Lp(a) binding was reduced by 56%, confirming actin as a binding site for these various ligands whilst attesting to the presence of other EC receptors for these proteins. Collectively, the data presented are consistent with actin playing a major role in localizing binding not only of plasminogen, but also of tissue plasminogen activator and Lp(a) to the surface of human endothelial cells.
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PMID:Endothelial cell surface actin serves as a binding site for plasminogen, tissue plasminogen activator and lipoprotein(a). 885 56

Cerebral ischemia is caused by reduced blood supply at the microcirculatory level. In the microvessels, the main elements of the reperfusion injury following brain ischemia are the transformation of endothelial cell-surface from anticoagulant to procoagulant property, leukocyte adhesion, sludge or clot formation. There is a paucity of information on how hemostatic factors, cytokines, lipoprotein(a) (Lp(a)) and endothelin-1 (ET-1), being responsible for ischemic/reperfusion injury, interact with human brain microvessel endothelium (HBEC). There are no data furthermore about the expression of complement proteins of HBEC influenced by cytokines or fibrinolytic factors. Previously we established optimal conditions for culturing HBEC. Cell contraction induced by thrombin, plasmin, miniplasmin was recorded. The reassembly of F-actin was observed after thrombin treatment. ICAM-1 upregulation was measured following TNF-alpha, IL-1-alpha and thrombin incubation. Plasmin and miniplasmin downregulated the ICAM-1 in our cell culture system. Lp(a) modulated the thromboresistant cell-surface by reduction of t-PA and u-PA, but PAI-1 remained unchanged. Lp(a) modulated the ET-1 production by early increasing and late decreasing, in a bimodal manner. The increased secretion of ET-1 by cytokines (TNF-alpha, IL-1-alpha) was reduced in the presence of Lp(a). Gradual increase of complement proteins (factor H, factor B, C4) was induced by cytokines. Plasmin and miniplasmin augmented a rapid increase of C4. Some factors of complex relationship between regulators and modulators of endothelial adhesion molecules have been demonstrated in a human cell culture system prepared from brain microvessel endothelium. A unified concept of sequential events of ischemia/reperfusion in the brain has not yet developed.
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PMID:Human brain microvessel endothelial cell culture as a model system to study vascular factors of ischemic brain. 889 62

Monocyte-derived foam cells figure prominently in rupture-prone regions of atherosclerotic plaque. As urokinase/urokinase-receptor (u-PA/u-PAR) is the trigger of a proteolytic cascade responsible for ECM degradation, we have examined the effect of atherogenic lipoproteins on monocyte surface expression of u-PAR and u-PA. Peripheral blood monocytes, isolated from 10 healthy volunteers, were incubated with 10 to 200 microg/ml of native or oxidised (ox-) atherogenous lipoproteins for 18 h and cell surface expression of u-PA and u-PAR was analysed by flow cytometry. Both LDL and Lp(a) induced a dose-dependent increase in u-PA (1.6-fold increase with 200 microg/ml of ox-LDL) and u-PAR [1.7-fold increase with 200 microg/ml of ox-Lp(a)]. There is a great variability of the response among the donors, some of them remaining non-responders (absence of increase of u-PA or u-PAR) even at 200 microg/ml of lipoproteins. In positive responders, enhanced u-PA/u-PAR is associated with a significant increase of plasmin generation ( .9-fold increase with 200 microg/ml of ox-LDL), as determined by an amidolytic assay. Furthermore, monocyte adhesion to vitronectin and fibrinogen was significantly enhanced by the lipoproteins [respectively 2-fold and 1.7-fold increase with 200 microg/ml of ox-Lp(a)], due to the increase of micro-PAR and ICAM-1, which are receptors for vitronectin and fibrinogen. These data suggest that atherogenous lipoproteins could contribute to the development of atheromatous plaque by increasing monocyte adhesion and trigger plaque weakening by inducing ECM degradation.
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PMID:Increased expression of u-PA and u-PAR on monocytes by LDL and Lp(a) lipoproteins--consequences for plasmin generation and monocyte adhesion. 1023 46

During recent years it has become increasingly recognized that the plasmin activation system is involved in the development of atherosclerosis and restenosis. Responsible pathophysiologic mechanisms, however, remain elusive. This review focuses primarily on the clinicians, point of view, suggesting that increases in plasminogen activator inhibitor type-1 (PAI-1) plasma levels after balloon angioplasty or permanently elevated lipoprotein (a) (Lp(a)) plasma levels might be helpful in the prediction of restenosis after coronary angioplasty. In contrast, tissue-type plasminogen activator (tPA) plasma levels appear unrelated to restenosis, and data regarding a possible role of urokinase-type plasminogen activator (uPA) in circulation are not available at present. Furthermore, a new hypothesis on the pathophysiological role of local PAI-1 overexpression as a beneficial negative feedback mechanism to limit excess cellular proliferation in atherogenesis and restenosis is presented.
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PMID:Plasmin activation system in restenosis: role in pathogenesis and clinical prediction? 1037 89

The serine-proteinase domain in human apolipoprotein(a) [apo(a)] and plasminogen exhibit 89% sequence identity including the catalytic triad. Cleavage of the Arg(561)-Val(562) activation site in plasminogen by either tissue- or urokinase-type plasminogen activator results in formation of the fibrinolytic enzyme plasmin. Apo(a) does not contain measurable amidolytic activity nor can it be activated by plasminogen activators. It has been suggested that the latter finding might be explained by the substitution of the plasminogen Arg-Val activation site by Ser-Ile in apo(a). To investigate if introduction of the Arg-Val activation site in apo(a) might result in sensitivity towards plasminogen activators, we expressed wild-type and Arg-Val mutant recombinant apo(a) [r-apo(a)] in human embryonic kidney and hepatocyte cell lines. Free r-apo(a) and lipoprotein-like particles [r-Lp(a)] were obtained in the culture supernatants of transfected 293 and HepG2 cells, respectively. Incubation of mutant r-apo(a)/r-Lp(a) with plasminogen activators produced neither plasmin-like activity nor cleavage at the Arg-Val activation site, even in the presence of various stimulators of plasminogen activation. Our data suggest that the high selectivity of activators for plasminogen activation requires interactions with regions in plasminogen distant from the activation disulfide loop which are not present in apo(a).
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PMID:Effect of plasminogen activators on human recombinant apolipoprotein(a) having the plasminogen activation cleavage site. 1055 66

Angiostatin, which consists of the kringle I-IV domains of plasminogen and which is secreted into urine, is an efficient inhibitor of angiogenesis and tumor growth. Because N-terminal apolipoprotein(a) [apo(a)] fragments, which also contain several types of kringle IV domains, are found in urine as well, we evaluated the potential angiostatic properties of these urinary apo(a) fragments and of a recombinant form of apo(a) [r-apo(a)]. We used human microvascular endothelial cell (hMVEC)-based in vitro assays of tube formation in 3-dimensional fibrin matrixes. Purified urinary apo(a) fragments or r-apo(a) inhibited the basic fibroblast growth factor/tumor necrosis factor-alpha-induced formation of capillary-like structures. At concentrations varying from 0.2 to 10 microgram/mL, urinary apo(a) fragments inhibited tube formation by as much as 70%, whereas there was complete inhibition by r-apo(a). The highest concentrations of both inhibitors also reduced urokinase plasminogen activator production of basic fibroblast growth factor-induced hMVEC proliferation. The inhibitors had no effect on plasminogen activator inhibitor-1 expression. If our in vitro model for angiogenesis is valid for the in vivo situation as well, our data point toward the possibility that apo(a) may also be physiologically operative in modulating angiogenesis, as the concentration of free apo(a) found in humans exceeds that tested herein.
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PMID:Impact of apolipoprotein(a) on in vitro angiogenesis. 1123 25

Thrombogenesis depends on the balance between coagulation and fibrinolysis in vasculature. Vascular endothelial cells (EC) synthesize activators and inhibitors for fibrinolysis, tissue and urokinase plasminogen activators (tPA and uPA) and plasminogen activator inhibitor-1 (PAI-1). Increased levels of PAI-1 with various levels of tPA have been frequently found in plasma of patients with coronary heart disease (CHD) or diabetes mellitus (DM). Dyslipidemia is common feature in patients with CHD or DM, which is characterized by elevated levels of total cholesterol, triglycerides, low or very low density lipoproteins (LDL or VLDL) and decreased levels of high density lipoprotein (HDL). LDL and VLDL stimulated the generation of PAI-1 from cultured EC. LDL and lipoprotein(a) [Lp(a)], another lipoprotein risk factor for CHD, reduced the generation of tPA from EC. HDL did not greatly alter the release of PAI-1 from EC. Oxidative modification by copper, ultraviolet or long exposure to EC enhanced the effect of LDL on the generation of PAI-1 and tPA from EC. Glycation amplified the effect of LDL and Lp(a) on the changes in the generation of the fibrinolytic regulators from EC. Treatment with antioxidants or HDL normalized glycated LDL-induced changes in the generation of fibrinolytic regulators from EC. Activation of protein kinase C is required for oxidized LDL or Lp(a)-induced PAI-1 production in EC. VLDL, but not LDL or its oxidized form, stimulated PAI-1 production through the activation of the VLDL-responsive element in the PAI-1 promoter. Plasma levels of fibrinolytic regulators in CHD or DM patients may be normalized by HMG-CoA reductase inhibitors and angiotensin II converting enzyme inhibitors. This review summarizes the up-to-date information on effects, mechanism and management for disorders in EC-derived fibrinolytic regulators induced by modified lipoproteins.
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PMID:Impact and mechanism for oxidized and glycated lipoproteins on generation of fibrinolytic regulators from vascular endothelial cells. 1284 45

The fibrinolytic system is comprised of a series of serine proteases and serine protease inhibitors which are involved in the dissolution of fibrin in the vascular lumen, but also in the migration of cells and in the remodeling of the extracellular matrix of the vascular wall. The transcription, expression and degradation of the various fibrinolytic enzymes by cells in the vascular wall is influenced by lipoproteins and this interrelationship may play a significant role in the development of the atherosclerotic plaque: the transcription of plasminogen activator inhibitor-1 is influenced by very low-density lipoproteins, the expression of both tissue plasminogen activator and plasminogen activator inhibitor-1 is influenced by low-density lipoproteins and lipoprotein(a) (Lp(a)) and the internalization of the urokinase: plasminogen activator inhibitor-1 complex occurs via the low-density lipoprotein related protein. Several clinical studies have shown correlations between fibrinolytic parameters and lipoproteins in healthy populations and in patients with dyslipidemia, but the correlation between single plasma fibrinolytic enzymes and the severity of coronary atherosclerosis is less well documented. The reduction of plasma lipids with lipid-lowering drugs also affects the concentration of fibrinolytic enzymes, although this may also be due to direct effects of the drugs on the expression of the various fibrinolytic enzymes. The reduction of fibrinolytic and proteolytic activity in the atherosclerotic plaque by their lipid-lowering effect and by their direct action on the fibrinolytic system may be one of the mechanisms by which some lipid-lowering drugs achieve plaque stabilization.
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PMID:Interrelationships between the fibrinolytic system and lipoproteins in the pathogenesis of coronary atherosclerosis. 1513 52

Apolipoprotein(a), the plasminogen-like component of lipoprotein(a), is transformed into fragments by polymorphonuclear neutrophils (PMNs) elastase. Since stimulated PMNs express urokinase-type plasminogen activator (uPA), we sought to investigate the relevance of apo(a) fragmentation on plasminogen activation by neutrophils. Freshly isolated human PMNs stimulated by a 10 kringle recombinant apo(a), r-apo(a), activate plasminogen in a specific and saturable manner (Km = 476 +/- 42 nM, Vmax = 896 +/- 18 pmol min(-1)). This activation is prevented by amiloride, an inhibitor of u-PA, and epsilon-aminocaproic acid, epsilon-ACA, a lysine analogue that blocks plasminogen binding to PMNs. Stimulation of PMNs by apo(a) results in the formation of elastase-derived apo(a) fragments. These fragments produce a concentration-dependent decrease in the formation of plasmin. Addition of elastase inhibitors to PMNs prevented degradation of apo(a) and partially restored the formation of plasmin. In a similar manner, isolated r-apo(a) fragments were able to produce a 100% decrease in plasmin generation as compared to intact r-apo(a). These data indicate that apo(a) fragments produce a more pronounced inhibition in the generation of cell-bound plasmin by uPA than the parent apo(a). These effects of apo(a) and its fragments were neutralised by a monoclonal antibody directed against the lysine-binding site of apo(a). This mechanism may be of biological relevance to the effects of Lp(a) in conditions where PMNs accumulate and release elastase, i.e. thrombus lysis and inflammatory lesions.
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PMID:Neutrophils stimulated by apolipoprotein(a) generate fragments that are stronger inhibitors of plasmin formation than apo(a). 1554 35


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