Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.69 (APC)
 16,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Venous occlusion (VO) during which thrombin (Th) is postulated to be generated is routinely used for evaluation of fibrinolytic potential of endothelium (E). This study was performed to find out whether VO can also be used for assessment of anticoagulant function of E. VO was performed in 98 male patients (pts) with ischemic heart disease. Levels of protein C (PrC) which is related to Th binding by thrombomodulin and fibrinopeptide A (FpA)--a marker of presence of free Th--were determined together with some other factors of coagulation and fibrinolysis. Differences between pre- and postVO PrC levels fluctuated from -54.8% to +57.3%. According to reaction of PrC to VO pts were divided into 2 groups: 13 pts with increase or no change and 17 pts with decrease (consumption) of PrC. In pts without PrC consumption there was a significant increase in FpA. In pts with PrC consumption FpA was unchanged. In pts with PrC consumption exceeding its median value for this group (14%) PAI-1 antigen level fell significantly (-8.4 + 4%) during VO. Thus PrC consumption after VO indicates that TH is effectively removed from blood stream by endothelial factors. Absence of consumption of PrC is a sign of ineffective anticoagulant function of E. Increase in PrC level during VO in some pts may be due to its escape from tissue depot.
 ...
PMID:[The anticoagulant properties of the endothelium studied by the standard venous occlusion test]. 129 87

The objective of this study was to clarify the specificity of anticardiolipin antibodies (aCL). Eighteen monoclonal hybridoma aCL from systemic lupus erythematosus (SLE)-prone MRL/Mp-lpr/lpr mice were established, and the reactivity of monoclonal aCL to phospholipids, DNA, nuclei of human epithelial cells, platelets, vascular endothelial cells, heparin, protein C and thrombomodulin was examined. All the 18 monoclonal aCL reacted with phosphatidylserine and some showed reactivity to phosphatidylinositol and phosphatidylcholine. Six of 16 monoclonal aCL were demonstrated to have the property of lupus anticoagulant. Monoclonal aCL were classified into three categories, in terms of DNA-binding specificity. Ten of 18 aCL had characteristics of antinuclear antibodies. Six of 11 aCL reacted with platelets. Three of 18 aCL were bound to vascular endothelial cells and to heparin. No monoclonal aCL reacted with protein C or thrombomodulin. Therefore, the conclusion was made that monoclonal aCL from SLE mice showed a polyspecific nature.
 ...
PMID:Monoclonal autoantibodies to cardiolipin derived from SLE mice. 130 87

The structural domains of protein C involved in its interaction with thrombin-thrombomodulin on the endothelial cell surface have been investigated using isolated intact domains of bovine protein C produced from controlled proteolytic digests of the protein. The fragments investigated include the gamma-carboxyglutamic acid (Gla)-rich module, the two epidermal growth factor (EGF)-like modules, and a fragment consisting of the Gla and the two EGF-like modules. The effects of these fragments on the catalytic efficiency (Km and Vmax) of activation of protein C by the endothelial cell surface thrombin-thrombomodulin complex (IIa-TM) have been evaluated in vitro using a stirred microcarrier cell culture of bovine aortic endothelial cells and purified proteins. Neither the Gla nor the two EGF-like modules alone had any discernible effect on protein C activation. The intact Gla-EGF fragment, however, inhibited protein C activation. The results are consistent with a rapid equilibrium competitive inhibition model, in which the Gla-EGF fragment competes with protein C for binding to IIa-TM, and indicate that the Gla-EGF fragment alone accounts for most of the binding energy of intact protein C for IIa-TM. In addition, a requirement for the Gla residues of protein C for binding is implied by the observation that heat-decarboxylated Gla-EGF fragment was not an inhibitor of protein C activation. In addition, chloromethyl ketone-inactivated activated protein C was found to bind to IIa-TM with the same affinity as protein C, suggesting that the changes which occur in protein C upon activation do not affect that part of the protein responsible for binding to IIa-TM, that is the Gla-EGF region. The Gla-EGF region from factor X also weakly inhibited the IIa-TM activation of protein C.
 ...
PMID:Identification of structural domains in protein C involved in its interaction with thrombin-thrombomodulin on the surface of endothelial cells. 130 72

Fibrin deposition is a common accompaniment of renal allograft rejection, indicating disruption of the normal physiologic balance between procoagulant and anticoagulant pathways. In vitro, tumor necrosis factor (TNF) induces endothelial expression of the procoagulant, tissue factor, and downregulation of thrombomodulin, a key component of the thrombomodulin/protein C (PC)/protein S (PS) pathway, which normally maintains an anticoagulant state by inactivating thrombin, preventing further thrombin formation by degrading factors Va and VIIIa, and decreasing plasminogen activator inhibitor activity. Raised levels of TNF were recently demonstrated within the blood of patients during episodes of renal allograft injection, and may be an early and discriminatory marker of rejection. This led us to investigate prospectively whether monitoring of serum TNF levels was of value clinically, and was associated with effects on circulating PC and PS levels, or alterations in intragraft thrombomodulin expression. Plasma samples (n = 454) were collected three times/week from all patients (n = 25) undergoing renal transplantation during a 9-month consecutive period, and assayed by ELISA and functional assays for TNF, PC, and free PS (FPS). Portions of renal biopsies, taken to evaluate episodes of acute deterioration of renal function, were evaluated by immunoperoxidase labeling for the presence and distribution of TNF, thrombomodulin, PC, PS, thrombin, fibrin, and factors V and VIII. Comparison of 78 plasma samples collected during 26 episodes of biopsy-proven acute cellular rejection with samples collected during periods of stable renal function (n = 349) showed that TNF levels rose significantly (390 +/- 242 pg/ml, p less than 0.01) above background levels 3 days before rising serum creatinine concentrations, and peaked (2,426 +/- 978 pg/ml) on the day of clinical rejection. PC-antigen (Ag) concentrations also decreased 3 days before rejection (68 +/- 13%, p less than 0.05), and were maximally depressed (49% +/- 16%, p less than 0.001) on the day of rejection. FPS levels were normal until the day before rejection (63% +/- 8%, p less than 0.01) and, like PC, were maximally depressed (43 +/- 10%) at rejection. Plasma TNF levels were significantly and inversely correlated with PC-Ag (p less than 0.001) and FPS (p less than 0.005) levels during rejection, regardless of whether such rejection episodes were steroid responsive or required OKT3 monoclonal antibody therapy. TNF, PC, and FPS levels were normal during episodes of cyclosporine toxicity and viral infection.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Tumor necrosis factor production during human renal allograft rejection is associated with depression of plasma protein C and free protein S levels and decreased intragraft thrombomodulin expression. 130 55

The two-way and three-way interactions among active-site-blocked bovine thrombin, bovine protein C, and the elastase fragment of rabbit thrombomodulin (elTM) were examined by analytical ultracentrifugation at 23.3 degrees C in 100 mM NaCl, 50 mM Tris (pH 7.65), and 1 mM benzamidine, in the presence of 0 to 5 mM calcium chloride. Thrombin and elTM form a tight (Kd less than 10(-8) M) 1:1 complex in the absence of Ca2+ that weakens with the addition of Ca2+ (Kd approximately 4 microM in 5 mM Ca2+). Without Ca2+, thrombin and protein C form a 1:1 complex (Kd approximately 1 microM) and what appears to be a 1:2 thrombin-protein C complex. The Kd for the 1:1 complex weakens over 100-fold in 5 mM CaCl2. Protein C and elTM form a Ca(2+)-independent 1:1 complex (Kd approximately 80 microM). Nearly identical binding to thrombin and elTM is observed when active-site-blocked activated bovine protein C is substituted for protein C. Thrombin inhibited by diisopropyl fluorophosphate and thrombin inhibited by a tripeptide chloromethyl ketone exhibited identical behavior in binding experiments, suggesting that the accessibility of protein C to the substrate recognition cleft of these two forms of thrombin is nearly equal. Human protein C binds with lower affinity than bovine protein C. Ternary mixtures also were examined. Protein C, elTM, and thrombin form a 1:1:1 complex which dissociates with increasing [Ca2+]. In the absence of Ca2+, protein C binds to the elTM-thrombin complex with an apparent Kd approximately 1 microM.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Ca2+ dependence of the interactions between protein C, thrombin, and the elastase fragment of thrombomodulin. Analysis by ultracentrifugation. 131 45

Annexin-V (PAP-I, lipocortin-V) acts as a potent anticoagulant in vitro by binding to negatively charged phospholipids with higher affinity than vitamin K-dependent proteins, with a Kd in the 10(-10) M range. The purpose of the present study was to use annexin-V as a probe to assess the catalytic potential of phospholipids in pro- and anti-coagulant reactions in purified systems and at the surface of endothelial cells in culture after stimulation. Procoagulant tissue factor and anticoagulant thrombomodulin activities were compared by using specific two-stage amidolytic assays performed with purified proteins. Procoagulant activity was estimated by the generation of Factor Xa by the Factor VII(a)-tissue factor complex. Anticoagulant activity was estimated by the generation of activated protein C by either the thrombin-thrombomodulin complex or Factor Xa. Annexin-V induced a decrease of 70% of thrombomodulin activity when thrombomodulin (5.4-214 nM) was reconstituted into phosphatidylcholine/phosphatidylserine (1:1, mol/mol) vesicles at 37.5 or 75 microM-phospholipid concentration, the apparent Ki being 0.5 microM at 75 microM-lipid. The saturating concentration of annexin-V was dependent on phospholipid concentration, but was independent of the phospholipid/thrombomodulin ratio. By contrast, when thrombomodulin was not reconstituted in vesicles, annexin-V had no effect. At 2 microM, annexin-V totally inhibited the generation of activated protein C by Factor Xa in the presence of 75 microM-lipid, the saturating inhibitory concentration being dependent on phospholipid concentration. At 0.1 microM, annexin-V totally inhibited tissue-factor activity present in crude brain thromboplastin. In the absence of stimulation, human endothelial cells in culture expressed significant thrombomodulin activity and no detectable tissue-factor activity. Basal thrombomodulin activity was only slightly inhibited (less than 15%) by 0.5 microM-annexin-V. Phorbol myristate acetate (PMA) induced the expression of tissue-factor activity and decreased thrombomodulin activity at the endothelial-cell surface. Annexin-V, at a concentration of 16 microM, caused an 80% decrease of tissue-factor activity induced by PMA at 10 ng/ml, whereas it inhibited thrombomodulin activity by only 15% on the same stimulated cells. Our results confirm that annexin-V inhibits, in vitro, procoagulant tissue-factor activity and anticoagulant activities (activation of protein C by the thrombin-thrombomodulin complex and by Factor Xa), through phospholipid-dependent mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Use of annexin-V to demonstrate the role of phosphatidylserine exposure in the maintenance of haemostatic balance by endothelial cells. 131 63

Thrombomodulin is an endothelium-associated glycoprotein that converts thrombin from a procoagulant protease to an anticoagulant. Thrombin, a key enzyme in thrombus formation, binds to thrombomodulin on the endothelium. However after thrombin binds to thrombomodulin, it fails to act on the coagulation factors and platelets, and its ability to activate protein C is enhanced more than 1,000-fold. This article reviews the recent progress in the study of thrombomodulin.
 ...
PMID:Thrombomodulin, an endothelial anticoagulant; its structure, function and expression. 131 51

Thrombomodulin is an endothelial glycoprotein that serves as a cofactor for protein C activation. To examine the ligand specificity of human thrombomodulin, we performed equilibrium binding assays with human thrombin, thrombin S205A (wherein the active site serine is replaced by alanine), meizothrombin S205A, and human factor Xa. In competition binding assays with CV-1(18A) cells expressing cell surface recombinant human thrombomodulin, recombinant wild type thrombin and thrombin S205A inhibited 125I-diisopropyl fluorophosphate-thrombin binding with similar affinity (Kd = 6.4 +/- 0.5 and 5.3 +/- 0.3 nM, respectively). However, no binding inhibition was detected for meizothrombin S205A or human factor Xa (Kd greater than 500 nM). In direct binding assays, 125I-labeled plasma thrombin and thrombin S205A bound to thrombomodulin with Kd values of 4.0 +/- 1.9 and 6.9 +/- 1.2 nM, respectively. 125I-Labeled meizothrombin S205A and human factor Xa did not bind to thrombomodulin (Kd greater than 500 nM). We also compared the ability of thrombin and factor Xa to activate human recombinant protein C. The activation of recombinant protein C by thrombin was greatly enhanced in the presence of thrombomodulin, whereas no significant activation by factor Xa was detected with or without thrombomodulin. Similar results were obtained with thrombin and factor Xa when human umbilical vein endothelial cells were used as the source of thrombomodulin. These results suggest that human meizothrombin and factor Xa are unlikely to be important thrombomodulin-dependent protein C activators and that thrombin is the physiological ligand for human endothelial cell thrombomodulin.
 ...
PMID:Ligand specificity of human thrombomodulin. Equilibrium binding of human thrombin, meizothrombin, and factor Xa to recombinant thrombomodulin. 131 33

Thrombomodulin is an endothelial cell thrombin receptor that serves as a cofactor for thrombin-catalyzed activation of protein C. Structural requirements for thrombin binding and cofactor activity were studied by mutagenesis of recombinant human thrombomodulin expressed on COS-7 and CV-1 cells. Deletion of the fourth epidermal growth factor (EGF)-like domain abolished cofactor activity but did not affect thrombin binding. Deletion of either the fifth or the sixth EGF-like domain markedly reduced both thrombin binding affinity and cofactor activity. Thrombin binding sequences were also localized by assaying the ability of synthetic peptides derived from thrombomodulin to compete with diisopropyl fluorophosphate-inactivated 125I-thrombin binding to thrombomodulin. The two most active peptides corresponded to (a) the entire third loop of the fifth EGF-like domain (Kp = 85 +/- 6 microM) and (b) parts of the second and third loops of the sixth EGF-like domain (Kp = 117 +/- 9 microM). These data suggest that thrombin interacts with two discrete elements in thrombomodulin. Deletion of the Ser/Thr-rich domain dramatically decreased both thrombin binding affinity and cofactor activity and also prevented the formation of a high molecular weight thrombomodulin species containing chondroitin sulfate. Substitutions of this domain with polypeptide segments of decreasing length and devoid of glycosylation sites progressively decreased both cofactor activity and thrombin binding affinity. This correlation suggests that increased proximity of the membrane surface to the thrombin binding site may hinder efficient thrombin binding and the subsequent activation of protein C. Membrane-bound thrombomodulin therefore requires the Ser/Thr-rich domain as an important spacer, in addition to EGF-like domains 4-6, for efficient protein C activation.
 ...
PMID:Functional domains of membrane-bound human thrombomodulin. EGF-like domains four to six and the serine/threonine-rich domain are required for cofactor activity. 131 30

Thrombomodulin plays a role as a cofactor for thrombin-catalyzed activation of protein C on endothelial cells. We examined the effect of homocysteine, a stimulant of atherosclerosis and thrombotic disease, on the cofactor activity and protein level of thrombomodulin and also on the expression of thrombomodulin in endothelial cells. Homocysteine inhibited the cofactor activity of thrombomodulin both on the surface of endothelial cells and in the whole cells dose- and time-dependently, and maximal inhibition of the cofactor activity occurred after a 3- to 6-hour incubation with 10 mmol/L homocysteine (10% of initial activity). Homocysteine also decreased the amount of intact (unreduced) thrombomodulin in endothelial cells. However, at the same condition the total protein level (reduced and unreduced form) of thrombomodulin, determined by dot immunoblot analysis using the monoclonal antibody that recognized both reduced and unreduced thrombomodulin, decreased slightly, and the mRNA level of thrombomodulin showed a twofold to three-fold increase. After 24 hours of incubation, the cofactor activity and total protein level of thrombomodulin were 60% and 165% of the initial values, respectively. When purified thrombomodulin fixed to a microwell plate was treated with homocysteine, both cofactor activity and thrombin-binding ability to the thrombomodulin were decreased in proportion to the concentration of homocysteine. These findings suggest that homocysteine directly inhibited the cofactor activity of thrombomodulin on endothelial cells by reducing the disulfide-bond rich epidermal growth factor-like structures of thrombomodulin. This would a result in the decrease of the antithrombotic property of endothelium and may also trigger off the synthesis of mRNA and protein of thrombomodulin to maintain the antithrombotic properties of the cells.
 ...
PMID:An atherogenic stimulus homocysteine inhibits cofactor activity of thrombomodulin and enhances thrombomodulin expression in human umbilical vein endothelial cells. 131 88


1 2 3 4 5 6 7 8 9 10 Next >>