Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.68 (tissue plasminogen activator)
 11,311 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To understand the mechanisms regulating osteoid removal by osteoblasts, mouse calvarial osteoblasts were grown on 14C-labelled type I collagen films and stimulated with 1,25-dihydroxyvitamin D-3 (2.5.10(-8) M) for 48-72 h. In the presence of 5% non-inhibitory rabbit serum this resulted in a 2-3-fold increase in collagen degradation and a dramatic change in osteoblast morphology, when compared with untreated osteoblasts. Collagenolysis was accompanied by increased synthesis and release of latent collagenase, gelatinase and stromelysin and a concomitant decrease in their specific inhibitor, TIMP (tissue inhibitor of metalloproteinases). In serum-free medium, osteoblasts failed to degrade collagen, but their ability to lyse collagen could be restored by adding plasminogen (5 micrograms/ml) to the cultures. Plasminogen-dependent collagenolysis was inhibited by human recombinant TIMP (5 units/ml), demonstrating that plasmin, derived from plasminogen, activated latent collagenase and did not itself degrade collagen. Plasminogen activator production was confirmed by culturing osteoblasts on 125I-labelled fibrin plates. Comparison with urokinase-type and tissue-type plasminogen activator standards suggested that osteoblast plasminogen activator was predominantly cell-associated and likely to be of the urokinase type. Immunocytochemistry indicated that osteoblasts also constitutively produce plasminogen activator inhibitor-1. These findings provide evidence for the involvement of a plasminogen-plasmin-latent metalloproteinase activation cascade in type I collagen degradation by osteoblasts, and for its regulation by TIMP and plasminogen activator inhibitor-1.
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PMID:Type I collagen degradation by mouse calvarial osteoblasts stimulated with 1,25-dihydroxyvitamin D-3: evidence for a plasminogen-plasmin-metalloproteinase activation cascade. 255 72

Expression vectors have been constructed for a region of the human retinoic acid receptor-alpha (hRAR-alpha) and transferred into F9 embryonal carcinoma (EC) cells. When the vectors are overexpressed in F9 cells, clones can be selected for resistance to retinoic acid-induced differentiation. This effect is obtained even when the hRAR-alpha region is expressed as a beta-galactosidase fusion protein. Using the beta-galactosidase component of the fusion protein as a marker, overexpression of the fusion protein has been correlated with the retinoic acid-resistance effect. The clones resistant to retinoic acid no longer exhibit the normal retinoic acid induction of endo B cytokeratin, laminin B-1, and tissue plasminogen activator mRNAs observed with normal F9 cells. Retinoic acid induction of type IV alpha-1 collagen and Hox-1.3 RNAs is observed with these clones. When transfected with a thyroid receptor DNA-binding sequence (TRE)/thymidine kinase promoter/luciferase construct, the retinoic acid-resistant clones do not yield the same retinoic acid-induced level of luciferase obtained with F9 cells. It is hypothesized that the RAR vectors are interfering with endogenous RAR(s) in a dominant-negative manner to inhibit retinoic acid-induced differentiation of F9 EC cells.
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PMID:Retinoic acid receptor expression vector inhibits differentiation of F9 embryonal carcinoma cells. 255 44

Experiments were carried out to characterize the specificity of uptake of tPA in rat liver cells. Endocytosis in liver endothelial cells of the native carbohydrate variants of tissue plasminogen activator (tPA), and tPA inactivated by diisopropyl fluorophosphate was found to be competitive, suggesting that the determinant being recognized by these cells is different from the active site. Fibronectin and urokinase, which show partial homology with tPA, did not compete with tPA for uptake in liver endothelial cells. Hyaluronic acid, collagen, or IgG, which are endocytosed by specific receptors in liver endothelial cells, did not interfere with the uptake. Reduced endocytosis by liver endothelial cells was observed with tPA modified in the carbohydrate side chains, suggesting that these structures are important for uptake. Ovalbumin, mannan, mannose, fructose, and EDTA, but not galactose, effectively inhibited uptake in liver endothelial cells of both native and diisopropyl fluorophosphate-inhibited tPA, but had very little effect on the uptake of tPA modified in the carbohydrate side chains. Endocytosis of native tPA by parenchymal cells could be inhibited by galactose, ovalbumin, and EDTA, but not by mannose. These results suggest that endocytosis of tPA by liver endothelial cells and parenchymal cells is mediated by the mannose and galactose receptors, respectively.
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PMID:Tissue plasminogen activator is endocytosed by mannose and galactose receptors of rat liver cells. 284 50

The relative contribution of platelets to plasminogen activator inhibitor (PA-inhibitor) activity in blood was investigated. From the difference in PA-inhibitor levels in platelet-poor plasmas of 12 donors (3 +/- 1 U/ml, mean +/- 95% confidence limits) and in the corresponding platelet-rich plasmas after induction of platelet aggregation by collagen, ADP or epinephrine (7 +/- 1 U/ml), it may be concluded that a greater amount of PA-inhibitor in blood is associated with platelets than with plasma. In collagen-stimulated platelets maximal release of PA-inhibitor and of beta-thromboglobulin (beta-TG) was attained within fifteen seconds, whereas in ADP-stimulated platelets the release of both factors was slower. In platelet-poor plasma no correlation was found between the level of PA-inhibitor and that of beta-TG. Thus, the PA-inhibitor found in plasma is not derived from platelets that had been stimulated after blood collection. The rate of complex formation and the Mr of the principal complexes of radioiodinated tissue-type plasminogen activator (t-PA) or urokinase (UK), in platelet-poor plasma, in platelet-rich plasma after platelet aggregation or in an extract of washed platelets was the same. Moreover, complexes of UK or t-PA with plasmatic PA-inhibitor or with the PA-inhibitor(s) from platelets bound to immobilized antibodies against bovine endothelial cell-derived PA-inhibitor. These results show that the PA-inhibitors in plasma and in platelets are very similar or identical.
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PMID:Studies on the release of a plasminogen activator inhibitor by human platelets. 294 Jul 23

Human diploid fibroblasts were cultured on microcarriers made from DEAE-dextran, denatured collagen, DEAE-dextran linked to denatured collagen, and glass. Cells grown on these four substrates were examined for the production of proteolytic enzymes and arachidonic acid metabolites. Culture fluids from cells grown on the DEAE-dextran microcarriers contained the highest amounts of proteolytic enzyme activity. Both plasminogen-independent and plasminogen-dependent fibrinolytic activities were present and the plasminogen-dependent activity seemed to result from the presence of both urokinase and tissue plasminogen activator. Culture fluid from the cells grown on the glass microcarriers contained the least amount of protease activity, and nearly all of the plasminogen-activator activity seemed to be of the urokinase type. Protease activity in the culture fluids of cells grown on the other two substrates were intermediate. With regard to arachidonic acid metabolites, cells grown on the DEAE-dextran microcarriers produced the highest amounts of cyclooxygenase products but very low levels of lipoxygenase metabolites. Cells grown on the other three substrates produced comparable amounts of various cyclooxygenase products (lower than that produced by cells on the DEAE-dextran substrate). Cells grown on the glass microcarriers also produced detectable amounts of two lipoxygenase metabolites--leukotriene B4 and leukotriene C4. Inasmuch as both proteolytic enzymes and arachidonic acid metabolites regulate basic cell properties, the differential amounts of these metabolites observed in the culture fluids on the various substrates may contribute to the biological differences that exist on these substrates.
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PMID:Proteolytic enzymes and arachidonic acid metabolites produced by MRC-5 cells on various microcarrier substrates. 309 7

In 1942, 53% of medically treated patients with cirrhosis were dead 6 months after the onset of ascites. Only 30% survived 1 year. This dismal outlook has improved only slightly with advances in medicine. Yet, some internists reject the peritoneovenous shunt (PVS) for this fatal condition even if they are aware that a diminished blood volume causes the abnormal sodium retention responsible for ascites. Their objections are based on life-threatening complications of PVS, especially post shunt coagulopathy (PSC). Blood shed into the peritoneal cavity becomes incoagulable. Such blood is immediately coagulated by a protocoagulant (soluble collagen) and concurrently lysed by tissue plasminogen activator (TPA) secreted by the peritoneal serosa. Wide zones of lysis surround peritoneal tissue placed on fibrin plates. Large volumes of ascitic fluid infused into circulating blood simulates the fate of blood shed into the peritoneal cavity with lysis playing the major role. Addition of ascitic fluid to normal platelet-rich plasma in vitro initiates clot lysis on thromboelastogram (TEG). Epsilon-aminocaproic acid (EACA) counteracts this lysis. EACA and clotting factors normalize the TEG and arrest PSC. Disposal of ascitic fluid at surgery prevents or ameliorates PSC. Mild PSC was encountered only twice in 150+ consecutive patients (1.3%) with only one case being clinically significant (0.6%). Severe PSC occurred seven times in 98 early shunt patients whose ascitic fluid was not discarded. Severe PSC requires shunt interruption and control of bleeding with clotting factors and EACA. Peritoneal lavage with saline prevents the recurrence of PSC on reopening the shunt. In four patients, EACA and clotting factors were adequate to arrest coagulopathy. Three earlier patients died of PSC before its cause and treatment were understood. Proper management eliminates this life-threatening complication, and PSC cannot be considered a deterrent to PVS. Disseminated intravascular coagulopathy (DIC) is produced in experimental animals only by the injection of thrombin or thromboplastin. PSC is a distinct entity differing from DIC; EACA and not heparin is the antidote for PSC.
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PMID:Coagulopathy post peritoneovenous shunt. 310 56

The ex vivo aggregability of rabbit platelets was assessed after rabbits were treated in vivo with thrombolytic doses of tissue plasminogen activator (t-PA) or streptokinase (SK). t-PA was evaluated at 2 doses; an effective thrombolytic dose of 10 micrograms/kg/min, i.v. and a higher dose of 30 micrograms/kg/min, i.v.. At both concentrations, ex vivo platelet hyperaggregability was observed when collagen, arachidonic acid or ADP were employed as the aggregating agonists. Significant falls in circulating platelet counts were observed after t-PA infusion. Infusion of SK also resulted in ex vivo platelet hyperaggregation. These data reveal that thrombolytic therapy may result in hyperaggregable platelets which may play a role in reocclusion of successfully recanalized blood vessels.
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PMID:Tissue-type plasminogen activator and streptokinase induce platelet hyperaggregability in the rabbit. 311 93

The effects of tissue-type plasminogen activator (t-PA) on the platelet aggregation were studied using citrated whole blood and platelet-rich plasma (PRP) obtained from human donors. t-PA suppressed adenosine 5'-diphosphate (ADP)- or collagen-induced platelet aggregation in a dose-dependent manner. The 50% inhibitory concentration (IC50) for t-PA was lower by one order of magnitude than that for urokinase (UK) in whole blood and PRP. The suppression of platelet aggregation was not completely inhibited by alpha-2-antiplasmin. t-PA did not cause the degradation of fibrinogen or fibrin in PRP, whereas UK caused the reduction of fibrinogen and fibrin, and the increase of fibrinogen- and fibrin-degradation products (FDP). These results suggest that the mode of action of t-PA in inhibiting platelet aggregation may be different from that of UK.
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PMID:Tissue-type plasminogen activator inhibits aggregation of platelets in vitro. 313 48

The migration of fibroblasts into a clot may be responsible at least in part, for its organization, thus leading to a defective thrombolysis. We have shown that collagen incorporated in a fibrin clot induces a dramatic decrease in fibrinolysis. Despite the fact that plasminogen binds to collagen, tissue plasminogen activator induced plasminogen activation in the presence of fibrin is only slightly decreased by the presence of collagen. This rather suggests that collagen induces a modification in clot structure, by rendering fibrin less accessible to fibrinolytic enzyme.
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PMID:Defective thrombolysis due to collagen incorporation in fibrin clots. 314 70

A human liver cDNA library was screened by colony hybridization with two mixtures of synthetic oligodeoxyribonucleotides as probes. These oligonucleotides encoded regions of beta-factor XIIa as predicted from the amino acid sequence. Four positive clones were isolated that contained DNA coding for most of factor XII mRNA. DNA sequence analysis of these overlapping clones showed that they contained DNA coding for part of an amino-terminal extension, the complete amino acid sequence of plasma factor XII, a TGA stop codon, a 3' untranslated region of 150 nucleotides, and a poly(A)+ tail. The cDNA sequence predicts that plasma factor XII consists of 596 amino acid residues. Within the predicted amino acid sequence of factor XII, we have identified three peptide bonds that are cleaved by kallikrein during the formation of beta-factor XIIa. Comparison of the structure of factor XII with other proteins revealed extensive sequence identity with regions of tissue-type plasminogen activator (the epidermal growth factor-like region and the kringle region) and fibronectin (type I and type II homologies). As the type II region of fibronectin contains a collagen-binding site, the homologous region in factor XII may be responsible for the binding of factor XII to collagen. The carboxyl-terminal region of factor XII shares considerable amino acid sequence homology with other serine proteases including trypsin and many clotting factors. A preliminary structural model of beta-factor XIIa is proposed based on the known high resolution x-ray diffraction structures of trypsin, chymotrypsin, and elastase.
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PMID:Characterization of human blood coagulation factor XII cDNA. Prediction of the primary structure of factor XII and the tertiary structure of beta-factor XIIa. 387 53


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