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PubMed1996

Plasminogen activator system in pemphigus vulgaris.

Pemphigus vulgaris (PV) is caused by autoantibodies against desmosomes and is characterized by intra-epidermal blisters. The pathology of PV has been linked with plasminogen activation in lesional epidermis. The plasminogen activator system (PA system) consists of urokinase-type plasminogen activator (uPA), tissue-type PA (tPA), as well as the two types of plasminogen activator inhibitors (PAI-1 and PAI-2). In keratinocytes, uPA binds to a specific cell surface receptor for uPA (uPA-R = CD87) in an autocrine manner. Cell-bound uPA is regulated by PAIs. The central PA system component plasminogen, which is present in plasma and interstitial fluids, is bound to the keratinocyte surface via plasmin(ogen) binding sites, where it can be activated by uPA-R-bound uPA. Cell surface-associated plasmin then mediates pericellular proteolysis. As the topographical organization of the distinct PA system components in lesional epidermis of PV remained elusive, we have performed the present immunohistological analysis of lesional and non-lesional epidermis of PV. In keratinocytes directly involved in the epidermal split formation, plasmin(ogen) was stained in nine of 10 cases, uPA-R and uPA in four of 10 cases and PAI-2 in seven of 10 cases. Together, acantholytic plasmin(ogen)+ keratinocytes appeared in three different phenotypes: uPA-R+/uPA+ and PAI-2+, uPA-R-/uPA- and PAI-2+, as well as uPA-R-/uPA- and PAI-2-. Our findings demonstrate that, in acantholytic keratinocytes of PV, PAs and PAIs appear as differentially regulated components of the PA system.

Adult↗
PubMed1998

Immunohistochemical demonstration of the plasminogen activator system in human gingival tissues and gingival fibroblasts.

The relative distribution of urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1) and plasminogen activator inhibitor-2 (PAI-2) was studied in cultured human gingival fibroblasts, healthy gingival tissues and inflamed gingival tissues by immunohistochemistry. In cultured gingival fibroblasts t-PA, u-PA and PAI-1 were expressed in cytoplasm; u-PA and PAI-1 were more intensely stained than t-PA; PAI-2 was not detectable in gingival fibroblasts. Following interleukin 1 beta (IL-1 beta) stimulation, the intensity of intracellular staining for t-PA was increased and a number of cells staining strongly for PAI-2 were seen; no difference in the intensity of immunostaining level was noted for the expression of u-PA and PAI-1 between IL-1 beta stimulated cells and unstimulated cells. In healthy gingival tissues, u-PA and PAI-1 displayed a wide distribution throughout all the connective tissue and epithelium; t-PA localized mainly in the connective tissue while PAI-2 showed little association with the connective tissue but did faintly stain in the epithelial layer. In inflamed gingival tissues, staining for t-PA was significantly increased in the extracellular matrix of the connective tissue, whereas staining for u-PA, PAI-1 and PAI-2 was found to be slightly increased, but no significant difference was noted for staining when compared with the healthy gingival tissues. A granular distribution of t-PA, u-PA, PAI-1 and PAI-2 was noted around areas of inflammatory cell infiltration. These immunohistochemical findings indicate that the plasminogen activator system produced by fibroblasts may be influenced by the presence of the inflammatory mediator IL-1 beta. In addition, the significant increase of t-PA in inflamed connective tissue and the wide expression of these components around inflamed cells may contribute to connective tissue degradation and may relate to the migration and localization of monocytes/macrophages in inflamed tissue.

Antibodies, Monoclonal↗
PubMed1997

Plasminogen activation in synovial tissues: differences between normal, osteoarthritis, and rheumatoid arthritis joints.

OBJECTIVE: To analyse the functional activity of the plasminogen activators urokinase (uPA) and tissue type plasminogen activator (tPA) in human synovial membrane, and to compare the pattern of expression between normal, osteoarthritic, and rheumatoid synovium. The molecular mechanisms underlying differences in PA activities between normal and pathological synovial tissues have been further examined. METHODS: Synovial membranes from seven normal (N) subjects, 14 osteoarthritis (OA), and 10 rheumatoid arthritis (RA) patients were analysed for plasminogen activator activity by conventional zymography and in situ zymography on tissue sections. The tissue distribution of uPA, tPA, uPA receptor (uPAR), and plasminogen activator inhibitor type-1 (PAI-1) was studied by immunohistochemistry. uPA, tPA, uPAR, and PAI-1 mRNA values and mRNA distribution were assessed by northern blot and in situ hybridisations respectively. RESULTS: All normal and most OA synovial tissues expressed predominantly tPA catalysed proteolytic activity mainly associated to the synovial vasculature. In some OA, tPA activity was expressed together with variable amounts of uPA mediated activity. By contrast, most RA synovial tissues exhibited considerably increased uPA activity over the proliferative lining areas, while tPA activity was reduced when compared with N and OA synovial tissues. This increase in uPA activity was associated with increased levels of uPA antigen and its corresponding mRNA, which were localised over the synovial proliferative lining areas. In addition, in RA tissues, expression of the specific uPA receptor (uPAR) and of the plasminogen activator inhibitor-type 1

Arthritis, Rheumatoid↗
PubMed1986

Endotoxin induction of an inhibitor of plasminogen activator in bovine pulmonary artery endothelial cells.

We have examined the effects of bacterial lipopolysaccharide (endotoxin) on the fibrinolytic activity of bovine pulmonary artery endothelial cells. Endotoxin suppressed the net fibrinolytic activity of cell extracts and conditioned media in a dose-dependent manner (threshold dose, 0.1 ng/ml; maximal dose, 10-100 ng/ml). The effects of endotoxin required at least 6 h for expression. Cell extracts and conditioned media contained a 44-kDa urokinase-like plasminogen activator. Media also contained multiple plasminogen activators with molecular masses of 65-75 and 80-100 kDa. Plasminogen activators in extracts and media were unchanged by treatment of cells with endotoxin. Diisopropyl fluorophosphate (DFP) abolished fibrinolytic activity of extracts and conditioned media. DFP-treated samples from endotoxin-treated but not untreated cells inhibited urokinase and tissue plasminogen activator, but not plasmin. Inhibitory activity was lost by incubation at pH 3 or heating to 56 degrees C for 10 min. These treatments did not affect inhibitory activity of fetal bovine serum. Incubation of 125I-urokinase with DFP-treated medium from endotoxin-treated cells produced an inactive complex with an apparent molecular mass of 80-85 kDa. The complex could be detected by chromatography on Sephadex G-100, but not by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These findings suggest that low doses of endotoxin suppress fibrinolytic activity in endothelial cells by stimulating the production or expression of a fast-acting, relatively labile inhibitor of plasminogen activator.

Animals↗
PubMed1996

The plasminogen-activating system in hepatic stellate cells.

Urokinase plasminogen activator (uPA) generates plasmin, a process inhibited by plasminogen-activator inhibitor (PAI)-1 and localized to the cell surface by binding of uPA to a specific receptor. Plasmin degrades extracellular matrix (ECM) both directly and by activation of matrix metalloproteinases (MMPs). Because stellate cells play a central role in the pathogenesis of liver fibrosis both via production of ECM proteins and through secretion of MMPs, their contribution to plasmin generation was assessed. Stellate cells were prepared from rat liver and cultured on plastic. Northern analysis showed cellular expression of messenger RNA (mRNA) for PAI-1, uPA, and uPA receptor. Zymography/reverse zymography identified cell-surface-associated uPA activity and uPA and PAI-1 in culture media. Net uPA activity in culture media was maximal after 7 days in culture and then declined, whereas PAI-1 antigen levels remained consistently elevated between 7 and 21 days in culture. Stellate cell-mediated plasmin generation was also seen in in vitro cultures supplemented with plasminogen. Because hepatic stellate cells (HSCs) contain retinoids and release them on activation, the effect of retinoic acid on the plasminogen-activating system was also assessed. Treatment of cultured HSCs with retinoic acid (1 micromol/L) increased uPA secretion 2.6-fold but did not alter PAI-1. We conclude that stellate cells synthesize key components of the plasminogen-activating system and generate plasmin and therefore have the ability to regulate MMP activation. Upregulation of uPA synthesis by retinoic acid may have implications in matrix remodeling in sites of stellate cell activation in which high concentrations of retinoids may be achieved.

Adipocytes↗
PubMed1992

Plasminogen activator system in human breast cancer.

We measured antigen levels of 2 kinds of plasminogen activator, tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (UK), as well as those of their primary inhibitors, type-I plasminogen activator inhibitor (PAI-1) and type-2 plasminogen activator inhibitor (PAI-2), in tissue extracts from benign and malignant breast tumors. Tumor tissue samples from 40 fibroadenomas and 40 breast cancers were examined. t-PA antigen levels were the same in the 2 groups. Malignant tumors contained higher levels of UK antigen than did benign tumors. In the case of breast cancer, UK antigen levels of tumors with axillary lymph-node involvement were significantly higher than those of tumors without lymph-node involvement. PAI-1 and PAI-2 antigen levels of breast-cancer tissue samples were higher than those of fibroadenoma samples. PAI-1 antigen levels of carcinomas with lymph-node involvement were also significantly higher than those of carcinomas without node involvement. PAI-2 antigen levels, on the contrary, were higher in carcinomas without node involvement. UK, PAI-1 and PAI-2 antigen levels are potentially excellent independent factors for prediction of the metastatic potential of breast cancers.

Breast Neoplasms↗
PubMed1999

Electrochemical assay of plasminogen activators in plasma using polyion-sensitive membrane electrode detection.

Two relatively simple electrochemical assay methods suitable for the measurement of plasminogen activators (including urokinase (u-PA), streptokinase (SK), and tissue plasminogen activator (t-PA)) in plasma samples are described. In one approach, the initial rate of decrease in the potentiometric response of a polycation-sensitive membrane electrode toward protamine is monitored after addition of a preincubated reaction mixture containing the sample and exogenous plasminogen. The plasmin formed from plasminogen by the activators catalyzes the decomposition of the arginine-rich protamine substrate, yielding smaller polycationic fragments that are not sensed by the electrode. Alternately, the sample, plasminogen, and protamine can be incubated together, and the remaining protamine in this reaction mixture can be measured at a fixed point in time by placing the electrode into the mixture and recording the electromotive force response. Working curves found with both methods for plasma samples spiked with varying levels of the activators cover the expected therapeutic activity ranges found in the plasma of patients treated with these "clot-busting" drugs.

Blood Chemical Analysis↗
PubMed1996

Effect of purified, soluble urokinase receptor on the plasminogen-prourokinase activation system.

The extracellular proteolytic pathway mediated by the urokinase plasminogen activator (uPA) is a cascade system, initiated by activation of the zymogen, pro-uPA. Pro-uPA as well as uPA binds to the cellular uPA receptor (uPAR) which has a central function in cell-dependent acceleration of the cascade system. This role of uPAR is generally assumed to be a positioning effect since uPAR-expressing cells exclusively stimulate the activation of cell surface-bound plasminogen (Ellis et al. (1993) Methods Enzymol. 223, 223-233). However, it was recently reported that a recombinant, soluble uPAR (suPAR) was capable of accelerating plasminogen activation in solution (Higazi et al. (1995) J. Biol. Chem. 270, 17375-17380). In this work we show that suPAR as such has no accelerative role. In contrast, the progress of the activation reactions in a soluble system with pro-uPA and plasminogen was found to be attenuated by suPAR. This delay of the activation system was shown to include a partial inhibition of the plasmin-mediated activation of pro-uPA as well as of the uPA-mediated activation of plasminogen.

Animals↗
PubMed2006

Concentrations of plasminogen activators and their inhibitors in blood preconceptionally, during and after pregnancy.

BACKGROUND: Haemostasis is a complex balance of activating and inhibitory pathways resulting in coagulation and lysis. Normal pregnancy is associated with hypercoagulation that is even more profound in complicated pregnancies. OBJECTIVE: To study the role of the plasminogen-activator system in complicated pregnancy with regard to haemostasis, it is essential to have reference values of components of this system during uneventful pregnancy. In this study we investigated the concentrations of six different components of the plasminogen-activator system preconceptionally, during and after uncomplicated pregnancies. MATERIAL AND METHODS: Tissue-type and urokinase-type plasminogen activator (tPA and uPA), plasminogen inhibitor type-1 and -2 (PAI-1 and-2), and the complexes between tPA and PAI-1, and between uPA and PAI-1 (tPA-PAI-1, uPA-PAI-1) were measured by ELISAs in blood obtained preconceptionally, at 6, 10, 20, 32 weeks of gestation, and 6 weeks after delivery in uncomplicated pregnancies (n=41; all six parameters n=22). RESULTS: tPA and uPA concentrations decreased in the first 10 weeks of pregnancy and subsequently increased in the third trimester. PAI-1 concentrations increased in the third trimester and PAI-2 concentrations increased throughout pregnancy (preconception versus 32 weeks of gestation; 38.73 versus 102.23ng/ml, and 0.024 versus 151.06ng/ml, respectively). tPA-PAI-1 and uPA-PAI-1 complex concentrations decreased in the first trimester, followed by an increase in the third trimester. The concentrations of all components returned to the preconception values 6 weeks after delivery. CONCLUSION: This study provides longitudinal data on activating and inhibitory components of the plasminogen-activator system during pregnancy. Insight in the longitudinal changes in these concentrations may be of help in the understanding of the thrombotic tendency in pregnancy complications such as preeclampsia.

Adult↗
PubMed2006

Complex congenital malformations and the impact of the plasminogen activator system and beta-hCG in amniotic fluid.

OBJECTIVE: The plasminogen activator system and beta-hCG may affect neural crest cells and angiogenesis, and thereby embryogenesis. Therefore, we investigated these parameters in amniotic fluids of pregnancies with a complex congenital malformation. STUDY DESIGN: In a case-control study amniotic fluid samples were collected from 62 pregnancies with a complex congenital malformation and from 110 healthy control pregnancies at an obstetric department of a large university hospital in the Netherlands. We determined concentrations of tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA), plasminogen activator inhibitors (PAI-1, PAI-2), tPA approximately PAI-1 and uPA approximately PAI-1 complexes, and beta-hCG with enzyme-linked immunosorbent assays. Mann-Whitney U-tests and analysis of covariance, adjusting for gestational and maternal age, were performed for data comparisons. RESULTS: Compared with controls, cases demonstrated significantly lower adjusted geometric mean levels of uPA (24%), tPA (> or =19%) and tPA approximately PAI-1 (35%). Cases showed significantly higher adjusted mean levels of beta-hCG (> or =48%) and PAI-2 (10 ng/mL) than controls. Mean PAI-1 and uPA approximately PAI-1 levels were comparable between both groups. CONCLUSIONS: Disturbances in the plasminogen activator system and beta-hCG levels are suggested to be involved in the pathogenesis of complex congenital malformations by affecting neural crest cell migration and angiogenesis.

Adult↗
PubMed2000

Importance of GlcUAbeta1-3GalNAc(4S,6S) in chondroitin sulfate E for t-PA- and u-PA-mediated Glu-plasminogen activation.

Chondroitin sulfate E (CSE) markedly enhanced plasminogen activation by tissue plasminogen activators (t-PAs) and urinary plasminogen activator (u-PA) in vitro; in the presence of 10 microg/ml of CSE, the potentiation factors of single chain of t-PA, two chain of t-PA and u-PA were 400, 140 and 130, respectively. Though the potentiation activity of CSE gradually decreased when it was depolymerized by chondroitinase ABC, the specific disaccharide from CSE still showed significant activity. Glycosaminoglycan (GAG) from sea cucumber, which possesses a very similar core structure to CSE, but has additional sulfated fucose branches exhibit very weak activity. These results suggested that the minimal structural requirement in CSE to enhance plasminogen activation by plasminogen activators is GlcUAbeta1-3GalNAc(4S,6S) and that additional branching sugars abolish the activity.

Animals↗
PubMed2002

Plasminogen activator-plasmin system potentiates the proliferation of hepatocytes in primary culture.

BACKGROUND/AIMS: Liver regeneration after partial hepatectomy is thought to be regulated by various molecules including the components of the plasminogen activator (PA)-plasmin system. We have examined the role of fibrinolytic factors, i.e., tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA), and their substrate, plasminogen, in the proliferation of hepatocytes in primary culture. METHODS: Hepatocyte and nonparenchymal liver cells were isolated from Wistar strain rat by a method perfusing the liver with collagenase. DNA synthesis was assessed by measuring the incorporation of [3H]-thymidine into cellular DNA fraction. tPA, uPA and type-1 plasminogen activator inhibitor (PAI-1) gene expressions were measured by Northern blotting. PA activity was measured by fibrin/agarose plate method. RESULTS: Cellular density-dependent DNA synthesis was observed in the primary cultured hepatocytes; DNA synthesis was lower at high cell density (1.0 x 10(5) cells/cm(2)) than that at low cell density (0.2 x 10(5) cells/cm(2)). DNA synthesis in the hepatocytes cultured at a low cell density was increased by co-culture with nonparenchymal liver cells. Under these growth-stimulated culture conditions, tPA and uPA mRNAs were induced and up-regulated. On the contrary, the PAI-1 mRNA level was decreased under these conditions, and total PA activity was augmented accordingly. The synthetic plasmin inhibitor tranexamic acid, a competitive inhibitor for the plasmin molecule, and PASI-535, a plasmin active center-directed inhibitor, both suppressed hepatocyte proliferation in a dose-dependent fashion. Anti-plasmin antibody also suppressed hepatocyte proliferation. CONCLUSIONS: The up-regulation of PA activity for ensuring plasmin activity should be an important mechanism in the proliferation of hepatocytes.

Animals↗
PubMed1998

Proteolysis of highly polysialylated NCAM by the tissue plasminogen activator-plasmin system in rats.

Tissue-type plasminogen activator (tPA), a serine protease which converts the zymogen plasminogen to the active protease plasmin, is believed to regulate neurite extension and neural cell migration by modulating extracellular metabolism. The highly polysialylated form of the neural cell adhesion molecule (NCAM-H) is strongly expressed in the developing brain and is believed to play a role in organizing the neural network. In this report, we incubated neonatal rat brain homogenates with human tPA and rat plasminogen in order to determine whether NCAM-H would be degraded. NCAM-H was degraded by plasmin which was formed from rat plasminogen by human tPA. The degradation was inhibited by the addition of plasminogen activator inhibitor type 1 (PAI-1) or aprotinin. These results suggest a possible contribution of the tPA-plasmin system to NCAM-H turnover in the developing brain.

Aging↗
PubMed2003

Effect of black-pigmented bacteria on the plasminogen-plasmin system in human pulp and osteoblastic cells.

OBJECTIVE: To date, there have been relatively few studies addressing the presence and expression of the plasminogen-plasmin system at the site of bacterial infection. The aim of the present study was to investigate the effect of black-pigmented bacteria on the expression of the plasminogen-plasmin system in human pulp and osteoblastic cells. STUDY DESIGN: The supernatants of Porphyromonas endodontalis, Porphyromonas gingivalis, and Prevotella intermedia were used to evaluate tissue-type plasminogen activator (t-PA) and type 1 plasminogen activator inhibitor (PAI-1) gene expression in human pulp and osteoblastic cells. The levels of mRNA were quantitatively measured by using reverse transcription-polymerase chain reaction. RESULTS: In this study, black-pigmented bacteria induced not only t-PA but also PAI-1 gene expression in human pulp and osteoblastic cells. In addition, the ratio of t-PA to PAI-1 was higher in human pulp and osteoblastic cells stimulated by black-pigmented bacteria than in untreated cell cultures (P <.05). CONCLUSIONS: A fine balance exists in the expression of components of the plasminogen-plasmin system, whereby tissue homeostasis is maintained. Black-pigmented bacteria activate the activator-inhibitor system in human pulp and osteoblastic cells through unbalance regulation of t-PA and PAI-1, which might result in an uncontrolled degradation of pulpal and periapical tissues.

Analysis of Variance↗
PubMed2006

Local heat shock priming promotes recanalization of thromboembolized microvasculature by upregulation of plasminogen activators.

OBJECTIVE: Thromboembolization and subsequent microvascular perfusion failure is implicated in the pathology of a variety of diseases, including transient ischemic attack (TIA), stroke, and myocardial infarction, and also for the complications after interventional and microsurgical procedures in coronary heart disease and peripheral arterial occlusive disease. In vitro heat shock priming has been suggested to induce plasminogen activators, which are the major upregulators of the fibrinolytic system. Herein, we determined whether local heat shock priming endogenously upregulates plasminogen activators also in vivo, and whether this promotes recanalization of thromboembolized microvasculature. METHODS AND RESULTS: To induce thromboembolization, a suspension of preformed microthrombi (maximum diameter: 40 microm) was injected via the femoral artery into the left hindlimbs of anesthetized rats. Local heat shock priming (42.5 degrees C, 30 minutes) was performed 24 hours before embolization and resulted in a significant increase of endothelium-derived plasminogen activator expression. The study of the microcirculation by intravital microscopy revealed in all tissues analyzed (muscle, periosteum, subcutis, and skin) that heat shock priming significantly (P<0.05) accelerates recanalization of the thromboembolized microvasculature when compared with nonprimed and sham-primed controls. Importantly, the addition of plasminogen activator inhibitor-1 to the microthrombi suspension completely blunted the heat shock-induced acceleration of microvascular recanalization. CONCLUSIONS: Heat shock induces endogenous hyperfibrinolysis by upregulation of plasminogen activators that promote recanalization of thromboembolized microvasculature.

Animals↗
PubMed2001

Plasminogen Activators and Inhibitors in the Corneas of Mice Infected with Pseudomonas aeruginosa.

PURPOSE: To characterize the presence of plasminogen activators and their inhibitors in the corneas during the inflammatory response in naïve and immunized mice intracorneally infected with Pseudomonas aeruginosa. METHODS: RT-PCR was used to detect gene expression for plasminogen activators and their inhibitors in naïve and immunized mice. Immunoblot analysis, zymography, and ELISA were used to demonstrate the syntheses of these proteins. RESULTS: Naïve mice intracorneally infected with P. aeruginosa showed a temporally enhanced expression of tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA), its receptor (uPAR), and plasminogen activator inhibitors 1 and 2 (PAI-1 and PAI-2), over a several-day holding period. Immunized mice demonstrated a lower and shorter expression of these factors over the same period. Expression of these factors at the mRNA and protein levels may have been due to enzymes and inhibitors present in inflammatory cells and in resident corneal cells. CONCLUSIONS: These results show a correlation between the overexpression of the PA system in infected naïve mice as part of the inflammatory response, with eventual ocular destruction. Immunized mice exhibit a more balanced and shorter expression of the PA system, which may contribute to the restoration of corneal clarity.

Animals↗
PubMed1990

Identification and characterization of human endothelial cell membrane binding sites for tissue plasminogen activator and urokinase.

Cultured human endothelial cells synthesize and secrete two types of plasminogen activator, tissue plasminogen activator (t-PA) and urokinase (u-PA). Previous work from this laboratory (Hajjar, K.A., Hamel, N. M., Harpel, P. C., and Nachman, R. L. (1987) J. Clin. Invest. 80, 1712-1719) has demonstrated dose-dependent, saturable, and high affinity binding of t-PA to two sites associated with cultural endothelial cell monolayers. We now report that an isolated plasma membrane-enriched endothelial cell fraction specifically binds 125I-t-PA at a single saturable site (Kd 9.1 nM; Bmax 3.1 pmol/mg membrane protein). Ligand blotting experiments demonstrated that both single and double-chain t-PA specifically bound to a Mr 40,000 membrane protein present in detergent extracts of isolated membranes, while high molecular weight, low molecular weight, and single-chain u-PA associated with a Mr 48,000 protein. Both binding interactions were reversible and cell-specific and were inhibitable by pretreatment of intact cells with nanomolar concentrations of trypsin. The relevant binding proteins were not found in subendothelial cell matrix, failed to react with antibodies to plasminogen activator inhibitor type 1 and interacted with their respective ligands in an active site-independent manner. The isolated t-PA binding site was resistant to reduction and preserved the capacity for plasmin generation. In contrast, the isolated u-PA binding protein was sensitive to reduction, and did not maintain the catalytic activity of the ligand on the blot. The results suggest that in addition to sharing a matrix-associated binding site (plasminogen activator inhibitor type 1), both t-PA and u-PA have unique membrane binding sites which may regulate their function. The results also provide further support for the hypothesis that plasminogen and t-PA can assemble on the endothelial cell surface in a manner which enhances cell surface generation of plasmin.

Binding Sites↗
PubMed1986

Characterization of the dexamethasone-induced inhibitor of plasminogen activator in HTC hepatoma cells.

Incubation of HTC rat hepatoma cells with the synthetic glucocorticoid dexamethasone rapidly inhibits plasminogen activator (PA) activity secondary to the induction of a specific acid-stable inhibitor of plasminogen activation (Cwikel, B. J., Barouski-Miller, P.A., Coleman, P.L., and Gelehrter, T.D. (1984) J. Biol. Chem. 259, 6847-6851). We have further characterized this inhibitor with respect to its interaction with both urokinase and tissue plasminogen activator, and its protease specificity. The HTC PA inhibitor rapidly inhibits urokinase and tissue plasminogen activator with an apparent second-order rate constant of 3-5 x 10(7) M-1 X s-1. The inhibitor forms stable covalent complexes with both urokinase and tissue plasminogen activator, with which plasmin, trypsin, and factor Xa apparently do not compete. Complex formation is saturable and requires the active site of the PA. The mass of the inhibitor-PA complex is 50,000 daltons greater than that of PA alone, consistent with an Mr for the PA inhibitor of 50,000 as demonstrated directly by reverse fibrin autography. The HTC PA inhibitor does not inhibit thrombin and differs in its kinetic and biochemical properties from protease nexin.

Animals↗