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Query: UNIPROT:P00750 (PLA)
 16,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Lipoprotein(a) (Lp[a]), a highly atherogenic lipoprotein particle, is the prominent apolipoprotein B-containing lipoprotein in the hedgehog (Laplaud PM et al, J Lipid Res 1988;29:1157-1170). In the present work, we studied the consequences of the structural homology between the specific Lp(a) glycoprotein, apoprotein(a), and plasminogen on the generation of plasmin by fibrin-bound tissue-type plasminogen activator. The activation of plasminogen was initiated by adding either native plasma or Lp(a)-free plasma supplemented with the equivalent of 0.25 mg/ml of either purified Lp(a) or albumin to a surface of fibrin prepared on micortitration plates and to which human tissue-type plasminogen activator was specifically bound. With the Lp(a)-free plasma, an increase in the binding and activation of plasminogen as a function of time was observed. In contrast, in the presence of Lp(a) (i.e., native plasma or the reconstituted system), a significant decrease in the binding of plasmin(ogen) (approximately 60%) was obtained. These data indicate that hedgehog Lp(a) interferes with the binding and activation of plasminogen at the fibrin surface and may thereby behave as a factor regulating the extent of fibrin deposition. These results support our previous data indicating that high levels of Lp(a) may have antifibrinolytic effects in humans (Rouy D et al, Arterioscler Thromb 1991;11:629-638), are in agreement with the observation that Lp(a) is a risk factor for atherosclerotic disease, and provide further support to the view of Lp(a) as a link between atherosclerosis and thrombosis.
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PMID:Hedgehog lipoprotein(a) is a modulator of activation of plasminogen at the fibrin surface. An in vitro study. 153 29

Endocytosis of tissue-type plasminogen activator (t-PA) by different types of rat liver cells was studied in immunocytochemically labelled cryosections as well as in biochemical experiments. For morphological localization of the ligand in different endocytic compartments involved in its catabolism, rat livers were fixed at various times (1-24 min) after injection of t-PA. Late-endosomal and lysosomal compartments were identified by double-labelling the sections with antibodies to the lysosomal proteins glycoprotein Igp 120 and cathepsin D. In liver t-PA was localized in sinusoidal endothelial cells (EC), parenchymal cells (PC) and to some extent in Kupffer cells (KC), indicating that it is internalized and degraded in all three cell types. In specimens fixed 6 min after injection PC, EC and KC were found to contribute to 69, 24 and 7% respectively of total t-PA endocytosed. The transfer from late endosomes to lysosomes was found to be faster in EC than in PC. The morphological findings were supported by studies of the endocytic mechanisms employing isolated perfused livers and primary hepatocytes. The presence of monensin, an inhibitor of lysosomal protein degradation, reduced the amount of t-PA degraded to about 50% of the control values. The catalytic site seems not to be required for the catabolism of t-PA in hepatic cells. The inhibition of t-PA by D-phenylalanyl-L-prolylarginyl-chloromethane did not influence receptor recognition and catabolic processing, as determined in morphological studies using labelled cryosections, in binding studies employing liver cell membranes and primary hepatocytes, as well as in liver-perfusion experiments.
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PMID:Endocytosis and intracellular processing of tissue-type plasminogen activator by rat liver cells in vivo. 155 69

Human tissue-type plasminogen activator (t-PA) is a glycoprotein used currently in thrombolytic therapy for patients with acute myocardial infarction. Due to its rapid rate of clearance from the circulation, continuous intravenous administration of approximately 100 mg over 3 h is recommended. We have previously characterized novel thrombolytic variant forms of t-PA which offer the potential of administration by bolus injection and reduced dosage due to their slower rates of clearance, relative to t-PA. This study was undertaken to quantitatively compare the pharmacokinetics, thrombolytic activity, and hemostatic effects of two of these variant forms, called delta FE1X and delta FE3X plasminogen activator (PA), with commercially available recombinant t-PA (Activase). These evaluations were performed in rabbits after bolus intravenous injection of the proteins. Following injection of 0.25 mg of protein/kg of body weight, the rates of clearance for delta FE3X and delta FE1X PA antigen were decreased approximately 9- and 18-fold, respectively, relative to Activase. Plasma plasminogen activator activity was also measured and the rates of clearance of delta FE3X and delta FE1X PA activity were similarly decreased by approximately 9- and 22-fold, respectively, relative to Activase. To quantitate thrombolytic activity we used the rabbit jugular vein thrombosis model and demonstrated that approximately 50% thrombolysis was achieved with delta FE1X and delta FE3X PA at approximately an 8.6- and 3-fold lower dose than Activase, respectively. No major differences in fibrinogen and alpha 2-antiplasmin depletion were observed among the agents at doses required to produce 50% thrombolysis, indicating similarities in fibrin specificities among these agents. These results demonstrate a reciprocal relationship between thrombolysis and rate of clearance for these thrombolytic proteins. The 8.6-fold increase in potency of delta FE1X PA relative to Activase supports the future clinical testing of this novel engineered protein as a thrombolytic agent.
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PMID:Protein engineering of novel plasminogen activators with increased thrombolytic potency in rabbits relative to activase. 170 73

Alpha 2-macroglobulin, a major glycoprotein component of plasma, is unique in its capacity to bind and inhibit the proteolytic activities of all classes of proteinases. Since proteinases implicated in cancer dissemination (type-IV collagenase, plasminogen activator, cathepsins B) are normal constitutents of blood, we have explored the hypothesis that elevated tissue levels of activated proteinases bound to alpha 2M might be detected in plasma of patients with cancer. To test this premise, blood was collected from 149 subjects (33 healthy controls, 31 patients with infections and non-malignant diseases, 16 with myeloproliferative disease, 10 with gastrointestinal cancer, 7 with genito-urinary cancer, 16 with lung cancer, 14 with lymphoma, 11 with miscellaneous cancers and 11 with chronic lymphocytic leukemia and myeloma). Plasma was assayed for alpha 2M-proteinase complexes using a sandwich ELISA which employs a mouse monoclonal antibody (MAb) that binds to a neo-antigenic determinant on complexed alpha 2M and a rabbit polyclonal anti-native human alpha 2M antibody. The concentration of complexed alpha 2M in healthy controls was 14.2 +/- 9.8 micrograms/ml (mean +/- standard deviation). No significant differences in complexed alpha 2M were noted between normal and cancer groups (range 7.4-14.6 micrograms/ml). On the basis of these data, we propose that, in patients with cancer, activated proteinases are bound locally to inhibitors in the tissues and are not available to form complexes with plasma alpha 2M. An alternative explanation is that proteinases are not secreted in excess by cancer cells in vivo.
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PMID:Proteinase-alpha 2 macroglobulin complexes are not increased in plasma of patients with cancer. 171 Feb 7

Laminin is a large multidomain glycoprotein with diverse biological activities which include stimulation of neurite outgrowth, enhancement of tumor metastasis, and promotion of cell growth, adhesion, and differentiation. A 19 amino acid synthetic peptide derived from the E8 fragment of the laminin A chain (Cys-Ser-Arg-Ala-Arg-Lys-Gln-Ala-Ala-Ser-Ile-Lys-Val-Ala-Val-Ser-Ala-Asp -Arg- NH2) was identified which promotes metastasis and stimulates collagenase IV activity in the culture medium of B16 melanoma cells (Kanemoto et al., 1990). We report that this peptide, here designated LamA2091-2108, is also a potent stimulator of tissue plasminogen activator (t-PA)-catalyzed plasminogen activation, resulting in a 22-fold increase in the kcat/Km of the activation reaction. The activity of purified type I and type IV collagenase was inhibited by LamA2091-2108 with IC50 values of 3 and 43 microM, respectively. These data support an alternative mechanism for the appearance of collagenase activity in the culture media of melanoma cells, namely, that the peptide stimulates plasminogen activation, subsequently generating collagenase activity.
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PMID:Modulation of plasminogen activation and type IV collagenase activity by a synthetic peptide derived from the laminin A chain. 184 24

In an earlier publication (Harvey, et al. (1982) J. Biol. Chem., 257, 5645-5651) the discovery of a family of unusually large molecules with plasminogen activator activity in the conditioned medium of a human lung cancer cell line was reported. These molecules are related to urokinase (uPA) by functional and immunological criteria. We have now purified two representatives of this glycoprotein family of Mr 900,000 (PA900) and Mr 660,000 (PA660). While these could be fractionated into subspecies exhibiting size and charge differences, reduction yielded in all cases two predominant chains of 70 and 40 kDa, respectively. Since the amino acid composition of the subfractions was identical, we conclude that the heterogeneity is due to demonstrated differences in glycosylation. The amino acid composition of the unreduced species and of the major reduced chains differed from that of 55 kDa uPA. These enzymes are active toward the substrate, plasminogen, as well as toward the uPA-specific synthetic substrate, Spectrozyme UK, and these activities are inhibitable by diisopropylphosphorofluoridate (DFP). Treatment of PA660 with [3H]DFP resulted in the incorporation of 1.4 mol of DFP into 1 mol of enzyme, suggesting the presence of a single active site. The label was quantitatively recovered in a 21 kDa fragment in a reduction experiment. This fragment also demonstrated immunological reactivity with antiurokinase. It is postulated that PA660 is composed of five or six pairs of the 70 and 40 kDa chains, and of a single uPA-like entity. All of these chains are linked by disfulfide bonds. Whether larger portions of uPA are also present in this molecule, is not yet clear. By electron microscopy, PA900 shows a filamentous structure, while PA660 is predominantly globular. The occurrence of large uPA-like activators in extracts of human colon carcinomas that crossreact with monospecific antibody against uPA, is discussed.
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PMID:Characterization of a family of high-molecular-weight plasminogen activators secreted by a lung tumor cell line. 185 26

The endothelial cells (ECs) are antithrombotic in the physiological states and maintains the integrity of blood circulation. However, ECs turn to be thrombotic upon being stimulated by various physiological mediators. These functions are mainly achieved by changing specific protein synthesis in ECs. Type 1 plasminogen activator inhibitor (PAI-1) is a serine protease inhibitor synthesized by ECs and thought to play a crucial role in the regulation of fibrinolysis. Basic research as well as clinical studies support this hypothesis. PAI-1 is a physiological inhibitor of both tissue-type plasminogen activator and urokinase-type plasminogen activator, key enzymes in the initiation of fibrinolysis. Thus PAI-1 regulates not only blood clot lysis but also a wide variety of biological reactions occurring in extracellular matrices such as tumor metastasis, neovascularization, inflammation, and cell migration. PAI-1 is a glycoprotein, of which molecular weight is approximately 50,000. Molecular biological analyses indicate that PAI-1 is synthesized as a single polypeptide composed of 402 amino acids containing a signal peptide. After post-translational modification, PAI-1 is secreted from ECs as a polypeptide composed of 379 amino acids and three N-linked carbohydrates. PAI-1 lacks Cys residues, indicating that PAI-1 may not be rigid and thus thermolabile. In fact, PAI-1 is unstable even at 37 degrees C decaying into an inactive form with a biological half life of 2-3 hours. PAI-1 binds to a cell adhesion molecule, vitronectin. The association of PAI-1 with vitronectin appears to stabilize PAI-1. PAI-1 in complex with vitronectin is still accessible to plasminogen activators.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Type 1 plasminogen activator inhibitor: its role in biological reactions]. 187 Feb 65

Catechins, a group of flavonoid molecules, inhibit invasion of mouse MO4 cells into embryonic chick heart fragments in vitro. The anti-invasive effects can be ranked as follows: (+)-catechin greater than (-)-epicatechin greater than 3-O-methyl-(+)-catechin greater than 3-O-palmitoyl-(+)-catechin. Most of the catechins are unstable in cell culture media, and their spontaneous rearrangement products tend to bind to extracellular matrix (ECM). Due to these interactions proteases such as tissue-type plasminogen activator (t-PA) are linked to the ECM glycoprotein laminin. This leads to a partial inactivation of the enzyme. Within the group of catechins we found a positive correlation between anti-invasive activity and linking of t-PA to laminin. Citrus flavonoids are also anti-invasive in vitro (tangeretin greater than nobiletin greater than hesperidin = naringin). However, these stable molecules show poor affinity for ECM, and do not link enzymes to laminin. These data suggest that catechins and citrus flavonoids inhibit invasion in vitro by different mechanisms.
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PMID:Effect of catechins and citrus flavonoids on invasion in vitro. 190 81

The glycoprotein tissue-type plasminogen activator (t-PA, alteplase, CAS 105857-23-6) is a serine protease consisting of 527 amino acids and can activate plasminogen to plasmin, which subsequently dissolves the fibrin network of a thrombus. This activation occurs selectively on the thrombus, making recombinant t-PA a very effective agent in the treatment of thromboembolic disorders. t-PA has a short in vivo half-life and is rapidly removed from the circulation by the liver. The catabolism of t-PA involves receptor-mediated endocytosis and intracellular degradation in several cell types of the liver namely hepatic endothelial, parenchymal and Kupffer cells. Liver endothelial cells have been reported to possess a specific uptake system for t-PA based on the recognition of the high mannose carbohydrate structures on Asn117. To further elucidate the involvement of the mannose receptor on sinusoidal endothelial cells in the hepatic catabolism of t-PA and to identify the mechanisms involved, biochemical as well as electron microscopic studies were performed. The biochemical studies revealed that the removal of the mannose side chain in t-PA significantly reduced its clearance and degradation in isolated perfused livers. The binding of t-PA to preparations of primary hepatocytes and liver cell membranes could not be competed for by various sugars and glycoproteins, and was not dependent on the presence of carbohydrates on the molecule. This ruled out a major relevance of the sugar moieties of t-PA in its recognition by liver cells that were not of endothelial origin.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Endocytosis of the recombinant tissue plasminogen activator alteplase by hepatic endothelial cells. 190 31

Recent studies suggest that the nature of events leading to the formation, maintenance, and elimination of synapses may be regulated by cascade-type, locally expressed proteases and protease inhibitors acting on adhesive extracellular matrix components. We have identified a molecule in conditioned medium of murine skeletal muscle cells that in molecular weight, target protease inhibition, heparin-binding and cross-reactivity with authenic antisera is similar to the human serine proteinase inhibitor, protease nexin I. Protease nexin I is a 43-50 kDa glycoprotein of the serpin superfamily (arg-serpin class). Purified anti-protease nexin I antibody (anti-47 kDa) stains adult mouse skeletal muscle in discrete foci that precisely superimpose on synaptic neuromuscular junctions. Protease nexin I appears in patches on surfaces of cultured mouse skeletal myotubes, but not on myoblasts. These patches co-localize with acetylcholine receptor clusters and acetylcholinesterase staining during cellular maturation in culture. Evidence that protease nexin I is a synaptic, extracellular antigen is particularly intriguing since it has been shown to be identical, in structure and activity, with a factor released by glial cells, called glia-derived nexin that stimulates mouse neuroblastoma cell neurite outgrowth and inhibits granule cell migration. Protease nexin I inhibits both tumor cell and myoblast plasminogen activator-mediated destruction of extracellular matrix. Thus, such observations as presented in this report provide further evidence for involvement of cascade proteolytic systems, and their post-translational regulation by specific serpins, in the remodeling that occurs in synapse formation and elimination.
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PMID:Plasminogen activators and inhibitors in the neuromuscular system: III. The serpin protease nexin I is synthesized by muscle and localized at neuromuscular synapses. 203 25


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