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

Activation and inhibition of the haemostatic system was reviewed including the interaction between the four biological systems involved in haemostasis: the vessel wall, the platelets, the coagulation system and the fibrinolytic system. The haemostatic mechanism is initiated at the site of injury through local activation of surfaces and release of tissue thromboplastin, resulting in formation and deposition of fibrin. The coagulation process is regulated by physiological anticoagulants. Activation of fibrinolysis is triggered by the presence of fibrin, and the role of tissue-type plasminogen activators (t-PA) at the site of fibrin formation in particular is emphasized. The process is regulated by physiological inhibitors, of which alpha 2-antiplasmin, histidine-rich glycoprotein and plasminogen activator inhibitor are reported to be of major physiological significance. The role of fibrinolysis in the regulation of the dynamic haemostatic balance is discussed, elucidated through examples of congenital deficiencies of the coagulation and the fibrinoytic system. Pharmacological inhibitors of fibrinolysis (i.e. epsilon-aminocaproic acid and tranexamic acid) and their possible effect on the haemostatic system are described. The systemic effects on the fibrinolytic system of surgery and oral surgery is reviewed, and it is concluded, that oral surgery has insignificant effects on blood fibrinolysis. In contrast, oral surgery induces changes of fibrinolysis in the oral environment; initially the fibrinolytic activity of saliva is reduced, due to the presence of inhibitors of fibrinolysis originating from the blood and the wound exudate. When bleeding and exudation cease, the fibrinolytic activity of the saliva will increase. Plasminogen and plasminogen activator, identified as t-PA are present in the oral environment under physiological conditions. Plasminogen is secreted in the saliva and the sources of t-PA include oral epithelial cells and gingival crevicular fluid. The presence of plasminogen and t-PA in the oral environment implies that when fibrin is present (i.e. after surgery), fibrinolysis is triggered. Haemorrhagic complications to oral surgery in patients without known defects of the coagulation system is reviewed. It is concluded that the investigations conducted to the present day do not permit final conclusions with respect to the pathophysiological role of defects in the coagulation and the fibrinolytic systems for the development of bleeding after oral surgery. Further investigations are necessary in order to clarify these aspects, and should include extensive laboratory analyses to reveal rare congenital defects such as factor XIII- and alpha 2-antiplasmin deficiencies.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Haemostasis in oral surgery--the possible pathogenetic implications of oral fibrinolysis on bleeding. Experimental and clinical studies of the haemostatic balance in the oral cavity, with particular reference to patients with acquired and congenital defects of the coagulation system. 180 33

Plasminogen activator activity (PAA), plasminogen activator inhibition (PAI) and plasmin inhibition (PI) have been studied with spectrophotometric methods in extracts of human, bovine, ovine and rat kidneys of both sexes. In all species studied, renal PAA (cortex or medulla) was higher in females than in males. The PAA was also higher in the medulla than in the cortex in all species and both sexes. The PAA was due to both types of plasminogen activator; tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). In the human kidney (cortex or medulla) the measurement of t-PA antigen showed that t-PA is higher in females than in males; t-PA is also higher in the medulla than in the cortex in both sexes. The PAI showed the opposite pattern in all species studied; it was lower in females than in males. It was also lower in the medulla than in the cortex. PAI-1 was identified in the human kidney. Sex-related differences in renal PAA or PAI almost disappeared after bilateral orchidectomy in rats. PI showed no sex or regional differences in the species studied. Sex-related differences in renal PAA and PAI in man and various animal species might be of physiological or pathophysiological importance.
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PMID:Sex-related differences in plasminogen activator activity and plasminogen activator inhibition of human and animal kidneys: effect of orchidectomy or ovariectomy. 180 59

The question whether single-chain urokinase-type plasminogen activator (Sc-uPA) possesses an enzymatic activity has been a subject of intense investigation for a number of years but still remains unresolved. Recent studies from several laboratories suggest that Sc-uPA or its plasmin-resistant mutants obtained by site-directed mutagenesis possess significant, albeit low, amidolytic and plasminogen activator activities, ranging from 0.1% to 1% of that observed for two-chain urokinase (Tc-uPA). In an effort to characterize these putative intrinsic activities, Sc-uPA was repeatedly treated with dansyl-Glu-Gly-Arg chloromethyl ketone (dansyl-EGRck) or diisopropyl fluorophosphate (DFP) (0.1-0.25 mM added thrice over a period of 24 h at 0 degrees C). This treatment exhaustively inactivated the Tc-uPA contaminant but did not affect Sc-uPA, as evidenced by the lack of significant incorporation of radiolabeled inhibitor in Sc-uPA and full activation of the inhibitor-treated Sc-uPA by plasmin. Assayed in the presence of excess DFP or dansyl-EGRck to ensure trapping of any Tc-uPA generated in the assay mixture, Sc-uPA (84 micrograms/mL, 10,500 latent units/mL) did not elicit any detectable cleavage of the chromogenic substrate S-2444 (detection limit 0.1 unit of Tc-uPA/mL). However, if the Tc-uPA inhibitors were removed prior to assay, a trace amount of amidolytic activity invariably reappeared in the Sc-uPA preparation. Incorporation experiments with [3H]DFP suggested that the appearance of this amidolytic activity was due to formation of Tc-uPA. Plasminogen activator assay of DFP- and dansyl-EGRck-treated Sc-uPA (0.45-2.25 microM), performed in the presence of these inhibitors and Trasylol (10 microM) to ensure entrapment of any Tc-uPA or plasmin generated in the reaction mixture, showed no significant cleavage of 125I-labeled plasminogen (detection limit 0.1 nM). However, if dansyl-EGRck and DFP were removed from the inhibitor-treated Sc-uPA and the assay was performed in the presence of Trasylol alone, there was significant cleavage of 125I-plasminogen due to contamination by Tc-uPA. Fibrin, a positive effector of plasminogen activation by Tc-uPA or Sc-uPA preparations in the absence of DFP and dansyl-EGRck, did not promote cleavage of plasminogen or S-2444 by Sc-uPA in the presence of the Tc-uPA inhibitors.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Single-chain urokinase-type plasminogen activator does not possess measurable intrinsic amidolytic or plasminogen activator activities. 182 71

Plasminogen receptors have been identified on the surface of a number of prokaryotic and eukaryotic cells. A receptor demonstrating high affinity for plasmin with minimal reactivity with the native zymogen Glu-plasminogen has been identified on the surface of certain group A streptococci. In this study the group A streptococcal plasmin receptor has been solubilized and purified to homogeneity. The isolated protein was an Mr approximately 41,000 molecule which retained its ability to bind plasmin following solubilization and affinity purification on a column of enzymatically inactivated human plasmin. The isolated plasmin receptor was compared functionally, antigenically, and physicochemically to the secreted plasminogen activator, streptokinase, produced by the same organism. The Mr approximately 41,000 surface plasmin receptor was shown to be functionally and antigenically distinct from the Mr approximately 48,000 streptokinase molecule produced by the same strain and lacked any plasminogen activator activity. The streptokinase molecule produced by this strain was shown to be closely related to the plasminogen activator protein secreted by other group A and C streptococci. This study represents the first report of the isolation of a plasmin receptor, either prokaryotic or eukaryotic, with functional activity.
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PMID:Isolation of a prokaryotic plasmin receptor. Relationship to a plasminogen activator produced by the same micro-organism. 184 29

Plasminogen activation on the cell surface is regulated by a variety of modulators which balance surface-bound plasminogen activators (PAs) and plasminogen activator inhibitors (PAIs). In this study, we developed as assay system to assess modulation of cell-associated plasminogen activation. Plasmin generation by endogenous plasminogen activators was measured with a combination of exogenously added plasminogen and a chromogenic substrate, S-2251, in the presence of living cells. A cell surface PA activity was quantitated by adopting a rate of plasmin generation. We used HT-1080, a human fibrosarcoma cell line, as representative of cells which have both PAs and PAIs on their cell surface. A basal level of cell surface PA activity was specifically reduced by anti-urokinase-type PA IgG and enhanced by anti-PAI-1 IgG, suggesting that the basal level is determined by a balance between uPA and PAI-1 on the cell surface. We examined effects of dexamethasone and thrombin on cell surface PA activity in the assay system. Dexamethasone appeared to suppress the cell surface PA activity by enhancing de novo synthesis of PAI-1, whereas thrombin suppressed it by inactivating single-chain urokinase-type plasminogen activators. These results indicate that our assay system can be adapted for the screening of various types of PA modulators.
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PMID:An assay system for the modulators of plasminogen activation on the cell surface. 189 67

Plasminogen activators are serine proteinases which transform the serum zymogen, plasminogen, into plasmin, a broad-spectrum protease with fibrinolytic effect. Two main plasminogen activators have been described in humans: urokinase (UK; molecular weight, 55,000) and tissue-type plasminogen activator (tPA; molecular weight, 74,000). Thirteen subjects were studied who had alopecia areata (AA), nine in the active phase and four in remission. There were alterations in the perivascular and peribulbar fibrinolytic activity in the nine subjects in the active phase of disease, suggesting a possible role of plasminogen activators in AA. A modified Todd's autohistographic method was used to evaluate cutaneous fibrinolytic activity (which depended on the activity of plasminogen activators) in the 13 AA subjects and five volunteer controls. Cutaneous fibrinolytic activity was reduced in perivascular areas, but increased in peribulbar areas, in the nine subjects in the active phase of disease. Tests with monoclonal antibodies directed against the catalytic sites of tPA and UK showed that the perivascular fibrinolytic activity was tPA dependent, and the peribulbar fibrinolytic activity was UK dependent.
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PMID:The role of plasminogen activators in alopecia areata. 189 52

Plasminogen activator activity was investigated in extracts of 42 surgically removed gastric carcinomas. The mean levels of total plasminogen activator (total-PA) and urokinase-type plasminogen activator (u-PA) activities in the gastric carcinomas were significantly higher than those in the background normal tissues (p less than 0.001). On electrophoresis, gastric cancers were found to contain u-PA as the predominant PA, this being confirmed using zymography by direct inhibition with anti-urokinase antibody. Assessment of the relationship between PA activity and biological behavior of gastric cancer revealed total-PA and u-PA levels to be significantly higher in differentiated than in undifferentiated tumors (p less than 0.001), and in aneuploid than in diploid ones (p less than 0.01). Immunohistochemical staining showed that the proportion of u-PA-positive cancer cells in the carcinoma tissues also correlated with activity as measured by the azocaseinolytic method. These findings suggest that the study of PA contents in gastric cancer, combined with a nuclear DNA ploidy and immunohistochemical analysis, might be useful for understanding the biological characteristics of the tumor.
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PMID:Plasminogen activators in human gastric cancers: correlation with DNA ploidy and immunohistochemical staining. 190 1

Tumor plasminogen activator (PA) has been alleged to play a role in the growth and metastasis of tumors. Before such a role can be realized, PA first must be released from tumor cells. Having determined intra- and extracellular PA and PA-inhibitor activities in an experimental pancreatic ascites tumor grown in hamsters, the release of PA from these cells was investigated. No PA activity was detected in the suspension medium of freshly isolated tumor cells; inclusion of plasminogen, fibrinogen, or collagen in the medium yielded similar negative results. On the other hand, PA activity was demonstrated to be released in a time-dependent manner from these tumor cells embedded in fibrin clots. Plasminogen activator activity also was not found in the suspension medium of frozen-thawed tumor cells, despite the fact that most of them had breaks on their cell membrane. Unlike freshly isolated tumor cells, PA was not released from frozen-thawed cells embedded in fibrin clots. Full PA activity was demonstrated in frozen-thawed cells treated with Triton X-100, however. Frozen-thawed cells exhibited signs of severe damage, and more than 80% of them failed to exclude trypan blue. Obviously PA is released from viable tumor cells embedded in fibrin clots but not suspended in artificial medium. The PA-release mechanism, not PA itself, is destroyed in cells rendered nonviable by freeze thawing.
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PMID:Importance of viability and attachment to an ascites tumor in the release of plasminogen activator. 190 26

Plasminogen activators, proteases associated with the fibrinolytic system, also play a major part in extravascular processes such as tissue remodelling, cell migration and activation of prohormones, growth factors and other proteases. It is likely that plasminogen activators participate in the pathophysiology of periodontal disease. Plasminogen activator has been identified in human gingival crevicular fluid in a concentration 100-fold greater than in plasma. The local activity of plasminogen activator in gingival tissues was examined and changes detected in its distribution in relation to the extent of disease. Frozen sections from human gingival biopsies were overlaid on fibrin-coated slides; tissue-type plasminogen activator activity was found in all samples. Focal activity was observed in healthy tissue, originating from the most superficial cells of the junctional epithelium. Biopsies of clinically healthy sites obtained 6 weeks after treatment for periodontitis also showed epithelial plasminogen activator activity localized to this area. In contrast, in diseased tissue the entire epithelium lining the periodontal pocket showed activity. This differential pattern of activity in health and disease is consistent with the hypothesis that plasminogen activator is a modulator of periodontal homeostasis.
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PMID:Plasminogen activator in human periodontal health and disease. 190 72

The heparin-binding p30 protein amphoterin is proposed to mediate adhesive interactions of the advancing plasma membrane in migrating and differentiating cells. Since the NH2-terminal part of amphoterin is exceptionally rich in lysine residues, we have studied its interactions with plasminogen and tissue plasminogen activator (t-PA). On immunostaining of N18 neuroblastoma cells, amphoterin and t-PA showed a close co-localization in the filopodia of the leading membrane and in the substrate-attached material. In purified systems, both t-PA and plasminogen bound to immobilized amphoterin, and their binding was inhibited by the lysine analogue epsilon-aminocaproic acid. Plasminogen bound to immobilized amphoterin was activated by t-PA, and this resulted in effective degradation of the immobilized amphoterin. Correspondingly, amphoterin-bound t-PA activated plasminogen. In solution amphoterin accelerated t-PA-catalyzed plasminogen activation maximally 46-fold. The results indicate that t-PA and plasminogen form through their lysine-binding sites a complex with amphoterin, which results in acceleration of plasminogen activation and effective degradation of amphoterin. We suggest that local acceleration of t-PA-catalyzed plasminogen activation by amphoterin at the leading membrane enhances the penetration of growing cytoplasmic processes through extracellular materials during cell migration, differentiation and regeneration. The amphoterin-mediated adhesion at the leading membrane may be transient in nature, because the protein also enhances its own breakdown by accelerating t-PA-catalyzed plasminogen activation.
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PMID:Interactions of plasminogen and tissue plasminogen activator (t-PA) with amphoterin. Enhancement of t-PA-catalyzed plasminogen activation by amphoterin. 190 31


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