Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.73 (urokinase-type plasminogen activator)
 10,685 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The capacity of purified tryptase from human lung mast cells to metabolize human fibrinogen, fibrin, and plasminogen was evaluated. Tryptase (5 micrograms/ml) inactivated the thrombin-induced clotting activity of fibrinogen (100 micrograms/ml) with essentially similar t 1/2 values of 4.6 min in the absence of heparin and 5.8 min in the presence of heparin (20 micrograms/ml) that were not appreciably different than with lysine-Sepharose-purified plasmin (5 micrograms/ml). Fibrinogen treated with tryptase together with heparin lost all detectable clotting activity by 4 hr at 37 degrees C, whereas fibrinogen treated with tryptase alone resulted in destruction of only 80% of fibrinogen clotting equivalents after 16 hr. Tryptase alone was observed to cleave only the alpha-chains of fibrinogen by electrophoresis of tryptase-treated, denatured, and reduced fibrinogen in polyacrylamide gradient gels. Tryptase together with heparin cleaved first the alpha-chain and then the beta-chain, the latter cleavage corresponding to complete loss of fibrinogen clotting activity by 4 hr. No fibrinogen fragments with anticoagulant activity were generated by tryptase. In contrast, plasmin left no residual clotting activity after 4 hr of incubation and generated fibrinogen fragments with anticoagulant activity. Plasmin sequentially cleaved the alpha, beta, and gamma subunits of fibrinogen. Tryptase alone (6 micrograms/ml) or together with heparin (20 micrograms/ml) failed to activate plasminogen (0.6 mg/ml) after a 60-min incubation at 37 degrees C. Addition of urokinase to tryptase-treated or untreated plasminogen resulted in essentially identical plasmin activities (0.32 and 0.34 U/ml, respectively), indicating that tryptase neither activates nor destroys plasminogen. Tryptase (700 ng) also failed to substantially solubilize cross-linked fibrin (2.6 micrograms) or the corresponding amount of fibrinogen bound to plastic microtiter plates with or without heparin. The failure to solubilize fibrinogen and, possibly, fibrin is consistent with the observation that the apparent m.w. by SDS polyacrylamide gel electrophoresis of unreduced fibrinogen is not appreciably altered by prior treatment with tryptase, even though cleavage of alpha-and beta-chains is revealed after reduction. Fibrinogenolysis by tryptase complements other mast cell mediators with anticoagulant properties such as heparin and suggests a significant prevention of coagulation by activated mast cells.
 ...
PMID:The fibrinogenolytic activity of purified tryptase from human lung mast cells. 316 48

Human fibrinogen is phosphorylated in vivo to an equal extent at two positions, one at Ser 3 located on fibrinopeptide A, the other at Ser 345 of the A alpha-chain. As has been shown previously, the degree of phosphorylation of the circulating fibrinogen pool can be determined in vitro from the ratio between the HPLC peaks formed by phosphorylated and non-phosphorylated fibrinopeptide A which has been cleaved from plasma fibrinogen by thrombin or reptilase. Plasma samples were obtained from patients with venous thrombosis undergoing fibrinolytic therapy with urokinase (n = 8). The degree of phosphorylation increased from about 35% before treatment to values between 50% and 70% within 48 hours. It remained at these high levels as long as urokinase was administered and declined slowly thereafter. This behaviour of the degree of phosphorylation of fibrinogen is explained by a model which assumes that fibrinogen is secreted in the phosphorylated form and then dephosphorylated in the circulation by an up to now unidentified phosphatase by first order kinetics. When this system is in steady state, the degree of phosphorylation is about 25% under normal conditions. If the elimination rate of fibrinogen is greatly enhanced by fibrinogenolysis the system will approach a new steady state with a higher degree of phosphorylation, the magnitude of which will depend on the new ratio of dephosphorylation and elimination.
 ...
PMID:Increase in the degree of phosphorylation of circulating fibrinogen under thrombolytic therapy with urokinase. 360 34

Hepatocyte growth factor/scatter factor (HGF/SF) is a heparin-binding polypeptide which shares structural domains with enzymes of the blood clotting cascade. HGF/SF is secreted by cells of mesodermal origin and has powerful mitogenic, motogenic and morphogenic activity on epithelial and endothelial cells. HGF/SF is produced as a biologically inactive single-chain precursor (pro-HGF/SF) most of which is sequestered on the cell surface or bound to the extracellular matrix. Maturation into the active alpha beta heterodimer results from proteolytic cleavage by a urokinase-type protease, which acts as a pro-HGF/SF convertase. The primary determinant for receptor binding appears to be located within the alpha-chain. The interaction of the alpha-chain with the receptor is sufficient for the activation of the signal cascade involved in the motility response. However, the complete HGF/SF protein seems to be required to elicit a mitogenic response. HGF/SF binds with high affinity to a transmembrane receptor, p190MET, encoded by the MET proto-oncogene. p190MET is the prototype of a distinct subfamily of heterodimeric tyrosine kinases, including the putative receptors Ron and Sea. The mature form of p190MET is a heterodimer of two disulfide-linked subunits (alpha and beta). The alpha-subunit is extracellular and heavily glycosylated. The beta-subunit consists of an extracellular portion involved in ligand binding, a membrane spanning segment, and a cytoplasmic tyrosine kinase domain. Both subunits derive from glycosylation and proteolytic cleavage of a common precursor of 170 kDa. In polarized epithelial cells the HGF/SF receptor is selectively exposed in the basolateral plasmalemma, where it is associated with detergent-insoluble components. Two Met isoforms, carrying an intact ligand binding domain but lacking the kinase domain due to truncation of the beta-subunit, arise from alternative post-transcriptional processing of the mature form. One truncated form is soluble and released from the cells. HGF/SF binding triggers tyrosine autophosphorylation of the receptor beta-subunit. Autophosphorylation on the major phosphorylation site Y1235 upregulates the kinase activity of the receptor, increasing the Vmax of the phosphotransfer reaction. Negative regulation of the kinase activity occurs through phosphorylation of a unique serine residue (S985) located in the juxtamembrane domain of the receptor. This phosphorylation is triggered by two distinct pathways involving either protein kinase C activation or increase in intracellular Ca2+ concentration. Upon ligand binding, the HGF/SF receptor recruits and activates several cytoplasmic effectors, including phosphatidylinositol 3-kinase (PI 3-K), phospholipase C-gamma (PLC-gamma), pp60c-Src, a tyrosine phosphatase, and a Ras-guanine nucleotide exchanger.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Identification of functional domains in the hepatocyte growth factor and its receptor by molecular engineering. 776 52

Adhesion and signaling by integrins require their dynamic association with nonintegrin membrane proteins. One such protein, the glycolipid-anchored urokinase receptor (uPAR), associates with and modifies the function of the beta(2)-integrin Mac-1 (CD11b/CD18). In this study, a critical non-I-domain binding site for uPAR on CD11b (M25; residues 424-440) is identified by homology with a phage display peptide known to bind uPAR. Recombinant soluble uPAR and cells expressing uPAR bound to immobilized M25, binding being promoted by urokinase and blocked by soluble M25, but not a scrambled control or homologous peptides from other beta(2)-associated alpha-chains. Mac-1, but not a mutated Mac-1 in which M25 was replaced with the homologous sequence of CD11c, co-precipitated with uPAR. In the beta-propeller model of alpha-chain folding, M25 spans an exposed loop on the ligand-binding, upper surface of alphaM, identifying uPAR as an atypical alphaM ligand. Although not blocking ligand binding to Mac-1, M25 (25-100 microM) inhibited leukocyte adhesion to fibrinogen, vitronectin, and cytokine-stimulated endothelial cells. M25 also blocked the association of uPAR with beta(1)-integrins and impaired beta(1)-integrin-dependent spreading and migration of human vascular smooth muscle cells on fibronectin and collagen. These observations indicate that uPAR associates with integrins directly and that disruption of this association broadly impairs integrin function, suggesting a novel strategy for regulation of integrins in the settings of inflammation and tumor progression.
 ...
PMID:Identification of a urokinase receptor-integrin interaction site. Promiscuous regulator of integrin function. 1074 8

Plasma hyaluronan biding protein (PHBP) is a novel serine protease, which has an amino acid sequence homology to that of hepatocyte growth factor activator (HGFA), and has a similar domain structure to that of urinary plasminogen activator (u-PA), found in human plasma. We searched the PHBP substrate in human plasma by measuring the digested protein bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results showed that fibrinogen and fibronectin were the major substrates of PHBP. PHBP cleaved the alpha-chain at multiple sites and the beta-chain between lysine53 and lysine54 but not the gamma-chain of fibrinogen. Therefore, PHBP did not initiate the formation of the fibrin clot and did not cause the fibrinolysis directly. PHBP did not cleave (activate) prothrombin and plasminogen, but it converted the inactive single chain urinary plasminogen activator to the active two chain form.
 ...
PMID:Identification of the substrates for plasma hyaluronan binding protein. 1121 80

A novel human plasma protein was found in the eluate from the dextran sulfate column, which was used for the treatment of the patients with hypercholesteremia to reduce plasma low density lipoprotein. The results of sequence analysis revealed that this protein was a homologue of heavy chains of inter-alpha-trypsin inhibitor (ITI) family, and it was termed IHRP (ITI family heavy chain related protein). IHRP was identified as an acute-phase protein in animals, and slightly increased concentrations in human plasmas were observed in the patients with inflammatory disorders. IHRP bound to actin and inhibited its polymerization, and IHRP suppressed the phagocytosis and chemotaxis of polymorphonuclear cells. These results suggest that IHRP may function as an anti-inflammatory protein. Plasma hyaluronan binding protein (PHBP) is a novel serine protease which was also found in human plasma. It is consisted of three epidermal growth factor domains, one kringle domain and one serine protease domain from its amino terminus. The amino acid sequence of PHBP is homologous to that of hepatocyte growth factor activator. Purified 75-kDa single chain pro-form of PHBP was auto-activated (auto-cleaved) to 50-kDa heavy chain and 25-kDa light chain, both of them are bridged by a disulfied bond. PHBP digested alpha-chain and beta-chain of fibrinogen to prevent coagulation and cleaved single chain urokinase type plasminogen activator (scuPA) to the active hetero dimer form (tcuPA). The auto-activation of PHBP was accelerated in the presence of dextran sulfate or phosphatidylethanolamine as well as factor XII of the coagulation system. C1 inhibitor of the complement system was identified as the main inhibitor of PHBP in human plasma. Partial hepatectomy and administration of carbon tetrachloride or galactosamine caused the conversion of pro-PHBP to the active form in mouse but administrations of turpentine and mercury chloride did not, suggesting the hepatic injury specific activation of PHBP. These results indicate that PHBP participates not only in the fibrinolytic system but also in the degradation cascade of extracellular matrix (ECM), i.e., PHBP activates scuPA to tcuPA, tcuPA activates matrix metalloproteases (MMPs) and activated MMPs degrade ECM for the tissue remodeling after hepatic injury.
 ...
PMID:Novel human plasma proteins, IHRP (acute phase protein) and PHBP (serine protease), which bind to glycosaminoglycans. 1532 Jul 89

Urokinase-type plasminogen activator receptors (uPARs), up-regulated during tumor progression, associate with beta1 integrins, localizing urokinase to sites of cell attachment. Binding of uPAR to the beta-propeller of alpha3beta1 empowers vitronectin adhesion by this integrin. How uPAR modifies other beta1 integrins remains unknown. Using recombinant proteins, we found uPAR directly binds alpha5beta1 and rather than blocking, renders fibronectin (Fn) binding by alpha5beta1 Arg-Gly-Asp (RGD) resistant. This resulted from RGD-independent binding of alpha5beta1-uPAR to Fn type III repeats 12-15 in addition to type III repeats 9-11 bound by alpha5beta1. Suppression of endogenous uPAR by small interfering RNA in tumor cells promoted weaker, RGD-sensitive Fn adhesion and altered overall alpha5beta1 conformation. A beta1 peptide (res 224NLDSPEGGF232) that models near the known alpha-chain uPAR-binding region, or a beta1-chain Ser227Ala point mutation, abrogated effects of uPAR on alpha5beta1. Direct binding and regulation of alpha5beta1 by uPAR implies a modified "bent" integrin conformation can function in an alternative activation state with this and possibly other cis-acting membrane ligands.
 ...
PMID:Regulation of alpha5beta1 integrin conformation and function by urokinase receptor binding. 1568 35