Chain Urokinase-type Plasminogen Activator Research Articles

A marine fibrinolytic compound FGFC1 stimulating enzymatic kinetic parameters of a reciprocal activation system based on a single chain urokinase-type plasminogen activator and plasminogen

Abstract A marine fibrinolytic compound FGFC1 enhancing fibrinolysis was obtained involving enzymatic kinetic parameters of a reciprocal activation system with a single chain urokinase type plasminogen activator and plasminogen. FGFC1, a kind of bisindole alkaloid from a metabolite of the rare marine fungi Starchbotrys longispora FG216, modulated enzymatic kinetic parameters including the fibrinolytic reaction rate and fibrin degradation characteristics. The enzymatic kinetics of fibrinolysis was described based on the enzymatic reaction of a chromogenic-substrate associated with p-nitroaniline (p-NA). While the single chain urokinase-type plasminogen activator (pro-uPA) activated plasminogen, kcat and kcat/Km increased significantly with an increase of FGFC1 concentration. Moreover, kcat and kcat/Km exhibited 26.5-fold and 22.8-fold enhanced activity at the concentration of 40 μg mL−1 of FGFC1, respectively. The results suggested that FGFC1 significantly improved the maximum catalytic efficiency and the total catalytic activity of fibrinolysis base on the reciprocal activation of pro-uPA and plasminogen. Km increased with increasing FGFC1 concentration, which indicated that FGFC1 slightly decreased the affinity activity of the pro-uPA and plasminogen versus the enzyme substrate. The marine bisindole alkaloid FGFC1 enhanced fibrinolysis, which was taken on enzymatic kinetic characteristics.

Antiphospholipid antibodies may impair factor XIIa–dependent activation of fibrinolysis in pregnancy: in vitro evidence with human endothelial cells in culture and monoclonal anticardiolipin antibodies

The purpose of this study was to analyze the in vitro activation of the contact complex with the use of human umbilical vein endothelial cells (HUVEC) in culture and monoclonal anticardiolipin antibodies (MaCL). Cultured HUVECs were incubated with pooled plasma from third-trimester pregnant women with the addition (20 mg/mL) of MaCL with anti-beta-2 glycoprotein I activity that was obtained from patients with antiphospholipid syndrome (APS), MaCL from an individual without APS, or from a control patient with immunoglobulin M without aCL activity. Supernatants were evaluated. Activated factors XII and VII, prothrombin-fragment 1 + 2, urokinase-type plasminogen activator (UPA), and differentiating 2 chain UPA were determined. In the cultured HUVEC supernatants, the addition of MaCL increased activated factor VII and prothrombin-fragment 1 + 2, did not modify UPA, and decreased activated factor XII and differentiating 2 chain UPA, in comparison with samples with control immunoglobulin M added. The MaCL without APS activity did not change any parameter that was evaluated. MaCL with anti-beta-2 activity that was obtained from patients with APS may interfere in the activation of the contact complex during pregnancy.

Factor VII-activating protease in patients with acute deep venous thrombosis

Factor VII-activating protease (FSAP) is involved in haemostasis and inflammation. FSAP cleaves single chain urokinase-type plasminogen activator (scu-PA). The 1601GA genotype of the 1601G/A polymorphism in the FSAP gene leads to the expression of a FSAP variant with reduced ability to activate scu-PA, without affecting the ability to activate coagulation Factor VII (FVII). Previous studies have investigated the association of the 1601GA genotype with incidence and progression of carotid stenosis and deep venous thrombosis (DVT). The present study is the first to evaluate the potential association between the FSAP phenotype and DVT. We studied the association between the 1601G/A polymorphism, FSAP activity, FSAP antigen, Factor VIIa (FVIIa), prothrombin fragment 1 + 2 (F1 + 2), and C-reactive protein (CRP) in plasmas of 170 patients suspected for DVT. FSAP genotypes were equally distributed in patients with ( n = 64) and without DVT ( n = 106), ( P = 0.94). The 1601GA genotype was associated with significant reduction of FSAP activity ( P < 0.001) and FSAP antigen levels ( P = 0.04). Patients with DVT showed significantly higher FSAP activity ( P = 0.008), FSAP antigen ( P = 0.003), and F1 + 2 levels ( P < 0.001) than patients without DVT. The association between the FSAP measures and DVT disappeared when adjusted for CRP levels. F1 + 2 correlated positively to FSAP antigen ( P = 0.01), while FVIIa-levels were comparable in patients with and without DVT. We conclude that even though FSAP measures are significantly increased in patients with acute DVT, alterations in the scu-PA activating properties of FSAP are presumably not markedly involved in the development of acute DVT, and that the association between FSAP and DVT disappears after adjustment for CRP.

Thrombin–thrombomodulin inhibits prourokinase-mediated pleural mesothelial cell-dependent fibrinolysis

Fibrin deposition is a hallmark of pleural inflammation and loculation but understanding of mechanisms by which mesothelial cells regulate intrapleural fibrinolysins remains incomplete. We speculated that pleural mesothelial cells regulate local fibrinolytic capacity via processing of single chain urokinase type plasminogen activator (scuPA). Pretreatment of human pleural mesothelial (MeT-5A) cells with TGF-β or thrombin, either alone or in combination, inhibited urokinase (uPA)-mediated fibrinolysis by MeT-5A. Thrombin, unlike TGF-β, inhibited fibrinolysis without induction of PAI-1, suggesting that thrombin-mediated cleavage of scuPA inhibits the fibrinolytic capacity of MeT-5A cells. Thrombin cleaves both purified scuPA as well as that secreted by MeT-5A cells and cell surface thrombomodulin accelerates thrombin-mediated cleavage of scuPA to inhibit cellular fibrinolytic activity. Molecular dynamics analyses demonstrated that thrombin-cleaved scuPA (uPAt) do not acquire a catalytically active conformation and that secondary plasminogen binding sites of uPA implicated in plasminogen activation are distorted in uPAt, explaining, at least in part, why uPAt is a poor enzyme. uPAt was detectable in transudative and exudative pleural effusions from patients. Intrapleural administration of scuPA generated increased levels of uPAt in PF of rabbits with pleural injury and loculation induced by tetracycline in vivo. This pathway is operative in diverse forms of pleural injury, restricts the urokinase-dependent fibrinolytic capacity of pleural mesothelial cells and contributes to local control of fibrinolytic activity via processing of endogenous or exogenous scuPA within the pleural compartment.

Novel human plasma proteins, IHRP (acute phase protein) and PHBP (serine protease), which bind to glycosaminoglycans.

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.

Characterization of hK4 (prostase), a prostate-specific serine protease: activation of the precursor of prostate specific antigen (pro-PSA) and single-chain urokinase-type plasminogen activator and degradation of prostatic acid phosphatase.

hK4 (prostase, KLK4), a recently cloned prostate-specific serine protease and a member of the tissue kallikrein family, is a zymogen composed of 228 amino acid residues including an amino-terminal propiece, Ser-Cys-Ser-Gln-. A chimeric form of hK4 (ch-hK4) was constructed in which the propiece of hK4 was replaced by that of prostate-specific antigen (PSA) to create an activation site susceptible to trypsin-type proteases. ch-hK4 was expressed in Escherichia coli, isolated from inclusion bodies, refolded, and purified with an overall yield of 25%. The zymogen was readily self-activated during the refolding process to generate an active form (21 kDa) of hK4 (rhK4). rhK4 cleaved the chromogenic substrates Val-Leu-Arg-pNA (S-2266), Pro-Phe-Arg-pNA (S-2302), Ile-Glu-Gly-Arg-pNA (S-2222), and Val-Leu-Lys-pNA (S-2251), indicating that rhK4 has a trypsin-type substrate specificity. The rhK4 was inhibited by aprotinin (6 kDa), forming an equimolar 27 kDa complex. rhK4 readily activated both the precursor of PSA (pro-PSA) and single chain urokinase-type plasminogen activator (scuPA, pro-uPA). rhK4 also completely degraded prostatic acid phosphatase but failed to cleave serum albumin, another protein purified from human seminal plasma. These results indicate that hK4 may have a role in the physiologic processing of seminal plasma proteins such as pro-PSA, as well as in the pathogenesis of prostate cancer through its activation of pro-uPA.

High-level expression and characterization of single chain urokinase-type plasminogen activator (scu-PA) produced in recombinant Chinese hamster ovary (CHO) cells

The high-level expression of a human single chain urokinase-type plasminogen activator (scu-PA) was achieved by employing a methotrexate (MTX)-dependent gene amplification system in Chinese hamster ovary (CHO) cells. By cotransfecting and coamplifying a scu-PA expression plasmid and dihydrofolate reductase (DHFR) minigene, several scu-PA expressing CHO cell lines were selected and gene-amplified. These recombinant cell lines, MGpUKs, recreted a completely processed scu-PA of 54kD and up to 60 mg/L was accumulated in the culture medium when they were adapted to an optimal MTX concentration. Over 95% of the scu-PA expressed was secreted in the culture medium and identified as having the proper function of a plasminogen activator when activated by plasmin. Based on a genomic Southern analysis, a representative subclone, MGpUK-5, exhibited MTX-dependent scu-PA gene amplification, plus the initial single-copy gene of scu-PA eventually turned into about 150 copies of the amplified gene of scu-PA after gradual adaptation to 2.0 μM of MTX. Meanwhile, the transcripts of the scu-PA gene increased, although-early saturation of transcription was identified at 0.1 μM of MTX. The scu-PA production by the MGpUK-5 subclone also increased relative to the gene amplification and increased transcripts, however, the relationship was not linearly proportional. Accordingly, since the MGpUK cell lines expressed elevated levels of enzymatically active scu-PA, these cell lines could be applied to the large-scale production of scu-PA.

New thrombolytic drugs.

Thrombolytic drugs reduce mortality from myocardial infarction and research is focused on newer drugs with improved clinical efficacy. The ideal thrombolytic drug should be effective in dissolving fresh and older thrombi, be rapid in its action with complete dissolution of the thrombus, be able to be given as a bolus and be safe without hypotensive or allergic or immunogenic reactions. The types of agents being developed fall into five broad categories: * mutants or variants of single chain urokinase type plasminogen activator; * mutants or variants of tissue type plasminogen activator; * recombinant chimaeric plasminogen activators; * conjugates of plasminogen activators and anti-fibrin monoclonal antibodies; * compounds derived from haemophagous animals. Within the mutant and variant groups there may be single point mutations which increase the half life or deletion of various amino acid sequences to increase resistance to plasma protease inhibitors or cause more selective binding to fibrin. The recombinant chimaeric plasminogen activators are designer drugs where the kringle regions, the growth hormone domain region, the finger domain region and the serine protease part of the molecules are all cleaved and recombined in various ways to improve potency. The conjugates of plasminogen activators and anti-fibrin and monoclonal antibodies improve the targeting of the agent to fibrin clot. Monoclonal antibodies are commonly used against the seven aminoterminal residues of the beta chain of fibrin. These are cross linked and bound to plasminogen activators. A variety of substances from haemophageous animals are currently being studied including salivary plasminogen activator from vampire bats, venom from southern copperhead snakes and staphylokinase from bacteria. Currently available thrombolytic agents have many limitations, but the novel thrombolytic agents have yet to be tested in clinical trials. With few exceptions, they all act via the plasminogen system and it may be in the future that combinations of anti-platelet and thrombolytic agents may prove to be more efficacious than thrombolytics and aspirin alone.

Pharmacology and clinical trial results of saruplase (scuPA) in acute myocardial infarction

Saruplase is the non-glycosylated form of single chain urokinase-type plasminogen activator; it is produced by recombinant technique in Escherichia coli. Saruplase has plasminogen activating properties; it can also be cleaved to the potent plasminogen activator, double chain urokinase, resulting in the generation of plasmin. By means of a positive feedback mechanism, plasmin itself is able to cleave saruplase. At present, a bolus of 20 mg followed by an infusion of 60 mg over 1 h and preceded by a heparin bolus of 5000 U, represents the standard saruplase regimen. The PRIMI trial showed that this standard saruplase regimen achieves higher early patency rates than streptokinase. In the COMPASS trial, saruplase has been shown to be at least as effective as streptokinase, in terms of 30 day mortality. A comparative trial with urokinase (SUTAMI) resulted in similar late coronary patency. Saruplase has been tested against alteplase (100 mg over 180 min) in the SESAM trial. The early coronary patency and safety of both regimens were comparable. In a recent study, three bolus applications of saruplase have been investigated. A double bolus of 40 mg each given 30 min apart, is suggested to be more effective than standard saruplase, but concerns about safety remain. Further studies are required to assess safety of the double bolus regimen, and to compare saruplase with the gold-standard of frontloaded alteplase, or the equivalent double bolus reteplase regimen.

High level expression of a mutant (K151E, R154G) of single chain urokinase-type plasminogen activator in silkworm

A cDNA of a mutant (K151E, R154G) of single chain urokinase-type plasminogen activator (mscu-PA) was constructed to include the natural scu-PA signal peptide sequences and transferred into the genome of Bombyx mori nuclear polyhedrosis virus (BmNPV) by transfer vectors pBE284 (derived from BmNPV) and pVL1392 (from AcNPV), respectively. Both Bombyx mori (BmN) cells and silkworm larvae were infected with the two recombinant viruses. Fibrin-plate assay showed that the re-virus from pVL1392 increased the yield of mscu-PA three times compared with the re-virus from pBE284.

Native Atherosclerosis and Vein Graft Arterialization: Association with Increased Urokinase Receptor Expression In Vitro and In Vivo

Interaction of proteases with cell surface receptors may modulate cell adhesion, migration, invasion, and matrix degradation. Since the plasminogen activator system has been hypothesized to play a role in intimal thickening after various types of vascular injury, we first studied the expression of urokinase receptor (u-PAR) protein and mRNA by smooth muscle cells (SMC) grown in explant cultures from normal and diseased vessels. Using equilibrium binding studies with radiolabeled 125I-labeled single chain urokinase-type plasminogen activator (scu-PA), we determined that SMC cultured from atherosclerotic arteries expressed a higher maximal number of binding sites/cell (3.6 +/- 0.4 x 10(5) sites/cell vs. 2.1 +/- 0.3 x 10(5), +/- SEM, p < 0.05) with a similar affinity (Kd = 1.5 +/- 0.1 vs. 1.2 +/- 0.2 nM, p = ns). However, SMC subcultured from diseased saphenous vein grafts expressed the highest levels of u-PAR compared to SMC from normal saphenous vein (4.8 +/- 0.6 x 10(5) sites/cell vs. 1.6 +/- 0.9 x 10(5), +/- SEM, p < 0.05). Using binding studies and Northern analysis, we demonstrated a dose and time dependent upregulation of u-PAR protein and mRNA expression respectively in human SMC in response to serum stimulation. Using a rabbit specific u-PAR cDNA probe, we demonstrated a similar upregulation of u-PAR mRNA both in rabbit aortic SMC in culture in response to serum stimulation and up to a 20 fold increase in u-PAR mRNA in rabbit jugular veins in response to implantation as arterial grafts in vivo. Finally, to confirm that u-PAR mRNA is upregulated in human vessels after injury, we performed immunohistochemistry and in situ hybridization studies on coronary arteries, normal saphenous veins and saphenous veins from 10 weeks to 13 years after implantation as grafts. u-PAR mRNA was found mainly in the periadventitial microcirculation in normal veins, but was found to be upregulated in the neointima and media of thickened veins in both macrophages and smooth muscle cells. SMC near the internal elastic laminae in diseased coronary arteries appeared to express increased u-PAR mRNA. These data suggest that this increased expression of u-PAR may contribute to early lesion development.

Characterization of the Precursor of Prostate-specific Antigen: ACTIVATION BY TRYPSIN AND BY HUMAN GLANDULAR KALLIKREIN

The precursor or zymogen form of prostate-specific antigen (pro-PSA) is composed of 244 amino acid residues including an amino-terminal propiece of 7 amino acids. Recombinant pro-PSA was expressed in Escherichia coli, isolated from inclusion bodies, refolded, and purified. The zymogen was readily activated by trypsin at a weight ratio of 50:1 to generate PSA, a serine protease that cleaves the chromogenic chymotrypsin substrate 3-carbomethoxypropionyl-L-arginyl-L-prolyl-L-tyrosine-p-nitroanili ne- HCl (S-2586). In this activation, the amino-terminal propiece Ala-Pro-Leu-Ile-Leu-Ser-Arg was released by cleavage at the Arg-Ile peptide bond. The recombinant pro-PSA was also activated by recombinant human glandular kallikrein, another prostate-specific serine protease, as well as by a partially purified protease(s) from seminal plasma. The recombinant PSA was inhibited by alpha1-antichymotrypsin, forming an equimolar complex with a molecular mass of approximately 100 kDa. The recombinant PSA failed to activate single chain urokinase-type plasminogen activator, in contrast to the recombinant hK2, which readily activated single chain urokinase-type plasminogen activator. These results indicate that pro-PSA is converted to an active serine protease by minor proteolysis analogous to the activation of many of the proteases present in blood, pancreas, and other tissues. Furthermore, PSA is probably generated by a cascade system involving a series of precursor proteins. These proteins may interact in a stepwise manner similar to the generation of plasmin during fibrinolysis or thrombin during blood coagulation.

A urokinase mutant with high fibrin-selectivity

BECAUSE of lacking fibrin selectivity two chain urokinase-type plasminogen activator(tcu-PA),which has been used as the clinical thrombolytic agent,may lead to bleeding by a remarkabledepletion of fibrinogen in plasma when injected in large doses,thus its clinical application islimited.Single chain urokinase-type plasminogen activator(scu-PA)is the precursor of tcu-

Effect of Changes in Liver Blood Flow on the Pharmacokinetics of Saruplase in Patients with Acute Myocardial Infarction

The recombinant unglycosylated single chain urokinase-type plasminogen activator saruplase is cleared for a large part by the liver. A large interindividual variation in saruplase concentration is found in acute myocardial infarction (AMI) patients. The variable cardiac performance after an infarct may induce differences in liver blood flow that could explain the concentration diversity. This study was performed to investigate the relation between hepatic blood flow and the pharmacokinetic and pharmacodynamic properties of saruplase. Thirteen AMI patients were enrolled in this open label study. Patients received a bolus injection of 20 mg saruplase followed by a one-hour infusion of 60 mg saruplase. Concurrently 36 mg intravenous indocyanine green (ICG) was given over 1 h to measure hepatic blood flow. Blood samples were taken at regular time intervals to measure plasma levels of urokinase-type plasminogen activator (u-PA) antigen and activity, the two-chain form (tcu-PA) activity, indocyanine green, fibrinogen, fibrin and fibrin degradation products, alpha2-antiplasmin and thrombin antithrombin III complex. A correlation was seen between the clearance of ICG and both those of u-PA antigen (r = 0.62; p <0.05) and u-PA activity (r = 0.57; p <0.05). A negative correlation was seen between the area under the curve of tcu-PA activity and the areas under the effect curves of both fibrinogen and alpha2-antiplasmin (r = -0.84; p <0.01 and r = -0.65; p <0.05). Liver blood flow is an important determinant of the clearance of u-PA antigen and activity and reduction of flow in patients with heart failure will lead to an increase in plasma concentrations. High plasma concentrations of tcu-PA activity lead to increased systemic fibrinogenolysis. These results may be used to optimize saruplase treatment in patients with impaired cardiac function or after co-medication with drugs that affect liver blood flow.

15 Role of the low density lipoprotein receptorrelated protein (LRP) in the clearance and liver uptake of recombinant single chain urokinase-type plasminogen activator (rscu-PA) in rats

Urokinase-type plasminogen activator (u-PA) is used as a thrombolytic agent in the treatment of acute myocardial infarction. In vitro, E.coli produced rscu-PA is recognized by LRP on parenchyma! liver cells. In this study we investigated the role of LRP in the liver uptake and plasma clearance of rscu-PA. A preinjection of the LRP inhibitor GSTRAP reduced the maximal liver uptake of IMl-rscu-PA from 50 to 30 % of the injected dose and decreased the clearance from 2.37 ml/min to 1.58 ml/min. Parenchymal, Kupffer and endothelial cells were responsible for 40, 50 and 10 % of the liver uptake, respectively. The 40 % reduction in liver uptake of rscu-PA by preinjection of GST-RAP was caused by a 91 % and 62 % reduction in the uptake by the parenchymal and Kupffer cells, respectively. Deletion of residue 11 -135 from rscu-PA (=delta125-rscu-PA) resulted in a 80 % reduction in liver uptake and a 2.4 times slower clearance (0.97 ml/min). The parenchymal, Kupffer and endothelial cells were responsible for the uptake of 60.2, 32.9 and 7.0 % of 125l-delta125-rscu-PA in the liver. Preinjection of GST-RAP completely reduced the liver uptake and reduced the clearance to 0.79 ml/min. Treatment of Kupffer cells with pl-PLC reduced the binding of rscu-PA by 40 %, indicating the involvement of u-PAR in the recognition of rscu-PA by the Kupffer cells. Our results demonstrate that in vivo LRP is responsible for the parenchymal liver cell mediated uptake of rscu-PA and for 60 % of the Kupffer cell interaction. It is also shown that u-PAR is involved in the Kupffer cell recognition of rscu-PA.

92 Single chain urokinase-type plasminogen activator bound to its receptor is relatively resistant to plasminogen activator inhibitor type 1

Urokinase-type plasminogen activator (uPA) is synthesized as single-chain protein (scuPA) with little intrinsic activity. scuPA is activated when it is converted to two-chain urokinase (tcuPA) by plasmin or when it binds as a single-chain molecule to its cellular receptor (uPAR). Previous data indicate that complexes between scuPA and its receptor have somewhat higher affinity for plasminogen than does tcuPA. The current study indicates that plasminogen activator activity of scuPA bound to recombinant, soluble uPAR (suPAR) is also fivefold less sensitive to inhibition by plasminogen activator type 1 (PAI-1) than is soluble or receptor-bound tcuPA. Binding of PaI-1 to suPAR/scuPA complexes is totally reversible and can be overcome by increasing the concentration of plasminogen, suggesting a competitive mechanism of inhibition (Ki = 18 nmol/L). Binding of scuPA to suPAR also retards its cleavage by plasmin. These results indicates that binding of single-chain urokinase to its receptor promotes its activity, retards its inhibition, and protects it from conversion to a two-chain form of the enzyme, a step that may precede its inactivation and clearance from cell surfaces. These results are consistent with a physiologic role for receptor-bound single-chain urokinase as a cellular plasminogen activator.

Characterization of single chain urokinase-type plasminogen activator with a novel amino-acid substitution in the kringle structure

ECV304 is a cell line established by a spontaneous transformation of endothelial cells of a human umbilical vein. It was shown that ECV304 secretes single chain urokinase-type plasminogen activator (scu-PA). A subclone, ECV304 clone 15, was obtained by acclimatization of the parental clone to serum-free medium followed by limiting dilution. The clone was found to produce approximately five times as much scu-PA (≈ 20 IU/10 6 cells per day) as the parental clone after a 40 days' culture. Though the biochemical characteristics of the purified scu-PA were indistinguishable from those of the native scu-PA, it had a lower affinity for fibrin clots under the employed conditions. Molecular cloning of a cDNA encoding the scu-PA has identified a novel substitution from C to T in the nucleotide sequence encoding the kringle structure. The substitution resulted in an alteration from Pro (CCG) to Len (CTG) at amino-acid position 121, which may be directly or indirectly involved in the decrease in the apparent affinity.

Epidermal growth factor-binding protein activates soluble and receptor-bound single chain urokinase-type plasminogen activator

Epidermal growth factor-binding protein (EGF-BP) is a serine proteinase that reversibly associates with epidermal growth factor (EGF). We analyzed the reaction of EGF-BP with urokinase type plasminogen activator (u-PA), a serine proteinase that promotes pericellular proteolysis and cellular migration. EGF-BP cleaved single chain u-PA (scu-PA) between Lys 158 and Ile 159, converting the zymogen into enzymatically active two-chain u-PA (tcu-PA), as shown by SDS-PAGE, N-terminal sequence analysis, and enzymatic assay. The k cat and K m of the activation reaction were (5.6 ± 0.6) × 10 −2 s −1 and 2,0 ± 0.3 μM, yielding a catalytic efficiency of 2.8 × 10 4 M −1. EGF-BP also activated scu-PA bound to receptors on U937 monocytes as demonstrated by the generation of amidase activity against a tcu-PA-specific fluorogenic substrate. By activating scu-PA, EGF-BP may initiate u-PA-dependent cell surface proteolysis and therefore enhance EGF activities that require cellular migration and/or tissue remodeling.

Increase of a urokinase receptor-related low-molecular-weight molecule in colorectal adenocarcinomas.

Proteolytic activity is important for tumor growth and metastasis. Plasminogen and urokinase-type plasminogen activator (u-PA) constitute one of the most extensively studied proteolytic systems believed to participate in these processes. u-PA cleaves plasminogen to plasmin, which in turn degrades surrounding extracellular matrix and allows tumor cells to migrate to other areas. The specific receptor for u-PA (u-PAR) has also been implicated as an essential modulator in this pathway. Eleven paired samples of colorectal cancers and normal mucosal tissues from the same patients were removed at surgery. The tissues were homogenized and the supernatants assayed for u-PAR immunoreactivity, u-PAR antigen concentration, u-PAR binding activity and u-PA activity. Immunoblot analysis showed that a major u-PAR species of approximately 55 kDa was present in all tissues. In addition, a protein band of approximately 41 kDa, which crossreacted with anti-u-PAR antibodies, was also found in the tumors. This protein band was either absent, or present in relatively small amounts in the normal colorectal tissues. Cross-linking experiments showed that the approximately 55 kDa band only, and not the approximately 41 kDa band, was able to bind either single chain urokinase-type plasminogen activator (scu-PA) or the amino terminal fragment of urokinase (ATF). The tumor samples also exhibited highly elevated u-PA activity and u-PAR antigen relative to the corresponding normal tissues. Elevated u-PA activity appeared to correlate with elevated u-PAR antigen in colorectal cancers, but not in the normal tissues. These increases were also associated with increase of the u-PAR-related, low-molecular-weight protein in the tumor samples. The measurement of u-PAR and the u-PAR-related protein, in addition to u-PA activity, could have diagnostic or prognostic value in this type of cancer.

Inactivation of the Intrinsic Activity of Pro-urokinase by Diisopropyl Fluorophosphate Is Reversible

Single chain urokinase-type plasminogen activator or pro-urokinase (pro-UK) has been reported to have a significant intrinsic amidolytic and plasminogen activator activity, estimated to be about 0.2-0.6% that of two-chain urokinase (UK). However, it has also been suggested that this reported activity is related entirely to trace UK contaminants generated during the analytic procedures. In an attempt to resolve this controversy, it was decided to measure the incorporation of diisopropyl fluorophosphate (DFP) by pro-UK and UK. Surprisingly, it was found that although > 98% of the apparent intrinsic activity of pro-UK was inhibited by 5 mM DFP, > 97% of this activity was recoverable after exhaustive dialysis of the preparation. This finding could not be explained by UK generation, which was excluded. Instead, the findings indicated that DFP inhibition of pro-UK, in contrast to UK and other serine proteases, was largely reversible. The reaction rate of the reversible inhibition was significantly slower than that of irreversible inhibition by DFP. When the hydrolysis of DFP (2 mM) during incubation (37 degrees C) with or without pro-UK (20 microM) was compared, a > 5-fold acceleration of DFP hydrolysis in the presence of pro-UK was found, whereas little loss of DFP occurred in the presence of UK (20 microM), consistent with 1:1 stoichiometry. This suggested that pro-UK acted as a slow DFPase in the reaction, a finding consistent with a reversible DFP-enzyme reaction. It was concluded that pro-UK has a distinct and measurable intrinsic catalytic activity, which is qualitatively unique and thereby distinguishable from that of UK as well as other serine proteases.