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)

In the present studies we have compared the structural and biochemical properties of human protease nexin-I (PN-I) and a protease inhibitor present in the serum-free culture fluid of normal rat brain astrocytes. The inhibitor binds to and forms covalent complexes with human urokinase and thrombin. The inhibitor has an approximate Mr = 43,000 based on the size of the complexes (deduced from SDS-PAGE) and mediates the cellular binding and uptake of the proteases to which it links. Binding is heparin sensitive and occurs on a cell surface receptor that also binds complexes formed between proteases and a well-characterized cell-secreted protease inhibitor, human PN-I. In addition, the inhibitor co-migrates with PN-I on SDS-PAGE and cross-reacts with anti-PN-I antibody on immunoblots. A similar molecule, designated NPF, is produced by C6 glioma cells in culture and has neurite promoting activity on a neuroblastoma cell line.
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PMID:Identification of a protease inhibitor produced by astrocytes that is structurally and functionally homologous to human protease nexin-I. 304 Jan 75

Epidermal growth factor carrier protein (CP) is an arginine endopeptidase bound to epidermal growth factor (EGF) in vivo that processes pro-EGF to EGF and potentiates EGF action. Here, we provide a base for studying the biological functions of CP by showing that highly purified 125I-labeled CP, free of contaminating EGF, is specifically bound and internalized by normal human fibroblasts in serum-free medium. The characteristics of the binding reaction, however, were unusual and not consistent with direct interaction of CP with cell surface receptors. Subsequent experiments showed that cellular binding of 125I-labeled CP was mediated via a cell-secreted protein. We named the protein carrier protein nexin (CPN) because of its close functional similarity to protease nexin, which mediates cellular binding of thrombin or urokinase. Both CPN and protease nexin are secreted by cells, form covalent complexes with regulatory proteases in the extracellular environment, and mediate cellular binding of these proteases, apparently via a cell surface receptor for the nexin moiety of the complex. By several criteria, however, CPN and protease nexin are unique entities. This finding of a specific interaction of a growth factor carrier protein with cells suggests the possibility of additional physiological functions for these carriers in growth factor action or metabolism or both.
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PMID:Epidermal growth factor carrier protein binds to cells via a complex with released carried protein nexin. 698 Apr 18

The low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor (LRP) is a large cell surface receptor consisting of a 515-kDa heavy chain and an 85-kDa light chain proteolytically derived from a 600-kDa precursor. Previous work has shown that LRP is responsible for mediating the internalization of urinary-type plasminogen activator (uPA) complexed to plasminogen activator inhibitor type I (PAI-1) (Nykjaer et al., 1992; Herz et al., 1992). The current study indicates that pro-urokinase (pro-uPA) and two chain urokinase (tc-uPA) bind directly to purified LRP, and that LRP mediates their internalization and degradation in Hep G2 cells. In vitro binding assays demonstrated that pro-uPA and tc-uPA bind to purified LRP with affinities (Kd = 45 and 60 nM, respectively) that are approximately 15 to 20-fold weaker than the affinity of uPA.PAI-1 complex for LRP (Kd = 3 nM). Competitive binding experiments revealed that pro-uPA and tc-uPA completely inhibit binding of uPA.PAI-1 complexes to purified LRP. The binding of 125I-pro-uPA to LRP is blocked by the 39-kDa receptor-associated protein, but not by an amino-terminal fragment of uPA, which is known to block binding of uPA to the urokinase receptor. 125I-Pro-uPA can be internalized and degraded by Hep G2 cells independent of PAI-1. Both the internalization and degradation are completely blocked by receptor-associated protein or affinity-purified LRP antibodies, indicating that LRP is mediating this process. These processes are also blocked by the amino-terminal fragment, which suggests that the favored pathway for uPA metabolism is initial binding to the urokinase receptor, followed by ligand transfer to LRP, then internalization leading to degradation.
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PMID:Low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor mediates cellular uptake of pro-urokinase. 769 18

Proteolytic enzymes such as urokinase-type plasminogen activator (uPA), plasmin, and collagenase mediate proteolysis by a variety of tumor cells. uPA secreted by tumor cells can be bound to a cell surface receptor via a growth factor-like domain within the amino-terminal fragment (ATF) of the uPA molecule with high affinity. Urinary trypsin inhibitor (UTI) efficiently inhibits the soluble and the tumor cell-surface receptor-bound plasmin and subsequently reduces tumor cell invasion and the formation of metastasis. The anti-invasive effect is dependent on the anti-plasmin activity of the UTI molecule, domain II in particular. We synthesized a conjugate between ATF of human uPA and a native UTI molecule or domain II of UTI (HI-8). The effect of the conjugates (ATF.UTI or ATF.HI-8) on tumor cell invasion in vitro was investigated. ATF.UTI and ATF.HI-8 bound to U937 cells in a rapid, saturable, dose-dependent, and reversible manner. A large part of receptor-bound ATF-UTI and ATF.HI-8 remains on the cell surface for at least 5 h at 37 degrees C. Inhibition of tumor cell-surface receptor-bound plasmin by ATF.UTI and ATF.HI-8 was markedly enhanced when compared with tumor cells treated either with ATF, UTI, or HI-8. Results of a cell invasion assay showed that ATF.UTI and ATF.HI-8 is very effective at targeting HI-8 specifically to uPA receptor-expressing tumor cells, whereas tumor cells devoid of uPA receptor may be less affected by the conjugates. Our results indicate that cell surface uPA and plasmin activity is essential to the invasive process and that the conjugates exhibit plasmin inhibition to the close environment of the cell surface and subsequently inhibit the tumor cell invasion through Matrigel in an in vitro invasion assay.
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PMID:Inhibitory effect of a conjugate between human urokinase and urinary trypsin inhibitor on tumor cell invasion in vitro. 771 45

The urokinase plasminogen activator (uPA) is a proteolytic enzyme which converts the proenzyme plasminogen to the active serine protease plasmin. A cell surface receptor for uPA (uPAR) is attached to the cell membrane by a glycosyl-phosphatidylinositol anchor. Binding of uPA to uPAR leads to an enhanced plasmin formation and thereby an amplification of pericellular proteolysis. We have shown previously that uPAR is expressed on normal blood monocytes and granulocytes, but is deficient on affected blood monocytes and granulocytes in patients with paroxysmal nocturnal haemoglobinuria (PNH), and that uPAR is present in plasma from these patients. In this study a newly established sensitive enzyme-linked immunosorbent assay (ELISA) has been applied for quantitation of uPAR in plasma. Unexpectedly, we found that uPAR is not only present in PNH plasma but also in plasma from healthy individuals. In 39 healthy individuals the mean plasma-uPAR value +/- SD was 31 +/- 15 pM, median 28 (range 11-108), and the corresponding value for six PNH patients was 116 +/- 67 pM, median 90 (range 61-228). The elevated uPAR-level in PNH patients was highly significant (Mann-Whitney test; P < 0.0001), and may possibly contribute to the propensity for thrombosis in PNH by inhibition of the fibrinolytic system. Binding of pro-uPA by uPAR in plasma may interfere with the appropriate binding of pro-uPA to cell-bound uPAR and therefore inhibit cell-associated plasmin generation and fibrinolysis. It is likely that the uPAR in normal plasma reflects the overall level of activity of the uPAR-mediated cell surface proteolysis. The present ELISA may be used for studies of uPAR levels in plasma from patients with conditions in which this activity might be increased, such as cancer and inflammatory disorders. Future studies will determine if uPAR in plasma is a parameter of clinical importance in these diseases.
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PMID:The receptor for urokinase plasminogen activator is present in plasma from healthy donors and elevated in patients with paroxysmal nocturnal haemoglobinuria. 773 57

The plasminogen activation system consists of plasminogen activators and their inhibitors, serine proteases, and serpins. The proteases and inhibitors regulate a variety of processes in tissue morphogenesis, differentiation, cell migration, and cancer cell invasiveness and metastasis. One of the plasminogen activators, urokinase-type plasminogen activator (uPA), binds to a specific surface and provides a localized cell surface proteolytic activity required for the destruction of extracellular matrix, which is a vital step in tumor cell invasion. The proteolytic activity of uPA is modulated by its cell surface receptor, as well as by plasminogen activator inhibitor type-1 (PAI-1) and, to a lesser degree, by other inhibitors. The role of plasminogen activators and their inhibitors in cancer invasion can be demonstrated in the development and progression of malignant brain tumors. Our findings indicate that uPA and PAI-1 expression are dramatically upregulated in malignant brain tumors in parallel with the histological progression of the tumors. The results suggest that these molecules may contribute to tumor invasion in addition to their significant role in angiogenesis. An evaluation of the plasminogen activation system could add diagnostic and prognostic significance to the evaluation of individual patients.
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PMID:Activities, localizations, and roles of serine proteases and their inhibitors in human brain tumor progression. 774 66

The receptor for urokinase-type plasminogen activator (uPA-R) localizes uPA to the cell surface. The receptor-bound uPA converts plasminogen to the trypsin-like endopeptidase plasmin. Thus uPA is involved in the initiation of pericellular proteolysis. Pericellular proteolysis is assumed to facilitate the cellular infiltration into surrounding tissue. The uPA-R has recently been identified as a surface antigen of activated human T lymphocytes. We have characterized the uPA-R of the human CD4 T cell line Jurkat by immunological (flow cytometry), biochemical (ligand blotting), and physico-chemical (Scatchard blotting) methods. The collective data suggest that the human CD4+ T cell line Jurkat expresses a cell surface receptor for uPA similar to that of myelo/monocytes and normal T cells with regard to size, affinity, ligand specificity, and antigenicity. Binding studies using exogenous uPA and subsequent functional assays revealed that receptor-bound uPA retains its enzymatic activity. Saturation of the Jurkat cell uPA-R with exogenous uPA facilitated cellular invasion into fibrin matrices in vitro. uPA-dependent invasion was inhibited in the presence of an anti-catalytic monoclonal anti-uPA antibody. We propose that uPA-R-bound uPA may facilitate the invasiveness of uPA-R-positive T lymphocytes.
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PMID:Urokinase-type plasminogen activator enhances invasion of human T cells (Jurkat) into a fibrin matrix. 791 95

The enzyme urokinase-type plasminogen activator (uPA) plays a role in cancer invasion, and high levels of uPA in detergent extracts of mammary cancer tissue have been reported to be associated with a poor prognosis. We have explored the possibility of using mammary cancer cytosol extracts routinely prepared for steroid receptor analysis for retrospective prognostic studies of uPA. A sandwich enzyme-linked immunosorbent assay (ELISA) for uPA was developed, using polyclonal catching antibodies and a mixture of three biotinylated monoclonal detecting antibodies, that were selected to recognize free uPA, inhibitor-bound uPA, and uPA bound to its cell surface receptor. The assay detects active uPA and its inactive proenzyme form, pro-uPA, equally well. The limit of detection is approximately 1 pg of pro-uPA in a volume of 100 microliters, and there is a linear dose-response up to 100 pg pro-uPA. The efficiency in extracting uPA of a neutral non-detergent buffer used to prepare cytosol extracts was compared with that of 4 other buffers. There was a pronounced difference in the efficiency, the most efficient being a pH 4.2 buffer containing the non-ionic detergent Triton X-100, while the least efficient was the buffer used to prepare cytosols. Nevertheless, uPA immunoreactivity was readily measurable in the cytosols, and there was a close correlation between the amounts of uPA extracted under optimal conditions and those routinely used for steroid hormone receptor analysis.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Enzyme-linked immunosorbent assay of urokinase-type plasminogen activator (uPA) in cytosolic extracts of human breast cancer tissue. 801 52

Plasminogen activation is regulated by the interaction between urokinase-type plasminogen activator (uPA) and its specific glycolipid-anchored cell surface receptor (uPAR). uPAR is composed of three homologous domains and is the only multi-domain member of the Ly-6 family of glycolipid-anchored membrane proteins. Recent evidence has highlighted similarities between the individual domains of uPAR and the large family of secreted, single domain snake venom alpha-neurotoxins, suggesting that uPAR may adopt the same gross folding pattern as these structurally well characterized proteins. Structural aspects of the binding between alpha-neurotoxins and the acetylcholine receptor may have a major influence on future studies of the interaction between uPA and uPAR.
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PMID:Structure-function relationships in the receptor for urokinase-type plasminogen activator. Comparison to other members of the Ly-6 family and snake venom alpha-neurotoxins. 805 May 60

The plasminogen activator urokinase promotes tumor invasion by converting plasminogen into plasmin, which degrades several extracellular matrix components. Urokinase can bind to a specific cell surface receptor, which leads to accelerated plasmin production. While there is good evidence indicating a role for this binding site in tumor invasion/metastasis, there is little information concerning the regulation of urokinase receptor expression in invasive cancer. To address this question a series of colon cancer cell lines, which demonstrate either a high or low ability to invade an extracellular matrix-coated porous filter, was characterized for receptor expression at the transcriptional and post-transcriptional levels. The invasive cell lines possessed 10-fold more receptors than their non-invasive counterparts as shown by cross-linking experiments and by Western blotting. Northern blotting indicated that this disparity in receptor number could be largely accounted for by a different amount of steady-state mRNA encoding the binding site. However, neither gene amplification nor enhanced mRNA stability could account for the augmented receptor protein observed for the invasive colon cancer cell types. In contrast, nuclear run-on experiments with representative cell lines revealed that the 10-fold difference in receptor display between the invasive-competent and invasive-deficient cells could be largely accounted for by differences in transcription rates. Transcription of the u-PAR gene in the receptor-deficient GEO cells, but not in the receptor-rich RKO cells, could be augmented by protein kinase C stimulation. These findings provide a clear rationale for studies to determine if the urokinase receptor promoter in invasive colon cancer is activated in cis or in trans.
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PMID:Transcriptional activation of the urokinase receptor gene in invasive colon cancer. 807 48


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