Ellis V, Behrendt N, Danø KPlasminogen activation by receptor-bound urokinase. A kinetic study with both cell-associated and isolated receptor. J Biol Chem 266:12752-12758

Finsen Laboratory, Rigshospitalet, Copenhagen, Denmark.
Journal of Biological Chemistry (Impact Factor: 4.57). 08/1991; 266(19):12752-8.
Source: PubMed


The specific cellular receptor for urokinase-type plasminogen activator (uPA) is found on a variety of cell types and has been postulated to play a central role in the mediation of pericellular proteolytic activity. We have studied the kinetics of plasminogen (Plg) activation catalyzed by uPA specifically bound to its receptor on the human monocytoid cell-line U937 and demonstrate this process to have properties differing widely from those observed for uPA in solution. The solution-phase reaction was characterized by a Km of 25 microM and for the cell-associated reaction this fell 40-fold to 0.67 microM, below the physiological Plg concentration of 2 microM. A concomitant 6-fold reduction in kcat resulted in an increase in the overall catalytic efficiency, kcat/Km, of 5.7-fold. This high affinity Plg activation was abolished in the presence of a Plg-binding antagonist. In contrast to intact cells, purified uPA receptor (isolated from phorbol 12-myristate 13-acetate-stimulated U937 cells) was observed to partially inhibit uPA-catalyzed Plg activation, although activity against low molecular weight substrates was retained. Therefore, the cellular binding of Plg appears to be of critical importance for the efficient activation of Plg by receptor-bound uPA. Plasmin generated in the cell-surface Plg activation system described here was also observed to be protected from its principal physiological inhibitor alpha-2-antiplasmin. Together, these data demonstrate that the cell surface constitutes the preferential site for Plg activation when uPA is bound to its specific cellular receptor, which therefore has the necessary characteristics to play an efficient role in the generation of pericellular proteolytic activity.

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    • "MMP-2 rather than MMP-9 was activated in the metastatic pancreatic cancer, and it is secreted as an inactive zymogen and requires distinct activation processes [46]. MMP-2 can be activated through plasminogen activator/plasmin system, in which pro-uPA binds to its receptor, uPAR [73], resulting in uPA activation, acceleration of the conversion of plasminogen to plasmin on the cell surface, and localization these enzymes to focal contact sites [46], [74]. Our data shows the effective down-regulation of uPAR and MMP-2 following the silencing of 5-HT1B and 5-HT1D receptors, supporting the notion of the distinct correlation between the expression of these receptors and the expression of uPAR/MMP-2. "
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    ABSTRACT: Pancreatic ductal adenocarcinoma is characterized by extensive local tumor invasion, metastasis and early systemic dissemination. The vast majority of pancreatic cancer (PaCa) patients already have metastatic complications at the time of diagnosis, and the death rate of this lethal type of cancer has increased over the past decades. Thus, efforts at identifying novel molecularly targeted therapies are priorities. Recent studies have suggested that serotonin (5-HT) contributes to the tumor growth in a variety of cancers including prostate, colon, bladder and liver cancer. However, there is lack of evidence about the impact of 5-HT receptors on promoting pancreatic cancer. Having considered the role of 5-HT-1 receptors, especially 5-HT1B and 5-HT1D subtypes in different types of malignancies, the aim of this study was to investigate the role of 5-HT1B and 5-HT1D receptors in PaCa growth and progression and analyze their potential as cytotoxic targets. We found that knockdown of 5-HT1B and 5-HT1D receptors expression, using specific small interfering RNA (siRNA), induced significant inhibition of proliferation and clonogenicity of PaCa cells. Also, it significantly suppressed PaCa cells invasion and reduced the activity of uPAR/MMP-2 signaling and Integrin/Src/Fak-mediated signaling, as integral tumor cell pathways associated with invasion, migration, adhesion, and proliferation. Moreover, targeting 5-HT1B and 5-HT1D receptors down-regulates zinc finger ZEB1 and Snail proteins, the hallmarks transcription factors regulating epithelial-mesenchymal transition (EMT), concomitantly with up-regulating of claudin-1 and E-Cadherin. In conclusion, our data suggests that 5-HT1B- and 5-HT1D-mediated signaling play an important role in the regulation of the proliferative and invasive phenotype of PaCa. It also highlights the therapeutic potential of targeting of 5-HT1B/1D receptors in the treatment of PaCa, and opens a new avenue for biomarkers identification, and valuable new therapeutic targets for managing pancreatic cancer.
    PLoS ONE 08/2014; 9(8):e105245. DOI:10.1371/journal.pone.0105245 · 3.23 Impact Factor
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    • "Upon activation, uPA converts plasminogen to plasmin. Plasmin activates several pro-forms of matrix metalloproteinases (MMPs), generating a cascade of proteinase activation at the cell surface [18,19]. This leads to degradation of the extracellular matrix and disruption of cell-cell and cell-matrix attachments. "
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    ABSTRACT: Diabetes-induced breakdown of the blood-retinal barrier (BRB) has been linked to hyperglycemia-induced expression of vascular endothelial growth factor (VEGF) and is likely mediated by an increase in oxidative stress. We have shown that VEGF increases permeability of retinal endothelial cells (REC) by inducing expression of urokinase plasminogen activator receptor (uPAR). The purpose of this study was to define the role of superoxide anion in VEGF/uPAR expression and BRB breakdown in diabetes. Studies were performed in streptozotocin diabetic rats and mice and high glucose (HG) treated REC. The superoxide dismutase (SOD) mimetic tempol blocked diabetes-induced permeability and uPAR expression in rats and the cell permeable SOD inhibited HG-induced expression of uPAR and VEGF in REC. Inhibiting VEGFR blocked HG-induced expression of VEGF and uPAR and GSK-3β phosphorylation in REC. HG caused β-catenin translocation from the plasma membrane into the cytosol and nucleus. Treatment with HG-conditioned media increased REC paracellular permeability that was blocked by anti-uPA or anti-uPAR antibodies. Moreover, deletion of uPAR blocked diabetes-induced BRB breakdown and activation of MMP-9 in mice. Together, these data indicate that diabetes-induced oxidative stress triggers BRB breakdown by a mechanism involving uPAR expression through VEGF-induced activation of the GSK3β/β-catenin signaling pathway.
    PLoS ONE 08/2013; 8(8):e71868. DOI:10.1371/journal.pone.0071868 · 3.23 Impact Factor
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    • "uPAR-bound uPA subsequently converts plasminogen to active plasmin that degrades ECM/basement membrane and releases active MMPs, thereby facilitating cancer cell invasion and metastasis 53, 54. Reciprocally, active plasmin can cleave and activate pro-uPA 55, exhibiting a positive feedback loop of uPA-plasmin cascade in cancer cells 56. Recently-solved crystal structure of uPA-uPAR complex reveals that uPAR recognizes an N-terminal growth-factor-like domain (GFD) of uPA where all three D domains of uPAR are packed closely and form a unique cone-shaped cavity at the center 10, 57. "
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