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Query: EC:3.4.21.73 (urokinase-type plasminogen activator)
 10,685 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Urokinase-type plasminogen activator (uPA), which binds to cells via a specific receptor (uPAR), participates in pericellular proteolysis during leukocyte migration. Previous studies have indicated that uPAR is physically associated with CR3 (CD11b/CD18). To test the functional interactions of CR3 and uPAR, we have examined the ability of uPA to elicit changes in cytosolic calcium levels of normal neutrophils, neutrophils from a leukocyte adhesion deficiency (LAD) patient, and 3T3 transfectants expressing CR3, uPAR, or both. We found that calcium levels of neutrophils increased from 106 +/- 6 nM in untreated cells to 199 +/- 25 nM in the presence of uPA. In contrast, no significant change in calcium was observed when neutrophils from an leukocyte adhesion deficiency patient were examined. The uPA-dependent calcium rise was inhibited by mAb directed against either CR3 or uPAR and required intact uPA. To substantiate further these findings, we prepared transfectants expressing genes encoding uPAR, CR3, and both receptors; only cells expressing both receptors experienced a rise in intracellular calcium. Although uPA's calcium signal is insufficient to trigger superoxide production, FMLP dose-dependent superoxide production was greatly enhanced by incubating neutrophils with intact, but not fragmented, uPA. Flow cytometry experiments utilizing an FMLP analogue exclude the possibilities that urokinase binds to the FMLP receptor or up-regulates its expression. We suggest that calcium is a second messenger of uPA, that this message is mediated in a CR3-dependent fashion, and that this signal primes neutrophils for superoxide production.
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PMID:Human urokinase-type plasminogen activator primes neutrophils for superoxide anion release. Possible roles of complement receptor type 3 and calcium. 783 67

13-trans retinoic acid (13-trans RA) is an effective inducer of differentiation of acute promyelocytic (APL) cells both in vivo and in vitro. It is used in the induction of remission of patients with APL. We found, by using the promyelocytic NB4 cell line established from a patient with APL, that the induction of differentiation with RA was accompanied by modulation of the plasminogen activation system. The expression of urokinase (uPA) activity was rapidly increased in the growth medium and at the surface of cells treated with RA. The high uPA activity was counteracted both in the growth medium and at the cell surface by an increased plasminogen activator inhibitor (PAI) production and reduction of uPA synthesis. The expression of uPA receptor and PAI-2 were stimulated and persisted at 48 hours from RA addition. The simultaneous induction of CD11b suggests that differentiation results in increased production of both. APL patients often encounter episodes of disseminated intravascular coagulation that are associated with secondary fibrinolytic events. Our results suggest that downregulation of uPA activity results in the decrease of plasmin on the surface of the differentiated cells, which may reduce the occurrence of fibrinolytic episodes of patients with APL.
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PMID:Induction of differentiation of promyelocytic NB4 cells by retinoic acid is associated with rapid increase in urokinase activity subsequently downregulated by production of inhibitors. 814 55

Urokinase (uPA) is hypothesized to provide proteolytic activity enabling inflammatory cells to traverse tissues during recruitment, and it is implicated as a cytokine modulator. Definitive evaluation of these hypotheses in vivo has previously been impossible because uPA could not completely and irreversibly be eliminated. This limitation has been overcome through the development of uPA-deficient transgenic mice (uPA-/-). Using these mice, we evaluated the importance of uPA in the pulmonary inflammatory response to Cryptococcus neoformans (strain 52D). C. neoformans was inoculated into uPA-/- and control mice (uPA+/+), and cell recruitment to the lungs was quantitated. The number of CFU in lung, spleen and brain was determined to assess clearance, and survival curves were generated. By day 21 after inoculation, uPA-/- mice had markedly fewer pulmonary inflammatory (CD45+), CD4+, and CD11b/CD18+ cells compared with uPA+/+ controls (P<0.0007); pulmonary CFUs in the uPA-/- mice continued to increase, whereas CFUs diminished in uPA+/+ mice(P<0.005). In survival studies, only 3/19 uPA+/+ mice died, whereas 15/19 uPA-/- mice died (p<0.001). We have demonstrated that uPA is required for a pulmonary inflammatory response to C. neoformans. Lack of uPA results in inadequate cellular recruitment, uncontrolled infection, and death.
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PMID:Urokinase is required for the pulmonary inflammatory response to Cryptococcus neoformans. A murine transgenic model. 862 64

Urokinase receptors (uPAR; CD87) from complexes with complement receptor 3 (CR3) (CD11b/CD18), a beta2 integrin. In this study, we sought to determine if this association modulates the adhesive function of CR3. Both CR3 and uPAR concentrate at the ventral surface of fibrinogen-adherent human monocytes, and CR3-uPAR coupling increases substantially upon adhesion to fibrinogen. Pretreatment with anti-uPAR monoclonal antibody reduced adhesion to CR3 counterligands (fibrinogen and keyhole limpet hemocyanin) by 50%, but did not affect adhesion to fibronectin, a beta1 integrin counterligand. Antisense (AS) oligonucleotides were used to determine if selectively suppressing uPAR expression also modulates CR3 adhesive function. AS-uPAR oligo reduced CR3-dependent adhesion by 43+/-9% (P<0.01), but did not affect CR3-independent adhesion. To determine if the effects of uPAR are mediated through its ligand, monocytes were pre-treated with AS oligo to block uPA expression. Unlike the effects of blocking uPAR expression, AS-uPA oligo increased adhesion by 46% (P<0.005), and exogenous intact uPA, but not uPA fragments, reversed this effect. We conclude that complex formation with uPAR facilitates the adhesive functions of CR3. This function of uPAR is not dependent upon its occupancy with uPA, which negatively influences adhesion.
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PMID:The urokinase receptor (CD87) facilitates CD11b/CD18-mediated adhesion of human monocytes. 862 79

Stimulation of monoblastic U937 cells with transforming growth factor beta 1 and 1,25-(OH)2 vitamin D3 (TGF-beta 1/D3) upregulates urokinase receptor (uPAR) and confers urokinase-dependent adhesiveness to the cells for serum- or vitronectin-coated surfaces. Recent studies show that uPAR itself is a high-affinity adhesion receptor for vitronectin and that urokinase (uPA) is an activator of this adhesive function. In the course of exploring possible G-protein involvement in this adhesion it was observed that TGF-beta 1/D3-primed U937 cells became adhesive to vitronectin in an uPAR-dependent manner when exposed to pertussis toxin (PTX). The adherent response is concentration- and time-dependent, and was not due to the ADP-ribosyltransferase activity of the toxin because the purified B-subunit of PTX was equally effective. Although promoting adhesion to serum- or vitronectin-coated surfaces, PTX blocked spontaneous cell adhesion to fibrinogen, an endogenous ligand for the Mac-1 receptor (CD11b/CD18). Flow cytometry study showed that expression of the alpha-subunit of Mac-1 (CD11b) on primed cells was increased by nearly threefold. Monoclonal antibody to CD11b abolished the PTX-induced cell adhesion and the binding of the primed cells to PTX-coated plates. Activation of Mac-1 receptor by its endogenous ligand fibrinogen induced cell adherent response similar to PTX. PTX, but not uPA, triggered a rapid rise in [Ca2+]i in primed U937 cells, and PTX-induced adhesion was significantly attenuated by 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid/acetoxy-methyl ester (BAPTA/AM), a selective membrane-permeant [Ca2+]i chelator. PTX-induced cell adhesion was also prevented by antibodies to uPAR and by conditioned medium containing soluble uPAR. Together these data indicate that PTX B-subunit may bind to Mac-1 integrin, which leads to a rapid rise in [Ca2+]i and subsequent activation of uPAR for adherence to vitronectin, suggesting a functional link between Mac-1 and activation of uPAR important to cellular trafficking and host defence in response to Bordetella pertussis infection.
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PMID:Mechanisms of pertussis toxin-induced myelomonocytic cell adhesion: role of Mac-1(CD11b/CD18) and urokinase receptor (CD87). 870 56

The leukocyte integrin Mac-1 (CD11b/CD18) and the urokinase receptor (uPAR, CD87) mediate complementary functions in myelomonocytic cells. Both receptors promote degradation of fibrin(ogen) and also confer adhesive properties on cells because Mac-1 and uPAR bind fibrin and vitronectin, respectively. Staining of lung biopsy specimens from patients with acute lung injury indicated that fibrin and vitronectin colocalize at exudative sites in which macrophages bearing these receptors accumulate. Because of the parallel roles and physical proximity of Mac-1 and uPAR, the capacity of these receptors to functionally interact was explored. Induction of Mac-1 and uPAR expression on monocytic cell lines by transforming growth factor- beta 1 and 1.25-(OH)2 vitamin D3 conferred urokinase and uPAR-dependent adhesion to vitronectin, which was further promoted by engagement of Mac-1. Vitronectin attachment promoted subsequent Mac-1-mediated fibrinogen degradation threefold to fourfold. In contrast, enhancement of uPAR occupancy by exogenous urokinase or receptor binding fragments thereof inhibited Mac-1 function. Addition of urokinase progressively inhibited Mac-1-mediated fibrinogen binding and degradation (maximal inhibition, 91% +/- 14% and 72% +/- 15%, respectively). Saturation of uPAR with urokinase also inhibited binding of the procoagulant Mac-1 ligand, Factor X. These inhibitory effects of uPAR were reproduced in fresh monocytes, cultured monocytic cells, and in Chinese hamster ovary (CHO) cells transfected with both human Mac-1 and human uPAR. These data show that the procoagulant and fibrinolytic potential of monocytic cells is co-ordinately regulated by ligand binding to both Mac-1 and uPAR and identify uPAR as a regulator of integrin function. Vitronectin-enhanced fibrin(ogen) turnover by Mac-1 may operate as a salvage pathway in the setting of urokinase and plasmin inhibitors to promote clearance of the provisional matrix and subsequent healing.
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PMID:Mac-1 (CD11b/CD18) and the urokinase receptor (CD87) form a functional unit on monocytic cells. 887 19

Urokinase (uPA) and its receptor (uPAR) have been proposed to be involved in monocyte migration by inducing degradation of matrix proteins. In addition, uPAR is also implicated in cell adhesion to the vascular wall. The adhesive function of uPAR depends on a direct interaction with vitronectin which is increased by uPA and by modification of cell surface integrin (such as CD11b-CD18) when associated to uPAR. In this study we analysed the role of three deactivating cytokines, IL-4, IL-10 and IL-13, on the surface expression of uPA, uPAR and CD11b by monocytes and their consequences on monocyte adhesion to immobilized fibrinogen and vitronectin. IL-10 induced a decrease in uPA and CD11b after 18 h incubation and a delayed decrease in uPAR which was only significant after 48 h incubation. These results may explain the decrease in monocyte adhesion, which was observed after an 18 h incubation with IL-10, on immobilized vitronectin and fibrinogen. In contrast, IL-4 and IL-13 induced a decrease in uPAR after 18 h and a significant increase in uPA both in the cell lysates and at the cell surface, as well as an increase in cell surface associated CD11b. These cytokines did not modify cell adhesiveness to vitronectin or fibrinogen despite the increase in CD11b-CD18. This could be due to the decrease in uPAR because CD11b-CD18/uPAR forms a cell adhesion complex. In addition, the increase in uPA induced by IL-4 could counterbalance the direct interaction of uPAR with vitronectin. The increase in uPA suggests that IL-4 and IL-13 could induce plaque fissuring by monocytes, whereas IL-10 may induce protection against matrix protein degradation by decreasing uPA.
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PMID:Regulation of the uPAR/uPA system expressed on monocytes by the deactivating cytokines, IL-4, IL-10 and IL-13: consequences on cell adhesion to vitronectin and fibrinogen. 945 Jul 89

1. The present study compares plasma urokinase plasminogen activator (uPA) peptide levels, plasma plasminogen inhibitor (PAI-1) activity and urokinase receptors (uPAR) on peripheral blood monocytes of patients with stable coronary artery disease (SCAD) and healthy volunteers. 2. Urokinase plasminogen activator levels were analysed by ELISA and PAI-1 activity was determined by a plasmin generation method using the chromogenic substrate S2390. Relative uPAR numbers and the adhesion molecules CD11b/CD18 on peripheral blood monocytes were estimated using specific antibodies and flow cytometry. 3. Patients with SCAD were found to have higher plasma uPA peptide levels than age-matched healthy subjects (10.40 +/- 0.99 vs 8.25 +/- 0.53 pmol/L, respectively; P < 0.05). 4. Plasma PAI-1 activity was also higher in patients with SCAD than in healthy subjects (13.6 +/- 2.5 vs 5.2 +/- 1.0 IU/mL, respectively; P < 0.05). 5. Relative uPAR and CD11b/CD18 adhesion molecules were similar on peripheral blood monocytes of patients with SCAD and in healthy subjects. 6. The data indicate a pattern of expression/activity of uPA and PAI-1 in patients with SCAD suggestive of an impaired fibrinolytic ability.
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PMID:Urokinase plasminogen activator system in humans with stable coronary artery disease. 1022 48

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.
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PMID:Identification of a urokinase receptor-integrin interaction site. Promiscuous regulator of integrin function. 1074 8

During acute inflammatory processes, beta(2) and beta(1) integrins sequentially mediate leukocyte recruitment into extravascular tissues. We studied the influence of VLA-4 (very late antigen-4) (alpha(4)beta(1)) engagement on beta(2) integrin activation-dependent cell-to-cell adhesion. Ligation of VLA-4 by the soluble chimera fusion product vascular cell adhesion molecule-1 (VCAM-1)-Fc or by 2 anti-CD29 (beta(1) chain) monoclonal antibodies (mAb) rapidly induced adhesion of myelomonocytic cells (HL60, U937) to human umbilical vein endothelial cells (HUVECs). Cell adhesion was mediated via beta(2) integrin (LFA-1 and Mac-1) activation: induced adhesion to HUVECs was inhibited by blocking mAbs anti-CD18 (70%-90%), anti-CD11a (50%-60%), or anti-CD11b (60%-70%). Adhesion to immobilized ligands of beta(2) integrins (intercellular adhesion molecule-1 [ICAM-1], fibrinogen, keyhole limpet hemocyanin) as well as to ICAM-1-transfected Chinese hamster ovary cells, but not to ligands of beta(1) integrins (VCAM-1, fibronectin, laminin, and collagen), was augmented. VCAM-1-Fc binding provoked the expression of the activation-dependent epitope CBRM1/5 of Mac-1 on leukocytes. Clustering of VLA-4 through dimeric VCAM-1-Fc was required for beta(2) integrin activation and induction of cell adhesion, whereas monovalent VCAM-1 or Fab fragments of anti-beta(1) integrin mAb were ineffective. Activation of beta(2) integrins by alpha(4)beta(1) integrin ligation (VCAM-1-Fc or anti-beta(1) mAb) required the presence of urokinase receptor (uPAR) on leukocytic cells, because the removal of uPAR from the cell surface by phosphatidylinositol-specific phospholipase C reduced cell adhesion to less than 40%. Adhesion was reconstituted when soluble recombinant uPAR was allowed to reassociate with the cells. Finally, VLA-4 engagement by VCAM-1-Fc or anti-beta(1) integrin mAb induced uPAR-dependent adhesion to immobilized vitronectin as well. These results elucidate a novel activation pathway of beta(2) integrin-dependent cell-to-cell adhesion that requires alpha(4)beta(1) integrin ligation for initiation and uPAR as activation transducer. (Blood. 2000;96:506-513)
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PMID:VLA-4 (alpha(4)beta(1)) engagement defines a novel activation pathway for beta(2) integrin-dependent leukocyte adhesion involving the urokinase receptor. 1088 12


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