Gene/Protein Disease Symptom Drug Enzyme Compound
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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)

We have recently shown that endothelial cell-derived IL-8 inhibits neutrophil adhesion to IL1-beta-activated human umbilical vein endothelial cell monolayers. IL-8 secreted by T lymphocytes or monocytes has been characterized as a promoter of neutrophil degranulation and chemotaxis. The IL-8 isolated from each of these cell types is a mixture of two IL-8 polypeptides, one consisting of 72 amino acids (herein called [ser-IL-8]72) and the other 77 amino acids (an N-terminal extended form herein called [ala-IL-8]77). IL-8 derived from T lymphocytes and monocytes is predominantly [ser-IL-8]72, whereas endothelial-derived IL-8 is highly enriched (greater than 80%) in [ala-IL-8]77. We address the relationship and activities of these two forms of IL-8 using recombinant proteins expressed by both mammalian cells and Escherichia coli. Thrombin was found to efficiently convert [ala-IL-8]77 to [ser-IL-8]72. In contrast, urokinase and tissue-type plasminogen activator were unable to cleave [ala-IL-8]77, and trypsin generated multiple IL-8 cleavage fragments. In competitive binding assays using 125I[ala-IL-8]77 neutrophils exhibited a twofold preference for [ser-IL-8]72 over [ala-IL-8]77. Both forms of IL-8 inhibited neutrophil adhesion to IL-1-beta-activated HUVEC monolayers by up to 90%. However, [ser-IL-8]72 was approximately 10-fold more potent than [ala-IL-8]77 in these assays (ED50 approximately 0.3 nM for [ser-IL-8]72 vs approximately 3 nM for [ala-IL-8]77. Both forms of IL-8 promoted degranulation of cytochalasin B-treated neutrophils [[ser-IL-8]72 (ED50 greater than 10 nM) was two- to three-fold more potent than [ala-IL-8]77], although in this regard they were less active than FMLP. Our data suggest that [ala-IL-8]77 and [ser-IL-8]72 have qualitatively similar and potentially complex biological activities, and that full activation of IL-8 requires cleavage to the [ser-IL-8]72 form. In the case of inflamed endothelial cells this activation could be mediated by thrombin generated in the procoagulant environment associated with these cells.
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PMID:Endothelial and leukocyte forms of IL-8. Conversion by thrombin and interactions with neutrophils. 221 72

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

Several functional defects have been found in neutrophils from leukocyte adhesion deficiency (LAD) patients who fail to express the CD11/CD18 leukoadhesins: Mo1, LFA-1, and p150,95. To better understand the functional defects of LAD neutrophils, we have performed capping experiments. Purified normal or LAD neutrophils were labeled with fluorochrome-conjugated concanavalin A (Con A) or F(ab')2 fragments of antiurokinase-type plasminogen activator receptor (uPAR), anti-Fc gamma RIII (CD16), anti-Mo5, and anti-CD14 antibodies. F(ab')2-labeled cells were capped using a second-step F(ab')2 fragment of an antimurine Fab antiserum. Cells were capped for 30 minutes at 37 degrees C, then observed by fluorescence microscopy. LAD neutrophils were found to be deficient in capping, but not clustering of all of the reagents tested to date. The percent of cells exhibiting capping of Con A, Fc gamma RIII, urokinase receptor, CD14, and Mo5 were 52%, 67%, 70%, 25%, and 64% for normal neutrophils but were only 10%, 5%, 2%, 3%, and 1%, respectively, for LAD neutrophils. Capping of this panel of membrane components in LAD or normal neutrophils was not augmented by the addition of either 10(-5) mol/L colchicine or 10(-7) mol/L FMLP. Because capping requires membrane-to-cytosol communication and an intact microfilament linkage, we suggest that leukoadhesins may play a broad role in promoting the redistribution of membrane components including adherence-related receptors such as Fc gamma RIII and the urokinase receptor.
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PMID:Aberrant capping of membrane proteins on neutrophils from patients with leukocyte adhesion deficiency. 812 56

Mononuclear phagocytes (Mphi) produce urokinase-type plasminogen activator (uPA) and also express a specific cell-surface receptor for urokinase, uPAR. The concomitant expression of these proteins provides a mechanism by which Mphi can degrade extracellular matrix proteins during directed cell migration. In this study, we sought to determine if uPAR plays a role in Mphi chemotaxis that is distinct from its role in matrix proteolysis. Exposing adherent monocytes to a chemotactic gradient causes plasma membrane uPAR to localize strongly to the leading edge of cell migration. Adherence alone or exposure to FMLP had no effect on uPAR expression. Using Boyden chamber chemotaxis assays, we demonstrate that treating mononuclear cells with an anti-uPAR mAb (either as an intact mAb or F[ab']2) ablates chemotaxis induced by FMLP and monocyte chemotactic peptide-1 (P < 0.001). Inactivating the catalytic activity of uPAR-bound uPA had no effect on chemotaxis. Similarly, blocking uPAR expression with an antisense oligonucleotide to uPAR completely ablates chemotaxis, but blocking uPA expression with an antisense oligonucleotide to uPA has a minimal effect. We therefore demonstrate that expression and unimpeded function of uPAR plays an obligate role in M phi chemotaxis by mechanisms that are largely independent of its ligand, uPA. Combined with its known role in mediating pericellular proteolysis, these observations demonstrate that uPAR is essential for both locomotion and traversing tissue barriers during M phi migration.
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PMID:The urokinase receptor is required for human monocyte chemotaxis in vitro. 816 42

The cellular receptor for urokinase-type plasminogen activator (uPAR) binds pro-urokinase (pro-uPA) and facilitates its conversion to enzymatically active urokinase (uPA). uPA in turn activates surface-bound plasminogen to plasmin, a process of presumed importance for a number of biologic processes including cell migration and resolution of thrombi. We have previously shown that uPAR is expressed on the plasma membrane of circulating neutrophils, and we now report that stimulation with phorbol myristate acetate (PMA), FMLP, or tumor necrosis factor-alpha results in a rapid increase in the expression of uPAR. This process is accompanied by an increased cell-associated plasminogen activation after preincubation of neutrophils with pro-uPA in vitro. By subcellular fractionation of unstimulated neutrophils, 50% of uPAR is recovered in fractions containing latent alkaline phosphatase, corresponding to an intracellular compartment of easily mobilizable secretory vesicles distinct from both primary and specific granules, whereas the remaining 50% of uPAR is associated with a compartment eluting close to the specific granules. In contrast, the ligand pro-uPA is primarily (approximately 80%) found in the specific granules, but small amounts of pro-uPA/uPA (approximately 20%) coelute with latent alkaline phosphatase. Stimulation of neutrophils with FMLP results in translocation of uPAR as well as of pro-uPA from the secretory vesicles, whereas stimulation with PMA is required to translocate material from specific granules. Flow cytometry of neutrophils saturated with exogenous diisopropyl fluorophosphate-uPA shows a large excess (approximately 90%) of unoccupied uPAR on resting as well as FMLP- and PMA-stimulated neutrophils, suggesting a possible role for exogenous pro-uPA in providing neutrophils with a potential for plasminogen activation. These processes may be important for neutrophil extravasation and migration through extracellular matrix and for the contribution of neutrophils to resolution of thrombi.
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PMID:The receptor for urokinase-type plasminogen activator and urokinase is translocated from two distinct intracellular compartments to the plasma membrane on stimulation of human neutrophils. 829 41

Fig. 1 depicts our current thinking about the ways in which Mo1 and p150,95 form cis interactions with other leukocyte receptors. With respect to the associations of Mo1 with Fc gamma RIIIB and uPAR, the inhibitory effect of saccharides such as NADG suggests a lectin-carbohydrate interaction that may involve the recognition of Mo1's beta-glucan site for N-linked carbohydrates4 that are expressed by both Fc gamma RIIIB and uPAR. This hypothesis is supported by the results of Stockl et al., who showed that the binding of C-terminal-specific mAb VIM12 to Mo1, which enhances the phospholipase C-mediated release of Fc gamma RIIIB, was inhibited by NADG. However, unlike the sample lectin-carbohydrate interaction that appears to govern the association between Mo1 and Fc gamma RIIIB, effective Mo1-dependent uPAR signaling also depends on the binding of intact uPA to uPAR (the receptor-binding ATF of uPA proving insufficient to prime neutrophils for an enhanced burst response to FMLP). We speculate that ATF (residues 6-135) binds to uPAR while the carboxyl terminal fragment (residues 136-411), which includes a glycosylation site at residue 144, binds to the lectinlike site of Mo1, thus fostering the linkage between the two receptors. In support of this model is the fact that exposure of neutrophils to ATF reduced the degree of molecular proximity between Mo1 and uPAR (the latter probably occupied by endogenous intact uPA) and increased the molecular association between Mo1 and Fc gamma RIIIB (both as detected by quantitative RET). This hypothesis is analogous to the concept proposed by Nykjaer et al in which plasminogen activator inhibitor-1 initially binds to uPA to form a complex that secondarily binds to the alpha 2 macroglobulin receptor, leading to internalization of the complex. Whereas the contribution of intact uPA to the interaction between Mo1 and uPAR remains speculative (based on the indirect data available), no such ambiguity exists for the role of the LPS/LBP ligand in regulating the association between Mo1 and CD14. In this circumstance, no physical linkage exists between the two receptors without the ligand complex. This observation is consistent with the previously described affinity of the beta 2 integrins for LPS, leading to the notion that the LPS portion of the LPS/LPB complex binds to Mo1, serving to link it with LPS/LBP bound to CD14. The observed reversibility of the interactions between the integrin glycoproteins and uPAR or CD14 illustrates the fact that these associations can be highly dynamic and tied to cellular processes that include directed motility (Mo1-uPAR), adherence to substrates (Mo1-CD14), and energy metabolism (p150,95-uPAR). We speculate that the GPI-anchored receptor proteins serve as rapidly diffusible, expendable "scouts" for the beta 2 integrins, which serve to expand their ligand binding repertoire in a cis-acting fashion.
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PMID:Beta 2 (CD11/CD18) integrins can serve as signaling partners for other leukocyte receptors. 914 45

Leukocytes use urokinase receptors (uPAR; CD87) in adhesion, migration, and proteolysis of matrix proteins. Typically, uPAR clusters at cell-substratum interfaces, at focal adhesions, and at the leading edges of migrating cells. This study was undertaken to determine whether uPAR clustering mediates activation signaling in human polymorphonuclear neutrophils. Cells were labeled with fluo-3/AM to quantitate intracellular Ca2+ ([Ca2+]i) by spectrofluorometry, and uPAR was aggregated by Ab cross-linking. Aggregating uPAR induced a highly reproducible increase in [Ca2+]i (baseline to peak) of 295 +/- 37 nM (p = 0.0002). Acutely treating cells with high m.w. urokinase (HMW-uPA; 4000 IU/ml) produced a response of similar magnitude but far shorter duration. Selectively aggregating uPA-occupied uPAR produced smaller increases in [Ca2+]i, but saturating uPAR with HMW-uPA increased the response to approximate that of uPAR cross-linking. Cross-linking uPAR induced rapid and significant increases in membrane expression of CD11b and increased degranulation (release of beta-glucuronidase and lactoferrin) to a significantly greater degree than cross-linking control Abs. The magnitude of degranulation correlated closely with the difference between baseline and peak [Ca2+]i, but was not dependent on the state of uPA occupancy. By contrast, selectively cross-linking uPA-occupied uPAR was capable of directly inducing superoxide release as well as enhancing FMLP-stimulated superoxide release. These results could not be duplicated by preferentially cross-linking unoccupied uPAR. We conclude that uPAR aggregation initiates activation signaling in polymorphonuclear neutrophils through at least two distinct uPA-dependent and uPA-independent pathways, increasing their proinflammatory potency (degranulation and oxidant release) and altering expression of CD11b/CD18 to favor a firmly adherent phenotype.
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PMID:Clustering of urokinase receptors (uPAR; CD87) induces proinflammatory signaling in human polymorphonuclear neutrophils. 1097 52