Growth stimulation of human epidermal cells by urokinase is restricted to the intact active enzyme

Natural and engineered plasmin inhibitors: applications and design strategies

The serine protease plasmin is ubiquitously expressed throughout the human body in the form of the zymogen plasminogen. Conversion to active plasmin occurs through enzymatic cleavage by plasminogen activators. The plasminogen activator/plasmin system has a well-established function in the removal of intravascular fibrin deposition through fibrinolysis and the inhibition of plasmin activity; this has found widespread clinical use in reducing perioperative bleeding. Increasing evidence also suggests diverse, although currently less defined, roles for plasmin in a number of physiological and pathological processes relating to extracellular matrix degradation, cell migration and tissue remodelling. In particular, dysregulation of plasmin has been linked to cancer invasion/metastasis and various chronic inflammatory conditions; this has prompted efforts to develop inhibitors of this protease. Although a number of plasmin inhibitors exist, they commonly suffer from poor potency and/or specificity of inhibition that either results in reduced efficacy or prevents clinical use. Consequently, there is a need for further development of high-affinity plasmin inhibitors that maintain selectivity over other serine proteases. This review summarises clearly defined and potential applications for plasmin inhibition. The properties of naturally occurring and engineered plasmin inhibitors are discussed in the context of current knowledge regarding plasmin structure, specificity and function. This includes design strategies to obtain the potency and specificity of inhibition in addition to controlled temporal and spatial distribution tailored for the intended use.

Urokinase induces activation of STAT3 in lung epithelial cells

Urokinase-type plasminogen activator (uPA) is a serine protease that plays a major role in diverse physiological and pathological processes. Studies from our laboratory have shown that exposure of human lung epithelial cells to uPA induces proliferation. To understand uPA mitogenic signaling events, we sought to elucidate its effects on tyrosine phosphorylation in a human bronchial epithelial cell line (Beas2B). uPA induced tyrosine phosphorylation of several proteins in a time-dependent manner. One of these proteins was identified as the 91-kDa signal transduction activator transcription (Stat)3 moiety. Tyrosine phosphorylation of Stat3 by uPA was time dependent. uPA induced Stat3-DNA binding activity in a time-dependent manner. uPA-induced Stat3 activation does not require uPA catalytic activity, as the uPA amino-terminal fragment alone was as potent as active two-chain uPA (tcuPA) in causing this effect. Single-chain uPA likewise induced tyrosine phosphorylation of Stat3 to a similar extent as intact tcuPA. Plasmin did not alter uPA-induced Stat3 activation. Furthermore, transfection of Beas2B cells with dominant-negative Stat3 blocked uPA-induced DNA synthesis. These results reveal for the first time that the uPA-uPAR interaction leads to activation of Stat3, independent of its catalytic activity but dependent on its interaction with its receptor, uPAR, leading to DNA synthesis in lung epithelial cells.

Induction of p53 by urokinase in lung epithelial cells

Urokinase plasminogen activator (uPA) is a serine protease that catalyzes the conversion of plasminogen to plasmin. The plasminogen/plasmin system includes the uPA, its receptor, and its inhibitor (plasminogen activator inhibitor-1). Interactions between these molecules regulate cellular proteolysis as well as adhesion, cellular proliferation, and migration, processes germane to the pathogenesis of lung injury and neoplasia. In previous studies, we found that uPA regulates cell surface fibrinolysis by regulating its own expression as well as that of the uPA receptor and plasminogen activator inhibitor-1. In this study, we found that uPA alters expression of the tumor suppressor protein p53 in Beas2B airway epithelial cells in both a time- and concentration-dependent manner. These effects do not require uPA catalytic activity because the amino-terminal fragment of uPA lacking catalytic activity was as potent as two chain active uPA. Single chain uPA also enhanced p53 expression to the same extent as intact two chain active uPA and the amino-terminal fragment. Pretreatment of cells with anti-beta1 integrin antibody blocked uPA-induced p53 expression. uPA-induced p53 expression occurs without increased p53 mRNA expression. However, uPA induced oncoprotein MDM2 in a concentration-dependent manner. uPA-induced p53 expression does not require activation of tyrosine kinases. Inactivation of protein-tyrosine phosphatase SHP-2 inhibits both basal and uPA-induced p53 expression. Plasmin did not alter uPA-mediated p53 expression. The induction of p53 expression by exposure of lung epithelial cells to uPA is a newly recognized pathway by which urokinase may influence the proliferation of lung epithelial cells. This pathway could regulate pathophysiologic alterations of p53 expression in the setting of lung inflammation or neoplasia.

Design of Novel and Selective Inhibitors of Urokinase-type Plasminogen Activator with Improved Pharmacokinetic Properties for Use as Antimetastatic Agents

The serine protease urokinase-type plasminogen activator (uPA) interacts with a specific receptor (uPAR) on the surface of various cell types, including tumor cells, and plays a crucial role in pericellular proteolysis. High levels of uPA and uPAR often correlate with poor prognosis of cancer patients. Therefore, the specific inhibition of uPA with small molecule active-site inhibitors is one strategy to decrease the invasive and metastatic activity of tumor cells. We have developed a series of highly potent and selective uPA inhibitors with a C-terminal 4-amidinobenzylamide residue. Optimization was directed toward reducing the fast elimination from circulation that was observed with initial analogues. The x-ray structures of three inhibitor/uPA complexes have been solved and were used to improve the inhibition efficacy. One of the most potent and selective derivatives, benzylsulfonyl-D-Ser-Ser-4-amidinobenzylamide (inhibitor 26), inhibits uPA with a Ki of 20 nm. This inhibitor was used in a fibrosarcoma model in nude mice using lacZ-tagged human HT1080 cells, to prevent experimental lung metastasis formation. Compared with control (100%), an inhibitor dose of 2 x 1.5 mg/kg/day reduced the number of experimental metastases to 4.6 +/- 1%. Under these conditions inhibitor 26 also significantly prolonged survival. All mice from the control group died within 43 days after tumor cell inoculation, whereas 50% of mice from the inhibitor-treated group survived more than 117 days. This study demonstrates that the specific inhibition of uPA by these inhibitors may be a useful strategy for the treatment of cancer to prevent metastasis.

Urokinase plasminogen activator system: a multifunctional role in tumor progression and metastasis

The urokinase plasminogen activator (uPA) system is central to a spectrum of biologic processes including fibrinoloysis, inflammation, atherosclerotic plaque formation, matrix remodeling during wound healing, tumor invasion, angiogenesis, and metastasis. Binding of uPA with its receptor (uPAR) initiates a proteolytic cascade that results in the conversion of plasminogen to plasmin. Plasmin through its own proteolytic function degrades a range of extracellular basement membrane components and activates others such as the metalloproteinases. Independent of catalytic activity, uPAR also is involved in cell signaling, interactions with integrins, cell motility, adhesion and invasion, and angiogenesis. Over expression of uPA or uPAR is a feature of malignancy and is correlated with tumor progression and metastasis. In contrast, inhibition of expression of these components leads to a reduction in the invasive and metastatic capacity of many tumors. Strategies that target uPA or its receptor with the aim of disrupting the interaction between the two or the ligand independent actions of uPAR include antisense technology, monoclonal antibodies, cytotoxic antibiotics, and synthetic inhibitors of uPA. Targeted therapy is a goal of future cancer treatment and the uPA system is a likely candidate for manipulation.

Molecular and functional interdependence of the urokinase-type plasminogen activator system with integrins

The serine protease urokinase-type plasminogen activator (uPA), its inhibitor PAI-1, and its cellular receptor uPA-R (CD87) are of crucial importance during cellular invasion and migration, required for a variety of physio- and pathophysiological processes. It has become increasingly evident in recent years that the uPA/uPA-R-system has far more functional properties than plasminogen activation alone. This is reflected by its involvement in cellular events such as proliferation, adhesion, migration, and chemotaxis. Since uPA-R lacks a transmembrane domain and thus on its own is not capable of transmitting signals into cells, association and functional cooperation with other signaling molecules/receptors is needed. In this respect, one group of adhesion and signaling receptors, the integrins, have been identified which constitute, together with the uPA/uPA-R-system, an interdependent biological network by which the uPA/uPA-R-system broadly affects integrin functions and vice versa. Moreover, there is a growing body of evidence that cellular uPA, uPA-R, and PAI-1 expression is under control of specific ECM/integrin interactions and also that integrins are regulated by components of the uPA/uPA-R-system. By this multifaceted crosstalk, cells may modulate their proteolytic, adhesive, and migratory activities and monitor ECM integrity in their microenvironment.

Induction of plasminogen activator inhibitor-1 by urokinase in lung epithelial cells

The plasminogen/plasmin system, urokinase-type plasminogen activator (uPA), its receptor (uPAR), and its inhibitor (PAI-1), influence extracellular proteolysis and cell migration in lung injury or neoplasia. In this study, we sought to determine whether tcuPA (two chain uPA) alters expression of its major inhibitor PAI-1 in lung epithelial cells. The expression of PAI-1 was evaluated at the protein and mRNA level by Western blot, immunoprecipitation, and Northern blot analyses. We found that tcuPA treatment enhanced PAI-1 protein and mRNA expression in Beas2B lung epithelial cells in a time- and concentration-dependent manner. The tcuPA-mediated induction of PAI-1 involves post-transcriptional control involving stabilization of PAI-1 mRNA. Inactivation of the catalytic activity of tcuPA had little effect on PAI-1 induction and the activity of the isolated amino-terminal fragment was comparable with full-length single- or two-chain uPA. In contrast, deletion of either the uPA receptor binding growth factor domain or kringle domain (kringle) from full-length single chain uPA markedly attenuated the induction of PAI-1. Induction of PAI-1 by exposure of lung epithelial cells to uPA is a newly recognized pathway by which PAI-1 could regulate local fibrinolysis and urokinase-dependent cellular responses in the setting of lung inflammation or neoplasia.

Urokinase induces its own expression in Beas2B lung epithelial cells

The urokinase-type plasminogen activator (uPA) interacts with its receptor (uPAR) to promote local proteolysis as well as cellular proliferation and migration. These functions contribute to the pathogenesis of lung inflammation and remodeling as well as the growth and invasiveness of lung neoplasms. In this study, we sought to determine if uPA alters its own expression in lung epithelial cells. Using immunoprecipitation and Western and Northern blotting techniques, we found that uPA treatment enhanced uPA expression in Beas2B lung epithelial cells in a time- and concentration-dependent manner. The induction of uPA expression is mediated through its cell surface receptor uPAR and does not require uPA enzymatic activity. The amino-terminal fragment of uPA, lacking the catalytic domain, is sufficient to induce uPA expression. The serine protease plasmin and the protease inhibitor aprotinin failed to alter uPA-mediated uPA expression, whereas alpha-thrombin potentiated the response. Pretreatment of Beas2B cells with a tyrosine kinase inhibitor, herbimycin, suggests that activation of tyrosine kinase(s) is involved in the uPA-mediated uPA expression. Induction of uPA expression by exposure of lung-derived epithelial cells to uPA is a newly defined pathway by which this protease could influence expression of local fibrinolytic activity and other uPA-dependent cellular responses germane to lung inflammation or neoplasia.

Plasminogen activator inhibitor type 2: a regulator of monocyte proliferation and differentiation

We have explored the role of plasminogen activator inhibitor type 2 (PAI-2) in THP-1 monocyte-like cells. These cells possess a mutation in the PAI-2 gene and do not produce an active PAI-2 protein. Transfection of THP-1 cells with plasmids expressing active PAI-2 reduced the cells' inherent adhesive properties and decreased the rate of cell proliferation. THP-1 cells expressing active PAI-2 also displayed an altered phenotype in response to phorbol ester-induced differentiation that was concomitant with a reduction in CD14 expression. THP-1 cells transfected with a variant PAI-2 containing a mutation in the reactive center (PAI-2(Ala380)) displayed no noticeable change in any of these parameters, suggesting the involvement of a PAI-2-sensitive serine protease(s). The antiproliferative effect of PAI-2 was attenuated by treating the PAI-2-expressing THP-1 cells with recombinant urokinase (u-PA), suggesting that PAI-2 was disruptive of a u-PA/u-PA receptor signaling pathway initiated on the cell surface. Consistent with this, treatment of wild-type THP-1 cells with recombinant PAI-2 also caused a reduction in cellular proliferation. These results implicate endogenous PAI-2 as a modulator of monocyte adhesion, proliferation, and differentiation.

Human endothelial cells grow poorly on vitronectin: role of PAI-1

The cell adhesive protein vitronectin is a common component of interstitial extracellular matrix and circulates in plasma. It competes effectively with other plasma proteins to adsorb to certain biomaterial surfaces, and is likely to represent an important cell adhesion mediator on the luminal surface of vascular grafts. It is also found associated with certain vascular pathologies. We have shown previously that human endothelial cells grow poorly on a vitronectin surface compared with other extracellular matrix molecules. In this paper we show that endothelial cells seeded on vitronectin and fibronectin produced substantially different profiles of extracellular matrix molecules. The most outstanding difference was in the amount of matrix-localised plasminogen activator-inhibitor-1 which was high on vitronectin and negligible on fibronectin. This was correlated with a small but significant inhibition of cell adhesion to vitronectin compared with fibronectin, and very significant interference with dissociation of cell: extracellular matrix contacts, resulting either from direct inhibition of the proteolytic activity of urokinase, or from interference with urokinase-receptor signaling and consequent focal adhesion turnover. Such interference would inhibit cell proliferation by disabling the cells from loosening their matrix contacts in order to proceed through mitosis. This would seriously compromise endothelial recovery in cases of damage to the vascular wall and placement of stents or grafts, where the presence of surface-adsorbed vitronectin is likely to modulate the tissue response.

Urokinase is a positive regulator of epidermal proliferation in vivo

The epidermis is a self-renewing tissue that must maintain a basal proliferative rate as well as respond to various perturbing stimuli. Regulation of keratinocyte proliferation involves diverse molecules, including growth factors, ions, and hormones. We recently proposed that a proteinase, urokinase-type plasminogen activator (uPA) may be added to this list, based on correlative evidence linking expression of uPA and murine epidermal hyperproliferation. Here we report that, during the first 3 d of life, the epidermis from mice that bear a targeted deletion of the uPA gene has a significantly lower proliferative rate than the epidermis from wild-type mice. In contrast, proliferation in the matrix keratinocytes of the hair follicles is not decreased in neonatal uPA-/- mice. Vertical migration of keratinocytes during terminal differentiation was not affected. We therefore conclude that lack of uPA is associated with a decrease in epidermal proliferation.

Suppression of keratinocyte proliferation by plasminogen activator inhibitor-2

We have previously shown that urokinase plasminogen activator (uPA) stimulates the growth of human keratinocytes in culture. For this effect, uPA activity is essential to generate the active amino terminal fragment, by an autolytic process. Our findings indicated further that inhibition of uPA may result in the suppression of growth of keratinoytes. Here, we provide evidence that plasminogen activator inhibitor (PAI)-2 has an anti-proliferative effect on keratinocytes. The uPA activity in cultured keratinocytes increased in parallel with cell proliferation, reaching a maximum level at confluency and decreasing gradually thereafter. The analysis of synchronized cells showed that the peak uPA activity in the medium occured just prior to S-phase, suggesting that the production and secretion of uPA is related to cell proliferation. In contrast, PAI-2 levels showed a steady increase, even after confluency. When PAI-2, purified from human cornified cells, was added to synchronized keratinocytes, S-phase was no longer evident and the peak uPA activity was eliminated. In experiments with a bacterially expressed PAI-2 fusion protein, [3H]thymidine incorporation by keratinocytes was significantly suppressed, confirming an anti-proliferative effect of PAI-2. These results strongly suggest that PAI-2 is involved in the regulation of keratinocyte proliferation and differentiation.

Urokinase induces proliferation of human ovarian cancer cells: characterization of structural elements required for growth factor function

Ovarian cancer metastasis is associated with an increase in the urokinase-type plasminogen activator (uPA) and its receptor uPAR. We present evidence that binding of uPA to uPAR provokes a mitogenic response in the human ovarian cancer cell line OV-MZ-6 in which endogenous uPA production had been significantly reduced by stable uPA 'antisense' transfection. High molecular weight (HMW) uPA, independent of its enzymatic activity, produced an up to 95% increase in cell number concomitant with 2-fold elevated [3H]thymidine incorporation as did the catalytically inactive but uPAR binding amino-terminal fragment of uPA, ATF. uPA-induced cell proliferation was significantly decreased by blocking uPA/uPAR interaction by the monoclonal antibody IIIF10 and by soluble uPAR. The efficiency of the uPAR binding synthetic peptide cyclo19,31 uPA19-31 to enhance OV-MZ-6 cell growth proved this molecular domain to be the minimal structural determinant for uPA mitogenic activity. Dependence of uPA-provoked cell proliferation on uPAR was further demonstrated in Raji cells which do not express uPAR and were thus not induced by uPA. However, upon transfection with full-length uPAR, Raji cells acquired a significant growth response to HMW uPA and ATF.

Induction of vascular SMC proliferation by urokinase indicates a novel mechanism of action in vasoproliferative disorders

The urokinase-type plasminogen activator (UPA) and its receptor are expressed in the vasculature and are involved in cell migration and remodeling of the extracellular matrix in the neointima. Vessels with atherosclerosis or neointimal hyperplasia, when compared with normal vessels, contain high UPA activity as well as increased levels of UPA receptor. In this study, we have identified the stimulation of vascular smooth muscle cell proliferation as a novel activity for UPA in the vessel wall. High-molecular-weight-UPA (12-200 nmol/L range) stimulated DNA synthesis and cell proliferation, which was half that induced by fetal calf serum or by platelet-derived growth factor-BB. UPA did not induce growth of endothelial cells, and tissue-type plasminogen activator showed no activity on either cell type. Induction of proliferation required the complete UPA molecule but was independent of the proteolytic activity of UPA, whereas neither the amino-terminal fragment nor the catalytic domain by itself was mitogenic. UPA also stimulated c-fos/c-myc mRNA expression and mitogen-activated protein kinase activity in smooth muscle cells. Blocking monoclonal antibodies against the UPA receptor and the enzymatic removal of receptors were ineffective in inhibiting the mitogenic effect of UPA, suggesting a UPA receptor-independent mechanism. Thus, we provide evidence for a novel function of UPA on vascular smooth muscle cell proliferation that, together with its previously documented involvement in regulating pericellular proteolysis-related events and cell migration, provides additional evidence for a role in the pathogenesis of atherosclerosis/restenosis.

Urokinase does not upregulate the vascular endothelial cell-mediated inflammatory response

PURPOSE

Urokinase is used clinically for thrombolysis, but little is known of its direct effect on vascular endothelial cells. The following experiments were preformed to assess the in vitro effects of urokinase on vascular endothelial cell growth, adhesion molecule expression, and interaction with lymphocytes, polymorphonuclear leukocytes, and platelets.

METHODS

Commercially available human umbilical vein endothelial cells (HUVEC) were cultured with varying concentrations of urokinase (0 to 10,000 IU/ml) (clinical dosage, < or = 500 IU/ml). HUVEC viability was determined from 1 to 4 days. HUVECs were incubated with urokinase (0 to 2000 IU/ml) from 4 to 72 hours. Adherence of 51-chromium-labeled polymorphonuclear leukocytes, platelets, or lymphocytes was then quantitated. In separate experiments HUVEC adhesion molecule expression (intercellular adhesion molecule-1, vascular cell adhesion molecule-1, or endothelial leukocyte adhesion molecule-1) was determined by flow cytometry.

RESULTS

There was a decrease of HUVEC viability at suprapharmacologic urokinase concentrations of > or = 2000 IU/ml compared with nontreated control samples (0 IU/ml, 73% +/- 2%, 2000 IU/ml, 60.5% +/- 1.9%, p < 0.05) presumably because of drug toxicity. There was no significantly increased polymorphonuclear leukocyte, lymphocyte, or platelet adhesion to urokinase-treated HUVEC monolayes at any time point. This was also true for each adhesion molecule tested.

CONCLUSIONS

Urokinase at clinically relevant concentrations (< or = 500 IU/ml) did not affect endothelial cell viability or growth, nor did it upregulate adhesion molecule expression or cellular adhesion associated with the cell vascular inflammatory response. It is therefore implied that the use of urokinase in vivo similarly would not initiate the vascular inflammatory response.

Inhibition of NF-kappa B-Rel A expression by antisense oligodeoxynucleotides suppresses synthesis of urokinase-type plasminogen activator (uPA) but not its inhibitor PAI-1

The essential role of urokinase-type plasminogen activator (uPA) in tumor invasion and metastasis stresses the necessity of a fine-tuned cellular control over its expression. It has been shown that changes in uPA directly correlate with changes in cell invasiveness. We examined the role of Rel-related proteins in uPA synthesis by human ovarian cancer cells by inhibiting their expression using the antisense (AS) oligodeoxynucleotide (ODN) technology. Exposure of OV-MZ-6 cells to 10 microM phosphorothioate (PS)-derivatized AS-ODN directed to Rel A led to a maximal 50% decrease of uPA antigen in cell lysates and a 70% reduction in cell cultures supernatants accompanied by a significant transient decline in uPA mRNA levels. Antisense-PS-ODN directed to NF-kappa B1 (p50) or c-rel had no effect on uPA protein expression. AS-PS-ODN directed to Rel A also affected the proteolytic capacity of OV-MZ-6 cells reflected by an approximately 70% decrease in the fibrinolytic capacity of the cells within 24 h compared to untreated controls. AS-PS-ODN directed to I kappa B alpha expression increased uPA in cell culture supernatants up to 50%. uPA receptor (uPAR) production and synthesis of plasminogen activator inhibitor type-1 (PAI-1) were not altered by either AS-PS-ODN applied. Western blot and gel retardation analyses revealed constitutive expression of Rel-related proteins in nuclear protein extracts of OV-MZ-6 cells. Thus these proteins seem to be implicated in uPA regulation and may thereby contribute to tumor spread and metastasis.

Regulation of plasminogen activation, matrix metalloproteinases and urokinase-type plasminogen activator-mediated extracellular matrix degradation in human osteosarcoma cell line MG63 by interleukin-1 alpha

Plasmin-mediated extracellular proteolysis has been implicated in the degradation of bone in normal and pathological conditions. Normal and malignant osteoblasts can produce both tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). We have used the osteosarcoma cell line MG63 to address the question of whether the enhanced bone turnover in osteosarcomas is mediated by t-PA or by u-PAA and to study the effect of the cytokine interleukin-1 alpha (IL-1 alpha), known to influence bone degradation, on the plasminogen activator production and extracellular matrix degradation in malignant osteoblastic cells. Furthermore, the effect of IL-1 alpha on the synthesis of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) was analyzed. u-PA production by MG63 was high (approximately 180 ng/10(6) cells/24 h). Also t-PA and PAI-1 production was observed. u-PA production was rapidly increased in MG63 by IL-1 alpha (10 ng/ml), whereas an effect on t-PA production was only found after a prolonged incubation and hardly any effect of IL-1 alpha on PAI-1 production was observed. mRNA analysis revealed similar effects. u-PA receptor (u-PAR) mRNA was detectable in MG63 cells and could be increased by IL-1 alpha after 24 h. In MG63, u-PA-mediated extracellular matrix degradation was detectable, and IL-1 alpha increased the u-PA-mediated matrix degradation (approximately 2-fold). Under control conditions in MG63, only MMP-2, TIMP-1, and TIMP-2 mRNA could be observed. After the addition of IL-1 alpha, a very rapid increase in MMP-1 and MMP-3 mRNA could be observed as well as a moderate increase in TIMP-1 mRNA. The presence of MMP-2 was demonstrated by gelatin zymography. These results show that IL-1 alpha can stimulate u-PA production and can regulate extracellular proteolytic activity mainly via u-PA induction in the MG63 osteosarcoma cell line. Furthermore, IL-1 alpha has a strong stimulating effect on the production of MMP-1 and MMP-3. These findings suggest that u-PA and possibly MMP-1 and MMP-3 play an important role in the process of bone turnover in osteosarcomas.

Antisense inhibition of urokinase reduces spread of human ovarian cancer in mice

Urokinase-type plasminogen activator (uPA) is a protease involved in the process of tissue remodelling and cell migration in vitro. To explore whether uPA is a prerequisite for human ovarian cancer spread in vivo the expression of uPA was suppressed in human ovarian cancer cells by antisense phosphorothioate oligonucleotides (PS-ODN). The suppression of uPA expression was dependent on PS-ODN concentration and only observed in the presence of liposomes. This phenomenon seemed to be due to the fact that PS-ODNs were taken up by the cancer cells only in concert with liposomes as studied by fluorescently-labeled PS-ODNs using flow cytofluorometry and laser scanning microscopy. uPA-deprived cancer cells exhibited a significantly reduced invasive capacity in vitro compared with untreated cancer cells or cells treated with control PS-ODNs (P = 0.003). The intraperitoneal spread of the cancer cells in vivo was significantly diminished when nude mice were treated with uPA antisense PS-ODNs in comparison with control mice (P = 0.009). These results suggest that uPA expression may be required for spread of human ovarian cancer and that its inhibition could provide a therapeutic approach.

Urokinase receptor is a multifunctional protein: influence of receptor occupancy on macrophage gene expression

Binding of urokinase to the glycolipid-anchored urokinase receptor (uPAR) has been implicated in macrophage differentiation. However, no biochemical markers of differentiation have yet been directly linked to uPAR occupancy. As extensive changes in proteolytic profile characterize monocytic differentiation, we have examined the role of uPAR occupancy on protease expression by differentiating phagocytes. Antibodies to either urokinase or to uPAR that prevent receptor binding inhibited induction of cathepsin B in cultured monocytes and both cathepsin B and 92-kD gelatinase mRNA and protein in phorbol diester-stimulated myeloid cells. Mannosamine, an inhibitor of glycolipid anchor assembly, also blocked protease expression. Anti-catalytic urokinase antibodies, excess inactive urokinase, or aprotinin had no effect, indicating that receptor occupancy per se regulated protease expression. Antibodies to the integrins CD11a and CD29 or to the glycolipid-anchored proteins CD14 and CD55 also had no effect. Protease induction was independent of matrix attachment. Antibodies to urokinase or uPAR affected neither the decrease in cathepsin G nor the increase in tumor necrosis factor-alpha in phorbol ester-stimulated cells. These data establish that uPAR is a multifunctional receptor, not only promoting pericellular proteolysis and matrix attachment, but also effecting cysteine- and metallo-protease expression during macrophage differentiation.

The urokinase inhibitor p-aminobenzamidine inhibits growth of a human prostate tumor in SCID mice

Malignant cells possess a high degree of proteolytic activity in which the plasminogen activator system plays an important role. An increased expression of urokinase type plasminogen activator (uPA) is of significance for degradation of the extracellular tumor matrix, facilitating invasiveness and growth. Inhibition of the active site of uPA makes it possible to evaluate the significance of uPA in tumor growth. We report here experiments on a uPA-producing human prostate xenograft (DU 145) using a competitive inhibitor of uPA, p-aminobenzamidine. In vitro experiments with DU 145 cells showed that p-aminobenzamidine caused a dose-dependent inhibition of uPA activity. DU 145 cells were inoculated s.c. in SCID mice and, once tumors were established, treatment with p-aminobenzamidine added to drinking water was started and lasted for 23 days. Mice receiving 250 mg/kg/day of p-aminobenzamidine showed a clear decrease in tumor-growth rate compared to the non-treated mice, resulting in 64% lower final tumor weight. In addition, uPA-antigen levels in the membrane fractions of DU 145 tumors from p-aminobenzamidine-treated mice were found to be decreased by 59%. We also show that p-aminobenzamidine has an anti-proliferative effect in cell culture at low cell number, correlating with a dose-dependent decrease in uPA production. In conclusion, we show that a low-molecular-weight uPA-inhibitor, p-aminobenzamidine, has a growth-inhibitory effect on a solid uPA-producing tumor.

The urokinase-type plasminogen activator receptor, a GPI-linked protein, is localized in caveolae

The urokinase plasminogen activator receptor (uPAR), a glycosylphosphatidylinositol-linked glycoprotein, plays a central role in the regulation of pericellular proteolysis and participates in events leading to cell activation. Here, we demonstrate that uPAR, on a human melanoma cell line, is localized in caveolae, flask-shaped microinvaginations of the plasma membrane found in a variety of cell types. Indirect immunofluorescence with anti-uPAR antibodies on the melanoma cells showed a punctated staining pattern that accumulated to stretches along sides of cell-cell contact and membrane ruffles. uPAR colocalized with caveolin, a characteristic protein in the coat of caveolae, as demonstrated by double staining with specific antibodies. Further, uPAR could be directly localized in caveolae by in vivo immunoelectron microscopy. Both uPAR and its ligand, uPA, were present in caveolae enriched low density Triton X-100 insoluble complexes, as shown by immunoblotting. From such complexes, caveolin could be coprecipitated with uPAR-specific antibodies suggesting a close spatial association between uPAR and caveolin that might have implications for the signal transduction mediated by uPAR. Further, functional studies indicated that the localization of uPAR and its ligand in caveolae enhances pericellular plasminogen activation, since treatment of the cells with drugs that interfere with the structural integrity of caveolae, such as nystatin, markedly reduced cell surface plasmin generation. Thus, caveolae promote efficient cell surface plasminogen activation by clustering uPAR, uPA, and possibly other protease receptors in one membrane compartment.

Plasminogen activation by human keratinocytes: molecular pathways and cell-biological consequences

Keratinocytes are the major cellular constituent of stratified epithelia. Defects in these epithelia are re-epithelialized by keratinocytes migrating from the edge of the defect into the wound. The cells form a monolayer with subsequent differentiation into a multilayered epithelium. It is thought that plasminogen activation by migrating keratinocytes is an important event during re-epithelialization. In the present report we summarize the studies on plasminogen activation by human keratinocytes in vitro and in vivo. Under the aspect of pericellular proteolysis the discussion is focused on the molecular mechanisms of plasminogen activation at the keratinocyte surface and on the cell-biological consequences of pericellular plasmin formation. We describe a cell surface-associated pathway of plasminogen activation which crucially depends on cell surface receptors for (pro)-uPA and plasmin(ogen). uPA bound to its receptor converts cell-bound plasminogen into the active protease plasmin. Compared to plasminogen activation in solution, activation at the keratinocyte cell surface is accelerated by a factor of approx. 7-10, and the plasmin generated and bound at the cell surface is protected against its specific inhibitor alpha 2-antiplasmin. Plasmin thus provided in the pericellular space leads to detachment of cultured keratinocytes from the growth substratum. Plasmin interferes with the adhesion of keratinocytes to fibrin, but not with the adhesion to collagen type I. By demonstrating that keratinocytes of the epithelial outgrowth in healing skin wounds express uPA and the uPA-R and that plasmin(ogen) is colocalized with uPA and/or uPA-R, indirect evidence is provided that this pathway may be operative in vivo. In view of previous findings that plasminogen activation is also observed under certain pathologic conditions in the epidermis, we conclude that plasminogen activation by keratinocytes is rather related to tissue damage and subsequent repair mechanisms than to a specific pathologic situation.

Recombinant soluble urokinase receptor as a scavenger for urokinase-type plasminogen activator (uPA). Inhibition of proliferation and invasion of human ovarian cancer cells

A recombinant soluble human urokinase receptor comprising amino acids 1-277 was cloned and transfected into CHO cells. The mutant protein (rec-uPAR277), purified from the CHO cell supernatant by affinity chromatography on immobilized urokinase (uPA), in a four-fold excess, completely abolished the binding of FITC-labeled pro-uPA to the human ovarian cancer cell line, OV-MZ-6. This invasive and tumorigenic cancer cell line expresses uPA, its inhibitor PAI-1, and the high-affinity receptor for uPA, uPAR. Rec-uPAR277 significantly reduced the proliferation of OV-MZ-6 cells in a concentration-dependent manner without altering the viability of the cells. Invasion of OV-MZ-6 cells tested in an in vitro Matrigel invasion assay was inhibited by rec-uPAR277 up to 75%. In conclusion, these results demonstrate that rec-uPAR277 can function as a scavenger for uPA in vitro by inhibiting proliferation and invasion of human cancer cells.

The plasminogen-plasmin system in malignancy

The study of the plasminogen-plasmin system has, in the past, contributed much to the understanding of fibrinolysis and thrombolysis. Attention is now focused on the role of the components of this system in many biologic functions. Findings of uPA, its receptor and its inhibitor in many tumor tissues and tumor cell lines, strongly implicate their involvement in tumor invasion, tumor cell proliferation and metastasis. The characteristics of the plasminogen activators, the uPA receptor and the plasminogen activator inhibitors as well as their expression and regulation in tumors and tumor cell lines are reviewed.

The role of urokinase-type plasminogen activator in aggressive tumor cell behavior

The correlation between urokinase-type plasminogen activator (uPA) expression and tumor cell invasion and metastasis has been well documented. Urokinase converts the zymogen plasminogen to plasmin, a trypsin-like enzyme with broad substrate specificities. Net uPA activity is determined not only by the amount of the enzyme itself, but also by its state of activation and the amount of specific plasminogen activator inhibitors (PAIs) present. Both uPA and its substrate, plasminogen, can bind to cells via specific membrane-associated receptors. Expression of uPA, uPA receptor (uPAR), and PAIs is regulated by growth factors, oncogenes, and other effector molecules. In the present review we discuss the interactions of uPA with its receptor, inhibitors, and substrate and how these interactions influence malignant behavior. We also review recent reports in which investigators have used anti-catalytic antibodies and/or gene transfection to demonstrate that uPA is directly involved in tumor cell invasion and metastasis.

A high-affinity receptor for urokinase plasminogen activator on human keratinocytes: characterization and potential modulation during migration

Low passage cultures of normal human keratinocytes produce several components of the plasminogen activator/plasmin proteolytic cascade, including urokinase plasminogen activator (uPA), tissue plasminogen activator (tPA), and two specific inhibitors. Studies here presented demonstrate that these cells also contain a high-affinity (Kd = 3 x 10(-10) M) plasma membrane-binding site for uPA. High molecular weight uPA, either as the single-chain precursor or two-chain activated form, bound to the receptor; however, low molecular weight (33 kD) uPA, tPA, or epidermal growth factor did not compete for binding, demonstrating specificity. Acid treatment, which removed endogenous uPA from the receptor, was required to detect maximal binding (45,000 sites per cell). To investigate the possibility that the uPA receptor on keratinocytes may be involved in epithelial migration during wound repair, cultures were wounded and allowed to migrate into the wounded site. Binding sites for uPA were localized by autoradiographic analysis of 125I-uPA binding as well as by immunocytochemical studies using anti-uPA IgG. With both techniques uPA binding sites were detected selectively on the plasma membrane of cells at the leading edge of the migrating epithelial sheet. This localization pattern suggests that uPA receptor expression on keratinocytes may be coupled to cell migration during cutaneous wounding.