The urokinase receptor

Fasciola hepatica juveniles interact with the host fibrinolytic system as a potential early-stage invasion mechanism

BACKGROUND

The trematode Fasciola hepatica is the most widespread causative agent of fasciolosis, a parasitic disease that mainly affects humans and ruminants worldwide. During F. hepatica infection, newly excysted juveniles (FhNEJ) emerge in the duodenum of the mammalian host and migrate towards their definitive location, the intra-hepatic biliary ducts. Understanding how F. hepatica traverses the intestinal wall and migrates towards the liver is pivotal for the development of more successful strategies against fasciolosis. The central enzyme of the mammalian fibrinolytic system is plasmin, a serine protease whose functions are exploited by a number of parasite species owing to its broad spectrum of substrates, including components of tissue extracellular matrices. The aim of the present work is to understand whether FhNEJ co-opt the functions of their host fibrinolytic system as a mechanism to facilitate trans-intestinal migration.

METHODOLOGY/PRINCIPAL FINDINGS

A tegument-enriched antigenic extract of FhNEJ (FhNEJ-Teg) was obtained in vitro, and its capability to bind the zymogen plasminogen (PLG) and enhance its conversion to the active protease, plasmin, were analyzed by a combination of enzyme-linked immunosorbent, chromogenic and immunofluorescence assays. Additionally, PLG-binding proteins in FhNEJ-Teg were identified by bidimensional electrophoresis coupled to mass spectrometry analysis, and the interactions were validated using FhNEJ recombinant proteins.

CONCLUSIONS/SIGNIFICANCE

Our results show that FhNEJ-Teg contains proteins that bind PLG and stimulate its activation to plasmin, which could facilitate the traversal of the intestinal wall by FhNEJ and contribute to the successful establishment of the parasite within its mammalian host. Altogether, our findings contribute to a better understanding of host-parasite relationships during early fasciolosis and may be exploited from a pharmacological and/or immunological perspective for the development of treatment and control strategies against this global disease.

Proteases as prognostic markers in human and canine cancers

The extracellular matrix (ECM) is composed of several types of proteins, which interact and form dynamic networks. These components can modulate cell behaviour and actively influence the growth and differentiation of tissues. ECM is also important in several pathological processes, such as cancer invasion and metastasis, by creating favourable microenvironments. Proteolysis in neoplastic tissues is mediated by proteinases, whose regulation involves complex interactions between neoplastic cells and non-neoplastic stromal cells. In this review, we discuss aspects of proteinase expression and tumor behaviour in humans and dogs. Different classes of proteases are summarized, with special emphasis being placed on molecules that have been shown to correlate with prognosis, reinforcing the need for a better understanding of the regulation of this microenvironment and its influences in tumor progression and metastasis, which should significantly aid the development of improved prognosis and treatment.

Expression of uPA, tPA, and PAI-1 in Calcified Aortic Valves

Purpose. Our physiopathological assumption is that u-PA, t-PA, and PAI-1 are released by calcified aortic valves and play a role in the calcification of these valves. Methods. Sixty-five calcified aortic valves were collected from patients suffering from aortic stenosis. Each valve was incubated for 24 hours in culture medium. The supernatants were used to measure u-PA, t-PA, and PAI-1 concentrations; the valve calcification was evaluated using biphotonic absorptiometry. Results. Aortic stenosis valves expressed normal plasminogen activators concentrations and overexpressed PAI-1 (u-PA, t-PA, and PAI-1 mean concentrations were, resp., 1.69 ng/mL ± 0.80, 2.76 ng/mL ± 1.33, and 53.27 ng/mL ± 36.39). There was no correlation between u-PA and PAI-1 (r = 0.3) but t-PA and PAI-1 were strongly correlated with each other (r = 0.6). Overexpression of PAI-1 was proportional to the calcium content of the AS valves. Conclusions. Our results demonstrate a consistent increase of PAI-1 proportional to the calcification. The overexpression of PAI-1 may be useful as a predictive indicator in patients with aortic stenosis.

Prognostic value of plasma soluble urokinase plasminogen activator receptor (suPAR) in Danish patients with recurrent epithelial ovarian cancer (REOC)

The level of the soluble urokinase plasminogen activator receptor (suPAR) is elevated in tumour tissue from several types of cancer. This is the first study aiming to predict the prognosis for survival by the use of a pre-chemotherapeutic plasma suPAR value in 71 patients with recurrent epithelial ovarian cancer (REOC). For determination of suPAR, pre-chemotherapeutic blood samples from the patients with REOC were processed into plasma (EDTA) within one working day from venipuncture. The plasma suPAR level is not correlated with performance status (p=0.41), FIGO stage (p=0.09), treatment-free interval (TFI) of 12 months (p=0.26), site of recurrence (peritoneum, p=0.50 or pelvis, p=0.44), age (p=0.43), or serum CA125 (p=0.09). Univariate as well as multivariate analyses cannot demonstrate that high pre-chemotherapeutic levels of plasma suPAR (p=0.22, p=0.80) are associated with shorter survival of REOC patients. Multivariate analysis showed that only TFI of 12 months (p=0.001) and performance score status of 2 (p=0.02) were independent prognostic factors. Our study indicates that pre-chemotherapeutic measurement of plasma suPAR level in REOC patients may not be useful to identify a subgroup of patients with poor prognosis.

Analysis of chicken serum proteome and differential protein expression during development in single-comb White Leghorn hens

Serum is believed to harbor thousands of distinct proteins that are either actively secreted or leak from various blood cells or tissues. Exploring protein composition in serum may accelerate the discovery of novel protein biomarkers for specific economic traits in livestock species. This study analyzed serum protein composition to establish a 2-DE reference map, and monitored protein dynamics of single-comb White Leghorn hens at 8, 19 and 23 weeks after hatching. A total of 119 CBB-stained and 315 silver-stained serum protein spots were analyzed by MALDI-TOF MS. Of these, 98 CBB-stained and 94 silver-stained protein spots were significantly matched to existing chicken proteins. The identified spots represented 30 distinctive proteins in the serum of laying hens. To compare protein expression during development, expression levels of 47 protein spots were quantified by relative spot volume with Melanie 3 software. Ten protein spots increased and 3 protein spots decreased as hen age increased. Previous research has suggested that some of these proteins play critical roles in egg production. The differentially expressed proteins with unknown identities will be valuable candidates for further explorations of their roles in egg production of laying hens.

Inhibition of invasion, angiogenesis, tumor growth, and metastasis by adenovirus-mediated transfer of antisense uPAR and MMP-9 in non-small cell lung cancer cells

Lung cancer is currently the leading cause of cancer deaths in the United States. Conventional therapeutic treatments, including surgery, chemotherapy, and radiation therapy, have achieved only limited success. The overexpression of proteases, such as urokinase-type plasminogen activator (uPA), its receptor (uPAR), and matrix metalloproteinases (MMP), is correlated with the progression of lung cancer. In the present study, we used a replication-deficient adenovirus capable of expressing antisense uPAR and antisense MMP-9 transcripts to simultaneously down-regulate uPAR and MMP-9 in H1299 cells. Ad-uPAR-MMP-9 infection of H1299 cells resulted in a dose- and time-dependent decrease of uPAR protein levels and MMP-9 activity as determined by Western blotting and gelatin zymography, respectively. Corresponding immunohistochemical analysis also showed that Ad-uPAR-MMP-9 infection inhibited uPAR and MMP-9 expression. As shown by Boyden chamber assay, Ad-uPAR-MMP-9 infection significantly decreased the invasive capacity of H1299 cells compared with mock and Ad-CMV (empty vector)-infected cells in vitro. Furthermore, Ad-uPAR-MMP-9 infection inhibited capillary-like structure formation in H1299 cells cocultured with endothelial cells in a dose-dependent manner compared with mock- and Ad-CMV-infected cells. Ad-uPAR-MMP-9 injection caused the regression of s.c. induced tumors after s.c. injection with H1299 lung cancer cells and inhibited lung metastasis in the metastatic model with A549 cells. These data suggest that Ad-uPAR-MMP-9 shows its antitumor activity against both established and early phases of lung cancer metastases by causing the destruction of the tumor vasculature. In summary, adenovirus-mediated inhibition of uPA-uPAR interaction and MMP-9 on the cell surface may be a promising anti-invasion and antimetastatic strategy for cancer gene therapy.

Regulation of urokinase receptor expression by phosphoglycerate kinase is independent of its catalytic activity

Posttranscriptional regulation of urokinase-type plasminogen activator receptor (uPAR) mRNA involves the interaction of a uPAR mRNA coding region sequence with phosphoglycerate kinase (PGK), a 50-kDa uPAR mRNA binding protein. PGK catalyzes a reversible transfer of a phosphoryl group from 1,3-biphosphoglycerate to ADP in the glycolytic pathway. Our previous studies showed that overexpression of PGK in uPAR-overproducing H157 lung carcinoma cells results in decreased cytoplasmic uPAR mRNA and cell surface uPAR protein expression through destabilization of the mRNA. In order to determine the role of PGK enzymatic activity on uPAR mRNA stability we mutated PGK by changing amino acid P204H and amino acid D219A. The mutant proteins were expressed in Epicurian coli BL21 cells, and the purified proteins were analyzed for PGK activity. We found that mutation of amino acid P204H and D219A reduced PGK activity by 99 and 83%, respectively. By gel mobility shift and Northwestern assay, we found that the mutant proteins were able to bind to uPAR mRNA as effectively as wild-type PGK. Overexpression of mutant, inactive PGK in H157 cells reduced cell surface uPAR protein as well as uPAR mRNA expression. Run-on transcription analysis indicated that overexpression of mutant PGKs fails to alter the rate of synthesis of uPAR mRNA, whereas transcription chase experiments demonstrated that both mutants and wild-type PGK reduce the stability of the uPAR mRNA transcripts to a similar extent. Overexpression of mutant PGK also inhibited the rate of DNA synthesis and the invasion-migration ratio. These results demonstrate that uPAR mRNA binding activity as well as PGK-mediated regulation of uPAR mRNA are independent of PGK enzymatic activity.

Urokinase plasminogen activator (uPA) and its receptor (uPAR) in gestational tissues; Measurements and clinical implications

BACKGROUND

Urokinase plasminogen activator (uPA) and urokinase plasminogen activator receptor (uPAR) are central molecules for uPA/uPAR/plasmin-dependent proteolysis, which is thought to play a significant role in the development of pregnancy, as well as its many complications.

OBJECTIVE

To measure the levels of uPA and uPAR in the placenta and myometrium, as well as in the foetal membranes and amniotic fluid.

STUDY DESIGN

The study group consisted of 35 women with normal course of pregnancy, but with complications arising during delivery, which led to Caesarean section. Samples of placenta, myometrium, foetal membranes, amniotic fluid and blood were obtained at the time of operation. Tissue extracts were prepared. Measurements were made by the ELISA method.

RESULTS

uPA and uPAR concentration in gestational tissues, including amniotic fluid, is 100-200 times higher than in plasma. Among tissues, the highest uPA level was found in placenta ( 1.32 +/- 0.48 ng/mg of protein), and the highest uPAR level in foetal membranes (3.33 +/- 1.20 ng/mg of protein).

CONCLUSIONS

uPA and uPAR are present in all gestational tissues, in some in relatively high concentrations. Our results support the modern clinical hypothesis that fibrinolytic system can participate in mechanisms of such obstetric complications as pre-term pre-mature rupture of foetal membranes and placental abruption.

Differential regulation of urokinase-type plasminogen activator expression by fluid shear stress in human coronary artery endothelial cells

Atherosclerotic plaques preferentially localize at arterial regions exposed to turbulent low-shear flow. Urokinase-type plasminogen activator (uPA) plays a role in vascular remodeling by facilitating smooth muscle cell migration and proliferation in addition to the proteolysis of extracellular matrix, and the expression of uPA is elevated in atherosclerotic lesions. In this study, we analyzed the effects of laminar and turbulent shear stress on uPA expression in cultured human coronary artery endothelial cells. The application of laminar shear stress (1.5 or 15 dyn/cm2) significantly decreased the amount of uPA mRNA as well as the secretion of uPA protein. In contrast, turbulent shear stress (average intensity, 1.5 dyn/cm2) markedly increased uPA gene expression and protein secretion. Laminar shear stress downregulated uPA gene expression transcriptionally and posttranscriptionally; laminar shear stress activated transcription factor GATA6, which binds to a GATA consensus element located between -692 and -687 bp in the uPA promoter, thereby inhibiting uPA gene transcription. Laminar shear stress also accelerated the degradation of uPA mRNA; the half-life of uPA mRNA decreased to about half of the static control's half-life. Although turbulent shear stress had no effect on the transcription of uPA, it significantly increased uPA mRNA stability; the half-life of uPA mRNA increased by about two times the static control's half-life. Our results suggest that endothelial uPA expression is flow sensitive and differentially regulated by laminar and turbulent shear stress in vitro. We speculate that this effect may contribute to the local nature of atherosclerosis.

Urokinase-mediated posttranscriptional regulation of urokinase-receptor expression in non small cell lung carcinoma

The urokinase-type plasminogen activator (uPA) and its cellular receptor (uPAR) are involved in the proteolytic cascade required for tumor cell dissemination and metastasis, and are highly expressed in many human tumors. We have recently reported that uPA, independently of its enzymatic activity, is able to increase the expression of its own receptor in uPAR-transfected kidney cells at a posttranscriptional level. In fact, uPA, upon binding uPAR, modulates the activity and/or the level of a mRNA-stabilizing factor that binds the coding region of uPAR-mRNA. We now investigate the relevance of uPA-mediated posttranscriptional regulation of uPAR expression in non small cell lung carcinoma (NSCLC), in which the up-regulation of uPAR expression is a prognostic marker. We show that uPA is able to increase uPAR expression, both at protein and mRNA levels, in primary cell cultures obtained from tumor and adjacent normal lung tissues of patients affected by NSCLC, thus suggesting that the enzyme can exert its effect in lung cells. We investigated the relationship among the levels of uPA, uPAR and uPAR-mRNA binding protein(s) in NSCLC. Lung tissue analysis of 35 NSCLC patients shows an increase of both uPA and uPAR in tumor tissues, as compared to adjacent normal tissues, in 27 patients (77%); 19 of these 27 patients also show a parallel increase of the level and/or binding activity of a cellular protein capable of binding the coding region of uPAR-mRNA. Therefore, in tumor tissues, a strong correlation is observed among these 3 parameters, uPA, uPAR and the level and/or the activity of a uPAR-mRNA binding protein. We then suggest that uPA regulates uPAR expression in NSCLC at a posttranscriptional level by increasing uPAR-stability through a cellular factor that binds the coding region of uPAR-mRNA.

Receptor-independent role of the urokinase-type plasminogen activator during arteriogenesis

To define the role of the plasminogen activators (PAs) urokinase PA (uPA) and tissue PA (tPA) as well as the uPA receptor (uPAR) in arteriogenesis, we investigated their impact in a rabbit and mouse model of adaptive collateral artery growth. Collateral artery growth was induced by occlusion of the femoral artery in rabbit and wild-type (WT) mice and in mice with targeted inactivation of uPA (uPA-/-), tPA (tPA-/-), or uPAR (uPAR-/-). Northern blot results revealed a significant up-regulation of uPA but not uPAR or tPA in the early phase of arteriogenesis in rabbit and WT mice. This up-regulation on RNA level was followed by an increased protein level and enzymatic activity. Impaired perfusion recovery upon femoral artery ligation was observed by laser Doppler analysis in vivo in uPA-deficient mice but not in uPAR or tPA deficiency compared with WT mice. Immunohistochemical studies revealed an association of leukocyte infiltration with arteriogenesis in WT mice that was strongly reduced in uPA-/- but not in uPAR- or tPA-deficient mice. We conclude that arteriogenesis is promoted by an uPA-mediated infiltration of leukocytes that is not dependent on uPAR.

Urokinase-type plasminogen activator up-regulates the expression of its cellular receptor through a post-transcriptional mechanism

We have recently reported that the urokinase-type plasminogen activator (uPA) up-regulates the cell surface expression of its own receptor (uPAR) in several cell types, independently of its enzymatic activity. uPA has no effect on kidney 293 cells which do not express uPAR and then cannot bind uPA. Kidney cells, transfected with the coding region of uPAR cDNA, express very large amounts of uPAR and respond to uPA stimulation by regulating uPAR both at mRNA and protein levels. uPA effect occurs also in the presence of the transcriptional inhibitor dichloro-ribobenzimidazole, whereas it is abolished by the protein synthesis inhibitor cycloheximide. Moreover, uPA-dependent uPAR up-regulation correlates with the increase of a complex between the coding region of uPAR mRNA and an unknown cellular factor. We then propose that uPA regulates uPAR expression at a post-transcriptional level, by promoting the binding of uPAR mRNA to a stabilizing factor.

Cancer cell expression of urokinase-type plasminogen activator receptor mRNA in squamous cell carcinomas of the skin

In this study we have used in situ hybridization with radiolabeled antisense RNA probes to examine the expression of mRNA for urokinase-type plasminogen activator and its receptor in histologic samples of squamous cell (n = 7) and basal cell (n = 7) carcinomas of the skin. Messenger RNA for both urokinase-type plasminogen activator and its receptor were expressed in all of the squamous cell carcinomas, but could not be detected in the basal cell carcinomas. In all of the seven squamous cell carcinomas a signal for urokinase-type plasminogen activator receptor mRNA was detected focally in well-differentiated cancer cells surrounding keratinized pearls, and in four specimens urokinase-type plasminogen activator receptor mRNA was in addition expressed by cancer cells at the edge of invasively growing strands of tumor. Urokinase-type plasminogen activator mRNA expression was found in virtually all the cancer cells of the squamous cell carcinomas, and importantly we found, by hybridizations for urokinase-type plasminogen activator and its receptor mRNA on adjacent sections of squamous cell carcinomas, that it was exactly the invading cancer cells that simultaneously expressed both these components required for plasmin-mediated proteolysis at the cell surface. We have previously shown that both urokinase-type plasminogen activator and its receptor mRNA are expressed by the leading-edge keratinocytes in regenerating epidermis during mouse skin wound healing, and that wound healing is impaired in mice made deficient in plasminogen by targeted gene disruption. We propose that there are similarities between the mechanisms of generation and regulation of extracellular proteolysis during skin re-epithelialization and squamous cell carcinoma invasion. The ability of the squamous carcinoma cells to mimic the "invasive" phenotype of re-epithelializing keratinocytes may be one of the factors that make squamous cell carcinomas more aggressive tumors than basal cell carcinomas.

Urokinase stimulates differentiation of fibroblasts into myofibroblasts and their proliferation in damaged adventitia

Urokinase expression in the adventitia of rat common carotid artery increased on the 4th day after periadventitial damage. Periadventitial application of recombinant urokinase increased the area of the adventitia and the content of contractile and proliferating cells, while proteolytically inactive recombinant urokinase was ineffective.

Transgenic mouse models in angiogenesis and cardiovascular disease

Novel gene technologies have allowed us to manipulate the genetic balance of candidate molecules in mice in a controllable manner. Homologous or site-specific recombination in embryonic stem cells allows us to study the consequences of deficiencies, mutations, and conditional or tissue-specific expression of gene products in transgenic mice. These technological breakthroughs have significantly advanced biomedical research and broadened our understanding of the pathophysiological role of candidate disease genes. In addition, gene transfer allows us to test the possible therapeutic use of gene products for gene therapy. A variety of assays have been miniaturized, allowing analysis of cardiovascular physiology in the mouse. With the advent of genome sequencing programmes, these gene technologies provide means of studying gene function in a conclusive manner. Furthermore, disease models can be generated which can be used as test models for (gene) therapy or for the discovery of novel genes using differential gene profiling techniques. The present review will focus on the molecular basis of how blood vessels form (angiogenesis and arteriogenesis) and how they become diseased. A selected number of molecules that have been studied in the authors' laboratory will be reviewed in more detail.

Gene response of human skin fibroblasts to urokinase- and tissue-type plasminogen activators

In a previous work we have reported evidences on the mitogenic activity of urokinase-type and tissue-type plasminogen activator (u-PA, t-PA) on serum-deprived human dermal fibroblasts. In this work we have studied the transcription-dependent changes of some cell-cycle related genes associated with the biological activity of PAs, as well as the possible involvement of protein tyr kinases (PTK) and/or protein kinase C (PKC) in the mitogenic signal transduction. The data obtained demonstrate that the growth factor activity of PAs is associated with: - a rapid transient activation of early response genes, c-fos, c-jun and c-myc; - the subsequent coordinated down-regulation of p53 and p21CIP1; - the constant expression of the MEK1 mRNA in every phase of the cell cycle. Quiescent (G0) cells did not express c-fos, c-jun, c-myc and cyclin A, but upon stimulation with mitogens (fetal calf serum (FCS), u-PA, t-PA) the cyclin A mRNA expression was observed in concomitance with the activation of DNA synthesis. Therefore u-PA, t-PA and FCS similarly modulate the expression of c-fos, c-jun, c-myc, p53, p21CIP1 and cyclin A with only slight differences likely related to the time required for activation of DNA synthesis. The PAs mitogenic stimulation of serum-starved cells was associated with the internalization of their molecules, as revealed by immunostaining. The biological activity of u-PA, t-PA, as well as that of limiting concentration of FCS (1%), was mediated by PTK and PKC. Conversely, PTK, but not PKC, was involved in the activation of the proliferative response of basic fibroblast growth factor in the same experimental conditions. In conclusion, u-PA and t-PA can utilize two different pathways, one depending on PTK and the other on PKC in a way similar to the mitogenic activity induced by low concentration of FCS (1%).

Chemotactic effect of urokinase plasminogen activator: a major role for mechanisms independent of its proteolytic or growth factor domains

Urokinase type plasminogen activator (uPA) converts plasminogen to plasmin and is highly chemotactic for many cell types. We examined, using recombinant wild type and mutated forms of uPA, the extent to which its proteolytic properties, its growth-like domain (GFD) and/or interactions with the specific receptor (uPAR) contribute to the chemotactic activity towards vascular smooth muscle cells (SMC). Recombinant wild type uPA (r-uPA) stimulated cell migration nearly 5.8-fold, inactive r-uPA, with a mutation in the catalitic domain (r-uPA(H/Q)), 3-fold, uPA without growth factor like domain (r-uPA(GFD )), 2.6-fold, and a form containing both mutations (r-uPA(H/Q, GFD ), 3.3-fold. All recombinant forms of uPA, wild type and those with mutations were equally and highly effective (IC50 approximately 20 nM) in displacing 125I-r-uPA bound to SMC. These results indicate that additional mechanisms, not dependent on uPA's proteolytic activity or the binding ability of its GFD to uPAR, are the major contributors to its chemotactic action on SMC.

Plasma urokinase antigen and plasminogen activator inhibitor-1 antigen levels predict angiographic coronary restenosis

BACKGROUND

The fibrinolytic system is intimately involved in several processes that contribute to restenosis, including clot dissolution, cell migration, and tissue remodeling. However, the role of the individual activators (urokinase [uPA] and tissue plasminogen [tPA] activators) and inhibitors (plasminogen activator inhibitor [PAI-1]) of the fibrinolytic system in maintaining patency after coronary artery angioplasty and stenting is unclear.

METHODS AND RESULTS

We prospectively studied 159 patients with stable angina who underwent successful elective angioplasty (n=110) or stenting (n=49) of de novo native coronary artery lesions. Plasma samples were drawn at baseline (before angioplasty) and serially after angioplasty (immediately afterward and 6 hours, 24 hours, 3 days, 7 days, 1 month, 3 months, and 6 months afterward). Antigen and activity assays were performed for uPA, tPA, and PAI-1. Follow-up quantitative coronary angiography was performed in 92% of eligible patients. The overall angiographic restenosis rate (diameter stenosis >50%) was 31% (37% in PTCA patients, 17% in stented patients). At all time periods, including baseline, uPA antigen levels were significantly higher and PAI-1 antigen levels were significantly lower in patients with restenosis. Restenosis rates for patients in the upper tertile of baseline uPA antigen levels were 2-fold higher than for those in the lower 2 tertiles (46% versus 24% and 22%, respectively; P<0.004). In a stepwise regression multivariate analysis, obstruction diameter after the procedure and uPA antigen were significant predictors of follow-up diameter stenosis.

CONCLUSIONS

Plasma uPA antigen levels and PAI-1 antigen levels identify patients at increased risk for restenosis after percutaneous coronary revascularization.

Urokinase-type plasminogen-activator and normal thyroid cell adhesion to the extracellular matrix

The urokinase-type plasminogen activator receptor (uPA-R) focuses the proteolytic activity of its ligand, the urokinase-type plasminogen activator (uPA), on the cell surface, and can also act as an adhesion receptor for vitronectin (VTN). uPA increases uPA-R affinity for VTN and is also able to cleave its receptor. We have previously shown that uPA-R is involved in the adhesion of normal thyroid cells to VTN. In the present report, we have investigated the effect of uPA on normal thyroid cell adhesion to some extracellular matrix (ECM) components. We show that a short-term treatment with uPA does not change normal thyroid cell adhesion to fibronectin (FNT), collagen (CGN), laminin (LMN) and VTN. The prolongation of uPA treatment increases cell adhesion to VTN, and, less efficiently, to other ECM components. Since the short term uPA treatment causes a partial cleavage of uPA-R, that does not increase with time, the observed increase in cell adhesivity cannot be related to the cleavage of uPA-R. We show that the adhesion improvement after the long term uPA treatment is instead due to a strong increase of the cell-surface expression of the integrin beta3 and a moderate increase of the integrin alpha(v). Both alpha(v) beta3 and alpha(v) beta1 are integrinic receptors for VTN.

Cancer cells overexpress mRNA of urokinase-type plasminogen activator, its receptor and inhibitors in human non-small-cell lung cancer tissue: analysis by Northern blotting and in situ hybridization

The transcriptional localizations of urokinase-type plasminogen activator (uPA), its receptor (uPAR) and its inhibitors (PAI-1 and PAI-2), which are possibly involved in cancer metastasis, have not been determined in human lung cancer. To identify their regulation in primary non-small-cell lung cancer, we assayed mRNA levels by Northern blot analysis in 25 cases and determined the localizations of mRNA by in situ hybridization in 10 cases. The amounts of uPA and PAI-2 mRNA were significantly higher in cancerous relative to normal lung tissues. However, no significant difference was observed in uPAR and PAI-1 mRNA levels. All transcripts were present in cancer cells and were predominantly located in tumor edges in several cases. In addition, PAI-1 transcripts were more abundant in poorly and moderately differentiated carcinomas relative to well-differentiated carcinomas and PAI-2 transcripts were more abundant in squamous cell carcinomas than in adenocarcinomas. Thus, PAIs may be involved in modulation of malignant potency. Our results indicate that human non-small-cell lung cancer cells can autonomously express the mRNAs of uPA, uPAR and PAIs, which are possibly involved in metastasis.

Function of the plasminogen/plasmin and matrix metalloproteinase systems after vascular injury in mice with targeted inactivation of fibrinolytic system genes

The matrix metalloproteinase (MMP) system, which may be activated via the plasminogen (Plg)/plasmin system, is claimed to play a role in matrix degradation and smooth muscle cell migration. To test the role of both systems, expression of fibrinolytic and gelatinolytic activity was quantified after vascular injury in mice with targeted inactivation of tissue-type Plg activator (tPA-/-), urokinase-type Plg activator (uPA-/-), or Plg (Plg-/-). Neointima formation 1 week after vascular injury was impaired in uPA-/- and Plg-/- mice compared with wild-type (WT) mice or tPA-/- mice (reduction of neointimal area to 30% and 10% of WT, respectively). Cell accumulation at the borders of the injury was significantly (P<0.01) impaired compared with that in WT mice. One week after injury of the femoral artery, tPA-mediated fibrinolytic activity in arterial sections or extracts of WT, uPA-/-, or Plg-/- mice was not altered, whereas uPA activity levels in tPA-/- and Plg-/- mice were 2- to 3-fold higher than in uninjured controls. Total levels (latent plus active) of MMP-2 (gelatinase A) were increased by 2- to 4-fold, whereas the contribution of active MMP-2 represented 38% to 63% of the total in the different genotypes. MMP-9 (gelatinase B) was not detectable in the majority of control arteries, whereas total MMP-9 levels after injury were dramatically increased (up to 50-fold above the detection limit). Active MMP-9 represented 20% to 46% of total MMP-9 in WT, tPA-/-, and uPA-/- mice but was not consistently detectable in Plg-/- mice. Similar results were obtained in carotid arteries. Thus, the unaltered ratios of active and latent MMP-2 suggest that proMMP-2 activation may occur in the absence of tPA, uPA, or Plg, whereas no active MMP-9 was detected in the absence of Plg. The data of this study confirm a role for uPA and Plg but not for tPA in smooth muscle cell migration and neointima formation after vascular injury and indicate that impairment of these phenomena may occur despite the observed increases in MMP-2 or MMP-9 levels after vascular injury.

Hypoxia Stimulates Urokinase Receptor Expression Through a Heme Protein-Dependent Pathway

Hypoxia underlies a number of biologic processes in which cellular migration and invasion occur. Because earlier studies have shown that the receptor for urokinase-type plasminogen activator (uPAR) may facilitate such events, we studied the effect of hypoxia on the expression of uPAR by first trimester human trophoblasts (HTR-8/SVneo) and human umbilical vein endothelial cells (HUVEC). Compared with control cells cultured under standard conditions (20% O2), HTR-8/SVneo cells and HUVEC cultured in 1% O2 expressed more uPAR, as determined by flow cytometric and [125I]-prourokinase ligand binding analyses. Increased uPAR expression paralleled increases in uPAR mRNA. The involvement of a heme protein in the hypoxia-induced expression of uPAR was suggested by the observations that culture of cells with cobalt chloride, or sodium 4,5-dihydroxybenzene-1,3-disulfonate (Tiron), an iron-chelating agent, also stimulated uPAR expression, and that the hypoxia-induced uPAR expression was inhibited by adding carbon monoxide to the hypoxic atmosphere. Culture of HTR-8/SVneo cells with vascular endothelial growth factor (VEGF) did not increase uPAR mRNA levels, suggesting that the hypoxia-mediated effect on uPAR expression by these cells did not occur through a VEGF-dependent mechanism. The functional importance of these findings is suggested by the fact that HTR-8/SVneo cells cultured under hypoxia displayed higher levels of cell surface plasminogen activator activity and greater invasion through a reconstituted basement membrane. These results suggest that hypoxia may promote cellular invasion by stimulating the expression of uPAR through a heme protein-dependent pathway.

Hypoxia Stimulates Urokinase Receptor Expression Through a Heme Protein-Dependent Pathway

Hypoxia underlies a number of biologic processes in which cellular migration and invasion occur. Because earlier studies have shown that the receptor for urokinase-type plasminogen activator (uPAR) may facilitate such events, we studied the effect of hypoxia on the expression of uPAR by first trimester human trophoblasts (HTR-8/SVneo) and human umbilical vein endothelial cells (HUVEC). Compared with control cells cultured under standard conditions (20% O2), HTR-8/SVneo cells and HUVEC cultured in 1% O2 expressed more uPAR, as determined by flow cytometric and [125I]-prourokinase ligand binding analyses. Increased uPAR expression paralleled increases in uPAR mRNA. The involvement of a heme protein in the hypoxia-induced expression of uPAR was suggested by the observations that culture of cells with cobalt chloride, or sodium 4,5-dihydroxybenzene-1,3-disulfonate (Tiron), an iron-chelating agent, also stimulated uPAR expression, and that the hypoxia-induced uPAR expression was inhibited by adding carbon monoxide to the hypoxic atmosphere. Culture of HTR-8/SVneo cells with vascular endothelial growth factor (VEGF) did not increase uPAR mRNA levels, suggesting that the hypoxia-mediated effect on uPAR expression by these cells did not occur through a VEGF-dependent mechanism. The functional importance of these findings is suggested by the fact that HTR-8/SVneo cells cultured under hypoxia displayed higher levels of cell surface plasminogen activator activity and greater invasion through a reconstituted basement membrane. These results suggest that hypoxia may promote cellular invasion by stimulating the expression of uPAR through a heme protein-dependent pathway.

Receptor-independent role of urokinase-type plasminogen activator in pericellular plasmin and matrix metalloproteinase proteolysis during vascular wound healing in mice

It has been proposed that the urokinase receptor (u-PAR) is essential for the various biological roles of urokinase-type plasminogen activator (u-PA) in vivo, and that smooth muscle cells require u-PA for migration during arterial neointima formation. The present study was undertaken to evaluate the role of u-PAR during this process in mice with targeted disruption of the u-PAR gene (u-PAR-/-). Surprisingly, u-PAR deficiency did not affect arterial neointima formation, neointimal cell accumulation, or migration of smooth muscle cells. Indeed, topographic analysis of arterial wound healing after electric injury revealed that u-PAR-/- smooth muscle cells, originating from the uninjured borders, migrated over a similar distance and at a similar rate into the necrotic center of the wound as wild-type (u-PAR+/+) smooth muscle cells. In addition, u-PAR deficiency did not impair migration of wounded cultured smooth muscle cells in vitro. There were no genotypic differences in reendothelialization of the vascular wound. The minimal role of u-PAR in smooth muscle cell migration was not because of absent expression, since wild-type smooth muscle cells expressed u-PAR mRNA and functional receptor in vitro and in vivo. Pericellular plasmin proteolysis, evaluated by degradation of 125I-labeled fibrin and activation of zymogen matrix metalloproteinases, was similar for u-PAR-/- and u-PAR+/+ cells. Immunoelectron microscopy of injured arteries in vivo revealed that u-PA was bound on the cell surface of u-PAR+/+ cells, whereas it was present in the pericellular space around u-PAR-/- cells. Taken together, these results suggest that binding of u-PA to u-PAR is not required to provide sufficient pericellular u-PA-mediated plasmin proteolysis to allow cellular migration into a vascular wound.

Urokinase but not tissue plasminogen activator mediates arterial neointima formation in mice

To define the role of the plasminogen activators (PAs) tissue PA (t-PA) and urokinase PA (u-PA) in vascular wound healing, neointima formation and reendothelialization were evaluated after electric or mechanical arterial injury in mice with a single or combined deficiency of t-PA (t-PA-/-) and/or u-PA (u-PA-/-). In both models, neointima formation and neointimal cell accumulation were reduced in u-PA-/- and in t-PA-/-/u-PA-/- arteries but not in t-PA-/- arteries. The electric injury model was used to characterize the underlying cellular mechanisms. Topographic analysis of vascular wound healing in electrically injured wild-type and t-PA-/- arteries revealed a similar degree of migration of smooth muscle cells from the noninjured borders into the necrotic center. In contrast, in u-PA-/- and t-PA-/-/u-PA-/- arteries, smooth muscle cells accumulated at the uninjured borders but failed to migrate into the necrotic center. Cultured u-PA-/- but not t-PA-/- smooth muscle cells also failed to migrate in vitro after scrape wounding. Proliferation of smooth muscle cells was not affected by PA deficiency. Reendothelialization after electric injury was similar in all genotypes. In situ analysis revealed markedly elevated u-PA zymographic activity, mRNA, and immunoreactivity in smooth muscle cells, endothelial cells, and leukocytes within 1 week after injury, eg, when cells migrated into the wound. Thus, u-PA plays a significant role in vascular wound healing and arterial neointima formation after injury, most likely by affecting cellular migration.

Molecular analysis of blood vessel formation and disease

Blood vessels affect the quality of life in many ways. They provide an essential nutritive function during growth and repair of tissues but, on the other hand, can become affected by disorders or trauma, resulting in bleeding, thrombosis, arterial stenosis, and atherosclerosis. Three molecular systems, the vascular endothelial growth factor (VEGF) system, the plasminogen system, and the coagulation system, have been implicated in the formation and pathobiology of blood vessels. This review focuses on the role of these systems in these processes. Recent gene-targeting studies have identified VEGF as a potent modulator of the formation of endothelial cell-lined channels. Somewhat unanticipated, the initiator of coagulation is not only involved in the control of hemostasis but also in the maturation of a muscular wall around the endothelium. With different murine models of cardiovascular disease, a pleiotropic role of the plasminogen system was elucidated in thrombosis, in arterial neointima formation after vascular wound healing and allograft transplantation, in atherosclerosis, and in the formation of atherosclerotic aneurysms. Surprisingly, tissue-type plasminogen activator is also involved in brain damage after ischemic or neurotoxic insults. The insights from these gene-targeting studies have formed the basis for designing gene therapy strategies for restenosis and thrombosis, which have been successfully tested in these knockout models.

The urokinase-type plasminogen activator system in cancer metastasis: a review

The urokinase-type plasminogen activator (u-PA) system consists of the serine proteinases plasmin and u-PA; the serpin inhibitors alpha2-anti-plasmin, PAI-1 and PAI-2; and the u-PA receptor (u-PAR). Two lines of evidence have strongly suggested an important and apparently causal role for the u-PA system in cancer metastasis: results from experimental model systems with animal tumor metastasis and the finding that high levels of u-PA, PAI-1 and u-PAR in many tumor types predict poor patient prognosis. We discuss here recent observations related to the molecular and cellular mechanisms underlying this role of the u-PA system. Many findings suggest that the system does not support tumor metastasis by the unrestricted enzyme activity of u-PA and plasmin. Rather, pericellular molecular and functional interactions between u-PA, u-PAR, PAI-1, extracellular matrix proteins, integrins, endocytosis receptors and growth factors appear to allow temporal and spatial re-organizations of the system during cell migration and a selective degradation of extracellular matrix proteins during invasion. Differential expression of components of the system by cancer and non-cancer cells, regulated by paracrine mechanisms, appear to determine the involvement of the system in cancer cell-directed tissue remodeling. A detailed knowledge of these processes is necessary for utilization of the therapeutic potential of interfering with the action of the system in cancers.

Soluble human urokinase receptor is composed of two active units

The mechanism by which single-chain urokinase (scuPA) binds to its receptor (uPAR) is incompletely understood. We report that a fragment comprising the first domain of recombinant soluble uPAR (sDI) as well as a fragment comprising the remaining domains (sDII-DIII) competes with the binding of recombinant full-length soluble uPAR (suPAR) to scuPA with an IC50 = 253 nM and an IC50 = 1569, respectively. sDII-III binds directly to scuPA with Kd = 238 nM. Binding of scuPA to each fragment also induces the expression of plasminogen activator activity. sDI and sDII-DIII (200 nM each) induced activity equal to 66 and 36% of the maximum activity induced by full-length suPAR (5 nM), respectively. Each fragment also stimulates the binding of scuPA to cells lacking endogenous uPAR. Although scuPA binds to sDI and to sDII-DIII through its amino-terminal fragment, the fragments act synergistically to inhibit the binding of suPAR and to stimulate plasminogen activator activity. Furthermore, sDII-DIII retards the velocity and alters the pattern of cleavage of sDI by chymotrypsin. These results suggest that binding of scuPA to more than one epitope in suPAR is required for its optimal activation and association with cell membranes.

Role of fibrin and plasminogen activators in repair-associated angiogenesis: in vitro studies with human endothelial cells

Angiogenesis, the formation of new blood vessels from existing ones, plays a central role in development and in a number of pathological conditions. Tissue repair-associated angiogenesis usually involves cell invasion into a fibrin structure and the presence of inflammatory cells. In this chapter the role of plasminogen activators in the dissolution of fibrin and the invasion of endothelial cells into a fibrin matrix is described. Tissue-type plasminogen activator is stored in endothelial cells and can be released acutely into the vessel lumen upon stimulation of the endothelium to activate fibrinolysis and to prevent fibrin deposition. At the basolateral side of the cell, urokinase-type plasminogen activator (uPA) bound to a specific cellular receptor is involved in the proteolytic modulation of matrix proteins and cell-matrix interaction. The cytokine tumor necrosis factor-alpha (TNF-alpha) cooperates with the angiogenic factors basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) in inducing human microvascular endothelial cells in vitro to invade a three dimensional fibrin matrix and to form capillary-like tubular structures. The formation of these capillary-like tubules requires cell-bound uPA activity.

Loss of fibrinogen rescues mice from the pleiotropic effects of plasminogen deficiency

Plasmin(ogen) is an extracellular serine protease implicated in the activation of latent growth factors and procollagenase, degradation of extracellular matrix components, and fibrin clearance. Plasminogen (Plg) deficiency in mice results in high mortality, wasting, spontaneous gastrointestinal ulceration, rectal prolapse, and severe thrombosis. Furthermore, Plg-deficient mice display delayed wound healing following skin injury, a defect partly related to impaired keratinocyte migration. We generated mice deficient in Plg and fibrinogen (Fib) and show that removal of fibrin(ogen) from the extracellular environment alleviates the diverse spontaneous pathologies previously associated with Plg deficiency and corrects healing times. Mice deficient in Plg and Fib are phenotypically indistinguishable from Fib-deficient mice. These data suggest that the fundamental and possibly only essential physiological role of Plg is fibrinolysis.

Urokinase-type plasminogen activator/type-2 plasminogen-activator inhibitor complexes are not internalized upon binding to the urokinase-type-plasminogen-activator receptor in THP-1 cells. Interaction of urokinase-type plasminogen activator/type-2 plasminogen-activator inhibitor complexes with the cell surface

The urokinase-type plasminogen activator (uPA) and its inhibitor PAI-2 form a covalent complex that, upon binding to the uPA receptor (uPA-R), is cleaved into two fragments of molecular masses 70 kDa and 22 kDa. The 70-kDa fragment results from the interaction of the B chain of uPA and PAI-2 whereas the 22-kDa fragment is the A chain of the enzyme [13]. We prove that, at 37 degrees C, the 70-kDa fragment is released into the medium, whereas the 22-kDa fragment remains bound to the cell surface. uPA complexed with its other specific inhibitor, PAI-1, is cleaved into fragments of identical sizes, but the 70-kDa component is internalized via the alpha 2-macroglobulin receptor. At 4 degrees C, both uPA/PAI-2 complex degradation products remain bound to the uPA-R. We propose that the 70-kDa molecule, which lacks the uPA binding region for uPA-R, is bound to uPA-R via a new binding site, unmasked only when uPA-R is occupied by uPA/PAI-2 complexes.

A competitive chromogenic assay to study the functional interaction of urokinase-type plasminogen activator with its receptor

Urokinase-type plasminogen activator (uPA) converts plasminogen to plasmin which degrades various extracellular matrix components. uPA is focused to the cell surface via binding to a specific receptor (uPAR, also termed CD87). uPAR-bound uPA mediates pericellular proteolysis in a variety of biological processes, e.g. cell migration, tissue remodeling and tumor invasion. We have developed a competitive microtiter plate-based chromogenic assay which allows the analysis of uPA/uPAR interaction. The plates are coated with recombinant uPAR expressed in Chinese hamster ovary (CHO) cells. Proteolytically active uPA (HMW-uPA) is added to the microtiter plate-attached uPAR. The amount of receptor-bound uPA is then determined indirectly via addition of plasminogen, which is activated to plasmin, followed by cleavage of a plasmin-specific chromogenic substrate. Substances interfering with binding of HMW-uPA to uPAR diminish the generation of plasmin, as indicated by a reduction of cleaved chromogenic substrate. This assay was used to analyze the inhibitory capacity of a variety of proteins and peptides, respectively, on the uPA/uPAR interaction: i) uPAR and uPAR-variants expressed in CHO cells, yeast or E. coli, ii) the aminoterminal fragment (ATF) of human uPA or yeast recombinant pro-uPA, iii) synthetic peptides derived from the sequence of the uPAR-binding region of uPA, and iv) antibodies directed against uPAR. This assay may be helpful in identifying uPA and uPAR analogues or antagonists which efficiently block uPA/uPAR interaction.

Mechanisms of physiological fibrinolysis

The fibrinolytic system comprises an inactive proenzyme, plasminogen, that is converted by plasminogen activators to the active enzyme, plasmin, which degrades fibrin. Two immunologically distinct plasminogen activators (PA) have been identified: tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). t-PA mediated plasminogen activation is mainly involved in the dissolution of fibrin in the circulation, whereas u-PA mediated plasminogen activation mainly plays a role in pericellular proteolysis. Plasminogen activation is regulated by specific molecular interactions between its main components, such as binding of plasminogen and t-PA to fibrin, or to specific cellular receptors resulting in enhanced plasminogen activation, inhibition of t-PA and u-PA by plasminogen activator inhibitors (PAI) and inhibition of plasmin by alpha 2-antiplasmin. Controlled synthesis and release of PAs and PAIs primarily from endothelial cells also contributes to the regulation of physiological fibrinolysis. The lysine binding sites situated in the kringle structures of plasminogen play a crucial role in the regulation of fibrinolysis by modulating its binding to fibrin and to cell surfaces, and by controlling the inhibition rate of plasmin by alpha 2-antiplasmin.

Physiological consequences of over- or under-expression of fibrinolytic system components in transgenic mice

Studies with transgenic mice over- or under-expressing components of the fibrinolytic system, have revealed a significant role of this system in fibrin clot surveillance, reproduction, (vascular) wound healing, brain function, health and survival. The distinct phenotypes associated with single loss and the more severe phenotype associated with combined loss of plasminogen activator gene function suggest that through evolution, both plasminogen activators have evolved with specific but overlapping biological properties. Interestingly, the role of the fibrinolytic system in thrombosis and vascular wound healing became more apparent after challenging mice single deficiencies of plasminogen activators with an inflammatory, or traumatic challenge, respectively. It therefore seems warranted to examine possible consequences of loss of plasminogen activator gene function in other processes including atherosclerosis, neoangiogenesis, inflammatory lung and kidney disease and malignancy. The plasminogen activator knock-out mice with their thrombotic phenotypes are also valuable models to evaluate whether adenoviral mediated gene-transfer of wild-type or mutant plasminogen activator genes is able to restore normal thrombolytic function and to prevent thrombosis. Preliminary evidence suggests that impaired thrombolysis of t-PA deficient mice can be completely restored using adenoviral-mediated gene transfer of rt-PA (Carmeliet et al, 1994c). In addition, analysis of neointima formation in plasminogen activator deficient mice suggests that controlled reduction of fibrinolytic activity in the vessel wall might be beneficial for the prevention or reduction of restenosis. Whether this can be achieved with gene transfer methodologies remains to be defined.

Plasminogen activator inhibitor type 1 in cancer: therapeutic and prognostic implications

Degradation of the extracellular matrix plays a crucial role in cancer invasion. This degradation is accomplished by the concerted action of several enzyme systems, including generation of the serine protease plasmin by the urokinase pathway of plasminogen activation, different types of collagenases and other metalloproteinases, and other extracellular enzymes. The degradative enzymes are involved also in tissue remodelling under non-malignant conditions, and the main difference appears to be that mechanisms which regulates these processes under normal conditions are defective in cancer. Specific inhibitors have been identified for most of the proteolytic enzymes, e.g. plasminogen activator inhibitors (PAI's) and tissue inhibitors of metalloproteinases (TIMP's). It has been contemplated that these inhibitors counteracted the proteolytic activity of the enzymes, thereby inhibiting extracellular tissue degradation which in turn should prevent tumor cell invasion. This review focuses on plasminogen inhibitor type 1 (PAI-1). It is described that PAI-1 is not produced by the epithelial cancer cell but by the stromal cells in the tumors, suggesting a concerted action between stroma and tumor cells in the processes controlling proteolysis in cancer. The specific localization of PAI-1 to the tumor stroma and in many cases to areas surrounding the tumor vessels has lead us to suggest that PAI-1 serves to protect the tumor stroma from the ongoing uPA-mediated proteolysis. This hypothesis is supported by recent clinical data showing increased levels of PAI-1 in metastases as compared to the primary tumor as well as data demonstrating that high levels of PAI-1 in tumor extracts from breast, lung, gastric and ovarian cancer is associated with a shorter overall survival.(ABSTRACT TRUNCATED AT 250 WORDS)