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1.  Regulation of Airway Contractility by Plasminogen Activators through N-Methyl-D-Aspartate Receptor–1 
Reactive airway disease is mediated by smooth muscle contraction initiated through several agonist-dependent pathways. Activation of type 1 N-methyl-D-aspartate receptors (NMDA-R1s) by plasminogen activators (PAs) has been linked to control of vascular tone, but their effect on airway smooth muscle contractility has not previously been studied to our knowledge. We observed that NMDA-R1s are expressed by human airway smooth muscle cells and constitutively inhibit the contraction of isolated rat tracheal rings in response to acetylcholine (Ach). Both tissue-type PA (tPA) and urokinase-type PA (uPA) bind to NMDA-R1 and reverse this effect, thereby enhancing Ach-induced tracheal contractility. Tracheal contractility initiated by Ach is reduced in rings isolated from tPA−/− and uPA−/− mice compared with their wild-type counterparts. The procontractile effect of uPA or tPA was mimicked and augmented by the nitric oxide synthase inhibitor, l-NAME. uPA and tPA further enhanced the contractility of rings denuded of epithelium, an effect that was inhibited by the NMDA-R antagonist, MK-801. Binding of PAs to NMDA-R1 and the subsequent activation of the receptor were inhibited by PA inhibitor type 1, by a PA inhibitor type 1–derived hexapeptide that recognizes the tPA and uPA docking domains, as well as by specific mutations within the docking site of tPA. These studies identify involvement of PAs and NMDA-R1 in airway contractility, and define new loci that could lead to the development of novel interventions for reactive airway disease.
PMCID: PMC2993090  PMID: 20097831
tissue plasminogen activator; urokinase NMDA receptor; lungs
2.  Constriction of Carotid Arteries by Urokinase-Type Plasminogen Activator Requires Catalytic Activity and is Independent of NH2-Terminal Domains 
Thrombosis and haemostasis  2009;102(5):983-992.
Urokinase-type plasminogen activator (uPA) is expressed at increased levels in stenotic, atherosclerotic human arteries. However, the biological roles of uPA in the artery wall are poorly understood. Previous studies associate uPA with both acute vasoconstriction and chronic vascular remodeling and attribute uPA-mediated vasoconstriction to the kringle—not the catalytic—domain of uPA. We used an in vivo uPA overexpression model to test the hypothesis that uPA-induced vasoconstriction is a reversible vasomotor process that can be prevented—and uPA fibrinolytic activity preserved—by: 1) removing the growth factor and kringle domains; or 2) anchoring uPA to the endothelial surface. To test this hypothesis we constructed adenoviral vectors that express: wild-type rabbit uPA (AduPA); a uPA mutant lacking the NH2-terminal growth-factor and kringle domains (AduPAdel); a mutant lacking catalytic activity (AduPAS→A), and a cell-surface anchored mutant (AdTMuPA). uPA mutants were expressed and characterized in vitro and in carotid arteries in vivo. uPAS→A had no plasminogen activator activity. Activity was similar for uPA and uPAdel, whereas AdTMuPA had only cell-associated activity. AduPAS→A arteries were not constricted. AduPA, AduPAdel, and AdTM-uPA arteries were constricted (approximately 30% smaller lumens; P ≤ 0.008 vs AdNull arteries). Papaverine reversed constriction of AduPA arteries. uPA-mediated arterial constriction is a vasomotor process that is mediated by uPA catalytic activity, not by the NH2-terminal domains. Anchoring uPA to the endothelial surface does not prevent vasoconstriction. uPA catalytic activity, generated by artery wall cells, may contribute to lumen loss in human arteries. Elimination of uPA vasoconstrictor activity requires concomitant loss of fibrinolytic activity.
PMCID: PMC2774917  PMID: 19888538
3.  Enhanced expression of genes involved in coagulation and fibrinolysis in murine arthritis 
Arthritis Research  2000;2(6):504-512.
We have analyzed the pattern of procoagulant and fibrinolytic gene expression in affected joints during the course of arthritis in two murine models. In both models, we found an increased expression of tissue factor, tissue factor pathway inhibitor, urokinase plasminogen activator, and plasminogen activator inhibitor 1, as well as thrombin receptor. The observed pattern of gene expression tended to favor procoagulant activity, and this pattern was confirmed by functional assays. These alterations would account for persistence of fibrin within the inflamed joint, as is seen in rheumatoid arthritis.
Accumulation of fibrin in the joints remains one of the most striking histopathological features of rheumatoid arthritis (RA). Recently, we have provided evidence of the deleterious role of synovial fibrin deposition in arthritic joints in antigen-induced arthritis (AIA), a well-established murine model of RA.
A local imbalance between fibrin formation and fibrin dissolution may result in fibrin deposition in the joints.
On the one hand, fibrin formation is mainly initiated by tissue factor (TF), a transmembrane protein serving as a receptor for factor VII. Under normal conditions, TF expression and activity are tightly regulated. Constitutive TF expression is restricted to perivascular and epithelial cells, and the catalytic activity of the TF/VIIa complex can be inhibited by tissue factor pathway inhibitor (TFPI). Pathological conditions can perturb the cell-type-restricted pattern of TF expression. In particular, recent reports have shown that transcriptional activation of TF can be mediated by molecular mechanisms involving induction of the early growth response gene 1 (EGR1) or of the protease-activated receptor (PAR1) or vascular endothelial growth factor (VEGF) genes.
On the other hand, fibrin degradation is mediated primarily by plasmin, which is the active form of the zymogen plasminogen. Conversion of plasminogen to plasmin is under the control of serine protease plasminogen activators, such as the urokinase plasminogen activator (uPA), and their inhibitors, such as the plasminogen activator inhibitor (PAI-1).
We hypothesized that the deposition of fibrin in the joints may result from an imbalance in the local expression of key genes involved in coagulation and fibrinolytic pathways. To test this hypothesis, we investigated mRNA levels in arthritic versus nonarthritic joint tissues from two murine models of RA: AIA and collagen-induced arthritis (CIA). Genes that are directly implicated in coagulation (TF, TFPI) and fibrinolysis (UPA, PAI1), and other genes that may influence the expression of TF (EGR1, PAR1, VEGF), were investigated using a novel multiprobe RNase protection assay (RPA). Furthermore, we evaluated coagulation activity in arthritic and nonarthritic mice.
Mice with AIA or CIA were sacrificed at different time points: 2, 4, and 16 h and 3, 7, and 14 d after intra-articular antigen injection for AIA; 42 d after the first immunization for CIA. Total RNA was prepared from arthritic and nonarthritic knees for AIA, or arthritic and nonarthritic hind paws for CIA. Messenger RNA (mRNA) levels of the genes described above were determined by RPA and normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA levels. Coagulation assays were performed on joint tissue extracts and concentrations of thrombin-antithrombin III (TAT) complex were measured in plasma.
In AIA, all the genes studied except VEGF were upmodulated as early as 2 h. PAR1, TFPI, EGR1, and UPA expression decreased to control levels by 16 h, whereas the expression of TF and PAI1 remained elevated. At later times, only TF, PAI1, and UPA showed sustained overexpression. In CIA, gene expression was assayed at only one time point (42 d after immunization) and all genes showed higher mRNA levels in the affected paws than in control paws. In AIA mice, procoagulant activity and TF activity were significantly increased in arthritic joints, and in CIA mice, plasma TAT levels were significantly enhanced.
Fibrin deposition in synovia is prominent in both RA and experimental arthritis, suggesting that this protein may play a role in the pathogenesis of chronic inflammation. In this study, we have tried to shed some light on the molecular mechanisms leading to extravascular fibrin deposition, using two well-established mouse models of RA: AIA and CIA. The kinetics of gene expression was first analyzed in mice with AIA, because this model allows for an accurate, temporally controlled sampling of synovial inflammation. We then extended our observations by analyzing one time point in CIA, 42 d after immunization, when chronic inflammation is present. We found that in both models, coagulation and fibrinolysis in arthritic joints were significantly increased, and that the most significant increases were in TF and PAI-1.
Although the molecular mechanism or mechanisms responsible for the transcriptional changes observed are not completely understood, the increases in TF, PAI-1, and uPA are probably due to the production of proinflammatory cytokines such as IL-1 and TGF-α. These cytokines, whose presence in the inflamed synovium is well documented, are known to induce these genes through the activation of nuclear factor κB (NF-κB), a transcription factor. TF induction is also under the control of a proximal enhancer containing a binding site for the inducible transcription factor EGR1. Indeed, the early rise of EGR1 expression in AIA is consistent with its classification as immediate-early gene and may be responsible for the induction of early expression of TF. Early TF stimulation in AIA can also be accounted for by the transient overexpression of PAR1. Contrary to what has been shown in RA, VEGF expression remained essentially unchanged throughout the progression of AIA, probably reflecting a peculiarity of this murine model.
The alteration of the patterns of gene expression was accompanied by increased functional coagulation activity, which was more marked in AIA than in CIA.
Prominent fibrin deposition in two different animal models of RA – AIA and CIA – can be attributed to modulations in key regulatory genes for coagulation and fibrinolysis.
PMCID: PMC17822  PMID: 11056680
arthritis; coagulation; fibrinolysis; mice; RNase protection
4.  Induction of Tissue Factor by Urokinase in Lung Epithelial Cells and in the Lungs 
Rationale: Urokinase-type plasminogen activator (uPA) regulates extracellular proteolysis in lung injury and repair. Although alveolar expression of uPA increases, procoagulant activity predominates.
Objectives: This study was designed to investigate whether uPA alters the expression of tissue factor (TF), the major initiator of the coagulation cascade, in lung epithelial cells (ECs).
Methods: Bronchial, primary airway ECs and C57B6 wild-type, uPA-deficient (uPA−/−) mice were exposed to phosphate-buffered saline, uPA, or LPS. Immunohistochemistry, protein, cellular, and molecular techniques were used to assess TF expression and activity.
Measurements and Main Results: uPA enhanced TF mRNA and protein expression, and TF-dependent coagulation in lung ECs. uPA-induced expression of TF involves both increased synthesis and enhanced stabilization of TF mRNA. uPA catalytic activity had little effect on induction of TF. By contrast, deletion of the uPA receptor binding growth factor domain from uPA markedly attenuated the induction of TF, suggesting that uPA receptor binding is sufficient for TF induction. Lung tissues of uPA-deficient mice expressed less TF protein and mRNA compared with wild-type mice. In addition, intratracheal instillation of mouse uPA increased TF mRNA and protein expression and accelerated coagulation in lung tissues. uPA−/− mice exposed to LPS failed to induce TF.
Conclusions: uPA increased TF expression and TF-dependent coagulation in the lungs of mice. We hypothesize that uPA-mediated induction of TF occurs in lung ECs to promote increased fibrin deposition in the airways during acute lung injury.
PMCID: PMC2894411  PMID: 20194819
urokinase; tissue factor; lung epithelial cells; idiopathic pulmonary fibrosis
Biochemistry  2011;51(1):205-213.
Urokinase-type plasminogen activator (uPA) is expressed by lung epithelial cells and regulates fibrin turnover and epithelial cell viability. PMA, LPS, and TNF-alpha, as well as uPA itself, induce uPA expression in lung epithelial cells. PMA, LPS, and TNF-alpha induce uPA expression through increased synthesis as well as stabilization of uPA mRNA, while uPA increases its own expression solely through uPA mRNA stabilization. The mechanism by which lung epithelial cells regulate uPA expression at the level of mRNA stability is unclear. To elucidate this process, we sought to characterize protein-uPA mRNA interactions that regulate uPA expression. Regulation of uPA at the level of mRNA stability involves the interaction of a ~40 kDa cytoplasmic-nuclear shuttling protein with a 66 nt uPA mRNA 3′UTR sequence. We purified the uPA mRNA 3′UTR binding protein and identified it as ribonucleotide reductase M2 (RRM2). We expressed recombinant RRM2 and confirmed its interaction with a specific 66 nt uPA 3′UTR sequence. Immunoprecipitation of cell lysates with anti-RRM2 antibody and RT-PCR for uPA mRNA confirmed that RRM2 binds to uPA mRNA. Treatment of Beas2B cells with uPA or LPS attenuated RRM2-endogenous uPA mRNA interactions, while overexpression of RRM2 inhibited uPA protein and mRNA expression through destabilization of uPA mRNA. LPS exposure of lung epithelial cells translocates RRM2 from the cytoplasm to the nucleus in a time-dependent manner leading to stabilization of uPA mRNA. This newly recognized pathway could influence uPA expression and a broad range of uPA-dependent functions in lung epithelial cells in the context of lung inflammation and repair.
PMCID: PMC3254797  PMID: 22166006
Urokinase; ribonucleotide reductase M2; Urokinase-type plasminogen activator; Acute lung injury
6.  Monocyte urokinase-type plasminogen activator up-regulation reduces thrombus size in a model of venous thrombosis 
Journal of Vascular Surgery  2009;50(5):1127-1134.
Our previous studies showed that the direct injection of an adenovirus construct expressing urokinase-type plasminogen activator (uPA) into experimental venous thrombi significantly reduces thrombus weight. The systemic use of adenovirus vectors is limited by inherent hepatic tropism and inflammatory response. As macrophages are recruited into venous thrombi, it is reasonable to speculate that these cells could be used to target the adenovirus uPA (ad-uPA) gene construct to the thrombus. The aims of this study were to determine whether macrophages transduced with ad-uPA have increased fibrinolytic activity and whether systemic injection of transduced cells could be used to target uPA expression to the thrombus and reduce its size.
The effect of up-regulating uPA was examined in an immortalized macrophage cell line (MM6) and macrophages differentiated from human blood monocyte-derived macrophages (HBMMs). Cells were infected with ad-uPA or blank control virus (ad-blank). Fibrinolytic mediator expression, cell viability, and cytokine expression were measured by activity assays and enzyme-linked immunosorbent assays. Monocyte migration was measured using a modified Boyden chamber assay. A model of venous thrombosis was developed and characterized in mice with severe combined immunodeficiency (SCID). This model was used to study whether systemically administered macrophages over-expressing uPA reduced thrombus size. Uptake of HBMMs into the thrombus induced in these mice was confirmed by a combination of PKH2-labeled cell tracking and colocalization with human leukocyte antigen (HLA) by immunohistology.
Compared with ad-blank, treated HBMMs transduction with ad-uPA increased uPA production by >1000-fold (P = .003), uPA activity by 150-fold (P = .0001), and soluble uPA receptor (uPAR) by almost twofold (P = .043). Expression of plasminogen activator inhibitor (PAI-1) and PAI-2 was decreased by about twofold (P = .011) and threefold (P = .005), respectively. Up-regulation of uPA had no effect on cell viability or inflammatory cytokine production compared with ad-blank or untreated cells. Ad-uPA transduction increased the migration rate of HBMMs (about 20%, P = .03) and MM6 cells (>twofold, P = .005) compared with ad-blank treated controls. Human macrophage recruitment into the mouse thrombus was confirmed by the colocalization of HLA with the PKH2-marked cells. Systemic injection of uPA-up-regulated HBMMs reduced thrombus weight by approximately 20% compared with ad-blank (P = .038) or sham-treated controls (P = .0028).
Transduction of HBBM with ad-uPA increases their fibrinolytic activity. Systemic administration of uPA up-regulated HBBMs reduced thrombus size in an experimental model of venous thrombosis. Alternative methods of delivering fibrinolytic agents are worth exploring.
Clinical Relevance
The use of thrombolysis in the treatment of acute iliofemoral deep vein thrombosis is not suitable for all patients. Our previous studies have shown that direct injection of an adenovirus construct expressing urokinase plasminogen activator (uPA) into experimental venous thrombi significantly reduced thrombus weight. The systemic use of adenovirus vectors is, however, limited by both their inherent hepatic tropism, which precludes targeted delivery to disease sites, and by the associated host inflammatory response. As macrophages are recruited into venous thrombi, these cells could be used to target uPA gene constructs to the thrombus after systemic administration.
PMCID: PMC2778796  PMID: 19703758
7.  Urokinase-Type Plasminogen Activator Inhibits Efferocytosis of Neutrophils 
Rationale: Phagocytosis of apoptotic cells, also called efferocytosis, plays an essential role in the resolution of inflammation. Urokinase-type plasminogen activator (uPA) is a multifunctional protein that has been implicated in inflammatory conditions, including pneumonia and severe infection, which are often accompanied by the development of acute lung injury. However, the role of uPA in modulating efferocytosis of apoptotic neutrophils has not been defined.
Objectives: To characterize the role of uPA in regulation of efferocytosis and to delineate the underlying mechanisms involved in this process.
Methods: In vitro and in vivo phagocytosis, immunoprecipitation, and Western blotting assays.
Measurements and Main Results: The phagocytosis of apoptotic neutrophils by macrophages was significantly inhibited by uPA. Mutant uPA lacking the growth factor domain and catalytically inactive uPA had similar inhibitory effects on efferocytosis, as did wild-type uPA. In contrast, absence of the kringle domain abrogated the ability of uPA to diminish efferocytosis. Both the αVβ3 integrin and vitronectin seemed to be involved in the inhibition of efferocytosis by uPA. Incubation of macrophages with uPA also diminished activation of the small GTPase Rac-1, which normally occurs during ingestion of apoptotic neutrophils. Under in vivo conditions in the lungs, uPA decreased the uptake of apoptotic neutrophils by alveolar macrophages.
Conclusions: Our data demonstrate a novel role for uPA in which it is able to diminish the uptake of apoptotic neutrophils by macrophages under both in vitro and in vivo conditions.
PMCID: PMC3029937  PMID: 20656938
phagocytosis; integrin αvβ3; inflammation; acute lung injury
8.  RNA Interference-Directed Knockdown of Urokinase Plasminogen Activator and Urokinase Plasminogen Activator Receptor Inhibits Prostate Cancer Cell Invasion, Survival and Tumorigenicity In vivo 
The Journal of biological chemistry  2005;280(43):36529-36540.
The invasive ability of tumor cells plays a key role in prostate cancer metastasis and is a major cause of treatment failure. Urokinase plasminogen activator (uPA) and its receptor (uPAR)-mediated signaling have been implicated in tumor cell invasion, survival and metastasis in a variety of cancers. This study was undertaken to investigate the biological roles of uPA and uPAR in prostate cancer cell invasion, survival and the potential of uPA and uPAR as targets for prostate cancer therapy. uPA and uPAR expression correlates with the metastatic potential of prostate cancer cells. Thus, therapies designed to inhibit uPA and uPAR expression would be beneficial. LNCaP, DU145 and PC3 are prostate cancer cell lines with low, moderate and high metastatic potential, respectively, as demonstrated by their capacity to invade extracellular matrix (ECM). In this study we utilized small hairpin RNAs (shRNAs), also referred to as small interfering RNAs (siRNAs), to target human uPA and uPAR. These siRNA constructs significantly inhibited uPA and uPAR expression at both the mRNA and protein levels in the highly metastatic prostate cancer cell line PC3. Our data demonstrate that uPA-uPAR knockdown in PC3 cells resulted in a dramatic reduction of tumor cell invasion as indicated by a matrigel invasion assay. Furthermore, simultaneous silencing of the genes for uPA and uPAR using a single plasmid construct expressing shRNAs for both uPA and uPAR significantly reduced cell viability and ultimately resulted in the induction of apoptotic cell death. RNAi for uPA and uPAR also abrogated uPA-uPAR signaling to downstream target molecules such as extracellular-signal regulated kinases 1/2 (ERK1/2) and the signal transducer and activator of transcription 3 (Stat 3). In addition, our results demonstrate that intratumoral injection with the plasmid construct expressing shRNAs for uPA and uPAR almost completely inhibited established tumor growth and survival in an orthotopic mouse prostate cancer model. These findings uncovered evidence of a complex signaling network operating downstream of uPA-uPAR that actively advances tumor cell invasion, proliferation and survival of prostate cancer cells. Thus, RNAi-directed targeting of uPA and uPAR is a convenient and novel tool for studying the biological role of the uPA-uPAR system and raises the potential of its application for prostate cancer therapy.
PMCID: PMC1351057  PMID: 16127174
RNAi; prostate cancer; invasion; survival; uPA and uPAR; siRNA (small interfering RNA); shRNA (small hairpin RNA); RNAi (RNA interference); uPA (urokinaseplasminogen activator); uPAR (uPA receptor); ANOVA (analysis of variance); RT (reverse transcription); TPBS (tween-20 (0.1%) phospate buffered saline); BSA (bovine serum albumin)
9.  Post-Transcriptional Regulation of Urokinase-type Plasminogen Activator Receptor Expression in Lipopolysaccharide-induced Acute Lung Injury 
Rationale: Urokinase-type plasminogen activator (uPA) receptor (uPAR) is required for the recruitment of neutrophils in response to infection. uPA induces its own expression in lung epithelial cells, which involves its interaction with cell surface uPAR. Regulation of uPAR expression is therefore crucial for uPA-mediated signaling in infectious acute lung injury (ALI).
Objectives: To determine the role of uPA in uPAR expression during ALI caused by sepsis.
Methods: We used Western blot, Northern blot, Northwestern assay, and immunohistochemistry. Phosphate-buffered saline– and lipopolysaccharide (LPS)-treated wild-type and uPA−/− mice were used.
Measurements and Main Results: Biological activities of uPA, including proteolysis, cell adhesion, migration, proliferation, and differentiation, are dependent on its association with uPAR. Bacterial endotoxin (LPS) is a major cause of pulmonary dysfunction and infection-associated mortality. The present study shows that LPS induces uPAR expression both in vitro and in vivo, and that the mechanism involves post-transcriptional stabilization of uPAR mRNA by reciprocal interaction of phosphoglycerate kinase (PGK) and heterogeneous nuclear ribonucleoprotein C (hnRNPC) with uPAR mRNA coding region and 3′ untranslated region determinants, respectively. The process involves tyrosine phosphorylation of PGK and hnRNPC. uPA−/− mice failed to induce uPAR expression after LPS treatment. In these mice, LPS treatment failed to alter the binding of PGK and hnRNPC protein with uPAR mRNA due to lack of tyrosine phosphorylation.
Conclusions: Our study shows that induction of LPS-mediated uPAR expression is mediated through tyrosine phosphorylation of PGK and hnRNPC. This involves expression of uPA as an obligate intermediary.
PMCID: PMC2643078  PMID: 19029002
LPS; urokinase-type plasminogen activator; urokinase-type plasminogen activator receptor; tyrosine phosphorylation
10.  Oestradiol regulation of the components of the plasminogen-plasmin system in MDA-MB-231 human breast cancer cells stably expressing the oestrogen receptor. 
British Journal of Cancer  1998;78(1):88-95.
To understand the hormonal regulation of the components of the plasminogen-plasmin system in human breast cancer, we examined the oestradiol (E2) regulation of plasminogen activators (PAs), namely urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA), plasminogen activator inhibitor type 1 (PAI-1) and uPA receptor (uPAR), in our model system. We used stable transfectants of the MDA-MB-231 human breast cancer cells that express either the wild-type (S30 cells) or the mutant 351asp-->tyr oestrogen receptor (ER) (BC-2 cells). Northern blot analysis showed that there was a concentration-dependent down-regulation of uPA, tPA and PAI-1 mRNAs by E2. In contrast, uPAR mRNA was not modulated by E2. The pure anti-oestrogen ICI 182,780 was able to block E2 action, indicating that the regulation of these genes is ER mediated. The E2 also inhibited the expression and secretion of uPA, tPA and PAI-1 proteins as determined by enzyme-linked immunosorbent assay (ELISA) in cell extracts (CEs) and conditioned media (CM). Zymography of the CM confirmed the inhibitory effect of E2 on uPA activity. Thus, we now report the regulation of uPA, PAI-1 and tPA by E2 in both mRNA and protein levels in ER transfectants. The association between down-regulation of the uPA by E2 and known E2-mediated growth inhibition of these cells was also explored. Our findings indicate that down-regulation of uPA by E2 is an upstream event of inhibitory effects of E2 on growth of these cells as the addition of exogenous uPA did not block the growth inhibition by E2.
PMCID: PMC2062932  PMID: 9662256
11.  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. 
Nucleic Acids Research  1995;23(19):3887-3893.
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.
PMCID: PMC307306  PMID: 7479032
12.  Plasminogen Activator Inhibitor 1 Functions as a Urokinase Response Modifier at the Level of Cell Signaling and Thereby Promotes Mcf-7 Cell Growth 
The Journal of Cell Biology  2001;152(4):741-752.
Plasminogen activator inhibitor 1 (PAI-1) is a major inhibitor of urokinase-type plasminogen activator (uPA). In this study, we explored the role of PAI-1 in cell signaling. In MCF-7 cells, PAI-1 did not directly activate the mitogen-activated protein (MAP) kinases, extracellular signal–regulated kinase (ERK) 1 and ERK2, but instead altered the response to uPA so that ERK phosphorylation was sustained. This effect required the cooperative function of uPAR and the very low density lipoprotein receptor (VLDLr). When MCF-7 cells were treated with uPA–PAI-1 complex in the presence of the VLDLr antagonist, receptor-associated protein, or with uPA–PAI-1R76E complex, which binds to the VLDLr with greatly decreased affinity, transient ERK phosphorylation (<5 min) was observed, mimicking the uPA response. ERK phosphorylation was not induced by tissue-type plasminogen activator–PAI-1 complex or by uPA–PAI-1 complex in the presence of antibodies that block uPA binding to uPAR. uPA–PAI-1 complex induced tyrosine phosphorylation of focal adhesion kinase and Shc and sustained association of Sos with Shc, whereas uPA caused transient association of Sos with Shc.
By sustaining ERK phosphorylation, PAI-1 converted uPA into an MCF-7 cell mitogen. This activity was blocked by receptor-associated protein and not observed with uPA–PAI-1R76E complex, demonstrating the importance of the VLDLr. uPA promoted the growth of other cells in which ERK phosphorylation was sustained, including β3 integrin overexpressing MCF-7 cells and HT 1080 cells. The MEK inhibitor, PD098059, blocked the growth-promoting activity of uPA and uPA–PAI-1 complex in these cells. Our results demonstrate that PAI-1 may regulate uPA-initiated cell signaling by a mechanism that requires VLDLr recruitment. The kinetics of ERK phosphorylation in response to uPAR ligation determine the function of uPA and uPA–PAI-1 complex as growth promoters.
PMCID: PMC2195772  PMID: 11266465
urokinase-type plasminogen activator; plasminogen activator inhibitor 1; urokinase receptor; VLDL receptor; extracellular signal–regulated kinase
13.  Plasminogen activator system, vascular endothelial growth factor, and colorectal cancer progression 
Molecular Pathology  2000;53(6):307-312.
Aims—The plasminogen activator system (PAS) consists of the plasminogen activators (urokinase (uPA) and tissue-type (tPA) plasminogen activators), the uPA receptor (uPAR), and the plasminogen activator inhibitors (PAI-1 and PAI-2). Plasminogen activators activate plasminogen to plasmin, which can break down extracellular matrix (ECM) components. Vascular endothelial growth factor (VEGF) is a mitogen for endothelial cells and is involved in angiogenesis. VEGF has been shown to upregulate uPA and this may facilitate tumour angiogenesis further.
Methods—PAS components and VEGF were determined by enzyme linked immunosorbent assay (ELISA) in paired colorectal tumour and normal tissue (n = 50) and correlated with pathological staging.
Results—uPA, uPAR, PAI-1, and VEGF values were significantly higher in tumour tissue (for example, tumour uPA: median, 2.3 (range, 0.1–6.7) ng/mg protein v normal uPA: median, 0.2 (range, 0–2.6) ng/mg protein). tPA was significantly higher in normal mucosa and there was no difference in PAI-2. uPA, uPAR, PAI-1, and VEGF values significantly correlated with each other and with Dukes's staging (uPA in adenomas: median, 0.42 (range, 0.1–1.2) ng/mg protein; upA in Dukes's B tumours: median, 2.1 (range, 0.4–4.3) ng/mg protein; and uPA in Dukes's D tumours: median, 4.0 (range, 3.7–4.2) ng/mg protein) and lymphatic invasion. In addition PAI-1 also correlated with tumour size and differentiation.
Conclusion—The involvement of the PAS and VEGF in colorectal cancer appears to be complex. uPA, uPAR, PAI-1, and VEGF were upregulated in tumour tissue and this correlated with Dukes's staging and lymphatic invasion.
PMCID: PMC1186985  PMID: 11193049
plasminogen activators; vascular endothelial growth factor; colorectal cancer
14.  A distinct basic fibroblast growth factor (FGF-2)/FGF receptor interaction distinguishes urokinase-type plasminogen activator induction from mitogenicity in endothelial cells. 
Molecular Biology of the Cell  1996;7(3):369-381.
Basic fibroblast growth factor (FGF-2) induces cell proliferation and urokinase-type plasminogen activator (uPA) production in fetal bovine aortic endothelial GM 7373 cells. In the present paper we investigated the role of the interaction of FGF-2 with tyrosine-kinase (TK) FGF receptors (FGFRs) in mediating uPA up-regulation in these cells. The results show that FGF-2 antagonists suramin, protamine, heparin, the synthetic peptide FGF-2(112-155), and a soluble form of FGFR-1 do not inhibit FGF-2-mediated uPA up-regulation at concentrations that affect growth factor binding to cell surface receptors and mitogenic activity. In contrast, tyrosine phosphorylation inhibitors and overexpression of a dominant negative TK- mutant of FGFR-1 abolish the uPA-inducing activity of FGF-2, indicating that FGFR and its TK activity are essential in mediating uPA induction. Accordingly, FGF-2 induces uPA up-regulation in Chinese hamster ovary cells transfected with wild-type FGFR-1, -2, -3, or -4 but not with TK- FGFR-1 mutant. Small unilamellar phosphatidyl choline:cholesterol vesicles loaded with FGF-2 increased uPA production in GM 7373 cells in the absence of a mitogenic response. Liposome-encapsulated FGF-2 showed a limited but significant capacity, relative to free FGF-2, to interact with FGFR both at 4 degrees C and 37 degrees C and to be internalized within the cell. uPA up-regulation by liposome-encapsulated FGF-2 was quenched by neutralizing anti-FGF-2 antibodies, indicating that the activity of liposome-delivered FGF-2 is mediated by an extracellular action of the growth factor. Taken together, the data indicate that a distinct interaction of FGF-2 with FGFR, quantitatively and/or qualitatively different from the one that leads to mitogenicity, is responsible for the uPA-inducing activity of the growth factor.
PMCID: PMC275890  PMID: 8868466
15.  Increased expression of the urokinase plasminogen activator system by Helicobacter pylori in gastric epithelial cells 
The gastric pathogen Helicobacter pylori (H. pylori) is linked to peptic ulcer and gastric cancer, but the relevant pathophysiological mechanisms are unclear. We now report that H. pylori stimulates the expression of plasminogen activator inhibitor (PAI)-1, urokinase plasminogen activator (uPA), and its receptor (uPAR) in gastric epithelial cells and the consequences for epithelial cell proliferation. Real-time PCR of biopsies from gastric corpus, but not antrum, showed significantly increased PAI-1, uPA, and uPAR in H. pylori-positive patients. Transfection of primary human gastric epithelial cells with uPA, PAI-1, or uPAR promoters in luciferase reporter constructs revealed expression of all three in H+/K+ATPase- and vesicular monoamine transporter 2-expressing cells; uPA was also expressed in pepsinogen- and uPAR-containing trefoil peptide-1-expressing cells. In each case expression was increased in response to H. pylori and for uPA, but not PAI-1 or uPAR, required the virulence factor CagE. H. pylori also stimulated soluble and cell surface-bound uPA activity, and both were further increased by PAI-1 knockdown, consistent with PAI-1 inhibition of endogenous uPA. H. pylori stimulated epithelial cell proliferation, which was inhibited by uPA immunoneutralization and uPAR knockdown; exogenous uPA also stimulated proliferation that was further increased after PAI-1 knockdown. The proliferative effects of uPA were inhibited by immunoneutralization of the EGF receptor and of heparin-binding EGF (HB-EGF) by the mutant diphtheria toxin CRM197 and an EGF receptor tyrosine kinase inhibitor. H. pylori induction of uPA therefore leads to epithelial proliferation through activation of HB-EGF and is normally inhibited by concomitant induction of PAI-1; treatments directed at inhibition of uPA may slow the progression to gastric cancer.
PMCID: PMC2536790  PMID: 18599586
gastric cancer; primary gastric epithelial cells; cagE; HB-EGF
16.  Expression of the urokinase receptor in vascular endothelial cells is stimulated by basic fibroblast growth factor 
The Journal of Cell Biology  1991;113(5):1193-1201.
Basic fibroblast growth factor, a potent angiogenesis inducer, stimulates urokinase (uPA) production by vascular endothelial cells. In both basic fibroblast growth factor-stimulated and -nonstimulated bovine capillary endothelial and human umbilical vein endothelial cells single-chain uPA binding is mediated by a membrane protein with a Mr of 42,000. Exposure of bovine capillary or endothelial human umbilical vein endothelial cells to pmolar concentrations of basic fibroblast growth factor results in a dose-dependent, protein synthesis-dependent increase in the number of membrane receptors for uPA (19,500-187,000) and in a parallel decrease in their affinity (KD = 0.144-0.790 nM). With both cells, single-chain uPA binding is competed by synthetic peptides whose sequence corresponds to the receptor-binding sequence in the NH2-terminal domain of uPA. Exposure of bovine capillary endothelial cells to transforming growth factor beta 1, which inhibits uPA production and upregulates type 1 plasminogen activator inhibitor, the major endothelial cell plasminogen activator inhibitor, has no effect on uPA receptor levels. These results show that basic fibroblast growth factor, besides stimulating uPA production by vascular endothelial cells, also increases the production of receptors, which modulates their capacity to focalize this enzyme on the cell surface. This effect may be important in the degradative processes that occur during angiogenesis.
PMCID: PMC2289004  PMID: 1645739
17.  Development of a Mammalian Suspension Culture for Expression of Active Recombinant Human Urokinase-type Plasminogen Activator 
Cytotechnology  2005;49(1):25-37.
The development of specific catalytic inhibitors for the serine protease urokinase-type plasminogen activator (uPA) has been hindered due to difficulties in producing sufficient amounts of active recombinant uPA that is catalytically equivalent to native uPA. The purpose of this study was to develop an efficient system for the expression of recombinant human uPA that exhibits comparable proteolytic activity to that of the native protein. Since post-translational modifications (e.g. glycosylations) of uPA are necessary for efficient proteolytic activity, we have used a mammalian cell line [Chinese hamster ovary (CHO)-S] to express recombinant human uPA. CHO-S cells were selected to stably express full-length recombinant human uPA containing a hexahistidine tag at its C-terminus to permit purification by nickel-based affinity chromatography. Secretion of recombinant uPA into the culture media was confirmed by immunoblotting and the presence of an N-linked glycosylation was confirmed by PNGase sensitivity. Enzymatic activity of purified recombinant uPA was demonstrated using zymography and quantitatively compared to native uPA by kinetic analysis using an uPA-specific substrate. Native uPA and the recombinant uPA demonstrated comparable Km values (55.7 and 39 μM, respectively). Furthermore, inhibition studies using benzamidine resulted in a Ki of 195 μM for native uPA, while recombinant uPA had a Ki of 112 μM. These data indicate that recombinant human uPA expressed by CHO-S cells is functionally comparable to native uPA.
PMCID: PMC3449752  PMID: 19003060
CHO-S; plasminogen; recombinant expression; serine protease; tumor cell motility; uPA; urokinase
18.  In vivo paracrine interaction between urokinase and its receptor: effect on tumor cell invasion 
The Journal of Cell Biology  1991;115(4):1107-1112.
Numerous studies have linked the production of increased levels of urokinase type plasminogen activator (uPA) with the malignant phenotype. It has also been shown that a specific cell surface receptor can bind uPA through a domain distinct and distant from the proteolytic domain. In an in vivo model of invasion, consisting of experimentally modified chorioallantoic membrane (CAM) of a chick embryo, only cells that concurrently expressed both uPA and a receptor for uPA, and in which the receptor was saturated with uPA, were efficient in invasion. To test whether uPA produced by one cell can, in a paracrine fashion, affect the invasive capacity of a receptor-expressing cell, we transfected LB6 mouse cells with human uPA (LB6[uPA]), or human uPA- receptor cDNA (LB6[uPAR]). LB6(uPA) cells released into the medium 1-2 Ploug units of human uPA per 10(6) cells in 24 h. The LB6(uPAR) cells expressed on their surface approximately 12,000 high affinity (Kd 1.7 x 10(-10) M uPA binding sites per cell. Unlabeled LB6(uPA) and 125-IUdR- labeled LB6(uPAR) cells were coinoculated onto experimentally wounded and resealed CAMs and their invasion was compared to that of homologous mixtures of labeled and unlabeled LB6(uPAR) or LB6(uPA) cells. Concurrent presence of both cell types in the CAMs resulted in a 1.8- fold increase of invasion of the uPA-receptor expressing cells. A four- fold stimulation of invasion was observed when cells were cocultured in vitro, prior to in vivo inoculation. Enhancement of invasion was prevented in both sets of experiments by treatment with specific antihuman uPA antibodies, indicating that uPA was the main mediator of the invasion-enhancing, paracrine effect on the receptor-expressing cells.
PMCID: PMC2289942  PMID: 1659573
19.  Urokinase-type plasminogen activator supports liver repair independent of its cellular receptor 
BMC Gastroenterology  2006;6:40.
The urokinase-type (uPA) and tissue-type (tPA) plasminogen activators regulate liver matrix remodelling through the conversion of plasminogen (Plg) to the active protease plasmin. Based on the efficient activation of plasminogen when uPA is bound to its receptor (uPAR) and on the role of uPA in plasmin-mediated liver repair, we hypothesized that uPA requires uPAR for efficient liver repair.
To test this hypothesis, we administered one dose of carbon tetrachloride (CCl4) to mice with single or combined deficiencies of uPA, uPAR and tPA, and examined hepatic morphology, cellular proliferation, fibrin clearance, and hepatic proteolysis 2–14 days later.
Absence of uPAR alone or the combined absence of uPAR and tPA had no impact on the resolution of centrilobular injury, but the loss of receptor-free uPA significantly impaired the clearance of necrotic hepatocytes up to 14 days after CCl4. In response to the injury, hepatocyte proliferation was normal in mice of all genotypes, except for uPAR-deficient (uPAR°) mice, which had a reproducible but mild decrease by 33% at day 2, with an appropriate restoration of liver mass by 7 days similar to experimental controls. Immunostaining and zymographic analysis demonstrated that uPA alone promoted fibrin clearance from centrilobular regions and efficiently activated plasminogen.
uPA activates plasminogen and promotes liver matrix proteolysis during repair via a process that neither requires its receptor uPAR nor requires a contribution from its functional counterpart tPA.
PMCID: PMC1697812  PMID: 17134505
20.  Urokinase and its Receptors in Chronic Kidney Disease 
Since the recognition that plasminogen activator inhibitor-1 (PAI-1) is a powerful profibrotic molecule, there has been considerable interest in deciphering the extent to which this effect is mediated by its ability to inhibit serine proteases with downstream effects on fibrogenesis. This review will summarize current knowledge about the serine protease urokinase-type plasminogen activator and its high affinity receptor uPAR/CD87 as it pertains to chronic kidney disease (CKD) progression. An emerging theme is that the effects of PAI-1 and uPAR appear to be organ- and site-specific. Normal kidney tubules produce a large quantity of uPA that is secreted into the urinary space. Activity levels increase during CKD presumably due to new sources of production by macrophages and fibroblasts. By activating hepatocyte growth factor and degrading fibrinogen uPA may have anti-fibrotic effects. However CKD severity after experimental ureteral obstruction is not altered by endogenous uPA deficiency. Beneficial effects of exogenous uPA have been reported in experimental models of fibrosis in the lung and liver but CKD awaits exploration.
Absent in normal kidneys uPAR is expressed by both renal parenchymal cells and inflammatory cells in a variety of pathological states. Such expression appears beneficial based on studies performed in uPAR-deficient mice. The uPAR promotes bacterial clearance in infectious diseases. In CKD uPAR expression is associated with high uPA activity but its most important effect appears to be due to scavenging activities and effects on cell recruitment and migration. Although uPAR itself is a non-signaling receptor, it interacts with a variety of co-receptors to modify cellular behavior. Best known are interactions with the low-density lipoprotein receptor-related protein (LRP-1) that lead to PAI-1 endocytosis and degradation, and interactions with several integrins to regulate matrix-dependent cell migration. Contacts with the receptor for the complement C5a component and the interleukin −6 receptor gp130 are examples of other recently recognized interactions.
In addition to uPA, vitronectin and high molecular weight kininogen are alternate uPAR ligands that could be implicated in CKD progression. uPAR may also be shed from cell membranes. This soluble form (suPAR) has been detected in plasma and urine and is known to be a chemoattractant for leukocytes that express the formyl-peptide-receptor-like receptor 1/lipoxin A4 receptor. In addition to uPAR several other receptors, including some of the uPAR co-receptors, may also bind directly to uPA and activate cell signaling pathways. The roles of these newer uPAR ligands and uPA receptors are just beginning to be investigated. Since many of them are expressed in the kidney, their potential participation in CKD pathogenesis will be of interest.
PMCID: PMC3142275  PMID: 18508599
urokinase; urokinase receptor; serine protease; plasminogen activator inhibitor-1; low density lipoprotein receptor-related protein; fibrosis; vitronectin; integrin
21.  An autocrine role for urokinase in phorbol ester-mediated differentiation of myeloid cell lines. 
Journal of Clinical Investigation  1991;87(3):1091-1097.
The human myeloid cell line HL60 secretes urokinase-type plasminogen activator (uPA) and expresses its receptor. When stimulated with phorbol myristate acetate (PMA), both secretion of uPA and the expression of its receptor are up-regulated, and these cells differentiate to an adherent phenotype. This adhesive response is markedly reduced in the presence of uPA antibodies. The PMA response is restored by the addition of native uPA, an amino-terminal fragment of uPA (residues 1-143) devoid of proteolytic activity, or a synthetic peptide (residues 12-32) from the uPA growth factor domain known to mediate receptor binding. In contrast, the addition of catalytically active low molecular weight uPA, which is missing the growth factor domain, or a peptide from the catalytic domain (residues 247-266) is ineffective. The influence of uPA antibodies on a second marker of macrophage differentiation, cysteine proteinase activity, was also examined. Cysteine proteinase activity of HL60 cells is increased in PMA-treated cells after 24 h but it fails to increase in the presence of anti-uPA. This increase in cathepsin B-like activity is also restored by exogenous uPA. These experiments indicate that an autocrine interaction of the growth factor domain of uPA with its receptor mediates an essential step in PMA-mediated myeloid cell differentiation.
PMCID: PMC329905  PMID: 1847936
22.  Regulation of urokinase receptors in monocytelike U937 cells by phorbol ester phorbol myristate acetate 
The Journal of Cell Biology  1989;108(2):693-702.
A specific surface receptor for urokinase plasminogen activator (uPA) recognizes the amino-terminal growth factor-like sequence of uPA, a region independent from and not required for the catalytic activity of this enzyme. The properties of the uPA receptor (uPAR) and the localization and distribution of uPA in tumor cells and tissues suggest that the uPA/uPAR interaction may be important in regulating extracellular proteolysis-dependent processes (e.g., invasion, tissue destruction). Phorbol myristate acetate (PMA), an inducer of U937 cell differentiation to macrophage-like cells, elicits a time- and concentration-dependent increase in the number of uPAR molecules as shown by binding, cross-linking, and immunoprecipitation studies. The effect of PMA is blocked by cycloheximide. Overall, the data indicate that PMA increases the synthesis of uPA. PMA treatment also causes a decrease in the affinity of the uPAR for uPA, thus uncovering another way of regulating the interaction between uPA and uPAR. In addition, the PMA treatment causes a modification of migration of the cross- linked receptor in mono- and bidimensional gel electrophoresis.
PMCID: PMC2115427  PMID: 2537321
23.  Plasminogen activation in synovial tissues: differences between normal, osteoarthritis, and rheumatoid arthritis joints 
Annals of the Rheumatic Diseases  1997;56(9):550-557.
OBJECTIVE—To analyse the functional activity of the plasminogen activators urokinase (uPA) and tissue type plasminogen activator (tPA) in human synovial membrane, and to compare the pattern of expression between normal, osteoarthritic, and rheumatoid synovium. The molecular mechanisms underlying differences in PA activities between normal and pathological synovial tissues have been further examined.
METHODS—Synovial membranes from seven normal (N) subjects, 14 osteoarthritis (OA), and 10 rheumatoid arthritis (RA) patients were analysed for plasminogen activator activity by conventional zymography and in situ zymography on tissue sections. The tissue distribution of uPA, tPA, uPA receptor (uPAR), and plasminogen activator inhibitor type-1 (PAI-1) was studied by immunohistochemistry. uPA, tPA, uPAR, and PAI-1 mRNA values and mRNA distribution were assessed by northern blot and in situ hybridisations respectively.
RESULTS—All normal and most OA synovial tissues expressed predominantly tPA catalysed proteolytic activity mainly associated to the synovial vasculature. In some OA, tPA activity was expressed together with variable amounts of uPA mediated activity. By contrast, most RA synovial tissues exhibited considerably increased uPA activity over the proliferative lining areas, while tPA activity was reduced when compared with N and OA synovial tissues. This increase in uPA activity was associated with increased levels of uPA antigen and its corresponding mRNA, which were localised over the synovial proliferative lining areas. In addition, in RA tissues, expression of the specific uPA receptor (uPAR) and of the plasminogen activator inhibitor-type 1 (PAI-1) were also increased.
CONCLUSION—Taken together, these results show an alteration of the PA/plasmin system in RA synovial tissues, resulting in increased uPA catalytic activity that may play a part in tissue destruction in RA.

PMCID: PMC1752434  PMID: 9370880
24.  siRNA-mediated Simultaneous downregulation of uPA and its receptor inhibits angiogenesis and invasiveness triggering apoptosis in breast cancer cells. 
International journal of oncology  2006;28(4):831-839.
A wide variety of tumor cells exhibit overexpression of urokinase plasminogen activator (uPA) and its receptor (uPAR). In breast cancer, expression of uPA and uPAR is essential for tumor cell invasion and metastasis. It is also known that uPA binds to uPAR and activates the RAS extra-cellular signal regulated kinase (ERK) signaling pathway. In our study, we have introduced small interfering RNA (siRNA) to downregulate the expression of uPA and uPAR in two breast cancer cell lines (MDA MB 231 and ZR 75 1). uPA and uPAR were downregulated individually using single constructs, and in combination using a bicistronic construct driven by a CMV promoter in a pcDNA-3 mammalian expression vector. Reverse transcription PCR (RT-PCR) and Western blot analyses indicated downregulation at both the mRNA and protein levels. In vitro angiogenesis studies using conditioned medium in HMEC-1 cells indicated a decrease in the angiogenic potential of conditioned media from treated cells when compared to the controls. This decrease in angiogenic potential was remarkably higher with the bicistronic construct. Similarly, the invasive potential of these cells decreased dramatically when treated with the bicistronic construct, thereby suggesting a synergistic effect from the downregulation of both uPA and uPAR. Furthermore, when uPA and uPAR were downregulated simultaneously, the apoptotic cascade was triggered as indicated by the upregulation of both initiator and effector caspases as well as other pro-apoptotic molecules. A mitochondrial permeability assay and FACS analysis revealed an increase in apoptotic cells in the uPA/uPAR treatment as compared to the other treatments. This overexpression of pro-apoptotic caspases in relation to the RNAi-induced downregulation of uPA and uPAR clearly suggests the involvement of the uPA-uPAR system in cell survival and proliferation in addition to their role in tumor progression.
PMCID: PMC1398074  PMID: 16525631
breast cancer cells; invasion; angiogenesis; uPA; uPAR
25.  Antipermeability Function of PEDF Involves Blockade of the MAP Kinase/GSK/β-Catenin Signaling Pathway and uPAR Expression 
MAP kinases are involved in the VEGF signaling pathways that lead to a permeability increase through the β-catenin pathway, and activation of the uPA/uPAR system and the antipermeability function of PEDF is implemented by blocking MAP kinase activation.
Pigment epithelium–derived factor (PEDF) is a potent inhibitor of vascular endothelial growth factor (VEGF)–induced endothelial permeability. The goal of this study was to understand the mechanism by which PEDF blocks VEGF-induced increases in vascular permeability.
The paracellular permeability of bovine retinal endothelial (BRE) cells was measured by assaying transendothelial cell electrical resistance and tracer flux. Western blot analysis was used to show phosphorylation of VEGFR2, MAP kinases, and glycogen synthase kinase 3 (GSK3)-β. Confocal imaging and Western blot analysis were used to determine subcellular distribution of β-catenin. Real-time RT-PCR and Western blot analysis were used to quantify urokinase plasminogen activator receptor (uPAR) expression.
PEDF blocked VEGF-induced phosphorylation of extracellular signal–regulated kinase (ERK), p38 MAP kinase, the p38 substrate MAP kinase-activated protein kinase-2 (MAPKAPK-2), and GSK3-β, but it had no effect on the phosphorylation of VEGFR2. In addition, the VEGF-induced transcriptional activation of β-catenin and uPAR expression were blocked by PEDF and by inhibitors of p38 and MEK. Finally, the VEGF-induced increase in permeability was blocked by both PEDF and the same kinase inhibitors.
The data suggest that p38 MAP kinase and ERK act upstream of GSK/β-catenin in VEGF-induced activation of the uPA/uPAR system and that PEDF-mediated inhibition of the VEGF-induced increase in vascular permeability involves blockade of this pathway. These findings are important for developing precise and potent therapies for treatment of diseases characterized by vascular barrier dysfunction.
PMCID: PMC2891479  PMID: 20089873

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