Differential expression of the urokinase receptor in fibroblasts from normal and fibrotic human lungs

Urokinase-Type Plasminogen Activator Receptor (uPAR) in Inflammation and Disease: A Unique Inflammatory Pathway Activator

The urokinase-type plasminogen activator receptor (uPAR) is a unique protease binding receptor, now recognized as a key regulator of inflammation. Initially, uPA/uPAR was considered thrombolytic (clot-dissolving); however, recent studies have demonstrated its predominant immunomodulatory functions in inflammation and cancer. The uPA/uPAR complex has a multifaceted central role in both normal physiological and also pathological responses. uPAR is expressed as a glycophosphatidylinositol (GPI)-linked receptor interacting with vitronectin, integrins, G protein-coupled receptors, and growth factor receptors within a large lipid raft. Through protein-to-protein interactions, cell surface uPAR modulates intracellular signaling, altering cellular adhesion and migration. The uPA/uPAR also modifies extracellular activity, activating plasminogen to form plasmin, which breaks down fibrin, dissolving clots and activating matrix metalloproteinases that lyse connective tissue, allowing immune and cancer cell invasion and releasing growth factors. uPAR is now recognized as a biomarker for inflammatory diseases and cancer; uPAR and soluble uPAR fragments (suPAR) are increased in viral sepsis (COVID-19), inflammatory bowel disease, and metastasis. Here, we provide a comprehensive overview of the structure, function, and current studies examining uPAR and suPAR as diagnostic markers and therapeutic targets. Understanding uPAR is central to developing diagnostic markers and the ongoing development of antibody, small-molecule, nanogel, and virus-derived immune-modulating treatments that target uPAR.

Do coagulation or fibrinolysis reflect the disease condition in patients with soft tissue sarcoma?

BACKGROUND

Coagulation and fibrinolysis are distinct processes that are highly correlated. Cells control coagulation and fibrinolysis by expression of tissue factor and urokinase-type plasminogen activator receptor on their surface. Tumor cells express these proteins, adjust their microenvironment and induce tumor exacerbation. We hypothesized that the expression of plasma markers for coagulation and fibrinolysis in patients with soft tissue sarcomas (STSs) was dependent on the level of tumor malignancy. To elucidate which markers are predictive of recurrence, metastasis and prognosis, coagulation or fibrinolysis, we analyzed the correlation between plasma levels of thrombin-antithrombin III complex (TAT), soluble fibrin (SF), plasmin-α2 plasmin inhibitor complex (PIC), D-dimer (DD) and clinical parameters in patients with STSs.

METHODS

TAT, SF, PIC or DD were measured in pre-treatment blood samples from 64 patients with primary STSs and analyzed with clinicopathological parameters, and 5-year recurrence free survival (RFS), 5-year metastasis free survival (MFS) and 5-year overall survival (OS) were evaluated.

RESULTS

The metastasis group had significantly higher DD (p = 0.0394), PIC (p = 0.00532) and SF (p = 0.00249) concentrations than the group without metastasis. The group that died of disease showed significantly higher DD (p = 0.00105), PIC (p = 0.000542), SF (p = 0.000126) and TAT (p = 0.0373) than surviving patients. By dividing the patients into low and high groups, the group with high DD, PIC, SF and TAT showed significantly lower 5-year MFS and 5-year OS than the corresponding low group. Furthermore, in multivariate COX proportional hazard analysis of continuous variables for 5-year MFS, only PIC was found to be a significant factor (HR: 2.14).

CONCLUSION

Fibrinolysis was better than coagulation at reflecting the disease condition of patients with STS. Notably, PIC levels ≥ 1.1 can not only predict the risk of metastasis and poor prognosis, but also increasing PIC levels correspond to further increases in risks of metastasis and poor prognosis.

Curcumin intervention during progressive fibrosis controls inflammatory cytokines and the fibrinolytic system in pulmonary fibrosis

Persistent injuries and chronic inflammation paired with dysregulated healing process in the lungs leads to scarring and stiffening of the tissue leading to a condition called pulmonary fibrosis. There is no efficacious therapy against the condition because of the poorly understood pathophysiology of the disease. Curcumin is well known anti-inflammatory natural compound and is shown to have beneficial effects in many diseases. It is also reported to show antifibrotic activities in pulmonary fibrosis. There are evidences that fibrinolytic system plays a crucial role in the development of pulmonary fibrosis. We aimed to see whether curcumin could regulate inflammation and fibrinolysis in murine model of pulmonary fibrosis. We prepared BLM induced pulmonary fibrosis model by administering BLM at a dose of 2 mg/ kg bodyweight. Curcumin (75 mg/kg body wt) was instilled intraperitoneally on different time points. The effect of curcumin on inflammatory cytokines and fibrinolytic system was studied using molecular biology techniques like RT-PCR, western blot and immunohistochemistry/immunofluorescence. We observed that BLM brought changes in the expressions of components in the fibrinolytic system, i.e. BLM favoured fibrin deposition by increasing the expression of PAI-1 (plasminogen activator inhibitor) and decreasing the expression of uPA (Urokinase plasminogen activator) and uPAR (Urokinase plasminogen activator receptor). We also demonstrate that curcumin could restore the normal expression of fibrinolytic components, uPA, uPAR and PAI-1. Curcumin could also minimize the expression of key enzymes in tissue remodeling in pulmonary fibrosis, MMP-2 and MMP-9, which were elevated in the BLM treated group. Our data suggest that curcumin exerts an anti-inflammatory and antifibrotic effect in lungs. We highlight curcumin as a feasible adjuvant therapy option against pulmonary fibrosis.

The Contribution of the Urokinase Plasminogen Activator and the Urokinase Receptor to Pleural and Parenchymal Lung Injury and Repair: A Narrative Review

Pleural and parenchymal lung injury have long been characterized by acute inflammation and pathologic tissue reorganization, when severe. Although transitional matrix deposition is a normal part of the injury response, unresolved fibrin deposition can lead to pleural loculation and scarification of affected areas. Within this review, we present a brief discussion of the fibrinolytic pathway, its components, and their contribution to injury progression. We review how local derangements of fibrinolysis, resulting from increased coagulation and reduced plasminogen activator activity, promote extravascular fibrin deposition. Further, we describe how pleural mesothelial cells contribute to lung scarring via the acquisition of a profibrotic phenotype. We also discuss soluble uPAR, a recently identified biomarker of pleural injury, and its diagnostic value in the grading of pleural effusions. Finally, we provide an in-depth discussion on the clinical importance of single-chain urokinase plasminogen activator (uPA) for the treatment of loculated pleural collections.

The fibrogenic actions of the coagulant and plasminogen activation systems in pulmonary fibrosis

Fibrosis causes irreversible damage to lung structure and function in restrictive lung diseases such as idiopathic pulmonary fibrosis (IPF). Extravascular coagulation involving fibrin formation in the intra-alveolar compartment is postulated to have a pivotal role in the development of pulmonary fibrosis, serving as a provisional matrix for migrating fibroblasts. Furthermore, proteases of the coagulation and plasminogen activation (plasminergic) systems that form and breakdown fibrin respectively directly contribute to pulmonary fibrosis. The coagulants, thrombin and factor Xa (FXa) evoke fibrogenic effects via cleavage of the N-terminus of protease-activated receptors (PARs). Whilst the formation and activity of plasmin, the principle plasminergic mediator is suppressed in the airspaces of patients with IPF, localized increases are likely to occur in the lung interstitium. Plasmin-evoked proteolytic activation of factor XII (FXII), matrix metalloproteases (MMPs) and latent, matrix-bound growth factors such as epidermal growth factor (EGF) indirectly implicate plasmin in pulmonary fibrosis. Another plasminergic protease, urokinase plasminogen activator (uPA) is associated with regions of fibrosis in the remodelled lung of IPF patients and elicits fibrogenic activity via binding its receptor (uPAR). Plasminogen activator inhibitor-1 (PAI-1) formed in the injured alveolar epithelium also contributes to pulmonary fibrosis in a manner that involves vitronectin binding. This review describes the mechanisms by which components of the two systems primarily involved in fibrin homeostasis contribute to interstitial fibrosis, with a particular focus on IPF. Selectively targeting the receptor-mediated mechanisms of coagulant and plasminergic proteases may limit pulmonary fibrosis, without the bleeding complications associated with conventional anti-coagulant and thrombolytic therapies.

The fibrogenic actions of lung fibroblast-derived urokinase: a potential drug target in IPF

The role of urokinase plasminogen activator (uPA) in idiopathic pulmonary fibrosis (IPF) remains unclear. uPA-generated plasmin has potent fibrogenic actions involving protease activated receptor-1 (PAR-1) and interleukin-6 (IL-6). Here we characterize uPA distribution or levels in lung tissue and sera from IPF patients to establish the mechanism of its fibrogenic actions on lung fibroblasts (LFs). uPA immunoreactivity was detected in regions of fibrosis including fibroblasts of lung tissue from IPF patients (n = 7). Serum uPA levels and activity were also higher in IPF patients (n = 18) than controls (n = 18) (P < 0.05), being negatively correlated with lung function as measured by forced vital capacity (FVC) %predicted (P < 0.05). The culture supernatants of LFs from IPF patients, as compared to controls, showed an increase in plasmin activity after plasminogen incubation (5–15 μg/mL), corresponding with increased levels of uPA and IL-6 (n = 5–6, P < 0.05). Plasminogen-induced increases in plasmin activity and IL-6 levels were attenuated by reducing uPA and/or PAR-1 expression by RNAi. Plasmin(ogen)-induced mitogenesis was also attenuated by targeting uPA, PAR-1 or IL-6. Our data shows uPA is formed in active regions of fibrosis in IPF lung and contributes to LF plasmin generation, IL-6 production and proliferation. Urokinase is a potential target for the treatment of lung fibrosis.

uPAR promotes tumor-like biologic behaviors of fibroblast-like synoviocytes through PI3K/Akt signaling pathway in patients with rheumatoid arthritis

Urokinase-type plasminogen activator receptor (uPAR), is a multifunctional receptor on cell surface, widely present in endothelial cells, fibroblasts, and a variety of malignant cells. Current studies have suggested that uPAR overexpressed on synovial tissues or in synovial fluid or plasma in patients with rheumatoid arthritis (RA). However, there are limited researches regarding the role of uPAR on fibroblast-like synoviocytes of rheumatoid arthritis (RA-FLSs) and its underlying mechanisms. Here, our studies show that the expression of uPAR protein was significantly higher in fibroblast-like synoviocytes (FLSs) from RA than those from osteoarthritis or traumatic injury patients. uPAR gene silencing significantly inhibited RA-FLSs cell proliferation, restrained cell transformation from the G0/G1 phase to S phase, aggravated cell apoptosis, interfered with RA-FLSs cell migration and invasion, and reduced activation of the PI3K/Akt signaling pathway, which may be associated with β1-integrin. Cell supernatants from uPAR gene-silenced RA-FLSs markedly inhibited the migration and tubule formation ability of the HUVECs (a human endothelial cell line). Therefore, we demonstrate that uPAR changes the biological characteristics of RA-FLSs, and affects neoangiogenesis of synovial tissues in patients with RA. All of these may be associated with the β1-integrin/PI3K/Akt signaling pathway. These results imply that targeting uPAR and its downstream signal pathway may provide therapeutic effects in RA.

Pleural mesothelial cells in pleural and lung diseases

During development, the mesoderm maintains a complex relationship with the developing endoderm giving rise to the mature lung. Pleural mesothelial cells (PMCs) derived from the mesoderm play a key role during the development of the lung. The pleural mesothelium differentiates to give rise to the endothelium and smooth muscle cells via epithelial-to-mesenchymal transition (EMT). An aberrant recapitulation of such developmental pathways can play an important role in the pathogenesis of disease processes such as idiopathic pulmonary fibrosis (IPF). The PMC is the central component of the immune responses of the pleura. When exposed to noxious stimuli, it demonstrates innate immune responses such as Toll-like receptor (TLR) recognition of pathogen associated molecular patterns as well as causes the release of several cytokines to activate adaptive immune responses. Development of pleural effusions occurs due to an imbalance in the dynamic interaction between junctional proteins, n-cadherin and β-catenin, and phosphorylation of adherens junctions between PMCs, which is caused in part by vascular endothelial growth factor (VEGF) released by PMCs. PMCs play an important role in defense mechanisms against bacterial and mycobacterial pleural infections, and in pathogenesis of malignant pleural effusion, asbestos related pleural disease and malignant pleural mesothelioma. PMCs also play a key role in the resolution of inflammation, which can occur with or without fibrosis. Fibrosis occurs as a result of disordered fibrin turnover and due to the effects of cytokines such as transforming growth factor-β, platelet-derived growth factor (PDGF), and basic fibroblast growth factor; which are released by PMCs. Recent studies have demonstrated a role for PMCs in the pathogenesis of IPF suggesting their potential as a cellular biomarker of disease activity and as a possible therapeutic target. Pleural-based therapies targeting PMCs for treatment of IPF and other lung diseases need further exploration.

Putting the Squeeze on Airway Epithelia

Asthma is characterized by chronic inflammation, airway hyperresponsiveness, and progressive airway remodeling. The airway epithelium is known to play a critical role in the initiation and perpetuation of these processes. Here, we review how excessive epithelial stress generated by bronchoconstriction is sufficient to induce airway remodeling, even in the absence of inflammatory cells.

Soluble Urokinase Receptor Is Released Selectively by Glioblastoma Cells That Express Epidermal Growth Factor Receptor Variant III and Promotes Tumor Cell Migration and Invasion

Genomic heterogeneity is characteristic of glioblastoma (GBM). In many GBMs, the EGF receptor gene (EGFR) is amplified and may be truncated to generate a constitutively active form of the receptor called EGFRvIII. EGFR gene amplification and EGFRvIII are associated with GBM progression, even when only a small fraction of the tumor cells express EGFRvIII. In this study, we show that EGFRvIII-positive GBM cells express significantly increased levels of cellular urokinase receptor (uPAR) and release increased amounts of soluble uPAR (suPAR). When mice were xenografted with human EGFRvIII-expressing GBM cells, tumor-derived suPAR was detected in the plasma, and the level was significantly increased compared with that detected in plasma samples from control mice xenografted with EGFRvIII-negative GBM cells. suPAR also was increased in plasma from patients with EGFRvIII-positive GBMs. Purified suPAR was biologically active when added to cultures of EGFRvIII-negative GBM cells, activating cell signaling and promoting cell migration and invasion. suPAR did not significantly stimulate cell signaling or migration of EGFRvIII-positive cells, probably because cell signaling was already substantially activated in these cells. The activities of suPAR were replicated by conditioned medium (CM) from EGFRvIII-positive GBM cells. When the CM was preincubated with uPAR-neutralizing antibody or when uPAR gene expression was silenced in cells used to prepare CM, the activity of the CM was significantly attenuated. These results suggest that suPAR may function as an important paracrine signaling factor in EGFRvIII-positive GBMs, inducing an aggressive phenotype in tumor cells that are EGFRvIII-negative.

The inflammatory actions of coagulant and fibrinolytic proteases in disease

Aside from their role in hemostasis, coagulant and fibrinolytic proteases are important mediators of inflammation in diseases such as asthma, atherosclerosis, rheumatoid arthritis, and cancer. The blood circulating zymogens of these proteases enter damaged tissue as a consequence of vascular leak or rupture to become activated and contribute to extravascular coagulation or fibrinolysis. The coagulants, factor Xa (FXa), factor VIIa (FVIIa), tissue factor, and thrombin, also evoke cell-mediated actions on structural cells (e.g., fibroblasts and smooth muscle cells) or inflammatory cells (e.g., macrophages) via the proteolytic activation of protease-activated receptors (PARs). Plasmin, the principle enzymatic mediator of fibrinolysis, also forms toll-like receptor-4 (TLR-4) activating fibrin degradation products (FDPs) and can release latent-matrix bound growth factors such as transforming growth factor-β (TGF-β). Furthermore, the proteases that convert plasminogen into plasmin (e.g., urokinase plasminogen activator) evoke plasmin-independent proinflammatory actions involving coreceptor activation. Selectively targeting the receptor-mediated actions of hemostatic proteases is a strategy that may be used to treat inflammatory disease without the bleeding complications of conventional anticoagulant therapies. The mechanisms by which proteases of the coagulant and fibrinolytic systems contribute to extravascular inflammation in disease will be considered in this review.

Components of the plasminogen activation system promote engraftment of porous polyethylene biomaterial via common and distinct effects

Rapid fibrovascularization is a prerequisite for successful biomaterial engraftment. In addition to their well-known roles in fibrinolysis, urokinase-type plasminogen activator (uPA) and tissue plasminogen activator (tPA) or their inhibitor plasminogen activator inhibitor-1 (PAI-1) have recently been implicated as individual mediators in non-fibrinolytic processes, including cell adhesion, migration, and proliferation. Since these events are critical for fibrovascularization of biomaterial, we hypothesized that the components of the plasminogen activation system contribute to biomaterial engraftment. Employing in vivo and ex vivo microscopy techniques, vessel and collagen network formation within porous polyethylene (PPE) implants engrafted into dorsal skinfold chambers were found to be significantly impaired in uPA-, tPA-, or PAI-1-deficient mice. Consequently, the force required for mechanical disintegration of the implants out of the host tissue was significantly lower in the mutant mice than in wild-type controls. Conversely, surface coating with recombinant uPA, tPA, non-catalytic uPA, or PAI-1, but not with non-catalytic tPA, accelerated implant vascularization in wild-type mice. Thus, uPA, tPA, and PAI-1 contribute to the fibrovascularization of PPE implants through common and distinct effects. As clinical perspective, surface coating with recombinant uPA, tPA, or PAI-1 might provide a novel strategy for accelerating the vascularization of this biomaterial.

Plasminogen activator inhibitor-1 suppresses profibrotic responses in fibroblasts from fibrotic lungs

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease characterized by progressive interstitial scarification. A hallmark morphological lesion is the accumulation of myofibroblasts or fibrotic lung fibroblasts (FL-fibroblasts) in areas called fibroblastic foci. We previously demonstrated that the expression of both urokinase-type plasminogen activator (uPA) and the uPA receptor are elevated in FL-fibroblasts from the lungs of patients with IPF. FL-fibroblasts isolated from human IPF lungs and from mice with bleomycin-induced pulmonary fibrosis showed an increased rate of proliferation compared with normal lung fibroblasts (NL-fibroblasts) derived from histologically "normal" lung. Basal expression of plasminogen activator inhibitor-1 (PAI-1) in human and murine FL-fibroblasts was reduced, whereas collagen-I and α-smooth muscle actin were markedly elevated. Conversely, alveolar type II epithelial cells surrounding the fibrotic foci in situ, as well as those isolated from IPF lungs, showed increased activation of caspase-3 and PAI-1 with a parallel reduction in uPA expression. Transduction of an adenovirus PAI-1 cDNA construct (Ad-PAI-1) suppressed expression of uPA and collagen-I and attenuated proliferation in FL-fibroblasts. On the contrary, inhibition of basal PAI-1 in NL-fibroblasts increased collagen-I and α-smooth muscle actin. Fibroblasts isolated from PAI-1-deficient mice without lung injury also showed increased collagen-I and uPA. These changes were associated with increased Akt/phosphatase and tensin homolog proliferation/survival signals in FL-fibroblasts, which were reversed by transduction with Ad-PAI-1. This study defines a new role of PAI-1 in the control of fibroblast activation and expansion and its role in the pathogenesis of fibrosing lung disease and, in particular, IPF.

Urokinase-type plasminogen activator receptor (uPAR) ligation induces a raft-localized integrin signaling switch that mediates the hypermotile phenotype of fibrotic fibroblasts

The urokinase-type plasminogen activator receptor (uPAR) is a glycosylphosphatidylinositol-linked membrane protein with no cytosolic domain that localizes to lipid raft microdomains. Our laboratory and others have documented that lung fibroblasts from patients with idiopathic pulmonary fibrosis (IPF) exhibit a hypermotile phenotype. This study was undertaken to elucidate the molecular mechanism whereby uPAR ligation with its cognate ligand, urokinase, induces a motile phenotype in human lung fibroblasts. We found that uPAR ligation with the urokinase receptor binding domain (amino-terminal fragment) leads to enhanced migration of fibroblasts on fibronectin in a protease-independent, lipid raft-dependent manner. Ligation of uPAR with the amino-terminal fragment recruited α5β1 integrin and the acylated form of the Src family kinase, Fyn, to lipid rafts. The biological consequences of this translocation were an increase in fibroblast motility and a switch of the integrin-initiated signal pathway for migration away from the lipid raft-independent focal adhesion kinase pathway and toward a lipid raft-dependent caveolin-Fyn-Shc pathway. Furthermore, an integrin homologous peptide as well as an antibody that competes with β1 for uPAR binding have the ability to block this effect. In addition, its relative insensitivity to cholesterol depletion suggests that the interactions of α5β1 integrin and uPAR drive the translocation of α5β1 integrin-acylated Fyn signaling complexes into lipid rafts upon uPAR ligation through protein-protein interactions. This signal switch is a novel pathway leading to the hypermotile phenotype of IPF patient-derived fibroblasts, seen with uPAR ligation. This uPAR dependent, fibrotic matrix-selective, and profibrotic fibroblast phenotype may be amenable to targeted therapeutics designed to ameliorate IPF.

Lipoprotein receptor-related protein 1 regulates collagen 1 expression, proteolysis, and migration in human pleural mesothelial cells

The low-density lipoprotein receptor-related protein 1 (LRP-1) binds and can internalize a diverse group of ligands, including members of the fibrinolytic pathway, urokinase plasminogen activator (uPA), and its receptor, uPAR. In this study, we characterized the role of LRP-1 in uPAR processing, collagen synthesis, proteolysis, and migration in pleural mesothelial cells (PMCs). When PMCs were treated with the proinflammatory cytokines TNF-α and IL-1β, LRP-1 significantly decreased at the mRNA and protein levels (70 and 90%, respectively; P < 0.05). Consequently, uPA-mediated uPAR internalization was reduced by 80% in the presence of TNF-α or IL-1β (P < 0.05). In parallel studies, LRP-1 neutralization with receptor-associated protein (RAP) significantly reduced uPA-dependent uPAR internalization and increased uPAR stability in PMCs. LRP-1-deficient cells demonstrated increased uPAR t(1/2) versus LRP-1-expressing PMCs. uPA enzymatic activity was also increased in LRP-1-deficient and neutralized cells, and RAP potentiated uPA-dependent migration in PMCs. Collagen expression in PMCs was also induced by uPA, and the effect was potentiated in RAP-treated cells. These studies indicate that TNF-α and IL-1β regulate LRP-1 in PMCs and that LRP-1 thereby contributes to a range of pathophysiologically relevant responses of these cells.

Mannose receptor 2 attenuates renal fibrosis

Mannose receptor 2 (Mrc2) expresses an extracellular fibronectin type II domain that binds to and internalizes collagen, suggesting that it may play a role in modulating renal fibrosis. Here, we found that Mrc2 levels were very low in normal kidneys but subsets of interstitial myofibroblasts and macrophages upregulated Mrc2 after unilateral ureteral obstruction (UUO). Renal fibrosis and renal parenchymal damage were significantly worse in Mrc2-deficient mice. Similarly, Mrc2-deficient Col4α3(-/-) mice with hereditary nephritis had significantly higher levels of total kidney collagen, serum BUN, and urinary protein than Mrc2-sufficient Col4α3(-/-) mice. The more severe phenotype seemed to be the result of reduced collagen turnover, because procollagen III (α1) mRNA levels and fractional collagen synthesis in the wild-type and Mrc2-deficient kidneys were similar after UUO. Although Mrc2 associates with the urokinase receptor, differences in renal urokinase activity did not account for the increased fibrosis in the Mrc2-deficient mice. Treating wild-type mice with a cathepsin inhibitor, which blocks proteases implicated in Mrc2-mediated collagen degradation, worsened UUO-induced renal fibrosis. Cathepsin mRNA profiles were similar in Mrc2-positive fibroblasts and macrophages, and Mrc2 genotype did not alter relative cathepsin mRNA levels. Taken together, these data establish an important fibrosis-attenuating role for Mrc2-expressing renal interstitial cells and suggest the involvement of a lysosomal collagen turnover pathway.

Urokinase receptor mediates lung fibroblast attachment and migration toward provisional matrix proteins through interaction with multiple integrins

Fibroblasts from patients with pulmonary fibrosis express higher levels of the receptor for urokinase, and the extent of fibrosis in some animal models exhibits a dependence on the urokinase receptor. Recent observations have identified the urokinase receptor as a trans-interacting receptor with consequences on signaling and cell responses that vary depending on its interacting partner, the relative levels of expression, and the state of cellular transformation. We undertook this study to define the urokinase-type plasminogen activator cellular receptor (u-PAR)-integrin interactions and to determine the functional consequences of such interactions on normal human lung fibroblast attachment and migration. u-PAR colocalizes in lammelipodia/filopodia with relevant integrins that mediate fibroblast attachment and spreading on the provisional matrix proteins vitronectin, fibronectin, and collagens. Inhibitory antibody studies have revealed that human lung fibroblasts utilize alpha(v)beta(5) to attach to vitronectin, predominantly alpha(5)beta(1) (and alpha(v)beta(3)) to attach to fibronectin, and alpha(1)beta(1), alpha(2)beta(1), and alpha(3)beta(1) to attach to collagen. Blocking studies with alpha-integrin subunit decoy peptides and u-PAR neutralizing antibodies indicate that u-PAR modulates the integrin-mediated attachment to purified provisional matrix proteins, to anti-integrin antibodies, or to fibroproliferative lesions from fibrotic lungs. Furthermore, these decoy peptides blunt fibroblast spreading and migration. We show that u-PAR can interact with multiple alpha-integrins but with a preference for alpha(3). Taken together, these data demonstrate that u-PAR may interact with multiple integrins in normal human lung fibroblasts thereby promoting attachment, spreading, and migration. Modulation of fibroblast invasion would be expected to lead to amelioration of fibroproliferative diseases of the lung.

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.

The fibrinolytic system and the regulation of lung epithelial cell proteolysis, signaling, and cellular viability

The urokinase-type plasminogen activator (uPA), its receptor (uPAR), and plasminogen activator inhibitor-1 (PAI-1) are key components of the fibrinolytic system and are expressed by lung epithelial cells. uPA, uPAR, and PAI-1 have been strongly implicated in the pathogenesis of acute lung injury (ALI) and pulmonary fibrosis. Recently, it has become clear that regulation of uPA, uPAR, and PAI-1 occurs at the posttranscriptional level of mRNA stability in lung epithelial cells. uPA further mediates its own expression in these cells as well as that of uPAR and PAI-1 through induction of changes in mRNA stability. In addition, uPA-mediated signaling controls the expression of the tumor suppressor protein p53 in lung epithelial cells at the posttranslational level. p53 has recently been shown to be a trans-acting uPA, uPAR, and PAI-1 mRNA-binding protein that regulates the stability of these mRNAs. It is now clear that signaling initiated by uPA mediates dose-dependent regulation of lung epithelial cell apoptosis and likewise involves changes in p53, uPA, uPAR, and PAI-1 expression. These findings demonstrate that the uPA-uPAR-PAI-1 system of lung epithelial cells mediates a broad repertoire of responses that encompass but extend well beyond traditional fibrinolysis, involve newly recognized interactions with p53 that influence the viability of the lung epithelium, and are thereby implicated in the pathogenesis of ALI and its repair.

Urokinase and its receptors in chronic kidney disease

This review focuses on the role of the serine protease urokinase-type plasminogen activator and its high affinity receptor uPAR/CD87 in chronic kidney disease (CKD) progression. An emerging theme is their organ- and site-specific effects. In addition to tubules, uPA is produced by macrophages and fibroblasts in CKD. By activating hepatocyte growth factor and degrading fibrinogen uPA may have anti-fibrotic effects. However renal fibrosis was similar between uPA wild-type and knockout mice in experimental CKD. The uPAR is expressed by renal parenchymal cells and inflammatory cells in a variety of kidney diseases. Such expression appears anti-fibrotic based on studies in uPAR-deficient mice. In CKD uPAR expression is associated with higher uPA activity but its most important effect appears to be due to effects on cell recruitment and migration that involve interactions with a variety of co-receptors and chemoattractant effects of soluble uPAR. Vitronectin and high molecular weight kininogen are alternate uPAR ligands, and receptors in addition to uPAR may also bind directly to uPA and activate cell signaling pathways.

Pathophysiology of the pleura

The pleural mesothelial cell is an essential cell in maintaining the normal homeostasis of the pleural space and it is also a central component of the pathophysiologic processes affecting the pleural space. In this review, we will review the defense mechanisms of the pleural mesothelium and changes in pleural physiology as a result of inflammatory, infectious, and malignant conditions with a focus on cytokine and chemokine networks. We will also review the processes involved in the pathogenesis of pleural fibrosis.

Systemic sclerosis fibroblasts inhibit in vitro angiogenesis by MMP-12-dependent cleavage of the endothelial cell urokinase receptor

Failure of endothelial cells to develop new vessels in response to hypoxia is a distinctive feature of systemic sclerosis (SSc) in the avascular phase. We have previously shown that SSc endothelial cells over-express matrix metalloproteinase-12 (MMP-12), which blocks angiogenesis by cleavage of the endothelial urokinase-type plasminogen activator receptor (uPAR). In the present study, we have investigated whether over-expression of MMP-12 and of angiostatic factors, or hypo-expression of angiogenic factors by SSc fibroblasts, contributes to impaired angiogenesis in SSc. Dermal fibroblasts were isolated from healthy subjects (N-Fb) and patients with diffuse SSc (SSc-Fb). Angiogenesis of target normal human microvascular endothelial cells (H-MVECs) was assayed by Matrigel invasion, cell proliferation, and capillary morphogenesis. uPAR cleavage and MMP-12 activity were evaluated by western blotting. We show that the over-expression of MMP-12 by SSc-Fb determines uPAR cleavage in H-MVECs. Conditioned medium from SSc-Fb impaired H-MVEC proliferation, invasion, and capillary morphogenesis. Anti-MMP-12 antibodies restored such impairment. Altered expression of angiostatic/angiogenic factors, including transforming growth factor beta1, did not account for SSc-Fb-dependent impairment of angiogenesis. The over-expression of MMP-12 by both SSc-Fb and SSc endothelial cells indicates that MMP-12 over-production may have a critical pathogenic role in SSc-associated vascular alterations.

The IL-1 type 1 receptor is required for the development of LPS-induced airways disease

BACKGROUND

The contribution of IL-1beta signaling through the IL-1 type 1 receptor (IL-1R1) to the development of persistent LPS-induced airway disease has not been investigated.

OBJECTIVE

To determine the importance of signaling through the IL-1 type 1 receptor in the development of LPS-induced airway disease.

METHODS

We exposed IL-1R1-deficient (C57BL/6(IL-1RI-/-)) mice to an aerosol of LPS or filtered air for 1 day, 1 week, or 4 weeks.

RESULTS

After 4 weeks of LPS inhalation, C57BL/6(IL-1RI-/-) mice failed to develop significant submucosal thickening, whereas C57BL/6 mice had significantly thickened submucosa in small, medium, and large airways compared with those of unexposed control mice. Cell proliferation in the airways of both the 1-week and 4-week LPS-exposed C57BL/6(IL-1RI-/-) mice was significantly reduced compared with LPS-exposed C57BL/6 mice. mRNA for type III alpha-3 procollagen was significantly elevated over baseline in C57BL/6 yet remained unchanged compared with baseline in C57BL/6(IL-1RI-/-) mice after 1 week or 4 weeks of LPS inhalation. mRNA for tissue inhibitor of metalloprotease 1 in C57BL/6 mice in the 1-week and 4-week groups was significantly elevated over both control mice and C57BL/6(IL-1RI-/-) mice.

CONCLUSION

These data support the hypothesis that signaling through the IL-1 receptor modulates extracellular matrix homeostasis in response to inhaled LPS.

CLINICAL IMPLICATIONS

Attenuating IL-1R1-mediated signaling might be an effective therapy against the development of airway remodeling in chronic inflammatory diseases.

Pleural fibrosis

Pleural fibrosis can result from a variety of inflammatory processes. The response of the pleural mesothelial cell to injury and the ability to maintain its integrity are crucial in determining whether normal healing or pleural fibrosis occurs. The pleural mesothelial cell, various cytokines, and disordered fibrin turnover are involved in the pathogenesis of pleural fibrosis. The roles of these mediators in producing pleural fibrosis are examined. This article reviews the most common clinical conditions associated with the development of pleural fibrosis. Fibrothorax and trapped lung are two unique and uncommon consequences of pleural fibrosis. The management of pleural fibrosis, including fibrothorax and trapped lung, is discussed.

Pathogenesis of pleural fibrosis

Pleural fibrosis resembles fibrosis in other tissues and can be defined as an excessive deposition of matrix components that results in the destruction of normal pleural tissue architecture and compromised function. Pleural fibrosis may be the consequence of an organised haemorrhagic effusion, tuberculous effusion, empyema or asbestos-related pleurisy and can manifest itself as discrete localised lesions (pleural plaques) or diffuse pleural thickening and fibrosis. Although the pathogenesis is unknown, it is likely that the complex interactions between resident and inflammatory cells, profibrotic mediators and coagulation, and fibrinolytic pathways are integral to pleural remodelling and fibrosis. It is generally considered that the primary target cell for pleural fibrosis is the subpleural fibroblast. However, increasing evidence suggests that mesothelial cells may also play a significant role in the pathogenesis of this condition, both by initiating inflammatory responses and producing matrix components. A greater understanding of the interactions between pleural and inflammatory cells, cytokines and growth factors, and blood derived proteins is required before adequate therapies can be developed to prevent pleural fibrosis from occurring.

The role of transforming growth factor beta in lung development and disease

Transforming growth factor (TGF) beta plays an important role in normal pulmonary morphogenesis and function and in the pathogenesis of lung disease. The effect of TGFbeta is regulated via a selective pathway of TGFbeta synthesis and signaling that involves activation of latent TGFbeta, specific TGFbeta receptors, and intracellular signaling via Smad molecules. All three isoforms of TGFbeta are expressed at high levels during normal lung development, being particularly important for branching morphogenesis and epithelial cell differentiation with maturation of surfactant synthesis. Small amounts of TGFbeta are still present in the adult lung, and TGFbeta is involved in normal tissue repair following lung injury. However, in a variety of forms of pulmonary pathology, the expression of TGFbeta is increased. These include chronic lung disease of prematurity as well as several forms of acute and chronic adult lung disease. While TGFbeta1 appears to be the predominant isoform involved, elevated levels of all three isoforms have been demonstrated. The increase in TGFbeta precedes abnormalities in lung function and detectable lung pathology, but correlates with the severity of the disease. TGFbeta plays a key role in mediating fibrotic tissue remodeling by increasing the production and decreasing the degradation of connective tissue via several mechanisms.

The urokinase receptor can be induced by Borrelia burgdorferi through receptors of the innate immune system

Monocytic cells exposed to Borrelia burgdorferi, through unknown receptors, overexpress the urokinase receptor (uPAR), a key mediator of the plasminogen activation system. We show that combined blockade of CD14 and TLR2 causes a significant inhibition of B. burgdorferi-induced uPAR in Mono Mac 6 (MM6) cells. Other pattern recognition receptors tested (CD11b/CD18, the mannose receptor, and the N-formyl-methionyl-leucyl-phenylalanine receptor) did not have demonstrated roles in B. burgdorferi-mediated uPAR induction. We dissected the result for CD14 andTLR2 by investigating the singular contributions of each. Independent functional blockade of CD14 or TLR2 failed to inhibit B. burgdorferi-mediated uPAR induction. 1,25-Dihydroxyvitamin D(3) differentiation of MM6 cells increased CD14 expression 12-fold but did not augment B. burgdorferi-mediated uPAR expression. Peritoneal exudate macrophages (PEM) from CD14- or TLR2-deficient mice were not defective in B. burgdorferi-mediated synthesis of uPAR mRNA and protein. Increased uPAR mRNA or protein or both were apparent in PEM from transgenic and control mice, even at a ratio of one Borrelia spirochete per cell. We conclude that signaling for the uPAR response, as mediated by B. burgdorferi, proceeds with CD14 and TLR2 as partial contributors. That part under control of CD14 and TLR2 represents a new link between the host plasminogen activation and innate immunity systems.

Collagen metabolism and enzymes of the urokinase plasminogen activator system in chronic myeloproliferative disorders: correlation between plasma-soluble urokinase plasminogen activator receptor and serum markers for collagen metabolism

Extracellular proteolytic enzymes of the urokinase-type plasminogen activator (uPA) system and the family of metalloproteinases (MMPs) catalyse the matrix degradation and remodelling processes characteristic of invasive malignant disorders. In a cohort of 50 patients with chronic myeloproliferative disorders (MPD) serum markers for collagen metabolism were compared to plasma levels of enzymes of the uPA and MMP system. Serum aminoterminal propeptide of type III procollagen (S-PIIINP) (P < 0.0001) concentration was significantly higher in the patients (median 3.7 micro g/L vs. 2.5 micro g/L) compared with controls. In a subgroup analysis comprising patients with myelofibrosis (MF), polycythaemia vera (PV) and essential thrombocythaemia (ET), respectively, S-PIIINP levels differed significantly with the highest values found in patients with MF (MF vs. PV vs. ET; P = 0.0027). Serum concentration of carboxyterminal telopeptide of type I collagen (S-ICTP) (P = 0.0006), reflecting type I collagen degradation, was significantly higher in patients compared with controls (median 4.0 micro g/L vs. 2.7 micro g/L). When comparing S-ICTP measurements between patient subgroups and controls there were only significantly higher values among MF and PV patients (MF vs. controls; P < 0.0001, PV vs. controls; P = 0.0016). A significant correlation between the marker for collagen synthesis (S-PIIINP) and degradation (S-ICTP) (r = 0.59; P < 0.0001) was demonstrated. A correlation analysis between serum markers for bone marrow remodelling processes (S-PIIINP, S-ICTP and S-hyaluronan) and plasma-soluble urokinase plasminogen receptor (suPAR) disclosed a significant relationship between suPAR and S-PIIINP (r = 0.48; P = 0.0009), S-hyaluronan (r = 0.56; P < 0.0001) and S-ICTP (r = 0.47; P = 0.0013), respectively. Plasma levels of MMP-2 and -9 were not correlated to serum markers for collagen metabolism. These findings suggest that enzymes of the uPA system might participate in the bone marrow remodelling processes characteristic of MPD.

Urokinase receptor deficiency accelerates renal fibrosis in obstructive nephropathy

The urokinase cellular receptor (uPAR) recognizes the N-terminal growth factor domain of urokinase-type plasminogen activator (uPA) and is expressed by several cell types. The present study was designed to test the hypothesis that uPAR regulates the renal fibrogenic response to chronic injury. Groups of uPAR wild-type (+/+) and deficient (-/-) mice were investigated between 3 and 14 d after unilateral ureteral obstruction (UUO) or sham surgery. Not detected in normal kidneys, uPAR mRNA was expressed in response to UUO in the +/+ mice. By in situ hybridization, uPAR mRNA transcripts were detected in renal tubules and interstitial cells of the obstructed uPAR+/+ kidneys. The severity of renal fibrosis, based on the measurement of total collagen (13.5 +/- 1.5 versus 9.8 +/- 1.0 microg/mg kidney on day 14; -/- versus +/+) and interstitial area stained by Masson trichrome (22 +/- 4% versus 14 +/- 3% on day 14; -/- versus +/+) was significantly greater in the uPAR-/- mice. In the absence of uPAR, renal uPA activity was significantly decreased compared with the wild-type animals after UUO (62 +/- 20 versus 135 +/- 13 units at day 3 UUO; 74 +/- 17 versus 141 +/- 16 at day 7 UUO; 98 +/- 20 versus 165 +/- 10 at day 14 UUO; -/- versus +/+). In contrast, renal expression of several genes that regulate plasmin activity were similar in both genotypes, including uPA, tPA, PAI-1, protease nexin-1, and alpha2-antiplasmin. Worse renal fibrosis in the uPAR-/- mice appears to be TGF-beta-independent, as TGF-beta activity was actually reduced by 65% in the -/- mice despite similar renal TGF-beta1 mRNA levels. Significantly lower levels of the major 2.3-kb transcript and the 69-kd active protein of hepatocyte growth factor (HGF), a known anti-fibrotic growth factor, in the uPAR-/- mice suggests a potential link between HGF and the renoprotective effects of uPAR. These data suggest that renal uPAR attenuates the fibrogenic response to renal injury, an outcome that is mediated in part by urokinase-dependent but plasminogen-independent functions.

Urokinase receptor modulates cellular and angiogenic responses in obstructive nephropathy

Interstitial cells have been implicated in the pathogenesis of renal fibrosis. Given that the urokinase receptor (uPAR) is known to play a role in cell adhesion, migration, and angiogenesis, the present study was designed to evaluate the role of uPAR in the regulation of the phenotypic composition of interstitial cells (macrophages, myofibroblasts, capillaries) in response to chronic renal injury. Groups of uPAR wild-type (+/+) and knockout (-/-) mice were investigated between 3 and 14 d after unilateral ureteral obstruction (UUO) or sham surgery (n = 8 mice per group). The density of F4/80+ interstitial macrophages (Mphi) was significantly lower in the -/- mice (3.3 +/- 0.4 versus 6.9 +/- 1.7% area at day 3 UUO; 10.8 +/- 1.6 versus 15.7 +/- 1.0% at day 14 UUO; -/- versus +/+). In contrast, in the -/- mice there were significantly more alpha smooth muscle actin (alphaSMA)-positive cells (12.9 +/- 3.2 versus 7.8 +/- 1.5% area at day 3 UUO; 21.0 +/- 4.7 versus 9.7 +/- 1.9% at day 14 UUO) and CD34-positive endothelial cells (8.4 +/- 1.9 versus 4.0 +/- 1.1% area at day 14 UUO). These differences were associated with significantly more interstitial fibrosis in the -/- mice based on Sirius red staining (4.6 +/- 0.9 versus 2.3 +/- 0.9% area at 14 d UUO). Absence of the uPAR scavenger receptor was associated with significantly greater accumulation of plasminogen activator inhibitor-1 protein (PAI-1) (20.5 +/- 3.5 versus 9.1 +/- 2.9% area, day 14 UUO) and vitronectin protein (2.4 +/- 1.1 versus 0.9 +/- 0.4% area, day 14 UUO). By immunostaining alphaSMA+ cells, CD34+ cells, vitronectin and PAI-1 co-localized to the same tubulointerstitial area. The number of apoptotic cells increased in response to UUO but was significantly higher in the -/- mice (2.0 +/- 0.2 versus 1.2 +/- 0.2 per 100 tubulointerstitial cells, day 14 UUO) while the number of proliferating cells was significantly lower in the uPAR-/- mice. These data suggest that uPAR deficiency suppresses renal Mphi recruitment, but the absence of this scavenger receptor actually accentuates the fibrogenic response, likely due in part to the delayed clearance of angiogenic/profibrotic molecules such as PAI-1 and decreased receptor-associated uPA activity.

Single-chain urokinase alone or complexed to its receptor in tetracycline-induced pleuritis in rabbits

Intrapleural loculation can increase morbidity in hemothoraces or parapneumonic effusions. Intrapleural fibrin precedes visceral-parietal pleural adhesions. We speculated that single-chain urokinase plasminogen activator alone or bound to its receptor could prevent these adhesions by their relative resistance to local inhibition by plasminogen activator inhibitors. We found that recombinant human single-chain urokinase-bound rabbit pleural mesothelial cells or lung fibroblasts with kinetics similar to that reported for human cells (kD of approximately 5 nM). The receptor-bound fibrinolysin maintained in vitro fibrinolytic activity in the presence of pleural fluids from rabbits with tetracycline-induced pleural injury over 24 hours. In rabbits given intrapleural single-chain urokinase 24 and 48 hours after intrapleural tetracycline (n = 10 animals), adhesions were prevented, whereas the receptor-complexed form (n = 12) attenuated adhesions versus vehicle/tetracycline-treated rabbits (n = 22, p <or= 0.005 in both cases). There were more adhesions in the complex than the single-chain urokinase group (p = 0.02). Residual antigenic but not functional evidence of the interventional agents remained in pleural fluids at 72 hours after tetracycline. No local or systemic bleeding occurred because of either interventional agent. The data demonstrate that single-chain urokinase inhibits, whereas lysin-receptor complexes attenuate, adhesion formation in tetracycline-induced pleural injury in rabbits.

Elevated soluble urokinase plasminogen activator receptor in plasma from patients with idiopathic myelofibrosis or polycythaemia vera

Extracellular proteolytic enzymes of the urokinase-type plasminogen activator (uPA) system and the family of metalloproteases play a crucial role in the matrix degradation and tissue remodelling processes characteristic of malignant disorders. The receptor for urokinase plasminogen activator (uPAR) serves to localise and intensify the action of uPA and is expressed on the surface of malignant as well as tumour stromal cells including fibroblasts. A soluble form of uPAR (suPAR) cleaved from its glycosyl-phosphatidylinositol anchor is detected in plasma from healthy individuals and increased levels of suPAR have been found in advanced malignancy, suggesting that suPAR may be a marker of extensive tissue remodelling. In an attempt to clarify whether suPAR might be a marker for bone marrow tissue remodelling we measured plasma suPAR levels in a patient cohort comprising 17 with myelofibrosis (MF), 17 with polycythaemia vera (PV), 15 with essential thrombocythaemia (ET), one with a transitional myeloproliferative disorder evolving from PV and 30 controls. Compared with controls suPAR levels were significantly higher in the patients (P < 0.0001) (median 3.35 vs. 2.32 microg L(-1)). Moreover, in subgroup analyses including patients with MF, PV, and ET, respectively, suPAR levels differed significantly with the highest levels found in patients with MF and PV (MF vs. PV vs. ET; P = 0.0003). When comparing suPAR levels of the individual patient subgroups with controls, only suPAR levels of PV and MF patients were significantly increased (P < 0.0001). Sixty-five percent of patients with PV and MF (22/34) had suPAR plasma values that were above the mean +2 standard deviations (SD) of controls. The concentration of suPAR was significantly correlated to plasma lactate dehydrogenase, thrombomodulin, and complex of tPA:PAI-1 in the patients. There was no difference between patients and controls when comparing plasma uPA levels. Increased plasma suPAR levels in patients with chronic myeloproliferative disorders may reflect increased uPAR production in the bone marrow, leading to enhanced bone marrow remodelling.

Endothelium and disordered fibrin turnover in the injured lung: newly recognized pathways

OBJECTIVES

To review derangements of pathways of fibrin turnover that promote pathologic fibrin deposition in the acute respiratory distress syndrome and to review the contribution of the endothelium and parenchymal lung cells to the derangements. In addition, to review how these pathways can be exploited in specific clinical circumstances, including sepsis and acute lung injury. Lastly, to review newly recognized posttranscriptional and urokinase-dependent pathways by which the fibrinolytic system is regulated in the lung.

DATA SOURCES

Medical literature published in English from 1966 to present.

DATA SUMMARY

Local abnormalities of fibrin turnover in the injured lung recapitulate the systemic changes observed in sepsis. In both circumstances, the procoagulant response is increased, whereas fibrinolytic activity is concurrently depressed. The increased procoagulant activity is related to tissue factor associated with factor VII/VIIa. Fibrinolytic activity in the vasculature is mainly attributable to tissue plasminogen activator, whereas extravascular fibrinolytic activity in the lung is mainly attributable to urokinase plasminogen activator (uPA). Depressed fibrinolytic activity is in large part attributable to plasminogen activator inhibitor-1. In sepsis, activated protein C is also deficient, potentiating the inflammatory response, coagulopathy, and depressed fibrinolysis. Recombinant human activated protein C (drotrecogin alfa [activated]) was successful as an intervention for sepsis in a recent phase 3 clinical trial (PROWESS). Recently, novel posttranscriptional pathways that regulate expression of uPA, its receptor (uPAR), and plasminogen activator inhibitor-1 have been identified. The responsible mechanisms involve cis-trans interactions between newly recognized messenger RNA (mRNA) binding sequences and mRNA binding proteins. A 51 nucleotide mRNA binding sequence within the coding region of uPAR mRNA interacts with a novel 50-kDa mRNA binding protein to destabilize the message. Sequences within the 3' untranslated region of uPA or plasminogen activator inhibitor-1 mRNA interact with 30- and 60-kDa proteins, respectively, to regulate message stability. All of these pathways operate in lung epithelial cells, and endothelial cells regulate uPA expression through a similar pathway. In addition, uPA itself is capable of inducing expression of other components of the fibrinolytic system, including uPAR. This observation defines another feedback loop that could amplify local fibrinolysis and other uPA- or uPAR-mediated cellular responses, including cellular proteolysis, proliferation, and directed cellular migration.

CONCLUSIONS

Novel posttranscriptional pathways regulate expression of uPA, uPAR, and plasminogen activator inhibitor-1. uPA itself is capable of inducing other components of the fibrinolytic system. Some or all of these newly recognized pathways are operative in endothelial and parenchymal lung cells and may influence disordered fibrin turnover in the injured lung.

Induction of the plasminogen activator system accompanies peripheral nerve regeneration after sciatic nerve crush

Peripheral nerve regeneration is dependent on the ability of regenerating neurites to migrate through cellular debris and altered extracellular matrix at the injury site, grow along the residual distal nerve sheath conduit, and reinnervate synaptic targets. In cell culture, growth cones of regenerating axons secrete proteases, specifically plasminogen activators (PAs), which are believed to facilitate growth cone movement by digesting extracellular matrices and cell adhesions. In this study, the PA system was shown to be specifically activated in sensory neurons after sciatic nerve crush in adult mice. The number of sensory neurons expressing urokinase PA receptor (uPAR) mRNA levels increased above sham levels by 8 hr after crush, whereas the number of sensory neurons expressing uPA and tissue PA (tPA) mRNAs was significantly increased by 3 d after crush. PA mRNA levels were also increased at the crush site, with uPA mRNA elevated by 8 hr after crush and tPA and uPAR mRNA levels markedly increased by 7 d. PA-dependent enzymatic activity was significantly increased from 1 to 7 d after crush in nerves that had been crushed compared with uncrushed nerves. Immunohistochemistry showed that tPA was localized within regenerating axons of the sciatic nerve. There were no significant changes in plasminogen activator inhibitor 1 activity between crush and sham after the injury. These results clearly demonstrated that after injury the PA system was rapidly induced in sensory neurons, where it may play an important role in nerve regeneration in vivo.

Mice lacking tPA, uPA, or plasminogen genes showed delayed functional recovery after sciatic nerve crush

Axonal outgrowth during peripheral nerve regeneration relies on the ability of growth cones to traverse through an environment that has been altered structurally and along a basal lamina sheath to reinnervate synaptic targets. To promote migration, growth cones secrete proteases that are thought to dissolve cell-cell and cell-matrix adhesions. These proteases include the plasminogen activators (PAs), tissue PA (tPA) and urokinase PA (uPA), and their substrate, plasminogen. PA expression and secretion are upregulated in regenerating mammalian sensory neurons in culture. After sciatic nerve crush in mice, there was an induction of PA mRNAs in the sensory neurons contributing to the crushed nerve and an upregulation of PA-dependent activity in crushed nerve compared with sham counterparts during nerve regeneration. To further assess the role of the PA system during peripheral nerve regeneration, PA-dependent activity as well as recovery of sensory and motor function in the injured hindlimb were assessed in wild-type, tPA, uPA, and plasminogen knock-out mice. Protease activity visualized by gel zymography showed that after nerve crush, the upregulation of PA activity in the tPA and uPA knock-out mice was delayed compared with wild-type mice. Recovery of sensory function was assessed by toe pinch, footpad prick, and the toe-spreading reflex. All knock-out mice demonstrated a significant delay in hindlimb response to these sensory stimuli compared with wild-type mice. For each modality tested, the uPA knock-out mice were the most dramatically affected, showing the longest delay to initiate a response. These studies clearly showed that PAs were necessary for timely functional recovery by regenerating peripheral nerves.

In vitro modulation of human lung cancer cell line invasiveness by antisense cDNA of tissue factor pathway inhibitor-2

Human tissue factor pathway inhibitor-2 (TFPI-2) is a Kunitz-type serine protease inhibitor that inhibits plasmin, trypsin, chymotrypsin, cathepsin G and plasma kallikrein but not urokinase (uPA) or tissue-type plasminogen activator and thrombin. Earlier studies from our and other laboratories have shown that the production of TFPI-2 is downregulated during the progression of various cancers. To investigate the role of TFPI-2 in the invasion and metastasis of lung tumors, the human lung cancer cell line A549, which produces high levels of TFPI-2, was stably transfected with a vector capable of expressing an antisense transcript complementary to the full-length TFPI-2 mRNA. Northern blot analysis was used to quantify the TFPI-2 mRNA transcript, and western blot analysis was used to measure TFPI-2 protein levels in parental cells and stably transfected (vector and antisense) clones. The levels of TFPI-2 mRNA and protein were significantly less in antisense clones than in the parental and vector controls. The invasive potential of the parental cells and stably transfected vector clones in vitro, as measured by the Matrigel invasion assay, was also markedly less than that of antisense clones. Further characterization of these clones showed that more cells migrated from antisense clones than from parental and vector clones. These data suggest that TFPI-2 is critical for the invasion and metastasis of lung cancer and that the downregulation of TFPI-2 production may be a feasible approach to increase invasiveness and metastasis.

Borrelia burgdorferi and other bacterial products induce expression and release of the urokinase receptor (CD87)

The urokinase-type plasminogen activator receptor (uPAR, CD87) is a highly glycosylated 55- to 60-kDa protein anchored to the cell membrane through a glycosylphosphatidylinositol moiety that promotes the acquisition of plasmin on the surface of cells and subsequent cell movement and migration by binding urokinase-type plasminogen activator. uPAR also occurs in a soluble form in body fluids and tumor extracts, and both membrane and soluble uPAR are overexpressed in patients with tumors. uPAR may be a factor in inflammatory disorders as well. We investigated whether Borrelia burgdorferi could stimulate up-regulation of cell membrane uPAR in vitro. B. burgdorferi, purified native outer surface protein A, and a synthetic outer surface protein A hexalipopeptide stimulated human monocytes to up-regulate membrane uPAR as measured by immunofluorescence/FACS and Western blot. The presence of soluble uPAR in culture supernatants, measured by Ag capture ELISA, was also observed. LPS from Salmonella typhimurium and lipotechoic acid from Streptococcus pyogenes also induced the up-regulation of both membrane and soluble uPAR protein by monocytes. Up-regulation of uPAR was induced by conditioned medium from B. burgdorferi/monocyte cocultures. The up-regulation of uPAR by B. burgdorferi was concomitant with an increase in uPAR mRNA, indicating that synthesis was de novo. The expression and release of uPAR in response to B. burgdorferi and other bacterial components suggests a role in the pathogenesis of Lyme disease as well as in other bacterial infections.

Profiling of genes which are differentially expressed in mouse liver in response to adenoviral vectors and delivered genes

The effects of transgene delivery by adenoviral vectors were studied by probing a 588 gene, mouse cDNA array with mRNA derived from infected liver. The liver tissues were obtained from naive mice and mice infected with replication-deficient adenovirus, adenovirus expressing transforming growth factor beta1 (TGFbeta1), and adenovirus expressing connective tissue growth factor (CTGF). Expression of 98 genes was detected in the array analysis. The increased expression of the transcripts for Stat1, gamma interferon-induced monokine (MIG) and interferon regulatory factor 1 (IRF1) clearly demonstrated the immune response induced by infection with a first generation, replication-incompetent adenovirus. In vivo expression of TGFbeta1 led to a down-regulation of genes involved in the immune response. The increased expression of u-PAR1, laminin receptor and BMP-1 confirms the importance of CTGF and TGFbeta1 in angiogenesis, and tissue repair. Expression of the serine protease inhibitors, Spi 2.4 and Spi 2, is also increased in response to AdTGFbeta1 and AdCTGF.

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.

Posttranscriptional regulation of plasminogen activator inhibitor-1 in human lung carcinoma cells in vitro

Plasminogen activator inhibitor-1 (PAI-1), the major circulating inhibitor of urokinase [urokinase-type plasminogen activator (uPA)], has been linked to the pathogenesis of lung cancer. PAI-1 belongs to the serpin family of inhibitors and inhibits both free urokinase (uPA) and receptor-bound urokinase (uPA receptor). Although PAI-1 has been related to a poor prognosis in lung carcinoma, mechanisms that regulate its expression in human lung cancer cells are not well understood. We used cultured human small cell and non-small cell lung carcinoma cell lines as model systems to elucidate the regulatory mechanisms that control expression of PAI-1. Levels of PAI-1 protein were significantly increased in selected lung carcinoma cells compared with those in normal small-airway epithelial cells. Corresponding steady-state levels of PAI-1 mRNA were similarly increased in these cells. The half-life of PAI-1 mRNA was prolonged in these lung carcinoma cell lines after transcriptional or translational blockade. We identified a 60-kDa protein that binds the 3'-untranslated region of PAI-1, and complex formation of this binding protein with PAI-1 mRNA reciprocally correlates with mRNA stability. The findings demonstrate that expression of PAI-1 is regulated at the posttranscriptional level in small cell- and non-small cell-derived human lung carcinoma cell lines. Altered regulation of PAI-1 at the posttranscriptional level may contribute to relative overexpression by malignant lung epithelial cells. A newly identified regulatory protein that binds to the 3'-untranslated region of PAI-1 mRNA appears to be involved in the posttranscriptional regulation of PAI-1 gene expression by human lung carcinoma cells in vitro.

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%).

Asbestos upregulates expression of the urokinase-type plasminogen activator receptor on mesothelial cells

Inhalation of asbestos is associated with pathologic changes in the pleural space, including pleural thickening, pleural plaques, and mesothelioma. These processes are characterized by altered local proteolysis, cellular proliferation, and cell migration, suggesting that the urokinase-type plasminogen activator receptor (uPAR) could be involved in the pathogenesis of asbestos-induced pleural disease. We hypothesized that mesothelial cell uPAR expression is induced by exposure to asbestos. To test this hypothesis, we used complementary techniques in rabbit and human mesothelial cells to determine whether uPAR expression is altered by exposure to asbestos. uPAR expression was induced by chrysotile and crocidolite asbestos, but not by wollastonite, as indicated by binding of radiolabeled urokinase-type plasminogen activator (uPA) to rabbit or human mesothelial cells. uPA was not induced by fiber exposure. Exposure to exogenous uPA increased uPA activity of cells exposed to wollastonite but not asbestos-treated MeT5A cells. uPAR expression increased further when asbestos was preincubated with vitronectin (VN) or serum. Increases in uPAR expression were confirmed by binding of uPA to uPAR in cell membrane preparations and immunofluorescent staining of uPAR at the cell surface, and were associated with increases in steady-state uPAR messenger RNA. Mesothelial cell uPAR expression was also induced by media from monocytes cultured with asbestos incubated with VN and serum. By antibody neutralization, the latter effect appeared to be in part mediated by transforming growth factor-beta. We found that asbestos increases uPAR at the surface of rabbit and human mesothelial cells, suggesting that altered expression of this receptor could be involved in asbestos-induced remodeling of the pleural mesothelium.

Posttranscriptional regulation of urokinase receptor gene expression in human lung carcinoma and mesothelioma cells in vitro

The urokinase-type plasminogen activator (uPA) interacts with its receptor (uPAR) to promote proteolysis as well as cell proliferation and migration. These functions contribute to the pathogenesis of neoplastic growth and invasiveness. Expression of uPAR in tumor extracts also inversely correlates with prognosis in many forms of cancer. In this study, we sought to determine if differences in uPAR expression were distinguishable between cultured human lung carcinoma and malignant mesothelioma subtypes. We also sought to determine if, as in malignant mesothelioma cells, uPAR expression is regulated at the posttranscriptional level in cultured malignant lung carcinoma cells. Using 125I-uPA binding and ligand blotting techniques, uPAR was expressed by phenotypically diverse lung carcinoma cell lines, including the H460, H157 and H1395 non-small cell lines and the H146 small cell lung carcinoma line. Increased uPAR expression was also detected in spindle-shaped (M33K) and epithelioid (M9K and MS-1) malignant mesothelioma cells. Selected mediators, including TGF-beta, TNF-alpha, LPS and PMA, uniformly enhanced uPAR expression in each of the tumor cell lines. Steady state uPAR mRNA expression was determined by RNase protection assay and correlated directly with the changes in cell surface uPAR expression. By gel mobility shift and UV-cross linking assays, a uPAR mRNA binding protein (uPAR mRNABp) implicated in the posttranscriptional control of message stability, was identified in each of the cell lines. Expression of uPAR and its message in cultured lung carcinoma and malignant mesothelioma cells is similarly influenced by effectors present in the tumor microenvironment. Regulation of the uPAR message occurs at the posttranscriptional level in cultured small and non-small cell lung carcinoma cells as well as spindle-shaped and fibrous malignant mesothelioma cell lines. Posttranscriptional regulation of uPAR in all these cells involves the interaction of the uPAR mRNABp with uPAR mRNA, which promotes uPAR mRNA destabilization.

Increase of urokinase-type plasminogen activator receptor expression in human gingival fibroblasts by Porphyromonas gingivalis lipopolysaccharide

BACKGROUND

Urokinase-type plasminogen activator receptor (uPAR) presenting on the cell surface with glycosylphosphatidylinositol (GPI) anchor is a key component in the plasminogen activator (PA)-plasmin system and plays a critical role in extracellular matrix degradation. It is believed that uPAR serves to localize and accelerate this generation system. In this study, we examined the levels of both uPA and uPAR in human gingival fibroblasts treated with Porphyromonas gingivalis lipopolysaccharide (LPS).

METHODS

Human gingival fibroblasts from the seventh to tenth doubling passages were plated at 5x10(4) cells per well in 24-well plates. The confluent-stage cells were cultured for 24 hours in alpha-MEM medium containing 2% fetal calf serum, after which they were incubated with P. gingivalis LPS. PA activity was measured using plasminogen and plasmin substrate S2251.

RESULTS

PA activity in the cell lysate was increased by LPS and reached maximum at 1 microg/ml LPS after being incubated for 8 hours. PA activity released by phosphatidylinositol-specific phospholipase C, which detaches the GPI anchor, was also increased by LPS. The activity was inhibited by amiloride, which is a specific inhibitor for uPA. LPS increased the protein and mRNA levels of both uPA and uPAR in gingival fibroblasts.

CONCLUSIONS

These findings suggest that increase of the uPAR level by LPS may play an important role in the progression of periodontal diseases through pericellular proteolysis.

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.

Expression and activity of urokinase and its receptor in endothelial and pulmonary epithelial cells exposed to asbestos

An elongated endothelial cell phenotype, which demonstrated increased ICAM-1-dependent neutrophil adherence, was induced when these cells were exposed to noncytotoxic concentrations of asbestos (Treadwell et al., Toxicol. Appl. Pharmacol. 139, 62-70, 1996). The present study examined mechanisms underlying this phenotypic change by investigating the effects of asbestos on transcription factor activation and expression of urokinase-type plasminogen activator (uPA) and its receptor uPAR. In situ zymography was used to compare the effects of these fibers on the activity of uPA. Cultures incubated with chrysotile or crocidolite asbestos, but not refractory ceramic fiber 1 (RCF-1), demonstrate localized cleavage of plasminogen, which was inhibited by amiloride. Immunocytochemistry showed that chrysotile-stimulated uPA activity was associated with a time-dependent augmentation of uPAR protein levels. RT-PCR analysis was used to investigate molecular mechanisms for these increases. Chrysotile asbestos, but not RCF-1, increased endothelial cell uPA message, relative to changes in beta-actin mRNA. This response to asbestos was not limited to endothelial cells, since both uPA and uPAR mRNA levels increase in human bronchial epithelial BEAS-2B cells exposed to chrysotile fibers. Finally, both types of asbestos, but not RCF-1, increased nuclear levels of nuclear factor-kappaB (NF-kappa B), a transcription factor common to increased expression of ICAM-1 and uPA. These data demonstrate that asbestos caused fiber-specific activation of endothelial and pulmonary epithelial cells, resulting in phenotypes capable of facilitating tissue remodeling.

A urokinase receptor mRNA binding protein-mRNA interaction regulates receptor expression and function in human pleural mesothelioma cells

Human pleural malignant mesothelioma (MS-1) or mesothelial (MeT5A) cells express the multifunctional urokinase receptor (uPAR) which influences neoplastic propagation via contributions to cellular proteolysis, migration, and mitogenesis. Recently, we reported that a 51-nucleotide fragment of the uPAR mRNA coding region contains regulatory information for uPAR message stability and that a cytoplasmic uPAR mRNA binding protein (uPAR mRNABp) specifically bound to this sequence in temporal association with uPAR mRNA destabilization in MS-1 cells. To determine if the uPAR mRNA-uPAR mRNABp interaction is a determinant of uPAR message stability as well as uPAR expression, we further characterized this cis-trans interaction and created stable transfected cell lines designed to exploit the interaction and to increase uPAR at the cell surface. The uPAR mRNABp was purified from MS-1 cells, has an apparent molecular mass of 50 kDa, selectively binds to the 51-nt fragment of the uPAR coding region, and does not degrade uPAR mRNA. To determine the role of the uPAR mRNABp on receptor expression, we overexpressed a chimeric beta-globin/uPAR/beta-globin mRNA containing the 51-nt binding fragment of uPAR mRNA in MS-1 cells and found that uPAR at the cell surface increased by twofold as measured by [125I]uPA binding or ligand blotting. Cellular proliferation of uPA-treated cells and invasiveness was similarly increased. The increase in cell surface uPAR was due to commensurately increased uPAR mRNA. The results suggest that competition between the overexpressed 51-nt fragment of the uPAR coding region and the wild-type uPAR mRNA transcript for uPAR mRNABp binding enables the cells to translate and express more uPAR at the cell surface. The interaction between the uPAR mRNABp and uPAR mRNA regulates message stability as well as uPAR expression by MS-1 cells.