A urokinase receptor mRNA binding protein from rabbit lung fibroblasts and mesothelial cells

Regulation of mRNA stability contributes to the function of innate lymphoid cells in various diseases

Innate lymphoid cells (ILCs) are important subsets of innate immune cells that regulate mucosal immunity. ILCs include natural killer cells, innate lymphoid cells-1 (ILC1s), ILC2s, and ILC3s, which have extremely important roles in the immune system. In this review, we summarize the regulation of mRNA stability mediated through various factors in ILCs (e.g., cytokines, RNA-binding proteins, non-coding RNAs) and their roles in mediating functions in different ILC subsets. In addition, we discuss potential therapeutic targets for diseases such as chronic obstructive pulmonary disease, cancer, and pulmonary fibrosis by regulation of mRNA stability in ILCs, which may provide novel directions for future clinical research.

Coagulation and Fibrinolysis in Obstructive Sleep Apnoea

Obstructive sleep apnoea (OSA) is a common disease which is characterised by repetitive collapse of the upper airways during sleep resulting in chronic intermittent hypoxaemia and frequent microarousals, consequently leading to sympathetic overflow, enhanced oxidative stress, systemic inflammation, and metabolic disturbances. OSA is associated with increased risk for cardiovascular morbidity and mortality, and accelerated coagulation, platelet activation, and impaired fibrinolysis serve the link between OSA and cardiovascular disease. In this article we briefly describe physiological coagulation and fibrinolysis focusing on processes which could be altered in OSA. Then, we discuss how OSA-associated disturbances, such as hypoxaemia, sympathetic system activation, and systemic inflammation, affect these processes. Finally, we critically review the literature on OSA-related changes in markers of coagulation and fibrinolysis, discuss potential reasons for discrepancies, and comment on the clinical implications and future research needs.

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.

Circulating Soluble Urokinase-Type Plasminogen Activator Receptor in Obstructive Sleep Apnoea

Background and Objectives: Obstructive sleep apnoea (OSA) is associated with heightened systemic inflammation and a hypercoagulation state. Soluble urokinase-type plasminogen activator receptor (suPAR) plays a role in fibrinolysis and systemic inflammation. However, suPAR has not been investigated in OSA. Materials and Methods: A total of 53 patients with OSA and 15 control volunteers participated in the study. Medical history was taken and in-hospital sleep studies were performed. Plasma suPAR levels were determined by ELISA. Results: There was no difference in plasma suPAR values between patients with OSA (2.198 ± 0.675 ng/mL) and control subjects (2.088 ± 0.976 ng/mL, p = 0.62). Neither was there any difference when patients with OSA were divided into mild (2.134 ± 0.799 ng/mL), moderate (2.274 ± 0.597 ng/mL) and severe groups (2.128 ± 0.744 ng/mL, p = 0.84). There was no significant correlation between plasma suPAR and indices of OSA severity, blood results or comorbidities, such as hypertension, diabetes, dyslipidaemia or cardiovascular disease. Plasma suPAR levels were higher in women when all subjects were analysed together (2.487 ± 0.683 vs. 1.895 ± 0.692 ng/mL, p < 0.01), and also separately in controls (2.539 ± 0.956 vs. 1.411 ± 0.534 ng/mL, p = 0.02) and patients (2.467 ± 0.568 vs. 1.991 ± 0.686 ng/mL, p < 0.01). Conclusions: Our results suggest that suPAR does not play a significant role in the pathophysiology of OSA. The significant gender difference needs to be considered when conducting studies on circulating suPAR.

Precision-guided, Personalized Intrapleural Fibrinolytic Therapy for Empyema and Complicated Parapneumonic Pleural Effusions: The Case for the Fibrinolytic Potential

Complicated pleural effusions and empyema with loculation and failed drainage are common clinical problems. In adults, intrapleural fibrinolytic therapy is commonly used with variable results and therapy remains empiric. Despite the intrapleural use of various plasminogen activators; fibrinolysins, for about sixty years, there is no clear consensus about which agent is most effective. Emerging evidence demonstrates that intrapleural administration of plasminogen activators is subject to rapid inhibition by plasminogen activator inhibitor-1 and that processing of fibrinolysins is importantly influenced by other factors including the levels and quality of pleural fluid DNA. Current therapy for loculation that accompanies pleural infections also includes surgery, which is invasive and for which patient selection can be problematic. Most of the clinical literature published to date has used flat dosing of intrapleural fibrinolytic therapy in all subjects but little is known about how that strategy influences the processing of the administered fibrinolysin or how this influences outcomes. We developed a new test of pleural fluids ex vivo, which is called the Fibrinolytic Potential or FP, in which a dose of a fibrinolysin is added to pleural fluids ex vivo after which the fibrinolytic activity is measured and normalized to baseline levels. Testing in preclinical and clinical empyema fluids reveals a wide range of responses, indicating that individual patients will likely respond differently to flat dosing of fibrinolysins. The test remains under development but is envisioned as a guide for dosing of these agents, representing a novel candidate approach to personalization of intrapleural fibrinolytic therapy.

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.

Mesothelial cells in tissue repair and fibrosis

Mesothelial cells are fundamental to the maintenance of serosal integrity and homeostasis and play a critical role in normal serosal repair following injury. However, when normal repair mechanisms breakdown, mesothelial cells take on a profibrotic role, secreting inflammatory, and profibrotic mediators, differentiating and migrating into the injured tissues where they contribute to fibrogenesis. The development of new molecular and cell tracking techniques has made it possible to examine the origin of fibrotic cells within damaged tissues and to elucidate the roles they play in inflammation and fibrosis. In addition to secreting proinflammatory mediators and contributing to both coagulation and fibrinolysis, mesothelial cells undergo mesothelial-to-mesenchymal transition, a process analogous to epithelial-to-mesenchymal transition, and become fibrogenic cells. Fibrogenic mesothelial cells have now been identified in tissues where they have not previously been thought to occur, such as within the parenchyma of the fibrotic lung. These findings show a direct role for mesothelial cells in fibrogenesis and open therapeutic strategies to prevent or reverse the fibrotic process.

Mechanism of fibroblast inflammatory responses to Pseudomonas aeruginosa elastase

Receptor tyrosine kinases, including the epidermal growth factor receptors (EGFR), are able to activate the mitogen-activated protein kinases (MAPK) via several adaptor proteins and protein kinases such as Raf. EGFR can be activated by a variety of extracellular stimuli including neutrophil elastase, but we are aware of no report as to whether Pseudomonas aeruginosa produced elastase (PE) could elicit such signalling through EGFR activation. We sought to test the inference that PE modulates inflammatory responses in human lung fibroblasts and that the process occurs by activation of the EGFR/MAPK pathways. We utilized IL-8 cytokine expression as a pathway-specific end point measure of the fibroblast inflammatory response to PE. Western blot analysis was performed to detect phosphorylation of EGFR and signal transduction intermediates. Northern blot, real-time PCR, and ELISA methods were utilized to determine cytokine gene expression levels. We found that PE induces phosphorylation of the EGFR and the extracellular signal-regulated proteins (ERK1/2) of the MAPK pathway, and nuclear translocation of NF-κB. Furthermore, enzymically active PE enhances IL-8 mRNA and protein secretion. Pretreatment of the cells with specific inhibitors of EGFR, MAPK kinase and NF-κB markedly attenuated the PE-induced signal proteins phosphorylation and IL-8 gene expression and protein secretion. Collectively, the data show that PE produced by Pseudomonas aeruginosa can modulate lung inflammation by exploiting the EGFR/ERK signalling cascades and enhancing IL-8 production in the lungs via NF-κB activation.

Wood bark smoke induces lung and pleural plasminogen activator inhibitor 1 and stabilizes its mRNA in porcine lung cells

Although aberrant fibrinolysis and plasminogen activator inhibitor 1 (PAI-1) are implicated in acute lung injury, the role of this serpin in the pathogenesis of wood bark smoke (WBS)-induced acute lung injury (SIALI) and its regulation in resident lung cells after exposure to smoke are unclear. A total of 22 mechanically ventilated pigs were included in this study. Immunohistochemical analyses were used to assess fibrin and PAI-1 in the lungs of pigs with SIALI in situ. Plasminogen activator inhibitor 1 was measured in bronchoalveolar lavage fluids by Western blotting. Induction of PAI-1 was determined at the protein and mRNA levels by Western and polymerase chain reaction analyses in primary porcine alveolar type II cells, fibroblasts, and pleural mesothelial cells. Plasminogen activator inhibitor 1 mRNA stability was determined by transcription chase studies. Gel shift analyses were used to characterize the mechanism regulating PAI-1 mRNA stability. Smoke-induced ALI induced PAI-1, with prominent extravascular fibrin deposition in large and small airways as well as alveolar and subpleural compartments. In pleural mesothelial cells, lung fibroblasts, and alveolar type II cells, PAI-1 mRNA was stabilized by WBS extract and contributed to induction of PAI-1. The mechanism involves dissociation of a novel 6-phospho-d-gluconate-NADP oxidoreductase-like PAI-1 mRNA binding protein from PAI-1 mRNA. Exposure to WBS induces prominent airway and mesothelial expression of PAI-1, associated with florid distribution of fibrin in SIALI in vivo Wood bark smoke components induce PAI-1 in vitro in part by stabilization of PAI-1 mRNA, a newly recognized pathway that may promote extravascular fibrin deposition and lung dysfunction in SIALI.

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.

Post-transcriptional regulation of plasminogen activator inhibitor type-1 expression in human pleural mesothelial cells

The plasminogen activator inhibitor type-1 (PAI-1) effectively blocks the activities of free and receptor-bound urokinase-type plasminogen activator. Incubation of cultured human pleural mesothelial (Met5A) cells with TGF-beta increased PAI-1 protein. TGF-beta, phorbol myristate acetate, and the translation inhibitor cycloheximide induced PAI-1 mRNA and slowed its degradation, suggesting that PAI-1 mRNA could be regulated by interaction of a PAI-1 binding protein (PAI-1 mRNABp) with PAI-1 mRNA. We found that an approximately 60 kD cytoplasmic PAI-1 mRNABp is detectable in cytoplasmic extracts of MeT5A human pleural mesothelial and malignant mesothelioma cells. The PAI-1 mRNABp specifically binds to a 33-nt sequence in the 3' untranslated region of PAI-1 mRNA. Insertion of this 33-nt sequence destabilizes otherwise stable beta-globin mRNA, indicating that the binding sequence accelerates decay of endogenous PAI-1 mRNA. Competitive inhibition by overexpression of the 33-nt binding sequence in MeT5A cells reduced PAI-1 mRNA decay and increased PAI-1 protein and mRNA expression, indicating that the PAI-1 mRNABp destabilizes PAI-1 mRNA by its interaction with the endogenous 33-nt binding sequence. Incubation of Met5A cells with TGF-beta attenuated the interaction of the PAI-1 mRNABp with the 33-nt sequence. By conventional and affinity purification, we isolated the PAI-1 mRNABp and confirmed its identity as 6-phospho-d-gluconate-NADP oxidoreductase, which specifically interacts with the full-length and the 33-nt sequence of the PAI-1 mRNA 3' untranslated region. This newly recognized pathway could influence expression of PAI-1 by mesothelial or mesothelioma cells at the level of mRNA stability in the context of pleural inflammation or malignancy.

Urokinase receptor expression involves tyrosine phosphorylation of phosphoglycerate kinase

The interaction of urokinase-type plasminogen activator (uPA) with its receptor, uPAR, plays a central role in several pathophysiological processes, including cancer. uPA induces its own cell surface receptor expression through stabilization of uPAR mRNA. The mechanism involves binding of a 51 nt uPAR mRNA coding sequence with phosphoglycerate kinase (PGK) to down regulate cell surface uPAR expression. Tyrosine phosphorylation of PGK mediated by uPA treatment enhances uPAR mRNA stabilization. In contrast, inhibition of tyrosine phosphorylation augments PGK binding to uPAR mRNA and attenuates uPA-induced uPAR expression. Mapping the specific peptide region of PGK indicated that its first quarter (amino acids 1-100) interacts with uPAR mRNA. To determine if uPAR expression by uPA is regulated through activation of tyrosine residues of PGK, we mutated the specific tyrosine residue and tested mutant PGK for its ability to interfere with uPAR expression. Inhibition of tyrosine phosphorylation by mutating Y76 residue abolished uPAR expression induced by uPA treatment. These findings collectively demonstrate that Y76 residue present in the first quarter of the PGK molecule is involved in lung epithelial cell surface uPAR expression. This region can effectively mimic the function of a whole PGK molecule in inhibiting tumor cell growth.

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.

Signal pathway of 17beta-estradiol-induced MUC5B expression in human airway epithelial cells

MUC5B is a major mucin of the human respiratory tract, and it is not clear how MUC5B expression is regulated in various airway diseases. The goal of this study was to determine the mechanisms by which 17beta-estradiol induces MUC5B gene expression in airway epithelial cells. It was found that E2, a sex hormone, stimulates MUC5B gene overexpression by interaction with estrogen receptor alpha (ERalpha) and by acting through extracellular signal-regulated kinase 1/2 (ERK1/2)-mitogen-activated protein kinase (MAPK). Pretreatment with ER antagonist ICI 182,780 blocked both E2-induced ERK1/2-MAPK activation and MUC5B gene expression. It was also found that the activation of p90 ribosomal S 6 protein kinase 1 (RSK1), cAMP-response element-binding protein (CREB), and cAMP-response element (CRE) (-956 region of the MUC5B promoter)-responsive signaling cascades via ERK1/2 MAPK are crucial aspects of the intracellular mechanisms that mediate MUC5B gene expression. Taken together, these studies give additional insights into the molecular mechanism of hormone-induced MUC5B gene expression and enhance our understanding of abnormal mucin secretion in response to hormonal imbalances.

Intrapleural activation, processing, efficacy, and duration of protection of single-chain urokinase in evolving tetracycline-induced pleural injury in rabbits

Intrapleural fibrinolysins have been used to treat pleural loculations. However, the efficacy of clinically available agents has recently been questioned, providing a rationale for investigation of new interventions. Single-chain urokinase plasminogen activator resists inhibition by serpins, and repeated, daily intrapleural administration of this agent prevents intrapleural loculation more effectively than complexes of this proenzyme with its receptor (Idell S, Mazar A, Cines D, Kuo A, Parry G, Gawlak S, Juarez J, Koenig K, Azghani A, Hadden W, McLarty J, Miller E. Am J Respir Crit Care Med 166: 920-926, 2002). Understanding of the protective mechanism and intrapleural processing remains unclear. We speculated that single-chain urokinase could induce sustained local fibrinolysis and protection by selective administration either before, during, or following loculation after pleural injury induced by tetracycline in rabbits. Enzymography, immunoassays, histology, immunohistochemistry, morphology, and morphometry were used to test the efficacy, duration of protective effect, and processing of single-chain urokinase. Intrapleural single chain urokinase prevented loculation at 72 h after injury (P < 0.01) if given either before or during adhesion formation and was converted to two-chain high-molecular-weight urokinase, which remained active for at least 24 h within pleural fluids. The effect was dose dependent, and established loculations at 72 h after tetracycline-induced injury were reversed at 96 h by single-dose treatment. Single-chain urokinase bound and saturated intrapleural plasminogen activator inhibitory (PAI)-1-like activity and urokinase-related immunoreactivity of the mesothelium was comparable in treatment or vehicle-control groups. Adhesions recurred by 2 wk after treatment with recurrence of excess local PAI activity. Single-chain urokinase induces sustained local fibrinolysis and reversibly prevents pleural loculation for up to 48 h after intrapleural administration after tetracycline-induced injury.

Regulation of urokinase receptor mRNA stability by hnRNP C in lung epithelial cells

Increased urokinase receptor (uPAR) expression as well as stabilisation of uPAR mRNA contribute to the pathogenesis of lung inflammation and neoplasia. Post-transcriptional regulation of uPAR mRNA involves interaction of both coding and 3'-UTR sequences with regulatory uPAR mRNA binding proteins (Bps). In order to identify novel regulatory interactions, we performed gel mobility shift and UV cross-linking assays and found two distinct uPAR mRNA-protein complexes. We identified a rapidly migrating 40 kDa uPAR mRNABp that selectively bound a 110 nucleotide (nt) fragment of the uPAR mRNA 3'UTR. Chimeric beta-globin/uPAR mRNA containing the 110 nt 40 kDa protein binding fragment destabilised stable beta-globin mRNA with a rate of decay identical to that of chimeric beta-globin/uPAR containing the full uPAR 3'UTR. The 40 kDa uPAR 3'UTR Bp was purified using poly (U) sepharose and identified as heterogeneous nuclear ribonucleoprotein C (hnRNPC). Finally, we confirmed its interaction with the uPAR mRNA 3' UTR by gel mobility supershift assay using an anti-hnRNPC antibody. Direct in vivo interaction of hnRNPC with the uPAR mRNA 3'UTR was demonstrated by immunoprecipitation and combined RT PCR-Southern blotting assay. Co-transfection of hnRNPC cDNA in Beas2B cells reversed destabilisation of chimeric beta-globin/uPAR 3'UTR mRNA and its over-expression also induced uPAR protein and mRNA expression through stabilisation of uPAR mRNA. These observations indicate a novel mechanism of uPAR gene regulation in lung epithelial cells in which cis elements within a 110 nt uPAR mRNA 3'UTR sequence interact with hnRNPC to regulate uPAR mRNA stability.

Preservation of the characteristics of the cultured human type II alveolar epithelial cells

The human type II alveolar epithelial cells lost their specific characteristics during cultivation. We examined the ultrastructural and biochemical nature of the human type II cells cultured by two culture systems. To make a physiological alveoli model, the epithelial cells were seeded onto the cell culture insert and allowed contact with the air directly. The cells exposed to the air expressed polarity and immature lamellar bodies in their cytoplasm. Separately, the alveolar epithelial cells were cultured as spheroids to construct the three-dimensional condition. These cells expressed mature morphological characteristics as epithelial cells and lamellar bodies. The expression of the surfactant apoprotein-A (SP-A) and -C (SP-C) mRNA was compared in the cells cultured as a monolayer, the air exposed and the spheroids. SP-A mRNA was detected in all the cultured epithelial cells, but SP-C mRNA, a specific protein for the type II cells, was expressed only in the cells forming spheroids. The expression of uPA, one of the fibrinolytic enzymes, its receptor (uPAR) and its inhibitor-1 (PAI-1) were also examined. The epithelial cells exposed to the air and formed spheroids expressed a larger amount of uPA mRNA than the monolayer, although the amount of uPAR mRNA were comparable in these cells. The amount of PAI-1 mRNA significantly increased when the epithelial cells were exposed to the air. These results indicate that the type II alveolar epithelial cells induced and preserved their specific characteristics by taking the physiological three-dimensional structure, and these characteristics were partially restored by exposure to the air. Those findings suggest that the alveolar epithelial cells should be cultivated in three-dimensional form with contact to the air to regenerate an appropriate alveolar tissue.

Regulation of urokinase receptor expression by phosphoglycerate kinase

Post-transcriptional regulation represents a major mechanism by which eukaryotic gene expression is regulated through cis-trans interactions that serve as signals for rapid alterations of messenger RNA (mRNA) stability. Regulation of urokinase-type plasminogen activator receptor (uPAR) mRNA involves the interaction of a uPAR mRNA coding region sequence with a 50 kD uPAR mRNA binding protein. We purified this protein from human bronchial epithelial (Beas2B) cells and identified it as phosphoglycerate kinase (PGK). We cloned PGK cDNA by polymerase chain reaction and expressed the recombinant PGK protein, which specifically bound the uPAR mRNA coding region by gel mobility shift and Northwestern blotting. We also confirmed a direct interaction of PGK protein with uPAR mRNA by immunoprecipitation. Overexpression of PGK in uPAR-overproducing H157 lung carcinoma cells resulted in decreased cytoplasmic uPAR mRNA and cell surface uPAR protein expression. Reduced uPAR mRNA expression involved decreased stability of the uPAR mRNA. Decline in 3H-thymidine incorporation and migration occurred in H157 cells transfected with PGK cDNA. These results demonstrate that PGK regulates uPAR expression at the post-transcriptional level.

Urokinase receptor mRNA stability involves tyrosine phosphorylation in lung epithelial cells

Interaction between urokinase-type plasminogen activator (uPA) and its receptor (uPAR) localizes cellular proteolysis and promotes cellular proliferation and migration, effects that may contribute to the pathogenesis of lung inflammation and neoplasia. Enhanced uPAR expression as well as stabilization of uPAR mRNA by transforming growth factor-beta and phorbol myristate acetate (PMA) shares a common mechanism involving phosphorylation and dephosphorylation of a uPAR mRNA-binding protein (uPAR mRNABp). PMA-induced tyrosine phosphorylation of the uPAR mRNABp inhibited the uPAR mRNA-uPAR mRNABp interaction, stabilized uPAR mRNA and enhanced uPAR protein expression. Downregulation of the uPAR mRNA and uPAR mRNABp interaction by PMA and transforming growth factor-beta can be reversed by pretreatment of cells with herbimycin which in turn inhibits expression of uPAR protein via a decrease in uPAR mRNA stability. Our experiments indicate that post-transcriptional regulation of uPAR expression requires activation of tyrosine kinases. Cytokines can regulate uPAR expression of lung-derived epithelial cells at the post-transcriptional level by tyrosine phosphorylation of the uPAR mRNA binding protein and may thereby influence tissue remodeling in lung injury or neoplasia.

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.

Cytoplasmic-nuclear shuttling of the urokinase mRNA binding protein regulates message stability

Treatment of small airway epithelial (SAEC) cells or lung epithelial (Beas2B) cells with TNF-alpha or PMA induces urokinase-type plasminogen activator (uPA) expression. Treatment of these cells with TNF-alpha, PMA or cycloheximide but not TGF-beta increased steady-state expression of uPAmRNA. TNF-alpha, PMA or cycloheximide caused 8-10 fold extensions of the uPAmRNA half-life in SAEC or Beas2B cells treated with DRB, a transcriptional inhibitor. These findings suggest that uPA gene expression involves a post-transcriptional regulatory mechanism. Using gel mobility shift and UV cross-linking assays, we identified a 30 kDa uPA mRNA binding protein (uPA mRNABp) that selectively binds to a 66 nt protein binding fragment of uPA mRNA containing regulatory information for message stabilization. Binding of cytoplasmic uPA mRNABp to uPA mRNA was abolished after treatment with TNF-alpha but not TGF-beta. In addition, we found the accumulation of 30 kDa uPAmRNABp in the nuclear extracts of TNF-alpha but not TGF-beta treated cells. The uPA mRNABp starts moving to the nucleus from the cytoplasmic compartment as early as three hours after TNF-alpha treatment. Complete translocation is achieved between 12-24 h, which coincides with the maximal expression of uPA protein effected by cytokine stimulation. Treatment of Beas2B cells with NaF inhibited TNF-alpha-mediated translocation of uPA mRNABp from the cytoplasm to the nucleus and concomitant inhibition of uPA expression. TNF-alpha stabilizes uPA mRNA by translocating the uPA mRNABp from the cytoplasm to the nucleus. Our results demonstrate a novel mechanism governing uPA mRNA stability through shuttling of uPA mRNABp between the nucleus and cytoplasm. This newly identified pathway may have evolved to regulate uPA-mediated functions of the lung epithelium in inflamation or neoplasia.

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.

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.