Urokinase (uPA) interacts with its receptor (uPAR) to promote proteolysis and tumor migration, functions of potential importance in the pathogenesis of malignant mesothelioma. Immunohistochemistry of human malignant mesothelioma tissue and mesothelioma cells (MS-1) showed that mesothelioma cells express uPAR. We isolated uPAR from MS-1 cells by metabolic labeling and showed that it could be induced by phorbol myristate acetate (PMA), lipopolysaccharide (LPS), a transforming growth factor-beta (TGF-beta) or tumor necrosis factor-alpha (TNF-alpha). Experiments with MS-1 cells showed that uPA binding was saturable, specific, and reversible with a mean dissociation constant (Kd) of 5.4 +/- 1.1 nM. Binding was inhibited by a blocking antibody to uPAR and by the uPA amino-terminal fragment (ATF), but not by low molecular weight uPA. uPAR expression was regulated transcriptionally and translationally; antisense oligonucleotides blocked expression of uPAR protein. Plasminogen activator inhibitor-1 (PAI-1) inhibited PA activity of preformed uPA/uPAR complexes and increased cycling of the receptor from the cell surface. Stimulation of subconfluent MS-1 cells by high molecular weight or recombinant uPA, but not ATF or low molecular weight fragment, caused concentration-dependent incorporation of [3H]thymidine. These data indicate a novel mechanism by which malignant mesothelioma cells localize pericellular proteolysis and concurrently regulate tumor cell proliferation.

Binding of urokinase-type plasminogen activator (uPA) to a specific receptor (uPAR) on human lung fibroblasts enables it to regulate cellular proteolysis and remodeling of the extracellular matrix. Binding studies with radiolabeled uPA indicated that both normal and fibrotic lung fibroblasts express the receptor, but cells from fibrotic tissues bound significantly more uPA (P < 0.001). Phorbol myristate acetate, lipopolysaccharide, transforming growth factor-beta (TGF-beta), and tumor necrosis factor-alpha (TNF-alpha) increased uPA binding and plasminogen activation at the cell surface, with a greater maximal effect on fibrotic than on normal fibroblasts. Excess unlabeled uPA, specific antibody, or antisense oligonucleotides inhibited uPA binding. Ribonuclease (RNase) protection assays showed higher levels of uPAR messenger ribonuleic acid (mRNA) in each of the five fibrotic cell lines than in normal fibroblasts. uPA was mitogenic for normal as well as fibrotic fibroblasts, indicating that receptor binding concurrently localizes cellular proteolytic activity and stimulates mitogenesis. Morphometry and immunohistochemical analysis showed that uPAR, as well as uPA, was increased in fibroblasts in fibrotic lung tissue. Increased expression of uPAR by fibrotic lung fibroblasts and enhanced urokinase binding induced by proinflammatory cytokines suggest a novel mechanism by which fibroblast-mediated matrix remodeling and proliferation may be regulated in interstitial lung diseases.

Tissue factor pathway inhibitor expression by human pleural mesothelial and mesothelioma cells. M.S. Bajaj, U. Pendurthi, K. Koenig, S. Pueblitz, S. Idell. #ERS Journals Ltd 2000. ABSTRACT: The mesothelial lining of the pleura and malignant mesothelioma promote fibrin deposition in pleural injury or neoplasia via expression of tissue factor (TF). It was hypothesized that these cells might also regulate intrapleural coagulation by elaborating TF pathway inhibitor (TFPI).TFPI activity and antigen in pleural fluids were assayed from patients with congestive heart failure (CHF), pneumonia, empyema, metastatic pleural cancer and malignant mesothelioma. The authors also assessed expression of TF and TFPI messenger ribonucleic acid (mRNA) as well as TFPI activity and antigen by human pleural mesothelial cells, malignant mesothelioma cells (MS-1 cell line) and human lung fibroblasts. Immunohistochemical analyses of normal, fibrotic, and neoplastic pleura were performed to determine whether TFPI antigen was expressed in vivo.The study revealed that TFPI was present in transudates from patients with CHF and exudative pleural effusions from patients with pneumonia, empyema or pleural carcinoma. TFPI mRNA, activity and antigen were expressed by pleural mesothelial cells, MS-1 cells and lung fibroblasts. Cytokines and serum stimulated a significant early increase in TF mRNA levels with minimal enhancement of TFPI mRNA, activity and antigen levels. TFPI antigen was found in normal, fibrotic and neoplastic pleural tissues.The current observations indicate that tissue factor pathway inhibitor is locally expressed in pleural disease, but that it does not prevent the development of a prothrombotic environment favouring local fibrin deposition in pleural inflammation or cancer. Eur Respir J 2000; 15: 1069±1078.

The developmental field defect in the DiGeorge anomaly (DGA) principally affects derivatives of the third and fourth branchial pouches (areas containing a large population of cephalic neural crest cells), including the ultimobranchial body (UB), the reputed source of thyroid calcitonin-producing cells (C cells) in humans. To evaluate the content of C cells in children with DGA, sections of the thyroid in 16 cases of DGA (group I) (8 incomplete and 8 complete forms) and 16 age-matched controls (group II) were stained by immunoperoxidase for calcitonin and chromogranin. Eleven of 16 (69%) cases in group I [4 of 8 (50%) of the complete and 7 of 8 (88%) of of the incomplete cases] and 14 of 16 (88%) of group II exhibited positive-staining cells for both markers, either individually or in small clusters within the follicular epithelial basement membrane. The average number of C cells per high-power field (HPF) (400x) for group I was 1.6 +/- 0.9 and for group II 4.9 +/- 1.7 (P < .005). Although the percentage of positive incomplete DGA cases was the same as that of the control cases, the average number of C cells/HPF was 2.0 +/- 1.1 and similar to that of complete DGA cases (1.2 +/- 0.6). These results demonstrated that C cells are present in the thyroid of patients with DGA more frequently than expected, although in deficient numbers when compared quantitatively to age-matched controls showing a normal infantile pattern of thyroid C cell distribution. Although this observation confirms that there is deficiency of thyroid C cell development in DGA and is in keeping with the assumption that the cells are of neural crest origin, our data raise the possibility of an additional source of C cells, perhaps from thyroid endoderm, in a manner analogous to the endocrine cells of the gut and respiratory tract.