Pleural Mesothelial Cell (PMC) Defense Mechanisms Against Malignancy

Abstract

Tumors such as ovarian, lung, and breast have been found to have a predilection for the pleura. Pleural mesothelial cells (PMCs) play an active role in pleural inflammation via release of cytokines. However, mechanisms whereby PMCs defend themselves against invading malignant cells are unknown. In the present study, we hypothesized that PMCs release the antiangiogenic factor endostatin and inhibit malignant cell invasion. We evaluated the endostatin levels in malignant (MAL) and congestive heart failure (CHF) pleural fluids (PF). Endostatin expression by PMC was also demonstrated by Western analysis and confocal microscopy. Our results demonstrate that CHF PF contained significantly higher levels of endostatin when compared with MAL PF. PMCs alone released a significantly greater amount of endostatin when compared with ovarian cancer cells (OCCs). When the PMC were cocultured with OCCs without contact, there was an increase in the endostatin production. However, when the PMCs were cocultured in direct contact with OCCs the endostatin levels significantly decreased. Endostatin production was upregulated in the presence of tumor cells but not when OCCs were adherent to underlying PMC monolayer. Immunofluorescent staining of PMCs for endostatin correlated with endostatin release. These findings suggest that PMCs play a key role in the antiangiogenesis process by producing endostatin in the pleural space, and thus preventing tumor spread and metastasis in the pleura.

Silencing the receptor EphA2 suppresses the growth and haptotaxis of malignant mesothelioma cells

“…The mesothelial cells were characterized by the presence of classic cobblestone morphology, the absence of factor VIII antigen, and the presence of cytokeratin, as reported previously. 18 When the cells were confluent, they were trypsinized and seeded into culture flasks/transwell chambers as required for different assays. All experiments were performed on cells from 1 lot.…”

“…18 In brief, the cells were cultured to confluence on gelatinized glass coverslips and fixed in 5% paraformaldehyde (with 50 mM phosphate buffer) in 50% Tris wash buffer (TWB). The glass coverslips were rinsed 3 times and permeabilized with 1.2% Triton X-100 for 5 minutes, rinsed 3 times, incubated with 1% bovine serum albumin (BSA) in 100% TWB for 1 hour, then stained for the expression EphA2 receptor using primary antibody rabbit anti-EphA2 at 1:150 dilution and secondary antibody goat antirabbit immunoglobulin G conjugated with fluorescein isothiocyanate (FITC) (Zymed Laboratories, San Francisco, CA).…”

“…The cells were lysed in lysis buffer, as reported previously. 18 Total protein was estimated by using the bichloroacetic acid method (Pierce, Rockford, IL). Equal amounts of protein (20 mg per lane) were loaded.…”

Talc mediates angiostasis in malignant pleural effusions via endostatin induction

“…Endostatin is a 20-kDa fragment of collagen XVIII that specifically inhibits endothelial cell migration, and induces cell cycle arrest, apoptosis, and reduces tumour growth [18]. The present authors recently reported that PMC release endostatin and invading tumour cells enhance the production of endostatin in PMCs [19]. In the present study, the authors hypothesise that talc induces PMC to release the anti-angiogenic factor, endostatin, and that this may modulate malignant growth on the pleura by tilting the pro-angiogenic environment of the pleural space to an anti-angiogenic milieu.…”

“…Estimation of endostatin by ELISA Endostatin levels in the PF (0, 4 and 24 h) and culture medium obtained from activated PMC and MMC (0, 10, 25, 50, 100 and 200 mg?cm -2 ) and resting PMC and MMC were quantified using a sandwich enzyme immunoassay kit (Chemicon International, Inc., Temecula, CA, USA) as previously described elsewhere [19].…”