Mitogen-independence and Autocrine Growth Factor Secretion Displayed by Human Mesothelioma Cells and Oncogene-Transfected Mesothelial Cells

Abstract

The mesothelium is the simple squamous epithelium that lines the pleural, pericardial and peritoneal cavities and covers the outer surfaces of the organs contained within these cavities. We have identified the growth factor and nutritional requirements of normal human mesothelial cells for clonal and serial proliferation in culture. An optimal medium is M199/MCDB105 (1:1 v/v) + 10ng/ml EGF or bFGF + 0.4 μ g/ml HC + ≥ 5% bovine serum. Several mesothelioma cell lines we have examined grow optimally in the absence of EGF or FGF and they secrete a mitogen (“transformed mesothelial growth factor” (TMGF)) which can satisfy the EGF/FGF requirement of normal mesothelial cells. When a mutationally activated H- ras gene or the SV40 large T gene is introduced via calcium phosphate-or defective retrovirus-mediated transfection into normal mesothelial cells, the resulting cells are able to grow independent of added EGF. The SVLT transfectants are also HC-independent, exhibit a reduced requirement for serum, and become replicatively immortal, but they are not tumorigenic in nude mice. Ras transfectants apparently differ in growth characteristics from normal cells only by their EGF/FGF independence. Ras or SVLT transfectants secrete a mitogen with the same biological activity as the TMGF secreted by mesothelioma cells. TMGF appears to be a novel heparin-binding growth factor that remains to be characterized.