Studies of MDM2 gene expression in human mesothelioma cell lines have now been completed. These studies show that this gene is neither amplified nor overexpressed in the cell lines analyzed and cannot account for the expression of wild-type p53 in these tumorigenic cell lines. In addition, mesothelioma tumors and cell lines have been studied to establish whether loss of the tumor suppressor gene, p16, is an important step in mesothelial carcinogenesis. Southern blot analysis of 19 tumor samples reveals that 74% (14/19) have shown a loss of p16. Analysis of normal human mesothelial cells in culture, as well as mesothelioma cell lines, shows that p16 is present in all normal cells but is lost in 16/17 cell lines. Single strand conformational polymorphism (SSCP) analysis of the retained p16 indicates that it is a wild-type gene. Passage of the p16 positive cell line through nude mice yielded a p16 minus tumor explant cell line which, by karyotypic analysis, was derived from the p16 positive parental cell. Since both cells have a fuctional retinoblastoma (Rb) gene product, analysis of these cells should provide unique insights into the gene products involved in the function of p16. In order to understand the mechanism by which epithelial tumors lose sensitivity to transforming growth factor-beta (TGF-beta) growth inhibition, we showed that resistance of the human bronchial epithelial cell line, Beas-2B R.1 to TGF-beta signalling is not a result of genetic or phenotypic defects in the TGF-beta receptors. In a study to determine how c-erbB-2 contributes to lung carcinogenesis, an analysis of E6 cells, human bronchial epithelial cells (Beas-2B) which overproduce c-erbB-2, shows that these cells also produce TGF-alpha. Transfection of these cells with an antisense TGF-alpha construct yielded clones which no longer produced detectable TGF-alpha protein. These cells were no longer tumorigenic. Immunoprecipitation analysis of complexes of c-erbB-2 revealed that this molecule was activated and found in complex with the epidermal growth factor (EGF) receptor in cells producing TGF-alpha, but not in cells which did not produce this EGF receptor ligand.
