Spontaneous and asbestos-induced transformation of mesothelial cells in vitro

The processes of spontaneous and asbestos-induced transformation of rat mesothelium were studied using cell cultures obtained in the laboratory. The same changes in cell properties were established in both spontaneous and asbestos-induced transformation: change in epidermal growth factor (EGF) response, in some cases appearance of fibroblast-like cells instead of polygonal ones, appearance of multilayer cell growth foci, and ability to grow in semisolid agar. The response to fibroblast growth factor, insulin-like growth factor 1, and insulin did not change during transformation as well as the P450 system activity measured by benz(a)pyrene (BP) and 7,12-dimethylbenzanthracene (DMBA) cytotoxicity. The asbestos-induced transformation began earlier than the spontaneous one. EGF began to stimulate mesothelium proliferation instead of its inhibition at 6-7 passages in the case of asbestos-induced transformation, whereas during spontaneous transformation this change began at 9-10 passages. Elongated rather than polygonal cells appeared at 10-11 instead of 17-18 passages (this morphological change did not take place at all lines studied). The ability to grow in semisolid agar was found at 14-16 passages with asbestos and at 22-24 passages without it. The results allow us to propose the necessity of a positive EGF response for mesothelial cell transformation and the similarity of mechanisms of spontaneous and asbestos-induced transformation.