A continuum of transformed phenotypes in C3H/10T1/2 derivatives

Two-stage transformants have been isolated from C3H/10T1/2 cells exposed to UV-irradiation followed by treatment with TPA. These UV-TDTx cells form foci in co-culture with C3H/10T1/2 cells only in the presence of TPA. In the absence of TPA, UV-TDTx cells are indistinguishable from control C3H/10T1/2 cells in co-cultures. Single-step transformants of C3H/10T1/2 cells isolated after exposure to high doses of chemical carcinogens, however, show TPA-independent focus formation in co-culture with C3H/10T1/2 cells. We now show that three independently isolated two-stage UV + TPA transformants as well as a single-step, high dose methylcholanthrene (MCA) transformant (MCATx1e) isolated in our laboratory are anchorage-dependent and non-tumorigenic. In contrast, another single-step, high dose MCA transformant (MCACl#16/39) known to contain an activated c-Ki-ras gene shows TPA-independent focus formation in mixed culture with C3H/10T1/2 cells, anchorage independence and tumorigenicity. Analysis of UV-TDTx:C3H/10T1/2 and MCACl#16/39:C3H/10T1/2 somatic cell hybrids indicates that a similar percentage of hybrids of each cell type are able to form foci in co-culture with C3H/10T1/2 cells. However, focus-forming UV-TDTx:C3H/10T1/2 hybrids remain dependent on TPA for focus formation in mixed culture.