ABSTRACT
We have examined the mechanism of transformation of a line of immortalized hamster dermal fibroblasts (4DH2 cells) following treatment with the simple alkylating agents, N-methyl-N-nitrosourea (MNU), N-ethyl-N-nitrosourea (ENU) and dimethyl sulphate (DMS). Treatment of 4DH2 cells with the potent point mutagens MNU and ENU gave rise to a spectrum of foci of different sizes, including progressively growing large foci and compact small foci. In contrast, treatment with the weak point mutagen DMS produced mostly large foci. The ability of cell lines derived from morphologically transformed foci to grow in soft agar in general reflects their original size. Thus most cell lines derived from large foci grew in soft agar while most lines derived from small foci did not. Transfection of cellular DNAs into the parent 4DH2 cell line and into NIH3T3 mouse fibroblasts has revealed the presence of dominantly acting transforming genes in the chemically transformed cell lines. Thus DNA from five of six cell lines derived by culturing large foci and from one of three cell lines derived by culturing small foci induced efficient morphological transformation of the recipient cells. Southern analyses of DNA from primary and secondary transfectants showed that several of the transforming genes transferred in these experiments were not closely related to H-ras, K-ras or N-ras.