Transformation of a mammary epithelial cell line by the v-raf and v-mos oncogenes

Defective retroviruses were used to investigate the effects of the oncogenes v-raf and v-mos on the behaviour of mammary epithelial cells. Cultures of the mammary epithelial cell lines #43 and NMuMG infected with either virus showed obvious areas of overgrowing cells, which were not seen when cells were infected with control viruses not containing an oncogene. Several clonal cell lines were derived from the areas of overgrowth on #43 cells. Most of these were tumorigenic on subcutaneous inoculation. In culture, several of the cloned lines showed marked morphological abnormalities, had altered rates of growth and saturation densities, and were able to clone in soft agar. Unexpectedly, one raf-containing and one mos-containing line grew more slowly in culture than did control or uninfected cells. Other lines showed only some of these changes. In the mos-containing lines the level of viral transcript corresponded approximately to the extent of transformation, whereas the raf-containing lines showed no such correlation.