Analysis of v‐Ha‐ras and v‐fos oncogene transduction into a mouse epidermal cell line with “initiated” phenotype in culture but normal skin phenotype in vivo

Cell line SCR722 was derived from adult SENCAR mouse epidermal cells initiated in culture by treatment with the carcinogen N‐methyl‐N′‐nitro‐N‐nitrosoguanidine and selection for foci proliferating in medium with calcium levels that induce terminal differentiation in normal cells. Expansion of one of these foci and two additional cell clonings produced cell line SCR722, which was near‐tetraploid and formed normal skin when grafted to athymic nude mouse hosts. However, unlike normal keratinocytes, SCR722 cells fail to suppress papilloma formation when grafted along with papilloma cell line SP‐1. For optimum growth in culture, SCR722 cells required fibroblast‐conditioned medium and 0.5 mM Ca²⁺. SCR722 cells had a wild‐type c‐Ha‐ras gene but had lost their requirement for conditioned medium in culture and produced dysplastic papillomas in grafts when transduced with the v‐Ha‐ras gene. SCR722 cells stably expressing the v‐fos gene produced normal epidermis in grafts, but when these cells were transduced with the v‐Ha‐ras gene, they produced carcinomas. Clones with greater expression of the transfected v‐fos gene had a more invasive phenotype in vivo. These results indicate that carcinogen treatment of epithelial cells can result in an altered but nontumorigenic phenotype that may be at risk for becoming a more advanced neoplastic state with additional genetic alterations. © 1995 Wiley‐Liss. Inc.