In vitro analysis of multistage epidermal carcinogenesis: development of indefinite renewal capacity and reduced growth factor requirements in colony forming keratinocytes precedes malignant transformation

Using a culture system that supports both extensive proliferationand differentiation of mouse keratinocytes, we analysed alterationsin cellular growth control that occur during multistage carcinogenesisin vivo. Normal diploid keratinocytes derived from newborn mousehair follicles had a limited replicative potential of 50 populationdoublings in vitro, and colony formation was highly dependentupon cholera toxin, serum growth factors, and mesenchymal feedercell support. In contrast, keratinocyte lines from benign epidermallesions or malignant tumors induced by chemicals showed indefiniterenewal capacity of the colony forming population, and greatlyreduced dependence on cholera toxin and serum growth factors.Cell lines from benign lesions did not readily produce tumorsin syngeneic hosts, but cells derived from malignant tumorsproduced squamous cell carcinomas within a short latent period.