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 proliferation and differentiation of mouse keratinocytes, we analysed alterations in cellular growth control that occur during multistage carcinogenesis in vivo. Normal diploid keratinocytes derived from newborn mouse hair follicles had a limited replicative potential of approximately 50 population doublings in vitro, and colony formation was highly dependent upon cholera toxin, serum growth factors, and mesenchymal feeder cell support. In contrast, keratinocyte lines from benign epidermal lesions or malignant tumors induced by chemicals showed indefinite renewal capacity of the colony forming population, and greatly reduced dependence on cholera toxin and serum growth factors. Cell lines from benign lesions did not readily produce tumors in syngeneic hosts, but cells derived from malignant tumors produced squamous cell carcinomas within a short latent period.