Development of improved culture conditions that allow optimal proliferation and differentiation of mouse epidermal cells : effects of polycyclic aromatic hydrocarbons and 12-0-tetradecanoylphorbol-13-acetate (TPA) on epidermal cells

In order to examine the biological effects of chemicals associated with epidermal carcinogenesis on normal epidermal cells, I developed a quantitative assay for proliferation (secondary cloning efficiency) using newborn mouse epidermal cells. With this assay, I found that epidermal cells from SENCAR mice (a strain bred for sensitivity to skin carcinogenesis) were more susceptible than BALB/c epidermal cells (from a strain less sensitive to skin carcinogenesis) to PAH toxicity in vitro, implying that the SENCAR sensitivity may reside at the cellular level. SENCAR cells also proliferated much better in vitro, indicating a greater autonomy perhaps important in epidermal carcinogenesis. Since subsequent colony development did not necessarily parallel initial toxicity, factors other than toxicity were apparently involved in long-term epidermal proliferation. Toxicity of several different PAH roughly paralleled their carcinogenic potency, similar to results obtained in the past with fibroblast systems.

The epidermal-A31 interaction, which may reflect phenomena associated with carcinogenesis or differentiation in vivo, was found to be specific for the feeder type, probably requiring cell-cell contact since secondary epidermal colony production was not supported by A31-conditioned medium or culture surfaces. The tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA), previously shown to interfere with metabolic cooperation in vitro, also blocked epidermal colony formation, probably not through simple toxicity, These data imply that the A31-epidermal effect is apparently not a typical mesenchymal-epithelial interaction (as has been suggested for the similar Swiss 3T3-human epidermal interaction), since the basement membrane would prevent this contact in intact skin, and may involve direct transfer of some critical molecule. TPA may function as a promoter by interfering with normal cellular communication, a phenomenon that appears to be very important for normal epidermal growth in vitro.

The biological properties of epidermal cells have long been neglected because of the lack of a suitable in vitro system. Epidermal cells grown under the conditions I have described should be more suitable for studies of cellular carcinogenesis and differentiation in vitro and in vivo.