Mouse cell clones for improved quantitation of carcinogen-induced altered differentiation

Two new mouse epidermal cell lines have been isolated and characterized as target cells for three chemical carcinogens. The ability to grow these cells at low density ( ∼5 clonogenic cells/cm²) has permitted more precise quantitation of chemical carcinogen-induced changes in epidermal differentiation. The cell lines, designated 291 and 271c, retain the property previously observed in primary cultures of mouse epidermal cells, that is the regulation of terminal differentiation by extracellular Ca²⁺ ion. Altered response to extracellular Ca²⁺ after carcinogen treatment of these cells is the basis of the assay endpoint. Other normal properties demonstrated by these cells are keratin immunofluorescence patterns, ability to form cornified envelopes in response to Ca²⁺ and a lack of tumorigenicity. Both of the lines have high cloning efficiencies (up to 20%) and characteristic epidermal morphology. Their chromosome number, however, is near tetraploid. Dose response studies indicated an increase in colonies with altered response to Ca²⁺ proportional to the dose of three chemical carcinogens: DMBA 0.001 - 0.5 μg/ml × 24 h, MCA 0.01 - 5 μg/ml × 24 h and MNNG 0.01 - 0.2 μg/ml × 1 h. The optimized assay protocol has provided a reproducible means of quantitating carcinogen-altered epidermal cells relative to carcinogen dose, and of isolating cell clones for studies of altered differentiation in carcinogenesis and chemotherapy.