Growth and structural properties of epithelial cell cultures established from normal rat liver and chemically induced hepatomas.

Epithelial cultures established from adult rat liver and from rat hepatomas induced in vivo with aromatic amine carcinogens have been compared by light and electron microscopy and by growth properties in liquid medium and in agar. The morphology and growth patterns of all of these cultures indicate that they have characteristics of epithelial rather than fibroblast cells. The criteria generally used to score for transformation of fibroblasts were not satisfactory for distinguishing normal epithelial cells from hepatoma cells in culture. Growth in agar, however, provides a simple and objective method of scoring for transformed epithelial cells, because only the tumorigenic cells grow in agar. Since none of the normal cultures had hydrocortisone-inducible tryosine aminotransferase, we lack definitive evidence that they are derived from liver parenchymal cells. The outstanding feature in the ultrastructure of the hepatoma cells in culture was the presence of type A and C viral particles. Whereas five hepatoma cultures and a spontaneously transformed normal liver cell line were positive for these particles, five independently isolated cell cultures from normal adult rat liver were negative. Evidence is presented that the viral particles seen in hepatoma cultures are due to activation of latent viruses rather than to in vitro contamination. The possible significance of these particles in hepatocarcinogenesis is discussed.