In order to charcterize the changes in cytoskeletal, cell-cell and cell-matrix interactions which are indicative of epithelial cell transformation, we have used as a model system ethionine-transformed liver epitehlial cells of the TRL 1215 cell line for which controls are available both at low and at high passage levels. In this line transformation is accompained by an increase in cell-substrate adhesion, cell spreading, marked by increased amounts of actin stress fibers, vinculin plaques, adhesion plaques, and cell-associated fibronectin. Thus, the capacities for tumorigenicity and anchorage independent growth coexist with the capacity for a high level of cell-substrate adhesion in these cells. At the same time there are decreases in the immunocytochemical expression of laminin and in the extent of junctional complexes, indicating that changes in the specific molecular interactions involved in cell-cell and cell-substrate adhesion are more important to transformation than changes in adhesion per se. The finding of increased fibronectin in tumor-bearing livers of ethionine-fed rats, by paralleling the results obtained in vitro, shows the value of the TRL 1215 line as a model which relates to in vivo carcinogenesis. The promotable mouse epidermal cell line, JB6, has been subjected to a similar protocol to define promotion specific events. To establish a phenotypically transformed, turmorigenic cell type, a combination of repeated exposure to the promoter and clonal propagation of anchorage independent cells is necessary. Our novel finding regarding the presence of the H-ras gene produce, p21, in focus-forming cells of a line JB6 may be indicative of the protein's role in initiating focus formation in addition to its known role in cell proliferation.
