Study of the interactions between the mechanisms that control the differentiated state and tumorigenicity in rat hepatoma line cells.

Summary Development associates with differentiation, a control of cell proliferation that takes place throughout the life of the organism. Morphogenesis reflects the existence of interactions between these two levels of cell physiology that are also found associated in pathological situations (malignancy). This work is a study of the effect of a transient inhibition of proliferation on the phenotypic properties of variant cells of a rat hepatoma line in in vitro culture. The original h4iiec3 line cells express many hepatocyte functions and induce tumors in compatible animals. The c2 variant clone is characterized by loss of the differentiated state and tumorigenicity. Partial copper deficiency applied to c2 cells results in: (1) transient inhibition of cell proliferation. (3) induction of reporter gene amplification events, consistent with a dissociation between cell proliferation and dna synthesis observed under these conditions. (4) cell death by apoptosis recorded at the time of reversion induction. A second series of experiments exploits the association of tumorigenicity with the ability of cells to grow in vitro in semi-solid medium. Under these culture conditions, a fraction of the c2 cells develop colonies. Once acquired, the ability to multiply in semi-solid medium is stable. These c2ag cells are characterized by an increased reversion frequency and by the expression of transcription factors enriched in the liver. All the data acquired reveal the inducing effect of a transient inhibition of proliferation on the generation of stable differential revertants. These results also suggest that a key step in the transition to the malignant state involves the involvement of transformed cells in the differentiation process. The nature of the observations made on this system reveals the non-linear character of the mechanisms involved in the dynamics of cellular responses and thus the extreme sensitivity to initial conditions.