Evidence for interactions between rat hepatoma cell apoptosis and differentiation

Partial copper depletion of a variant rat hepatoma cell line induces a transient inhibition of growth and the genesis of stable, well-differentiated revertants. We report a burst of cell death, synchronous with the peak of reversion. The characteristics of this cell mortality were typical of apoptosis and included detachment from the plastic support, chromatin condensation and fragmentation, and internucleosomal DNA degradation. Although commitment to cell death was induced by copper deficiency, the apoptotic process was partially inhibited as assessed from electrophoretic patterns of DNA degradation. Redifferentiation was closely linked to the apoptotic death program. Analysis of rescued detached cells in all three media (standard, Cu-, Fe-) indicated that the frequency of revertants was significantly higher among floating as opposed to adherent cell populations. Nevertheless, experimental copper depletion increased by 10(4) times the revertant frequency among adherent cells. We propose that redifferentiation of the variant hepatoma cells (and concomitant recovery of tumorigenicity) is determined by the gene expression pattern of programmed cell death.