Dexamethasone prevents the growth inhibitory effects of recombinant tumor necrosis factor in a rat hepatoma cell line reuber-RC-3: An association with the changes in the messenger RNA levels for multidrug resistance gene

Abstract Two days exposure to recombinant tumor necrosis factor (rTNF-α) produced a dose-dependent reduction in (methyl- 3 H) thymidine incorporation in RC-3 cells (ID 50 =25 units/ml). Prolonged treatment with rTNF-α further resulted in a significant reduction in colony formation (ID 50 = 200 units/ml), which was reversed upon removal of the agent. Interferon levels were undetectable in the supernatants of the rTNF-α treated cells. Simultaneous exposure to dexamethasone prevented the growth inhibition in rTNF-α - treated RC-3 cells. Significant dose-dependent increase in the steady state levels of the mRNA for multidrug resistance (MDR1) gene was observed after rTNF-α treatment while simultaneous exposure to dexamethasone produced a substantial reduction in the mRNA levels for MDR1 gene. These data suggest that growth inhibitory effects of TNF are regulated by dexamethasone and are associated with changes in MDR1 mRNA levels in hepatoma-derived cells.