Resistance to tumor necrosis factor-α (TNF-α)-induced apoptosis in rat hepatoma cells expressing TNF-α is linked to low antioxidant enzyme expression

Abstract

In order to study the mechanisms of resistance to tumor necrosis factor-α (TNF-α), we have constructed two stable transfectants producing TNF-α (Yv12-2 and Yv13-44) from the rat hepatoma H4IIE cell, which does not produce TNF-α. H4IIE cells were highly sensitive to apoptosis induced by TNF-α, whereas Yv2-12 and Yv13-44 cells were resistant. Manganous superoxide dismutase was not up-regulated in Yv2-12 and Yv13-44 cells and was unresponsive to induction by exogenous TNF-α and by H2O2 in H4IIE cells and in the transfectants. Catalase expression and activity were lower in Yv2-12 and Yv13-44 cells than in H4IIE cells; furthermore, the transfectants were more susceptible to H2O2. Treatment with exogenous TNF-α down-regulated catalase in H4IIE cells but not in Yv2-12 and Yv13-44 cells. Treatment of H4IIE cells with the catalase inhibitor 3-amino-1,2,4-triazole rendered them resistant to exogenous TNF-α. These data suggest a causal relationship between resistance to TNF-α and low catalase activity. Expression of copper and zinc containing superoxide dismutase was also decreased, whereas expression of glutathione peroxidase-1 was unchanged in Yv2-12 and Yv13-44 cells. Data from a microarray point to a down-regulation of genes in the resistant clones that code for antioxidative proteins and proteins involved in glutathione synthesis and function. We assume that a prooxidant signal linked to the down-regulation of antioxidant defense may be associated with resistance to apoptosis induced by TNF-α.