Down-regulation of tumor necrosis factor receptors by blockade of mitochondrial respiration

Abstract

We have studied the effect of blockade of mitochondrial respiration on the binding of human 125I-TNFα to L929 cell receptors. Specific TNFα binding was decreased to about 20-40% of controls by blocking mitochondrial respiration. This effect was dose- and time-related and was observed independently of the level at which the respiration was blocked (respiratory chain, proton backflow, ATPase, anaerobiosis). This blockade had no effect on the half-life of the specific TNFα binding, the internalization or degradation of TNFα-receptor complexes, or the number of TNFα-binding sites. Scatchard analysis of TNFα binding data indicated a 2-4-fold decrease in the affinity of these binding sites. These effects did not appear to be related to the protein kinase C activity or to reactive oxygen radicals, since they were not antagonized by pretreatment of cells with oxygen radical scavengers, deferoxamine, or inhibitors of protein kinase C. Decrease in TNFα binding capacity correlated significantly with cellular ATP content (r = 0.94; p < 0.01) and with the cytocidal activity of TNFα against L929 cells. These findings suggest that blockade of mitochondrial respiration down-regulates the binding of TNFα to cells, most likely by changing the affinity of receptors for this cytokine. This down-regulation may increase the resistance of cells to TNFα cytotoxicity.