DOWN-REGULATION OF TUMOR-NECROSIS-FACTOR RECEPTORS BY BLOCKADE OF MITOCHONDRIAL RESPIRATION

We have studied the effect of blockade of mitochondrial respiration on the binding of human I-125-TNF alpha to L929 cell receptors. Specific TNF alpha binding was decreased to about 20-40% of controls by blocki ng mitochondrial respiration. This effect was dose- and time-related a nd was observed independently of the level at which the respiration wa s blocked (respiratory chain, proton backflow, ATPase, anaerobiosis). This blockade had no effect on the half-life of the specific TNF alpha binding, the internalization or degradation of TNF alpha-receptor com plexes, or the number of TNF alpha-binding sites. Scatchard analysis o f TNF alpha 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 t hey were not antagonized by pretreatment of cells with oxygen radical scavengers, deferoxamine, or inhibitors of protein kinase C. Decrease in TNF alpha binding capacity correlated significantly with cellular A TP content (r = 0.94; p < 0.01) and with the cytocidal activity of TNF alpha against L929 cells. These findings suggest that blockade of mit ochondrial respiration down-regulates the binding of TNF alpha to cell s, most likely by changing the affinity of receptors for this cytokine . This down-regulation may increase the resistance of cells to TNF alp ha cytotoxicity.