Dexamethasone and pentoxifylline inhibit endotoxin-induced cachectin/tumor necrosis factor synthesis at separate points in the signaling pathway

The induction of cachectin/tumor necrosis factor (TNF) synthesis by bacterial endotoxins is a process that entails activation at several levels. Cachectin/TNF gene transcription is accelerated, leading to rapid accumulation of mRNA within the macrophage cytosol. In addition, translational derepression occurs, leading to far more efficient message utilization. Through the use of post-transcriptional reporter constructs, we now demonstrate that certain agents capable of inhibiting cachectin/TNF biosynthesis operate through different mechanisms. In RAW 264.7 macrophages, pentoxifylline blocks cachectin/TNF mRNA accumulation but has no effect upon the efficiency of reporter mRNA translation. Dexamethasone, on the other hand, has only a modest effect on cachectin/TNF mRNA accumulation, but strongly impedes translational derepression. Combined application of dexamethasone and pentoxifylline to macrophages causes a greater suppression of cachectin/TNF biosynthesis than can be achieved by either agent alone. These findings suggest that the signaling pathway activated by endotoxin is branched, and that selective inhibition of different parts of the pathway may be achieved through the use of distinct agents.