DEFECTIVE TRANSLATION OF TUMOR-NECROSIS-FACTOR MESSENGER-RNA IN LIPOPOLYSACCHARIDE-TOLERANT MACROPHAGES

Macrophage activation by lipopolysaccharide (LPS) results in the trans lational activation of tumor necrosis factor (TNF) mRNA. The initial p hase of macrophage activation is followed by a refractory state called LPS tolerance characterized by an impaired TNF production in response to a secondary LPS challenge. LPS-tolerant macrophages contain high a mounts of TNF mRNA, suggesting a translational regulation of TNF biosy nthesis. The induction of LPS tolerance was studied in RAW 264.7 macro phages stably transfected with a chloramphenicol acetyl-transferase (C AT) reporter gene construct driven by a constitutive cytomegalovirus p romoter and containing the 3' untranslated region of the murine TNF ge ne. We found that primary stimulation of transfected cells by LPS (1 n g/ml, 12 hr) resulted in a marked suppression (80%) of CAT accumulatio n in response to a secondary LPS challenge (1 mu g/ml, 6 hr). In contr ast the accumulation of CAT mRNA was not influenced by LPS tolerance. Using the same CAT reporter, we observed that the serine/threonine pho sphatases 1 and 2A inhibitor okadaic acid induced TNF mRNA translation and that this activation was not inhibited by LPS-tolerance. In concl usion, these data indicate that deficient production of TNF in LPS-tol erant macrophages in response to a second LPS challenge is characteriz ed by a defective translation of TNF mRNA. However, this hyporesponsiv eness to LPS is specific, since translation of TNF mRNA induced by oka daic acid is not inhibited in LPS-tolerant macrophages. (C) 1996 Wiley -Liss, Inc.