Transcriptional Inhibition of Interleukin-8 Expression in Tumor Necrosis Factor-tolerant Cells EVIDENCE FOR INVOLVEMENT OF C/EBPβ

Abstract There is some evidence that the potent cytokine tumor necrosis factor (TNF) is able to induce tolerance after repeated stimulation of cells. To investigate the molecular mechanisms mediating this phenomenon, the expression of interleukin-8 (IL-8), which is regulated by transcription factors NF-κB and C/EBPβ, was monitored under TNF tolerance conditions. Pretreatment of monocytic cells for 72 h with low TNF doses inhibited TNF-induced (restimulation with a high dose) IL-8 promoter-dependent transcription as well as IL-8 production. Under these conditions neither activation of NF-κB nor IκB proteolysis was affected after TNF re-stimulation, albeit a slightly reduced IκB-α level was found in the TNF pretreated but not re-stimulated sample. Remarkably, in tolerant cells an increased binding of C/EBPβ to its IL-8 promoter-specific DNA motif as well as an elevated association of C/EBPβ protein with p65-containing NF-κB complexes was observed. Finally, overexpression of C/EBPβ, but not p65 or Oct-1, markedly prevented TNF-induced IL-8 promoter-dependent transcription. Taken together, these data indicate that the expression of IL-8 is inhibited at the transcriptional level in TNF-tolerant cells and C/EBPβ is involved under these conditions in mediating the negative-regulatory effects, a mechanism that may play a role in inflammatory processes such as sepsis.