Lipopolysaccharide-triggered desensitization of TNF-α mRNA expression involves lack of phosphorylation of IκBα in a murine macrophage-like cell line, P388D1

Abstract

Abstract Activation of nuclear factor κB (NF-κB) is thought to be required for cytokine production by lipopolysaccharide (LPS)-responsive cells. Here, we investigated the contribution of NF-κB in preventing LPS-induced transcription of the tumor necrosis factor α (TNF-α) gene in a murine macrophage cell line, P388D1, when tolerance was induced in the cells with a short exposure to a higher dose of LPS. Electrophoretic mobility shift assays with the κB elements of the murine TNF-α promoter and enhancer revealed that nuclear mobilization of heterodimers of p65/p50, c-rel/p50 and p65/c-rel, and homodimers of p65 was markedly reduced in LPS-tolerant cells, whereas that of p50 homodimers was only slightly increased. Western blot analysis showed that the phosphorylation of Ser32 on IκBα and its transient degradation did not occur in LPS-tolerant cells. These results thus suggest that desensitization of TNF-α gene expression in this LPS-tolerant state is closely associated with down-regulation of transactivating NF-κB and may involve a defect in the LPS-induced IκBα kinase pathway.