Activation of the transcription factor NF-κB in lipopolysaccharide-stimulated U937 cells

Abstract

During the course of serious bacterial infections, lipopolysaccharide (LPS) interacts with monocyte/macrophage receptors, resulting in the generation of inflammatory cytokines. Transcription factor NF-κB is crucial in activating the transcription of genes encoding proinflammatory cytokines. In this paper, we demonstrate that the activation of NF-κB by LPS in a promonocytic cell line (U937) followed a rather slow kinetics, depending on the rate of IκB-α inhibitor hydrolysis. No degradation of p105 and p100 inhibitors was observed under these conditions. The transduction pathway leading to NF-κB activation in U937 cells involved the intracellular generation of reactive oxygen species (ROS), as demonstrated by the concomitant inhibitory effects of antioxidants on NF-κB activation and the emission of a fluorescent probe reacting intracellularly with hydrogen peroxide. This ROS pathway was also characterized by the use of other inhibitors. This finding indicates that phospholipase A2 and 5-lipoxygenase are also involved. However, the NP-κB activation pathway involving the acidic sphingomyelinase of the endolysosomial membrane did not seem to participate in the LPS-induced NF-κB activation in U937 cells.