Toll-like receptor-4 mediates lipopolysaccharide-induced signal transduction

TLR4 is a member of the recently identified Toll-like receptor family of pr oteins and has been putatively identified as Lps, the gene necessary for po tent responses to lipopolysaccharide in mammals. In order to determine whet her TLR4 is involved in lipopolysaccharide-induced activation of the nuclea r factor-kappa B (NF-kappa B) pathway, HEK 293 cells were transiently trans fected with human TLR4 cDNA and an NF-kappa B-dependent luciferase reporter plasmid followed by stimulation with lipopolysaccharide/CD14 complexes. Th e results demonstrate that lipopolysaccharide stimulates NF-kappa B-mediate d gene expression in cells transfected with the TLR4 gene in a dose- and ti me-dependent fashion. Furthermore, E5531, a lipopolysaccharide antagonist, blocked TLR4-mediated transgene activation in a dose-dependent manner (IC50 similar to 30 nM). These data demonstrate that TLR4 is involved in lipopol ysaccharide signaling and serves as a cell-surface co-receptor for CD14, le ading to lipopolysaccharide-mediated NF-kappa B activation and subsequent c ellular events.