Lipopolysaccharide and CpG DNA synergize for tumor necrosis factor-alpha production through activation of NF-kappa B

Unmethylated CpG motifs in bacterial DNA (CpG DNA) activate host innate imm une responses synergistically with some other microbial products, such as e ndotoxins, and may contribute to disease pathogenesis through excessive pro duction of proinflammatory cytokines. Because monocyte-derived tumor necros is factor (TNF)-alpha is an important mediator of disease, we investigated whether CpG DNA and lipopolysaccharide (LPS) synergize for inducing TNF-alp ha biosynthesis. CpG DNA and LIPS synergistically induce TNF-alpha producti on in RAW264.7 cells and J774 cells through activation of NF-kappaB. Furthe rmore, transient transfection with a super-repressive mutant of I kappaB al pha (I kappaB alpha -AA) demonstrated that NF-kappaB plays a critical role in CpG DNA-mediated TNF-alpha expression. Like NF-kappaB activation, CpG DN A-induced activation of mitogen-activated protein kinases (MAPK) regulates TNF-alpha production. Both extracellular receptor kinase (ERK) and p38 can regulate TNF-alpha gene transcription induced by CpG DNA. Although CpG DNA at the higher concentration slightly enhanced LPS-mediated phosphorylation of ERK, it did not alter the LPS-mediated activation of c-Jun N-terminal ki nase and p38. In addition, CpG DNA showed little or no enhancement of LPS-m ediated AP-1 activation. These results suggest that CpG DNA- and LIPS-media ted signals converge at or above the level of NF-kappaB and ERK, and that t here are distinct, as well as common, signaling pathways which are utilized by both CpG DNA and LIPS for activating various transcription factors and MAPK.