H-pylori activates NF-κB through a signaling pathway involving IκB kinases, NF-κB-inducing kinase, TRAF2, and TRAF6 in gastric cancer cells

Background & Aims: H. pylori infection on gastric epithelial cells has been shown to induce NF-kappa B activation, but the mechanism of intracellular signal conduction that leads to NF-kappa B activation is not clear. The aim of this study was to analyze the molecular mechanism responsible for H. pylori-mediated NF-kappa B activation on gastric cancer cells. Methods: NF-kappa B activation by H. pylori was tested by using luciferase reporter assay. I kappa B alpha degradation by H. pylori infection was assessed by immunoblotting. IKK alpha and IKK beta activation was analyzed by kinase assay. In transfection experiments, effects of dominant negative 1 kappa B alpha, IKK alpha, IKK beta, NF-kappa B-inducing kinase (NIK), TRAF2, and TRAF6 mutants were investigated. The effects of an IKK beta-specific inhibitor, aspirin, on NF-kappa B activation and IL-8 secretion were also analyzed. Results: H, pylori promotes degradation of 1 kappa B alpha, a cytoplasmic inhibitor of NF-kappa B. In kinase assay, H. pylori induced IKK alpha and IKK beta catalytic activity in gastric cancer cells. Transfection of kinase-deficient mutant of either IKK inhibited H. pylori-mediated NF-kappa B activation dose-dependently. Aspirin inhibited both NF-kappa B activation and IL-8 secretion induced by H. pylori. NF-kappa B activation was also inhibited by transfection of kinase-deficient NIK or a dominant negative mutant of upstream adapter protein TRAF2 or TRAF6. Conclusions: H. pylori induces NF-kappa B activation through an intracellular signaling pathway that involves IKK alpha, IKK beta, NIK, TRAF2, and TRAF6.