H-pylori activates NF-kappa B through a signaling pathway involving I kappa B kinases, NF-kappa B-inducing kinase, TRAF2, and TRAF6 in gastric cancercells

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. py lori-mediated NF-kappa B activation on gastric cancer cells. Methods: NF-ka ppa B activation by H. pylori was tested by using luciferase reporter assay . I kappa B alpha degradation by H. pylori infection was assessed by immuno blotting. IKK alpha and IKK beta activation was analyzed by kinase assay. I n transfection experiments, effects of dominant negative 1 kappa B alpha, I KK alpha, IKK beta, NF-kappa B-inducing kinase (NIK), TRAF2, and TRAF6 muta nts were investigated. The effects of an IKK beta-specific inhibitor, aspir in, on NF-kappa B activation and IL-8 secretion were also analyzed. Results : H, pylori promotes degradation of 1 kappa B alpha, a cytoplasmic inhibito r of NF-kappa B. In kinase assay, H. pylori induced IKK alpha and IKK beta catalytic activity in gastric cancer cells. Transfection of kinase-deficien t mutant of either IKK inhibited H. pylori-mediated NF-kappa B activation d ose-dependently. Aspirin inhibited both NF-kappa B activation and IL-8 secr etion induced by H. pylori. NF-kappa B activation was also inhibited by tra nsfection 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 alp ha, IKK beta, NIK, TRAF2, and TRAF6.