Abstract

Gastric epithelial cells were incubated with a panel of clinical isolates of Helicobacter pylori, including nonulcer dyspepsia with gastritis (HS, n = 20), gastric ulcer (HU, n = 20), duodenal ulcer (HD, n = 21), and gastric cancer (HC, n = 20). HC strains induced a higher cyclooxygenase-2 (COX-2) expression than those from HS, HD, and HU. The bacterial virulence factors and the host cellular pathways were investigated. Virulence genes of iceA, vacA, babA2, cagA 3′ repeat region, and hrgA failed to show any association with the disease status and COX-2 expression. Methylation-specific polymerase chain reaction revealed HC strains not affecting the methylation status of COX-2 promoter. Nuclear factor (NF)-κB, NF-interleukin 6, and cAMP response element were found to be involved in COX-2 induction. We explored a novel NF-κB activation pathway. The mutants of TLR2 and TLR9, but not TLR4, inhibited H. pylori-induced COX-2 promoter activity, and neutralizing antibodies for TLR2 and TLR9 abolished H. pylori-induced COX-2 expression. Phosphatidylinositol-specific phospholipase C (PI-PLC), protein kinase C (PKC), and Src inhibitors inhibited COX-2 induction. The dominant-negative mutants of NIK and various IκB kinase complexes, including IKKβ (Y188F), IKKβ (Y199F), and IKKβ (FF), inhibited the COX-2 promoter activity. Phosphorylation of GST-IKKβ (132-206) at Tyr¹⁸⁸ and Tyr¹⁹⁹ by c-Src was found after H. pylori infection. In summary, H. pylori induces COX-2 expression via activations of NF-κB, NF-interleukin 6, the cAMP response element. In NF-κB activation, H. pylori acts through TLR2/TLR9 to activate both the cascade of PI-PLCγ/PKCα/c-Src/IKKα/β and the cascade of NIK/IKKα/β, resulting in the IκBα degradation and the expression of COX-2 gene. The COX-2 overexpression may contribute to the carcinogenesis in patients colonized with these strains.