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Chronic infection of the gastric mucosa by Helicobacter pylori is associated with an increased risk of developing gastric cancer; however, the vast majority of infected individuals never develop this disease. One H. pylori virulence factor that increases gastric cancer risk is the cag pathogenicity island, which encodes a bacterial type IV secretion system. Cyclooxygenase-2 (COX-2) expression is induced by proinflammatory stimuli, leading to increased prostaglandin E₂ (PGE₂) secretion by gastric epithelial cells. COX-2 expression is increased in gastric tissue from H. pylori-infected persons. H. pylori also activates the epidermal growth factor receptor (EGFR) in gastric epithelial cells. We now demonstrate that H. pylori-induced activation of COX-2 in gastric cells is dependent upon EGFR activation, and that a functional cag type IV secretion system and direct bacterial contact are necessary for full induction of COX-2 by gastric epithelial cells. PGE₂ secretion is increased in cells infected with H. pylori, and this induction is dependent on a functional EGFR. Increased apoptosis in response to H. pylori occurs in cells treated with a COX-2 inhibitor, as well as COX-2-/- cells, indicating that COX-2 expression promotes cell survival. In vivo, COX-2 induction by H. pylori is significantly reduced in mice deficient for EGFR activation compared with wild-type mice with a fully functional receptor. Collectively, these findings indicate that aberrant activation of the EGFR-COX-2 axis may lower the threshold for carcinogenesis associated with chronic H. pylori infection.