PPG PROJECT 3 SUMMARY Persistent colonization of the human stomach with the Gram-negative bacterium Helicobacter pylori is associated with a markedly increased risk for the development of gastric adenocarcinoma. Gastric cancer is the fourth leading cause of cancer-related death worldwide, and H. pylori has been classified as a type I carcinogen by the World Health Organization. The long-term goal of this work is to define the mechanisms by which H. pylori infection can lead to gastric cancer, and to develop improved approaches for identifying individuals who have an increased risk for gastric cancer so they can be targeted for therapeutic intervention. Our previous studies have shown that both a high-salt diet and a low-iron diet increase the risk of gastric cancer in an animal model of H. pylori infection. High-salt- or low-iron-induced alterations in H. pylori gene expression likely account at least in part for the detrimental effects of these diets on gastric cancer risk. With Project 1 and Core A, we have shown that high-salt and low-iron diets also influence the evolution of H. pylori in the stomach, selecting for mutations that confer a survival advantage in a carcinogenic environment and potentially leading to enhanced oncogenic potential. One such mutation encodes an amino acid substitution near the metal-binding site of Fur, a regulatory protein that controls genes involved in iron homeostasis. The overarching hypothesis of this proposal is that gastric cancer risk is influenced by both strain-specific H. pylori genetic features and dietary composition. The three interrelated Specific Aims are to (i) define interrelated effects of salt and iron on H. pylori gene expression, physiology, and fitness; (ii) elucidate interrelated effects of fur sequence variation, dietary salt, and dietary iron on H. pylori-induced gastric pathology and gastric cancer risk; and (iii) identify molecular alterations linked to gastric preneoplastic and neoplastic pathology. These Aims will interdigitate with work proposed in Projects 1 and 2 and will utilize Gastric Histopathology Core A, Proteomics and Metabolomics Core B, as well as Administrative Core C for biostatistical support. These studies will lead to important advances in our understanding of the molecular mechanisms by which H. pylori infection, high-salt diets, and low-iron diets promote the development of gastric cancer. Ultimately, these studies should lead to advances in the prevention and therapy of malignancies that develop in the setting of chronic inflammation.