EGFR Activation and Polyamines in H.Pylori-Induced Gastric Cancer

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Helicobacter pylori infects half the world and is the principal cause of gastric cancer, the second leading cause of cancer death worldwide. However, universal eradication is not feasible and there is a strong need to identify persons at high risk for cancer development and develop new strategies for intervention. We have directly implicated phosphorylation of the epidermal growth factor receptor (pEGFR) and induction of spermine oxidase (SMO) in the aberrant signaling response to H. pylori in gastric epithelial cells. Our published and preliminary data show that oxidation of the polyamine spermine by SMO results in generation of H2 02 that is the cause of DNA damage in infected gastric epithelial cells, and that pEGFR is required for SMO expression and mediates the generation of a subpopulation of cells with SMO-driven DNA damage that are resistant to apoptosis. These events occur in conditionally immortalized gastric epithelial cells and in in vivo models of gastric carcinogenesis (INS-GAS mice and Mongolian gerbils), and human tissues exhibit a strong correlation of SMO and DNA damage. Inhibition of polyamine synthesis or SMO reduces gastric dysplasia and carcinoma in gerbils. Our phosphoproteomics and human tissue microarray studies have implicated EGFR and ErbB2 signaling in addition to SMO in the initiation of gastric carcinogenesis. Additionally, depletion of polyamines in vitro and in vivo reduces oxidative DNA damage and carcinoma despite substantially increasing pEGFR. Our hypothesis is that polyamines determine the effects of EGFR phosphorylation on H. pylori-induced inflammation, DNA damage, and gastric carcinogenesis. Our Specific Aims are to determine the following in H. pylori-induced gastric carcinogenesis: 1) the role of EGFR transactivation and apoptosis-resistant cells; 2) if polyamines are required for the deleterious effects of pEGFR; and 3) the positive and negative regulators of EGFR signaling that are involved. These studies will incorporate unique in vitro and ex vivo models such as gastric organoids, and proven models of gastric dysplasia and carcinoma in mice and gerbils that are employed across this PPG to pursue these aims. We will benefit from continued close collaborations with Projects 1 and 3 that will include exchange of H. pylori mutant strains and output strains from our different animals systems, sharing of samples and expertise related to signaling, and our analysis of SMO-induced oxidative stress and DNA damage. This project will leverage the exceptional quality of Histopathology Core A for Aims 1-3 and Proteomics Core 8 for Aim 3, and will benefit from the uniquely strong environment at Vanderbilt for studies of H. pylori and gastric cancer.