Molecular Understanding and Targeting of Determinant Factors in Gastric Tumorigenesis

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ABSTRACT Gastric cancer (GC) is the fifth most common malignancy and the third most lethal cancer worldwide, with a 5-year survival rate of 5-10% in advanced stages. The long-term goal of our research is to develop novel interventions to prevent and treat gastric cancer (GC) based on molecular targeting of crucial events in GC carcinogenesis. This application is based on an exciting finding that mice with villin-promoter– driven PPAR-d overexpression (villin-PPAR-d mice) spontaneously developed large and invasive GCs. Our published data showed that PPAR-d was upregulated in human GC tissues and this upregulation was associated with poor prognosis of patients. Villin promoter is active in a small subpopulation of gastric epithelial cells that are considered villin-positive gastric progenitor cells (V-GPCs). Cancer stem cells (CSCs) are thought to arise from transformation of normal stem/progenitor cells to drive tumor formation. We found that PPAR-d enhanced the stemness of V-GPCs and enabled V-GPCs to form tumors via activating the PPAR-d–interferon- gamma (IFNG) signaling loop. Furthermore, we also found 1) CCL20 is the most markedly upregulated chemokine by PPAR-d overexpression in V-GPCs, and 2) CCR6+CD45+ cells (CCR6 is the sole receptor of CCL20) have significantly higher IFNG mRNA expression than CCR6-CD45+ cells do. Helicobacter pylori (H. pylori) is a class I carcinogen for human GC. Chronic H. pylori infection, currently affecting nearly half of the world population, is a known strong risk factor for human GC. H. pylori infection increases PPAR-d, CCL20, and IFNG, which in turn promotes H. pylori–induced gastric inflammation, enhances GPCs’ stemness and promotes gastric epithelial proliferation in mice and humans. Whether this PPAR-d overactivation is required for H. pylori– induced GC is largely unknown. Addressing this knowledge gap is important to the public, especially for individuals who suffer from chronic H. pylori infection, because PPAR-d is a druggable protein for which both agonists and antagonists have been developed, and PPAR-d agonists are being used for noncancerous indications (e.g. enhancing muscle endurance). Thus, we hypothesize that PPAR-d overactivation in GPCs drives GC via upregulating the PPAR-d–CCL20/CCR6–IFNG signaling pathway and molecular targeting of this pathway could be a novel intervention modality for GC. Aim 1 will determine the role of PPAR-d upregulation in V-GPCs and Lgr5-positive GPCs (L-GPCs) at adult onset on GC carcinogenesis. Aim 2 will determine the effect of PPAR-d genetic deletion/loss of function in V-GPCs or L-GPCs on H. felis-induced GC tumorigenesis. H. felis is a close relative of H. pylori that has analogous effects in mice to those of H. pylori in humans. Aim 3 will determine the molecular mechanisms underlying dysregulated PPAR-d–IFNG signaling and evaluate the effects of molecular targeting of this pathway on GC carcinogenesis. We expect that completion of this proposal will not only provide new insights into the molecular pathogenesis of GC, but also advance the development of novel mechanism-based approaches for GC prevention and therapy.