Abstract 1339: The role of TNF-α in PGE2-induced tumorigenesis in gastric cancer mouse model

Abstract Accumulating evidence has indicated that chronic inflammation is associated with cancer development. Mouse genetic studies have shown that the proinflammatory mediator, PGE2, plays an essential role in gastrointestinal tumorigenesis. Moreover, the proinflammatory cytokine TNF-α also plays a key role in tumorigenesis, including colitis-associated colon cancer. However, the relationship between PGE2 and TNF-α in tumorigenesis has not yet been fully investigated. We previously constructed a gastric tumor mouse model, Gan mice, that recapitulates human intestinal-type gastric cancer, in which both the PGE2 pathway and Wnt signaling are activated simultaneously in the stomach by transgenic expression of the COX-2, mPGES-1, and Wnt1 genes. The induction of the PGE2 pathway triggers an inflammatory response in the Gan mouse stomach, and the expression of proinflammatory cytokines and chemokines is induced in gastric tumor tissues. We herein examined the role of TNF-α in the PGE2-induced inflammation-associated gastric tumorigenesis by crossing Gan mice with TNF-α knockout mice. Importantly, the gastric tumorigenesis in the Gan TNF-α (-/-) compound mice was significantly suppressed in comparison to the control Gan mice. Moreover, the β-catenin level decreased significantly in the gastric tumors of Gan TNF-α (-/-) mice, suggesting a role for TNF-α in the promotion of Wnt signaling. Interestingly, inflammatory cells, including macrophages and CD4+ T cells, still infiltrated into the Gan TNF-α (-/-) mouse tumors, and the expression levels of IL-1α and IL-6 were almost the same as those in the control Gan mouse tumors. Accordingly, it is possible that TNF-α is an important tumor-promoting factor for gastric tumorigenesis, although TNF-α is not essential for PGE2-induced inflammation in the stomach. Notably, macrophages in the Gan TNF-α (-/-) mouse tumors lost their expression of the M2 marker CD206. It has been suggested that macrophages polarized to the M2(-like) type are important for tissue remodeling and tumorigenesis. It is therefore possible that TNF-α is required for macrophage polarization to a pro-tumorigenic status, which may be important for Wnt activation and gastric tumor promotion. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1339. doi:1538-7445.AM2012-1339