Abstract 409: Bacterial protein AvrA targets intestinal stem cells via beta-catenin pathway and enhances intestinal tumorigenesis
Authors: Lu Rong , Wu Shaoping , Liu Xingyin , Zhang Yong-guo , Xia Yinglin , Zhou Zhongren , Bissonnette Marc , Li Linheng , Sun Jun 
Published: August 2012

Abstract
Bacterial infection contributes to tumorigenesis and the progression of established cancerous lesions. However, how enteric bacterial products directly contribute to cancer is still unknown. Salmonella infection is a common public health problem that can become chronic and increase the risk of cancer. Moreover, alive and mutated Salmonella is used as a vector to target cancer cells. However, studies are lacking on chronic infection with mutated Salmonella in the host. Salmonella AvrA is a multifunctional protein that influences eukaryotic cell pathways utilizing ubiquitin and acetylation. AvrA protein acts as a deubiquintinase to regulate beta-catenin ubiquitination and stabilize beta-catenin, a key player in intestinal development and tumorigenesis. We hypothesize that the bacterial effector AvrA activates the beta-catenin pathway to promote colonic tumorigenesis. In a colitis-associated colon cancer model, mice were infected with Salmonella AvrA- sufficient or deficient bacterial strains, then stimulated with a carcinogen azoxymethane (AOM) and dextran sodium sulfate (DSS, induced colitis). We investigated consequences of the bacterial AvrA-mucosal interactions in tumorigenesis. The tumor incidence in the AvrA+ infected group is 100% compared to 51.4% in the AOM/DSS only group and 56.3% in the AvrA- infected mice. Mice infected with AvrA-expressed bacteria had significant high incidence of tumor. In contrast, chronic infection of Salmonella AvrA-/- mutation strain was not sufficient to increase the tumor incidence. The AOM/DSS mice had most of the tumors close to the distal colon. In contrast, the location of tumors in the infected mice was moved closer to proximal colon, where has more bacterial growth. We further determined the mechanisms by which bacterial AvrA directly activates beta-catenin signaling by enhancing nuclear beta-catenin in the infected colon cancer models. AvrA expression increased the expression of phosphorylated-beta-catenin (ser552), indicating involvement in inflammation-induced stem-progenitor cell expansion. We confirmed the colonization of Salmonella in the intestine by immunostaining, real-time PCR, and bacterial culture. Salmonella was identified not only at the top of the villus, but also at the basal side, stem cell niches of the intestinal epithelium. Inflammatory cytokines, such as IL-6, were increased by infection and promotes epithelial cancer. Overall, we demonstrated bacterial AvrA activation of the beta-catenin pathway in colonic tumorigenesis. Our findings provide important insights into how a bacterial effector protein contributes to the development of colon cancer. This study also allows for a better understanding of intestinal stem cells targeted by a bacterial protein. It will bring us one step closer to understanding the therapeutic strategies that may hamper dysregulation of stem cells in infection and cancer.
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 409. doi:1538-7445.AM2012-409