4th Annual BMRP Investigator Meeting - Abstract
Absence of T and B Cells in Smad3-KO Mice with TGF- Dysregulation Increases Susceptibility to Bacterial-Induced Inflammation and Colon Cancer
Lillian Maggio-Price1,a, Piper Treuting1, Mark Tsang1 and Brian M. Iritani1,2
1Department of Comparative Medicine, School of Medicine, University of Washington and 2Fred Hutchinson Cancer Research Center (Seattle, Washington, U.S.A.)
Intestinal microbial organisms play an important role in triggering and sustaining inflammation in inflammatory bowel disease (IBD) and patients with IBD are at increased risk for developing colorectal cancer. Evidence from human and animal studies suggests that altered responses to TGF-signaling may be contributory. Mice deficient in the TGF- signaling molecule SMAD3 (Smad3 exo2/exo2) were previously reported to spontaneously develop colon cancer (Zhu et al., Cell, 1998). However, we recently determined that bacterial infection is required for inflammation and colon cancer to develop in Smad3-/- mice (Maggio-Price et al. Cancer Research, 2006). Smad3-/- mice housed in a helicobacter-free environment for up to nine months do not manifest the previously reported colon cancer phenotype. Experimental infection with helicobacter triggered colon cancer (mucinous adenocarcinomas) at the ceco-colic junction in 50-66% of the animals. Tumor development was preceded by an early inflammatory phase. In order to determine if abnormalities in TGF- signaling in lymphocytes were contributing to the Smad3-/- mice cancer susceptibility, we crossed Smad3-/- mice with Rag2-/-129SvEv mice to achieve homozygosity in the SMAD3 and RAG2 loci. We have found that helicobacter infection of Smad3/Rag2 double-null (DKO) mice results in a more severe cancer phenotype, relative to helicobacter-infected Smad3-/- mice. 100% (10/10) of H. bilis and H. hepaticus-infected Smad3/Rag2-DKO develop highly invasive adenocarcinomas in multiple sites of the large bowel by 9-23 weeks PI, and there is marked and persistent inflammation throughout the large bowel. Immunohistochemistry of proximal colon indicated that Smad3/Rag2-DKO mice had increased numbers of proliferating epithelial cells (Ki67), and minimal differences in MHC Class II expression and numbers of F4/80+ macrophages relative to Smad3 KO mice. Our findings suggest that T and B lymphocytes are not required for the induction of colon cancer in Smad3-/- mice. Furthermore, our results suggest that Smad3-/- lymphocytes (likely regulatory T cells) were minimizing the degree of inflammation and restricting the location of tumors to the cecum and proximal colon. Studies are underway to delineate which regulatory cell populations are playing a role in reducing inflammation and tumor severity in Smad3/Rag2-DKO mice.
aPrincipal Investigator