Abstract SY12-04: Wnt, Lgr5 stem cells, and cancer

Abstract

Abstract Lgr5 Stem Cells in self-renewal and cancer Hans Clevers Hubrecht Institute, Royal Netherlands Academy of Arts and Sciences & University Medical Centre Utrecht, Uppsalalaan 8, 3584 CT Utrecht, the Netherlands The intestinal epithelium is the most rapidly self-renewing tissue in adult mammals. Current models state that 4-6 crypt stem cells reside at the +4 position immediately above the Paneth cells in the small intestine; colon stem cells remain undefined (1). Lgr5/Gpr49 was selected from a panel of intestinal Wnt target genes for its restricted crypt expression. Two knock-in alleles revealed exclusive expression of Lgr5 in cycling, columnar cells at the crypt base. In addition, Lgr5 was expressed in rare cells in several other tissues. Using an inducible Cre knock-in allele and the Rosa26-LacZ reporter strain, lineage tracing experiments were performed in adult mice. The Lgr5+ve crypt base columnar cell (CBC) generated all epithelial lineages over a 14 month period, implying that it represents the stem cell of the small intestine and colon. The expression pattern of Lgr5 suggests that it marks stem cells in multiple adult tissues and cancers (2). We have established long-term culture conditions under which single crypts undergo multiple crypt fission events, whilst simultanously generating villus-like epithelial domains in which all differentiated cell types are present. Single sorted Lgr5+ve stem cells can also initiate these crypt-villus organoids. Tracing experiments indicate that the Lgr5+ve stem cell hierarchy is maintained in organoids. We conclude that intestinal crypt-villus units are self-organizing structures, which can be built from a single stem cell in the absence of a non-epithelial cellular niche (3). Intestinal cancer is initiated by Wnt pathway-activating mutations in genes such as APC. As in most cancers, the cell of origin has remained elusive. Deletion of APC in in Lgr5+ve stem cells leads to their transformation within days. Transformed stem cells remain located at crypt bottoms, while fueling a growing microadenoma. These microadenomas display unimpeded growth and develop into macroscopic adenomas within 4-6 weeks. When APC is deleted in short-lived Transit Amplifying (TA) cells using a different Cre mouse, the growth of the induced microadenomas rapidly stalls. Even after 30 weeks, large adenomas are very rare in these mice. We conclude that stem cell-specific loss of APC results in progressively growing neoplasia. Moreover, a stem cell/progenitor cell hierarchy is maintained in early stem cell-derived adenomas, lending support to the “cancer stem cell”-concept (4). In the stomach, Lgr5 expression is confined to a small population of cells at the gland base in the pyloric region, the gastroesophageal junction and the boundary between the corpus and squamous forestomach. This expression pattern mirrors that of the endogenous Wnt target gene Axin2. In-vivo lineage tracing reveals that the pyloric Lgr5+ve cells generate entire gastric units within 7-10 days and maintain this multipotent stem cell activity over at least 20 months. We conclude that Lgr5 is marking an active stem cell population at the base of the pyloric glands contributing to the long-term renewal of the gastric epithelium. Mutational activation of the Wnt pathway by APC deletion in these Lgr5+ve stem cells rapidly initiates tumor formation, implying a central role for Wnt signaling in self-renewal and cancer of the distal stomach (5). 1) Barker, N., van de Wetering, M., Clevers, H. The intestinal stem cell. Review Genes Dev. 22: 1856-1864. (2008) 2) Barker, N., Van Es, J.H., Kuipers, J., Kujala, P., Van den Born, M., Cozijnsen, M., Haegebarth, A., Korving, J., Begthel, H., Peters, P.J., Clevers, H. Identification of stem cells in small intestine and colon by the marker gene LGR5 Nature 449: 1003-1007 (2007) 3) Sato, T., Vries, R., Snippert, H., van de Wetering, M., Barker, N., Stange, D., van Es, J., Abo, A., Kujala, P., Peters, P., and Clevers, H. Single lgr5 gut stem cells build crypt-villus structures in vitro without a stromal niche. Nature 459 :262-265 (2009) 4) Barker, N., Ridgway, R.A., van Es, J.H.,van de Wetering, M., Begthel, H., van den Born, M., Danenberg, E., Clarke, A.R., Sansom, O.J., Clevers, H. Crypt Stem Cells as the Cells-of-Origin of Intestinal Cancer Nature 457: 608-611 (2009) 5) Barker, N., Huch et al. and H. Clevers Lgr5 Marks stomach stem cells Cell Stem Cell, in press Citation Format: Hans Clevers. Wnt, Lgr5 stem cells, and cancer [abstract]. In: Proceedings of the AACR 101st Annual Meeting 2010; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr SY12-04