Abstract 5205: Selectively high Wnt pathway activity in subpopulations of colon cancer cells and its significance for tumor initiation

Abstract

Abstract Several cell surface markers that are reported to enrich for tumor-initiating colon cancer cells are presumed targets of the canonical Wnt/beta-catenin pathway. Furthermore, colon cancers typically express the Wnt-effector beta-catenin in a heterogeneous pattern, with strong nuclear expression detected only in a small fraction of tumor cells. We therefore hypothesized that high beta-catenin expression and Wnt pathway activity mark a tumorigenic subpopulation. To label viable tumor cells according to the level of Wnt pathway activity, we constructed lentiviral vectors that express GFP under control of an optimal, beta-catenin-responsive TCF/LEF1 promoter (TOP-GFP). We transduced primary colon cancer xenografts and two well characterized colon cancer cell lines with these vectors, used flow cytometry to isolate cell subpopulations with differential GFP expression, and examined these subpopulations for tumorigenicity and gene expression. High GFP expression accurately marked tumor cells with nuclear beta-catenin immunostaining in Caco2 but not SW1222 cells and in a fraction of primary colon cancer xenografts. Gene expression analysis in the concordant cases was consistent with increased Wnt-pathway activity within the GFP-high cell population, including high expression of the putative stem cell markers CD133, CD44 and LGR5. In SW1222 cells and some primary tumor xenografts, the GFP-high fraction correlated poorly with nuclear beta-catenin localization and GFP flow cytometry did not separate cells with a gene expression profile suggesting Wnt pathway activity. Among these various sources, only Caco2 cells showed increased tumorigenicity of GFP-high cells in immunodeficient mouse xenografts. The utility of TOP-GFP and related reporters to identify tumor-initiating colon cancer cells with high Wnt activity thus varies among primary human colorectal tumors and established cell lines. Furthermore, Wnt pathway activity might fluctuate substantially within individual tumor cells. We conclude that high Wnt activity among tumor cell subpopulations does not necessarily signify tumor-initiating potential. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5205. doi:10.1158/1538-7445.AM2011-5205