Abstract LB-362: Both canonical and non-canonical autocrine Wnt signaling regulates clonogenic growth and epithelial-mesenchymal transition in colon cancer cells lacking mutational activation of Wnt pathway

Abstract Introduction: Wnt signaling in cells with mutationally-induced constitutive pathway activation promotes clonogenic growth and epithelial-mesenchymal transition (EMT). The role of autocrine Wnt signals in colon cancer cells lacking a Wnt pathway activating mutation is less clear. Hypothesis: Extracellular Wnt inhibitors will reduce clonogenic growth and EMT in colon cancer cell lines lacking mutational Wnt pathway activation by inhibiting basal levels of autocrine Wnt signaling. Methods: Two cells lines were utilized: HCT116B is a colon cancer cell line in which an abnormal beta-catenin allele has been removed by homologous recombination; RKO is a colon cancer cell line with no known Wnt pathway activation. The Wnt inhibitors DKK1, which blocks canonical Wnt signals by interaction with LRP5 and sFRP1 which blocks both canonical and non-canonical Wnt signals were utilized and transfected into each cell line. Canonical Wnt throughput was measured with a luciferase based reporter construct, clonogenic growth by colony formation in soft agar and EMT by morphology. Results: Untransfected HCT116B, but not RKO expressed DKK1. Neither cell line expressed sFRP1. Both cell lines expressed significant quantities of DKK1 or sFRP1 after transfection. Canonical Wnt signaling was suppressed in RKO by both DKK1 and sFRP1 but only by DKK1 in HCT116B. DKK1 inhibited clonogenic growth in RKO but not in HCT116B, while sFRP1 inhibited it in both cell lines. EMT was clearly suppressed by these inhibitors in RKO; such an effect was less visible in HCT116B. Discussion: Colon cancer cells lacking mutational activation of the Wnt pathway are susceptible to the actions of extracellular Wnt inhibitors, presumably via inhibition of autocrine Wnt signals and canonical Wnt signaling. However, cells with basal expression of a canonical Wnt inhibitor such as DKK1 (HCT116B) rely preferentially on non-canonical pathways for clonogenic growth and EMT which can be blocked by global Wnt ligand antagonists such as sFRP1. The importance of autocrine Wnt signaling and contributions by non-canonical pathways to clonogenic growth and EMT has important implications for the development of Wnt-targeted therapeutic agents for colon cancer. 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 LB-362. doi:10.1158/1538-7445.AM2011-LB-362