Given the relevance of CSCs to tumourigenesis and metastasis more effective tumour therapies require a better knowledge of the ASP1517 HIF inhibitor characteristics of this subset of cancer cells and of the factors, extrinsic and intrinsic, which contribute to their ��stemness��. Assessing the relevance and physiological role of the ����stem cell Gefitinib markers���� to the stem cell phenotype will substantially increase our understanding of CSCs and should aid in devising selective therapies. Most importantly, Barker et al. have shown inmousemodels that intestinal tumours arise from LGR5 positive cells, suggesting it marks the intestinal cancer stem cells. LGR5 is overexpressed in human colorectal adenomas and carcinomas relative to normal mucosa : thus LGR5 overexpression is detected from the early stages of colorectal tumourigenesis. LGR5 is a wnt target gene, and the wnt pathway is activated early in the progression of the majority of colorectal cancers through truncations of APC and, less frequently, mutations of b-catenin. It is unclear, however, whether LGR5 upregulation in colorectal cancer cells contributes significantly to tumourigenesis through maintenance of colorectal CSC, or is simply a reflection of activated wnt signalling, with no direct functional role. Little is known about LGR5 function in development and carcinogenesis. LGR5 is an ��orphan�� receptor belonging to the Gprotein receptor coupled family ; its ligand and mode of intracellular signalling are at present unclear. Knockout of LGR5 in mice results in neonatal mortality associated with craniofacial defects . A thorough study by Garcia et al of prenatal intestinal development in GPR49- LacZ mutant mice shows that loss of LGR5 does not affect proliferation or migration of intestinal cells. However the authors noted a strong induction of Paneth cell differentiation in LGR5 knockout embryos, and a molecular signature characteristic of upregulated wnt signalling. As LGR5 appears to be a marker of CCRCs, we have investigated which parameters of cell growth and differentiation are affected by modulation of LGR5 expression in colorectal cancer cell lines. Due to the functional redundancy of many signalling molecules and the strong feedback loops that maintain homeostasis, these studies are difficult to interpret in animal models, while low transfection efficiencies and restrictions on longterm culture prevent these studies in human primary tumour samples. To circumvent these difficulties we have used two colorectal carcinoma cell lines, LIM1215 and LIM 1899 as a model system. Our results show that LGR5 silencing and overexpression have opposing effects on cell phenotype, including anchorage-independent growth, migration and tumour formation as xenografts in mice. Paradoxically, suppression of LGR5 expression enhances tumourigenesis and is linked to a more mesenchymal phenotype.