LGR5 Is a Negative Regulator of Tumourigenicity, Antagonizes Wnt Signalling and Regulates Cell Adhesion in Colorectal Cancer Cell Lines

Pierre-Antoine Defossez,Antony W. Burgess,Francesca Walker,Annalisa Odorizzi,Hui-Hua Zhang

doi:10.1371/journal.pone.0022733

Abstract

BackgroundLGR5 (Leucine-rich repeat-containing G-protein coupled receptor 5) is the most established marker for intestinal stem cells. Mouse models show that LGR5+ cells are the cells of origin of intestinal cancer, and LGR5 expression is elevated in human colorectal cancers, however very little is known about LGR5 function or its contribution to the stem cell phenotype and to colorectal cancer.Principal FindingsWe have modulated the expression of LGR5 by RNAi (inhibitory RNAs) or overexpression in colorectal cancer cell lines. Paradoxically, ablation of LGR5 induces increased invasion and anchorage-independent growth, and enhances tumourigenicity in xenografts experiments. Conversely, overexpression of LGR5 augments cell adhesion, reduces clonogenicity and attenuates tumourigenicity. Expression profiling revealed enhanced wnt signalling and upregulation of EMT genes upon knockdown of LGR5, with opposite changes in LGR5 overexpressing cells. These findings suggest that LGR5 is important in restricting stem cells to their niche, and that loss of LGR5 concomitant with activated wnt signalling may contribute to the invasive phenotype of colorectal carcinomas.

Highlights

The concept of cancer stem cells (CSCs: reviewed by [1]) arises from the heterogeneity of most solid tumours and their resistance to chemotherapeutic regimes: according to this concept, after treatment a residual population of drug-resistant cancer stem cells will survive and rapidly proliferate to re-establish the tumours ([2])
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
If overexpression of LGR5 in colorectal cancer cells is mediated by hyper-activated wnt pathway, what role does LGR5 play in wnt responses, and does expression of LGR5 contribute to the maintenance of ‘‘cancer stemness’’? To address the functional relevance of LGR5 expression in CRC cell lines, we reduced its expression in cells carrying a b-catenin mutation (LIM1215 and LIM1899) using inhibitory RNAs

Summary

Introduction

The concept of cancer stem cells (CSCs: reviewed by [1]) arises from the heterogeneity of most solid tumours and their resistance to chemotherapeutic regimes: according to this concept, after treatment a residual population of drug-resistant cancer stem cells will survive and rapidly proliferate to re-establish the tumours ([2]). Support for the existence of human CSCs is the presence, within the tumours, of cellular subsets expressing proteins usually only found on stem cells and lost upon differentiation; these proteins have been used to enrich for the putative CSCs in different tumour types, and to prove that tumour cells enriched for these markers gives rise to tumours with greater efficiency than the unselected population [4]. Assessing the relevance and physiological role of the ‘‘stem cell markers’’ to the stem cell phenotype will substantially increase our understanding of CSCs and should aid in devising selective therapies. Mouse models show that LGR5+ cells are the cells of origin of intestinal cancer, and LGR5 expression is elevated in human colorectal cancers, very little is known about LGR5 function or its contribution to the stem cell phenotype and to colorectal cancer

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