LGR5 promotes survival in human colorectal adenoma cells and is upregulated by PGE2: implications for targeting adenoma stem cells with NSAIDs

Cyclooxygenase-2 is overexpressed in the majority of colorectal tumours leading to elevated levels of prostaglandin E-2 (PGE(2)), promoting many hallmarks of cancer. Importantly, PGE(2) is reported to enhance Wnt/-catenin signalling in colorectal carcinoma cells and in normal haematopoietic stem cells where it promotes stem cell function. Although Wnt signalling plays a crucial role in intestinal stem cells, the relationship between PGE(2) and intestinal stem cells is unclear. Given that the key intestinal cancer stem cell marker LGR5 (leucine-rich G-protein coupled receptor 5) is a Wnt target and PGE(2) enhances Wnt signalling, the focus of this study was to investigate whether PGE(2) regulated LGR5 expression in colorectal adenoma cells and whether LGR5 was important for tumour cell survival. PGE(2) upregulated LGR5 protein in adenoma (RG/C2) and carcinoma (DLD-1) cell lines. LGR5 knockdown induced cell death in RG/C2 and AA/C1 adenoma cells, suggesting that LGR5 has an important survival-promoting role in adenoma cells. Indeed, we detected LGR5 protein expression in 4 of 4 human adenoma cell lines. Furthermore, LGR5 small interfering RNA inhibited the survival-promoting effects of PGE(2) in RG/C2, suggesting that PGE(2) promotes adenoma cell survival, at least in part, by increasing LGR5 expression. These studies, therefore, show the first link between PGE(2) and LGR5 in human colorectal adenoma and carcinoma cells and demonstrate a survival-promoting role of LGR5. As non-steroidal anti-inflammatory drugs (NSAIDs) cause adenomas to regress in FAP patients, these studies could have important implications for the mechanism by which NSAIDs are chemopreventive, as lowering PGE(2) levels could reduce LGR5 expression and survival of LGR5 adenoma stem cells.