LGR5 promotes survival in human colorectal adenoma cells and is upregulated by PGE 2 : implications for targeting adenoma stem cells with NSAIDs

Abstract

Cyclooxygenase-2 is overexpressed in the majority of colorectal tumours leading to elevated levels of prostaglandin E2 (PGE2), promoting many hallmarks of cancer. Importantly, PGE2 is reported to enhance Wnt/β-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 PGE2 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 PGE2 enhances Wnt signalling, the focus of this study was to investigate whether PGE2 regulated LGR5 expression in colorectal adenoma cells and whether LGR5 was important for tumour cell survival. PGE2 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 PGE2 in RG/C2, suggesting that PGE2 promotes adenoma cell survival, at least in part, by increasing LGR5 expression. These studies, therefore, show the first link between PGE2 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 PGE2 levels could reduce LGR5 expression and survival of LGR5(+) adenoma stem cells.

Prognostic Value of Immunohistochemical Expressions of the Stem Cell Biomarker "LGR5" and the Proliferation Biomarker "TPX2" in Colorectal Carcinoma

“…Our results suggest that LGR5 is involved in the growth and progression of CRC and it may be an important biological marker of its invasion and metastasis. Our results are consistent with previous studies proving that overexpression of LGR5 was associated with poor prognosis in CRC [26][27][28][29] . The current results also are consistent with studies done in other organs stating that LGR5 overexpression is associated with poor prognosis and metastasis-initiating potentials in breast cancer, glioblastoma, lung cancer and esophageal adenocarcinoma [30][31][32][33] .…”

Cancer stem cells in human digestive tract malignancies

“…These reports are in agreement with other experiments indicating a significant decrease in survival [203], drug resistance [204], proliferation, migration, and tumorigenic abilities [205] of CRC cells upon LGR5 knockdown. Moreover, clinical analysis demonstrated enhanced expression of LGR5 in CRC tissues, although its association with clinicopathological features is controversial; based on a number of reports, LGR5 expression was correlated to progression, lymph node and distant metastasis, recurrence, clinical outcomes, and survival rate of CRC [197,198,204,[206][207][208][209][210][211][212], whereas other studies indicated an inverse correlation [213] or no association [214,215] between LGR5 upregulation and CRC progression.…”

“…In addition, NANOG-siRNA transfection induced apoptosis and enhanced chemosensitivity of ESCC cells [106], similar to downregulation of SOX2 with siRNA, which reduced colony forming, drug resistance, and in vivo tumorigenicity of gastric CSCs [149]. Reports have also demonstrated that RNAi targeting LGR5 in CRC-SCs enhanced drug sensitivity of cells [202,204], while decreased their survival, proliferation [203][204][205], migration, and tumorigenic [205] abilities.…”

The Evolving Role of Nonsteroidal Anti-Inflammatory Drugs in Colon Cancer Prevention: A Cause for Optimism

“…Interestingly, the anti-colon cancer stem cell effect of NSAIDs is mediated through both COX-dependent and -independent pathways (Moon et al, 2014). Paraskeva has elegantly linked PGE 2 with colon adenoma and carcinoma stem cells by showing that the former promotes the survival of the latter (Al- Kharusi et al, 2013). Although it appears that the definitive mechanism by which NSAIDs prevent CRC is far from complete, it is fair to state that its broad outlines have been identified and a deeper understanding should be forthcoming.…”