Chemotherapy failure is a major problem in patients with advanced colorectal carcinoma (CRC). Leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5) is a well-established target gene of the Wnt pathway and is a bona fide marker of CRC cancer stem cells (CSCs). Our previous study showed that CRC patients with higher Lgr5 level are associated with poor response to 5-fluoracil-based treatment. In this study, we investigated the mechanisms underlying Lgr5-associated chemoresistance in cancer stem cells derived from cultured CRC cells.

Cancer stem cells were isolated from CRC cell lines by spheroid culture. The effect of Lgr5 on CRC cancer stem cell was investigated using both gain- and loss-of-function approaches. Stemness property was evaluated using sphere formation assay, side population analysis, and stem cell marker expression. Lgr5 and ABCB1 expression in CRC tissues was determined using immunohistochemical staining.

Forced expression of Lgr5 increased the CRC sphere-forming efficiency and spheroid size while depletion of Lgr5 reduced the stem cell property in cultured CRC cells. Over-expression of Lgr5 also reduced the sensitivity of cultured CRC cells, including adherent and spheroids, towards 5-fluoracil and oxalipatin. In addition, Lgr5 positively regulates the expression of ABCB1 in both adherent and spheroid CRC cells. Finally, in human CRC tissues, higher expression levels of Lgr5 were associated with higher ABCB1 expression.

The present study demonstrated that Lgr5 plays an active role in promoting the cancer stem cell property and that Lgr5 confers chemoresistance to CRC cells via ABCB1 induction.