Autophagy of cancer stem cells is involved with chemoresistance of colon cancer cells

Abstract

Background: Chemoresistance is a major cause of treatment failure in colon cancer, and cancer stem cells have been found to be involved in the chemoresistance of colon cancer. However, the mechanisms driving the chemoresistance of colon cancer stem cells have not been addressed.

Methods: In this study, we investigated the cytotoxicity of paclitaxel in CD44(+)CD24(+) SW1222 colon cancer cells expressing Cdx1 (CD44(+)CD24(+)Cdx1(+) stem cells) and CD44(+)CD24(+) HCT116 colon cancer cells expressing wild-type p53 (CD44(+)CD24(+)p53wt stem cells).

Results: SW1222 cells were more resistant to paclitaxel-induced cytotoxicity than HCT116 cells. Conversely, HCT-116 cells had higher matrigel colony formation ability than SW1222 cells. The isolated CD44(+)CD24(+)Cdx1(+) cells showed higher resistance to paclitaxel-induced cytotoxicity than CD44(+)CD24(+)p53wt cells. The resistance of CD44(+)CD24(+)Cdx1(+) cells to paclitaxel is associated with upregulation of Cdx1 and Bcl-2 expression, caspase-3 activity, and the ratio of LC3-II/LC3-I. The sensitivity of CD44(+)CD24(+)p53wt cells to paclitaxel is associated with the downregulation of Bcl-2 expression, upregulation of Bax levels, and upregulation of caspase-3 activity. Silencing of Cdx1 expression and treatment with lysosomal inhibitor bafilomycin A increased paclitaxel-induced cytotoxicity in CD44(+)CD24(+)Cdx1(+) cells. Conversely, overexpression of Cdx1 decreased cell death in CD44(+)CD24(+)p53wt cells. Intratumoral injection of Cdx1 siRNA significantly inhibited tumor growth in a xenograft tumor model inoculated with CD44(+)CD24(+)Cdx1(+) cancer cells.

Conclusion: Cdx1 exerts a protective role in colon cancer stem cells, which play a crucial role in chemoresistance to paclitaxel through activation of autophagy. Autophagy is activated though the Cdx1-Bcl-2-LC3 pathway. In contrast, p53 exerts a major role in apoptosis and inhibits autophagy in colon cancer stem cells.