Upregulation of miR-199a/b contributes to cisplatin resistance via Wnt/β-catenin-ABCG2 signaling pathway in ALDHA1+ colorectal cancer stem cells.

Cisplatin resistance in colorectal cancer largely results from the colorectal cancer stem cells which could be targeted to improve the efficacy of chemotherapy. MicroRNAs are possible modulators of cancer stem cell characteristics and maybe involved in the retention of cancer stem cell chemoresistance. The aim of this study was to investigate the biological function of miR-199a/b on cisplatin resistance in colorectal cancer stem cells and its related mechanisms. Here, ALDHA1+ cells from primary colorectal cancer tissues behaved similar to cancer stem cells and were chemoresistant to cisplatin. The presence of a variable fraction of ALDHA1 was detected in 9 out of 10 colorectal cancer specimens. Significantly, increased miR-199a/b expression was detected in ALDHA1+ colorectal cancer stem cells, accompanied by a downregulation of Gsk3β and an overexpression of β-catenin and ABCG2. In patient cohort, enhanced miR-199a/b expression in colorectal cancer tissues was associated with cisplatin response and poor patient survival. In addition, 80% of colorectal cancer samples showed lower level of Gsk3β than their adjacent normal counterparts. Furthermore, Gsk3β was the direct target of miR-199a/b. MiR-199a/b regulated Wnt/β-catenin pathway by targeting Gsk3β in ALDHA1+ colorectal cancer stem cells. By blocking Wnt/β-catenin pathway, we implied that ABCG2 lies downstream of Wnt/β-catenin pathway. ABCG2 was further demonstrated to contribute cisplatin resistance in ALDHA1+ colorectal cancer stem cells and can be regulated by miR-199a/b. Thus, our data suggested that upregulation of miR-199a/b in ALDHA1+ colorectal cancer stem cells contributed to cisplatin resistance via Wnt/β-catenin-ABCG2 signaling, which sheds new light on understanding the mechanism of cisplatin resistance in colorectal cancer stem cells and facilitates the development of potential therapeutics against colorectal cancer.