Regulation of ATP-binding cassette subfamily B member 1 by Snail contributes to chemoresistance in colorectal cancer.

Although accumulating evidence has indicated the intimate association between epithelial-mesenchymal transition (EMT) and acquired resistance to chemotherapy for colorectal cancer (CRC), the underlying mechanisms remain elusive. Herein, we reported that Snail, a crucial EMT controller, was upregulated in CRC tissues. Colorectal cancer cells overexpressing Snail were found to be more resistant to 5-fluorouracil (5-Fu). Mechanistic studies reveal that Snail could increase the expression of ATP-binding cassette subfamily B member 1 (ABCB1) rather than the other 23 chemoresistance-related genes. Additionally, knockdown of ABCB1 significantly attenuated Snail-induced 5-Fu resistance in CRC cells. Oxaliplatin increased Snail and ABCB1 expression in CRC cells. Snail and ABCB1 were upregulated in 5-Fu-resistant HCT-8 (HCT-8/5-Fu) cells and inhibition of Snail decreased ABCB1 in HCT-8/5-Fu cells. These results confirm the vital role played by ABCB1 in Snail-induced chemoresistance. Further investigation into the relevant molecular mechanism revealed Snail-mediated ABCB1 upregulation was independent of β-catenin, STAT3, PXR, CAR and Foxo3a, which are commonly involved in modulating ABCB1 transcription. Instead, Snail upregulated ABCB1 transcription by directly binding to its promoter. Clinical analysis confirms that increased Snail expression correlated significantly with tumor size (P = .018), lymph node metastasis (P = .033), distant metastasis (P = .025), clinical stage grade (P = .024), and poor prognosis (P = .045) of CRC patients. Moreover, coexpression of Snail and ABCB1 was observed in CRC patients. Our study revealed that direct regulation of ABCB1 by Snail was critical for conferring chemoresistance in CRC cells. These findings unraveled the mechanisms underlying the association between EMT and chemoresistance, and provided potential targets for CRC clinical treatment.