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Epithelial cell adhesion molecule promotes breast cancer resistance protein‐mediated multidrug resistance in breast cancer by inducing partial epithelial–mesenchymal transition

Overexpression of breast cancer resistance protein (BCRP) plays a crucial role in the acquired multidrug resistance (MDR) in breast cancer. The elucidation of molecular events that confer BCRP‐mediated MDR is of major therapeutic importance in breast cancer. Epithelial cell adhesion molecule (EpCAM) has been implicated in tumor progression and drug resistance in various types of cancers, including breast cancer. However, the role of EpCAM in BCRP‐mediated MDR in breast cancer remains unknown. In the present study, we revealed that EpCAM expression was upregulated in BCRP‐overexpressing breast cancer MCF‐7/MX cells, and EpCAM knockdown using siRNA reduced BCRP expression and increased the sensitivity of MCF‐7/MX cells to mitoxantrone (MX). The epithelial–mesenchymal transition (EMT) promoted BCRP‐mediated MDR in breast cancer cells, and EpCAM knockdown partially suppressed EMT progression in MCF‐7/MX cells. In addition, Wnt/β‐catenin signaling was activated in MCF‐7/MX cells, and the inhibition of this signaling attenuated EpCAM and BCRP expression and partially reversed EMT. Together, this study illustrates that EpCAM upregulation by Wnt/β‐catenin signaling induces partial EMT to promote BCRP‐mediated MDR resistance in breast cancer cells. EpCAM may be a potential therapeutic target for overcoming BCRP‐mediated resistance in human breast cancer.