The MyoD family inhibitor domain-containing protein enhances the chemoresistance of cancer stem cells in the epithelial state by increasing β-catenin activity.

Cancer cells with mesenchymal attributes potentially display chemoresistance. Cancer stem cells (CSCs), which are intrinsically resistant to most chemotherapy agents, exhibit considerable phenotypic heterogeneity in their epithelial versus mesenchymal states. However, the drug response of CSCs in the epithelial and mesenchymal states has not been completely investigated. In this study, we found that epithelial-type (E-cadherinhigh/CD133high) CSCs displayed a higher sphere formation ability and chemoresistance than mesenchymal-type (E-cadherinlowCD133high) CSCs. Gene expression profiling of the CSC and non-CSC subpopulations with distinct epithelial-to-mesenchymal transition (EMT) states showed that MyoD family inhibitor domain-containing (MDFIC) was selectively upregulated in epithelial-type CSCs. Knockdown of MDFIC sensitized epithelial-type CSCs to chemotherapy agents. Ectopic expression of MDFIC increased the chemoresistance of mesenchymal-type CSCs. In a tissue microarray, high MDFIC expression was associated with poor prognosis of non-small cell lung cancer (NSCLC) patients. A mechanistic study showed that the MDFIC p32 isoform, which is located in the cytoplasm, interacted with the destruction complex, Axin/GSK-3/β-catenin. This interaction stabilized β-catenin by inhibiting β-catenin phosphorylation at S33/37 and increased the nuclear translocation and transcriptional activity of β-catenin. Knockdown of β-catenin decreased MDFIC-enhanced chemoresistance. These results suggested that the upregulation of MDFIC enhanced the chemoresistance of epithelial-type CSCs by elevating β-catenin activity. Thus, targeting MDFIC-regulated β-catenin signaling of epithelial-type CSCs may be a potential strategy to overcome chemoresistance in NSCLC.