BMI1 activates WNT signaling in colon cancer by negatively regulating the WNT antagonist IDAX

Aberrant activation of Wnt signaling plays a critical role in the development of colon cancer. BMI, a component of the polycomb repressive complex (PRC1), is upregulated in various types of cancer and contributes to epigenetic silencing of tumor suppressors. In this study, we showed that BMI1 is upregulated in colon cancer tissues and cell lines. Overexpression of BMI1 in primary epithelial colon cells promotes cellular growth and activates WNT pathway, while BMI1 silencing in colon cancer cells represses these effects. We also found that BMI1 binds to the promoter of IDAX, a Wnt antagonist, and decreases its transcription. Expression of IDAX is downregulated in colon cancer tissues and cell lines and negatively correlated with BMI1 in colon cancer tissues. Furthermore, Silencing of IDAX counteracts the effects of BMI1 suppression, while its overexpression reverses oncogenic effects of BMI1. Together, these findings indicate that BMI1-mediated IDAX epigenetic suppression is crucial for enhancement of colon carcinogenesis, suggesting that BMI1∖IDAX axis as a potential novel diagnostic and therapeutic target of colon cancer.