Abstract
Epigenetic activation of Wnt/β-catenin signaling plays a critical role in Wnt-induced tumorigenesis, notably in colorectal cancers. KDM3 and KDM4 histone demethylases have been reported to promote oncogenic Wnt signaling through demethylation of H3K9 on Wnt target gene promoters and are suggested to be potential therapeutic targets. However, potent inhibitors for these regulators are still not available. In addition, which family is most responsible for activation of Wnt target genes and Wnt-induced oncogenesis is not well documented, specifically in colorectal cancer. In this study, we characterized the functional redundancy and differences between KDM3 and KDM4 in regard to regulating Wnt signaling. Our data suggest that KDM3 may play a more essential role than KDM4 in regulating oncogenic Wnt signaling in human colorectal cancer. We also identified that IOX1, a known histone demethylase inhibitor, significantly suppresses Wnt target gene transcription and colorectal cancer tumorigenesis. Mechanistically, IOX1 inhibits the enzymatic activity of KDM3 by binding to the Jumonji C domain and thereby preventing the demethylation of H3K9 on Wnt target gene promoters. Taken together, our data not only identified the critical mechanisms by which IOX1 suppressed Wnt/β-catenin signaling and colorectal cancer tumorigenesis through inhibition of KDM3, but also suggested that IOX1 may represent an attractive small molecule lead for future drug design and discovery.