Identification of Two Wnt-Responsive Elements in the Intron of RING Finger Protein 43 (RNF43) Gene

RING finger protein 43 (RNF43), an E3-type ubiquitin ligase, is frequently up-regulated in human colorectal cancer. It has been shown that expression of RNF43 is regulated by the Wnt-signaling pathway. However the regulatory region(s) for its transcriptional activation has not been clarified. In this study, we have shown for the first time that RNF43 is a direct target of TCF4/beta-catenin complex, and that its expression is regulated by a regulatory region containing two Wnt-responsive elements (WREs) in intron2. A reporter gene assay revealed that nucleotide substitutions in the WREs decreased the reporter activity in colon cancer cells, suggesting that both WREs are involved in the transcriptional activation. Knockdown of beta-catenin by siRNA suppressed the reporter activity. In addition, ChIP assay showed that both elements associate with TCF4/beta-catenin complex in colon cancer cells. These data indicate that expression of RNF43 is regulated by the canonical Wnt/beta-catenin pathway through binding of the WREs with TCF4/beta-catenin complex. These findings should be useful for the understanding of the regulatory mechanism of RNF43 and may contribute to the clarification of signaling pathways regulated by RNF43.