Identification of a novel role of ZMIZ2 protein in regulating the activity of the Wnt/β-catenin signaling pathway.

ZMIZ2, also named ZIMP7, is a protein inhibitor of activated STAT (PIAS)-like protein and a transcriptional coactivator. In this study, we investigated the interaction between ZMIZ2 and β-catenin, a key regulator of the Wnt signaling pathway. We demonstrated that the expression of exogenous ZMIZ2 augments TCF (T cell factor) and β-catenin-mediated transcription. In contrast, shRNA knockdown of ZMIZ2 expression specifically represses the enhancement of TCF/β-catenin-mediated transcription by ZMIZ2. Using Wnt3a-conditioned medium, we demonstrated that ZMIZ2 can enhance Wnt ligand-induced TCF/β-catenin-mediated transcription. We also showed a promotional role of ZMIZ2 in enhancing β-catenin downstream target gene expression in human cells and in Zmiz2 null (Zmiz2(-/-)) mouse embryonic fibroblasts (MEFs). The regulatory role of Zmiz2 in Wnt-induced TCF/β-catenin-mediated transcription can be restored in Zmiz2(-/-) MEFs that were infected with adenoviral expression vectors for Zmiz2. Moreover, enhancement of Zmiz2 on TCF/β-catenin-mediated transcription was further demonstrated in Zmiz2 knockout and Axin2 reporter compound mice. Furthermore, the protein-protein interaction between ZMIZ2 and β-catenin was identified by co-immunoprecipitation and in vitro protein pulldown assays. We also observed recruitment of endogenous ZMIZ2 onto the promoter region of the Axin 2 gene, a β-catenin downstream target promoter, in a Wnt ligand-inducible manner. Finally, a promotional role of ZMIZ2 on cell growth was demonstrated in human cell lines and Zmiz2 knockout MEFs. Our findings demonstrate a novel interaction between ZMIZ2 and β-catenin and elucidate a novel mechanism for PIAS-like proteins in regulating Wnt signaling pathways.