Upregulated YAP promotes oncogenic CTNNB1 expression contributing to molecular pathology of hepatoblastoma.

Hepatoblastoma (HB) is one of the most common cancers in children. Recent studies have shown that the occurrence of nuclear accumulation of β-catenin reaches 90%-100% because of the anomalous activation of the Wnt pathway in HB patients. Furthermore, emerging studies have shown that concomitant activated forms of YAP and β-catenin trigger the formation and progression of HB. YAP might play a vital role in β-catenin-mediated HB development. However, the molecular mechanisms by which YAP/TEAD4 transcription factor regulates CTNNB1 underlying HB pathogenesis are still unclear. YAP and CTNNB1 expression and correlation were analyzed by a combination of network enrichment analysis and gene set enrichment analysis of the public microarray datasets (GSE131329 and GSE81928). The protein levels of YAP and β-catenin were further validated by Western blotting in paired patients' samples. The direct interplay between YAP/TEAD4 and the promoter region of CTNNB1 was proven by the combination of dual-luciferase report assay and chromatin immunoprecipitation assay. YAP-conserved signature and WNT signaling pathway were significantly enriched in HB patients, with upregulated expression of YAP and β-catenin compared to non-HB patients. Further functional assays demonstrated that YAP/TEAD4 transcription factor complex could bind to the CTNNB1 promoter region directly to promote β-catenin expression and cell proliferation. Targeting the YAP/TEAD4 complex with a specific small-molecule compound markedly suppressed HepaG2 cell proliferation. As the upstream transcription factor of CTNNB1, YAP/TEAD4 is a promising target for the treatment of HB patients with high levels of YAP and β-catenin.