Phosphorylation-Mediated Activation of β-Catenin-TCF4-CEGRs/ALCDs Pathway Is an Essential Event in Development of Aggressive Hepatoblastoma

SIMPLE SUMMARY: Pediatric liver cancer hepatoblastoma has a low rate of genetic mutations, suggesting additional mechanisms that involve epigenetics and signal transduction pathways. In this paper, we present evidence showing that the phosphorylation-dependent activation of wildtype β-catenin leads to the opening of genomic regions (called CEGRs/ALCDs) of oncogenes in HBL patients and to the subsequent development of liver cancer. The main activities of the ph-S675-β-catenin-CEGR/ALCD pathway are associated with the promotion of mitosis and proliferation of cancer cells. This study provides mutation-independent mechanisms that are involved in the development of aggressive HBL. ABSTRACT: Background and Aims: Hepatoblastoma (HBL), a deadly malignancy in children, is the most common type of pediatric liver cancer. We recently demonstrated that β-catenin, phosphorylated at S675 (ph-S675-β-catenin), causes pathological alterations in fibrolamellar hepatocellular carcinoma (FLC), by activating oncogenes and fibrotic genes via human genomic regions, known as cancer-enhancing genomic regions or aggressive liver cancer domains (CEGRs/ALCDs). The aim of this study was to determine the role of the ph-S675-β-catenin-TCF4-CEGRs/ALCDs pathway in HBL. Methods: The ph-S675-β-catenin-TCF4-CEGRs/ALCDs pathway was examined in a large cohort of HBL specimens, in HBL cell lines HepG2 and Huh6, and in patient-derived xenografts (PDXs). Results: β-catenin is phosphorylated at S675 in a large portion of tested HBL patients. In these patients, ph-S675-β-catenin forms complexes with TCF4 and opens CEGRs/ALCDs-dependent oncogenes for transcription, leading to a massive overexpression of the oncogenes. The inhibition of the β-catenin-TCF4-CEGRs/ALCDs axis inhibits the proliferation of cancer cells and tumor growth in HBL cell lines and HBL-PDXs. The ph-S675-β-catenin is abundant in mitotic cells. We found that markers of HBL Glypican 3 (GPC3) and Alpha Fetoprotein (AFP) are increased in HBL patients by β-catenin-TCF4-p300 complexes. Conclusions: The phosphorylation-mediated activation of the β-catenin-TCF4-p300-CEGRs/ALCDs pathway increases oncogene expression in patients with aggressive liver cancer and promotes the development of hepatoblastoma.