ß-Catenin mutations as determinants of hepatoblastoma phenotypes in mice.

Hepatoblastoma (HB) is the most common pediatric liver cancer. Although long-term survival of HB is generally favorable, it depends on clinical stage, tumor histology, and a variety of biochemical and molecular features. HB appears almost exclusively before the age of 3 years, is represented by seven histological subtypes, and is usually associated with highly heterogeneous somatic mutations in the catenin ß1 (CTNNB1) gene, which encodes ß-catenin, a Wnt ligand-responsive transcriptional co-factor. Numerous recurring ß-catenin mutations, not previously documented in HB, have also been identified in various other pediatric and adult cancer types. Little is known about the underlying factors that determine the above HB features and behaviors or whether non-HB-associated ß-catenin mutations are tumorigenic when expressed in hepatocytes. Here, we investigated the oncogenic properties of 14 different HB- and non-HB-associated ß-catenin mutants encoded by Sleeping Beauty vectors following their delivery into the mouse liver by hydrodynamic tail-vein injection. We show that all ß-catenin mutations, as well as WT ß-catenin, are tumorigenic when co-expressed with a mutant form of yes-associated protein (YAP). However, tumor growth rates, histologies, nuclear-to-cytoplasmic partitioning, and metabolic and transcriptional landscapes were strongly influenced by the identities of the ß-catenin mutations. These findings provide a context for understanding at the molecular level the notable biological diversity of HB.

Patient-Derived Mutant Forms of NFE2L2/NRF2 Drive Aggressive Murine Hepatoblastomas.

BACKGROUND & AIMS: Hepatoblastoma (HB), the most common pediatric liver cancer, often bears ß-catenin mutations and deregulates the Hippo tumor suppressor pathway. Murine HBs can be generated by co-expressing ß-catenin mutants and the constitutively active Hippo effector YAPS127A. Some HBs and other cancers also express mutants of NFE2L2/NRF2 (NFE2L2), a transcription factor that tempers oxidative and electrophilic stress. In doing so, NFE2L2 either suppresses or facilitates tumorigenesis. METHODS: We evaluated NFE2L2's role in HB pathogenesis by co-expressing all combinations of mutant ß-catenin, YAPS127A, and the patient-derived NFE2L2 mutants L30P and R34P in murine livers. We evaluated growth, biochemical and metabolic profiles, and transcriptomes of the ensuing tumors. RESULTS: In association with ß-catenin+YAPS127A, L30P and R34P markedly accelerated HB growth and generated widespread cyst formation and necrosis, which are otherwise uncommon features. Surprisingly, any 2 members of the mutant ß-catenin-YAPS127A-L30P/R34P triad were tumorigenic, thus directly establishing NFE2L2's oncogenicity. Each tumor group displayed distinct features but shared 22 similarly deregulated transcripts, 10 of which perfectly correlated with survival in human HBs and 17 of which correlated with survival in multiple adult cancers. One highly up-regulated transcript encoded serpin E1, a serine protease inhibitor that regulates fibrinolysis, growth, and extracellular matrix. Although the combination of mutant ß-catenin, YAPS127A, and serpin E1 did not accelerate cystogenic tumor growth, it did promote the widespread necrosis associated with mutant ß-catenin-YAPS127A-L30P/R34P tumors. CONCLUSIONS: Our findings establish the direct oncogenicity of NFE2L2 mutants and key transcripts, including serpin E1, that drive specific HB features.