Abstract
BACKGROUND & AIMS: The hepatocyte Notch pathway is a pathogenic factor in non-alcoholic steatohepatitis (NASH)-associated fibrosis, but its role in hepatocellular carcinoma (HCC) is less well defined. Herein, we aimed to characterize the molecular and clinical features of Notch-active human HCC, and to investigate the mechanisms by which Notch affects NASH-driven HCC. METHODS: Using a 14-gene Notch score, we stratified human HCCs from multiple comprehensively profiled datasets. We performed gene set enrichment analyses to compare Notch-active HCCs with published HCC subtype signatures. Next, we sorted Notch-active hepatocytes from Notch reporter mice for RNA sequencing and characterized Notch-active tumors in an HCC model combining a carcinogen and a NASH-inducing diet. We used genetic mouse models to manipulate hepatocyte Notch to investigate the sufficiency and necessity of Notch in NASH-driven tumorigenesis. RESULTS: Notch-active signatures were found in ~30% of human HCCs that transcriptionally resemble cholangiocarcinoma-like HCC, exhibiting a lack of activating CTNNB1 (β-catenin) mutations and a generally poor prognosis. Endogenous Notch activation in hepatocytes is associated with repressed β-catenin signaling and hepatic metabolic functions, in lieu of increased interactions with the extracellular matrix in NASH. Constitutive hepatocyte Notch activation is sufficient to induce β-catenin-inactive HCC in mice with NASH. Notch and β-catenin show a pattern of mutual exclusivity in carcinogen-induced HCC; in this mouse model, chronic blockade of Notch led to β-catenin-dependent tumor development. CONCLUSIONS: Notch activity characterizes a distinct HCC molecular subtype with unique histology and prognosis. Sustained Notch signaling in chronic liver diseases can drive tumor formation without acquiring specific genomic driver mutations. LAY SUMMARY: The Notch signaling pathway is known to be involved in the pathogenesis of liver fibrosis. However, its role in liver cancer has not been well defined. Herein, we show that Notch activity is increased in a subset of liver cancers and is associated with poor outcomes. We also used a mouse model to show that aberrant Notch activity can drive cancer progression in obese mice.