Notch activity characterizes a common hepatocellular carcinoma subtype with unique molecular and clinicopathologic features.

Abstract Background & Aims Hepatocellular carcinoma (HCC) is an increasing cause of cancer-related deaths worldwide, due in part through prevalent obesity-related nonalcoholic steatohepatitis (NASH). Hepatocyte Notch pathway is a pathogenic factor to NASH-associated fibrosis, but its role in HCC is less defined. We characterized the molecular and clinical features of Notch-active human HCC, and investigated the mechanisms of how Notch affects NASH-driven HCC. Methods Using a 14-gene Notch score, we stratified human HCCs in multiple datasets with comprehensive profiling. We performed gene set enrichment analyses comparing Notch-active HCCs to published HCC subtype signatures. Next, we sorted Notch-active hepatocytes from Notch reporter mice for RNA sequencing to study how Notch activation contributes to tumorigenesis in NASH, and characterized Notch-active tumors in a HCC model combining carcinogen and 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 with lack of activating CTNNB1 (β-catenin) mutations and overall poor prognosis. Endogenous Notch activation in hepatocytes is associated with repressed β-catenin signaling and hepatic metabolic functions, in lieu of increased interactions with 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 the tumor development reliant on β-catenin. Conclusions Notch activity characterizes a distinct HCC molecular subtype with unique histology and prognosis. Sustained Notch signaling in chronic liver diseases is a driver of tumor formation without acquiring specific genomic mutations.