Abstract 3487: NOTCH/HES5 signaling exhibits distinct pro- and anti-tumorigenic roles in liver carcinogenesis

The NOTCH pathway is an evolutionary conserved signaling pathway that is known to play a pivotal role in physiological liver development and regeneration. Thereby, the NOTCH pathway controls cell fate decisions of bipotential liver progenitor cells promoting a biliary lineage rather than hepatic differentiation. Furthermore, aberrant NOTCH signaling is also a potential driver of liver inflammation, formation and progression of hepatocellular (HCC) and intrahepatic cholangiocarcinoma (iCCA). Previous studies mainly focused on the expression levels of the NOTCH receptors (NOTCH1-4) and their ligands (DLL1/3/4, JAG1/2). However, little is known regarding mutational effects within components of the Notch pathway and their relevance in liver cancer. In a whole exome sequencing approach of 54 human HCC samples, we discovered 19 amino acid-altering mutations in 15 different NOTCH pathway genes which were confirmed by Sanger sequencing to be somatic. In summary, these 15 mutations affected 25.9% of patients (14 out of 54 patients) and presented at least one mutation in one of the included NOTCH pathway components (NOTCH1/3/4, DLL1, DTX1/3/4, HES5, DVL2, LFNG, NUMB, NCSTN, DMXL2, GXYLT2). Consistently, 30% of HCC patients have been reported to contain a tumor-associated hyper-activated NOTCH pathway. Using multiple online tools to predict the effect of the mutations on protein function and tumor relevance, we observed that HES5-Arg31Gly mutation ranked highest. In order to test, whether HES5 is activated by NOTCH in HCC cells, we generated cell lines with inducible expression of NOTCH1 or NOTCH3 intracellular domain and found that the transcription factor HES5 but not HES1 is strongly activated in several HCC cell lines. Furthermore, induction of HES5 in an inducible Hep3B cell line resulted in increased expression of stem cell markers and epithelial-mesenchymal transition markers. In contrary, CCND1, HNF4alpha and HES1 were downregulated. Interestingly, HES5-Arg31Gly failed to modulate the expression of the here tested target genes. The loss of function of HES5-Arg31Gly may be partially explained by lower nuclear translocation of HES5-Arg31Gly protein. In vivo, mouse models using hydrodynamic transduction of transposons expressing MYC and HES5 indicated a tumor suppressive role of HES5, whereas, in AKT-driven liver tumorigenesis, HES5 exhibited oncogenic potential. Consistent with our in vitro experiments, AKT/HES5-driven murine tumors exhibited partial downregulation of HNF4alpha and upregulation of the cholangiocyte marker cytokeratin suggesting a transdifferentiation towards a cholangiocytic phenotype. Thus, we identified somatic mutations in NOTCH pathway genes in 25.9% of HCC patients. Our functional in vitro and in vivo analyses suggest that HES5 has oncogenic or tumor suppressive properties depending on the underlying oncogene or tumor subtype, respectively. Citation Format: Sarah Luiken, Matthias Bieg, Angelika Fraas, Raisatun Sugiyanto, Benjamin Goeppert, Stephan Singer, Stefan Pusch, Arianeb Mehrabi, Thomas Longerich, Peter Schirmacher, Stephanie K. Roessler. NOTCH/HES5 signaling exhibits distinct pro- and anti-tumorigenic roles in liver carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3487.