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EpCAM-regulated intramembrane proteolysis induces a cancer stem cell-like gene signature in hepatitis B virus-infected hepatocytes

      Background & Aims

      Hepatocytes in which the hepatitis B virus (HBV) is replicating exhibit loss of the chromatin modifying polycomb repressive complex 2 (PRC2), resulting in re-expression of specific, cellular PRC2-repressed genes. Epithelial cell adhesion molecule (EpCAM) is a PRC2-repressed gene, normally expressed in hepatic progenitors, but re-expressed in hepatic cancer stem cells (hCSCs). Herein, we investigated the functional significance of EpCAM re-expression in HBV-mediated hepatocarcinogenesis.

      Methods

      Employing molecular approaches (transfections, fluorescence-activated cell sorting, immunoblotting, qRT-PCR), we investigated the role of EpCAM-regulated intramembrane proteolysis (RIP) in HBV replicating cells in vitro, and in liver tumors from HBV X/c-myc mice and chronically HBV infected patients.

      Results

      EpCAM undergoes RIP in HBV replicating cells, activating canonical Wnt signaling. Transfection of Wnt-responsive plasmid expressing green fluorescent protein (GFP) identified a GFP + population of HBV replicating cells. These GFP+/Wnt+ cells exhibited cisplatin- and sorafenib-resistant growth resembling hCSCs, and increased expression of pluripotency genes NANOG, OCT4, SOX2, and hCSC markers BAMBI, CD44 and CD133. These genes are referred as EpCAM RIP and Wnt-induced hCSC-like gene signature. Interestingly, this gene signature is also overexpressed in liver tumors of X/c-myc bitransgenic mice. Clinically, a group of HBV-associated hepatocellular carcinomas was identified, exhibiting elevated expression of the hCSC-like gene signature and associated with reduced overall survival post-surgical resection.

      Conclusions

      The hCSC-like gene signature offers promise as prognostic tool for classifying subtypes of HBV-induced HCCs. Since EpCAM RIP and Wnt signaling drive expression of this hCSC-like signature, inhibition of these pathways can be explored as therapeutic strategy for this subtype of HBV-associated HCCs.

      Lay summary

      In this study, we provide evidence for a molecular mechanism by which chronic infection by the hepatitis B virus results in the development of poor prognosis liver cancer. Based on this mechanism our results suggest possible therapeutic interventions.

      Graphical abstract

      Abbreviations:

      cccDNA (circular covalently closed DNA), EpCAM (epithelial cell adhesion molecule), EpICD (EpCAM intracellular domain), hCSCs (hepatic cancer stem cells), HBV (hepatitis B virus), HBc (hepatitis B virus core antigen), HCC (hepatocellular carcinoma), PRC2 (polycomb repressor complex 2), RIP (regulated intramembrane proteolysis)

      Keywords

      Linked Article

      • Stemness of liver cancer: From hepatitis B virus to Wnt activation
        Journal of HepatologyVol. 65Issue 5
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          Hepatocellular carcinoma (HCC) is a heterogeneous disease in terms of etiology, morphology, biological behavior, response to treatment, and clinical outcome. Efforts have been made on classifying HCCs according to the status of gene mutations, chromosomal aberrations, gene/protein expression, and epigenetic modification in order to find hidden molecular features that can explain this heterogeneity [1,2]. The recent advances in molecular classification and the re-emergence of a cancer stem cell (CSC) hypothesis have highlighted the central role of stemness in HCC pathogenesis [3].
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