Natural Killer Cell-Derived Interferon-Gamma Promotes Hepatocellular Carcinoma Through the Epithelial Cell Adhesion Molecule-Epithelial-to-Mesenchymal Transition Axis in Hepatitis B Virus Transgenic Mice

Hepatitis B virus (HBV) is a major risk factor for development of hepatocellular carcinoma (HCC), at least partially due to dysfunctional anti-HBV adaptive immunity; however, the role of innate immune response to HBV in this process is not well understood. In this study, low-dose polyinosinic:polycytidylic acid (poly [I:C]), a natural killer (NK) cell activator (3 mu g/g body weight, twice/week for 8 weeks), induced HCC in HBV transgenic (HBs-Tg) mice, with an incidence of 100% after 6 months, while HBs-Tg mice without treatment only had HCC with an incidence of 16.7%. In HBs-Tg mice, poly (I:C) induced liver inflammation with markedly increased infiltrating lymphocytes, along with the concurrently increased apoptosis and proliferation of hepatocytes, leading to the accelerated epithelial-to-mesenchymal transition (EMT) of hepatocytes shown by increased expression of the typical transcriptional factors (Slug, Twist, and mothers against decapentaplegic-interacting protein 1) and phenotypic proteins (vimentin and chemokine [C-X-C motif] receptor 4). The EMT and tumorigenesis in this model depended on the presence of NK cells because depletion of these cells significantly reduced the HCC rate to 28.6%. Further, intrahepatic NK cells highly expressed interferon-gamma (IFN-gamma), anti-IFN-gamma neutralizing monoclonal antibody might obviously alleviate the hepatitis, and hepatocyte-specific IFN-gamma overexpression promoted HCC. Moreover, IFN-gamma deficiency in HBs-Tg mice prevented HCC occurring, though hepatic NK cells existed and could be activated, suggesting the critical role of IFN-gamma in NK cell-mediated tumorigenesis. In an in vitro experiment, IFN-gamma up-regulated epithelial cell adhesion molecule (EpCAM) expression through phosphorylated signal transducer and activator of transcription (p-STAT1) pathway, which was followed by EMT, and p-STAT1 inhibitor might absolutely abolish the expression of EpCAM and EMT in HBV surface antigen-positive hepatocytes. Conclusion: This work demonstrates that NK cell-derived IFN-gamma promotes HCC through the EpCAM-EMT axis in HBs-Tg mice, revealing the importance of innate immunity in pathogenesis of HBV-associated HCC.