Hepatitis c virus infection induces pro- and antiapoptotic cell response: who is the winner?

Introduction: Apoptosis plays a central role in chronic hepatitis C virus (HCV) infection. Although the activation of cell death signals has been reported, HCV infection persists in most patients suggesting a pro-survival adaptation, eventually developing hepatocellular carcinoma. This study focused on the role of mitochondria in the activation of pro- and antiapoptotic response in cells expressing HCV proteins. Materials and Methods: Human Osteosarcoma U2-OS cells inducibly expressing the HCV polyprotein; huh7.5 hepatoma cells transfected with full length HCV genome. Results: Long term induction of viral proteins in U2-OS cells induced a cyclosporine A-sensitive cytochrome c partial release from mitochondria, revealed by immunofluorescence, western blot and spectral analysis. In HCV-transfected Huh7.5 cells, release of the apoptosis inducing factor (AIF) with no apparent nuclear translocation was also observed. HCV positive cells displayed an HIF-dependent enhanced glycolysis, charachterized by up-regulation of the mitochondria-bound Hexokinase II (HKII); preliminary data on signal transduction pathway revealed the iperphosphorylation of Glycogen synthase kinase 3b(GSK3b). Conclusion: HCV causes a cell stress activating an early apoptotic response, the entity of which likely depends on the cell type. Nevertheless a wide series of cell survival mechanisms are also triggered resulting in a metabolic adaptation possibly favouring carcinogenesis. Based on our results, we propose a pro-survival mechanism linking HCV infection to inhibition of GSK-3b, stabilization of HIF1a and up-regulation of HKII, the last events causing a glycolytic shift and protecting from apoptosis.