Proapoptotic effect of hepatitis C virus CORE protein in transiently transfected cells is enhanced by nuclear localization and is dependent on PKR activation

BACKGROUND/AIMS: HCV-CORE protein has been implicated in the regulation of apoptosis of infected cells acting as full-length or C-terminus deleted forms and resulting in both proapoptotic and antiapoptotic effects in different experimental conditions. METHODS: We have fused full-length and C-terminus deleted CORE with GFP to assess intracellular localization in transiently transfected cell lines and primary hepatocytes. Apoptosis of cells expressing different levels of chimeric proteins was quantified by cytometry. RESULTS: Full-length CORE localized mainly in the cytoplasm, but nuclear staining was also observed, being more evident in primary human hepatocytes. Nuclear staining only was observed in cells expressing truncated CORE. Full-length CORE induced apoptosis in approximately 15-20% of transfected cells with low expression and in approximately 40-50% of those with high expression of viral protein. Interestingly, 40-50% of cells transfected with truncated CORE underwent apoptosis, independently of protein expression levels. CORE-induced apoptosis was significantly reduced in the presence of a protein kinase R (PKR) inhibiting peptide and truncated CORE was able to enhance translocation of PKR into nucleoli where CORE/PKR colocalization was observed. CONCLUSIONS: These results suggest that nuclear forms of HCV-CORE are generated in vivo in primary hepatocytes and induce PKR-dependent apoptosis, a mechanism that might have a relevant role during natural infection.