Hepatitis C Virus Nonstructural Protein 5A Inhibits Tumor Necrosis Factor–a–Mediated Apoptosis

To analyze the influence of hepatitis C virus nonstructural protein 5A (NS5A) on apoptosis, we established Huh7 cells that stably express NS5A, and induced apoptosis using tumor necrosis factor (TNF)–a. The viability of control Huh7 cells was reduced to 40%, compared with untreated cells, after TNF-a treatment, whereas that of Huh7-NS5A cells was reduced only to 80%. DNA fragmentation also decreased to!50 % in Huh7-NS5A compared with control cells. Nuclear factor–kB activation was the same in both cell types, whereas caspase-8,-9, and-3 activity was decreased in Huh7-NS5A cells, compared with control cells, which indicates that the inhibition of caspase-8 activation is responsible for the antiapoptotic effect of the NS5A protein. The coexpression of NS5A did not inhibit apoptosis induced by caspase-8 or Fas-associating death domain protein expression. These findings suggest that the NS5A protein inhibits the apoptotic effect of TNF-a upstream of caspase-8 in the apoptosis cascade. Hepatitis C virus (HCV) has been identified as a major causative agent of acute and chronic hepatitis [1]. As many as 85 % of HCV-infected patients remain persis-tently infected [2], and chronic HCV infection is as-sociated with cirrhosis and hepatocellular carcinom