Hepatitis C virus nonstructural protein 5A inhibits tumor necrosis factor-α-mediated apoptosis in Huh7 cells

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) - alpha. The viability of control Huh7 cells was reduced to 40%, compared with untreated cells, after TNF- alpha 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 - κB 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- α upstream of caspase- 8 in the apoptosis cascade.