HCV non-structural NS4A protein of genotype 3a induces mitochondria mediated death by activating Bax and the caspase cascade

Abstract

Currently almost 170 million of the world population is suffering with Hepatitis C virus (HCV) that is the major cause of liver diseases, which leads to liver fibrosis, cirrhosis and hepatocellular carcinoma. Approximately 6% of the Pakistani population is chronically infected with HCV, with genotype 3a being the most prominent strain in Pakistan. Complex of HCV non-structural proteins NS3-4A plays an important role in the viral replication machinery that together has serine protease and helicase activity. Genetic heterogeneity within HCV genotypes makes it pertinent to assess the apoptotic pathway within different HCV genotypes. Findings of present study reveal that HCV genotype 3a NS4A and NS3-NS4A induce cell death in Huh-7 cells. Moreover, our results demonstrated that NS3-4A and NS4A proteins were not only localized on ER but also on the mitochondria. Bax a pro-apoptotic protein was found translocated to the mitochondria in the transfected cells, while up-regulated expression of Bax and down-regulated expression of anti-apoptotic Bcl-xL protein was also observed in the presence of NS4A and NS3-4A proteins. High level of mitochondrial superoxide generation was observed in the transfected cells and NS3-4A and NS4A triggered a cascade of activation starting from caspase-9, then caspase-7 and caspase-3 that ultimately led to the cleavage of poly (ADP-ribose) polymerase PARP. Collectively findings of the present study suggest that NS4A and co-expression of NS3-4A and NS4A of genotype 3a has similar capacity to induce apoptosis through a Bax-triggered, mitochondrial-mediated, caspase cascade.