Hepatitis C virus (HCV) is a single, positive-stranded RNA virus. HCV is an important human pathogen that causes chronic hepatitis that can progress to fibrosis, steatosis, cirrhosis, hepatocellular carcinoma (HCC), and liver failure. Currently, HCV is estimated to infect about 170 million people worldwide, including four million in the U.S. This virus is responsible for thousands of deaths and more than $600 million spent annually in health care and work-loss in the U.S. There is no vaccine available yet for HCV. New and improved antiviral therapy is urgently needed. However, the mechanism by which HCV replicates in human liver and causes various diseases is largely unknown.

Recently, new HCV proteins have been discovered that are produced from the HCV core coding sequence by translational frameshifting. During translation, ribosome shifts from the normal (i.e., zero) reading frame to -2/+1 and -1/+2 frames to produce F and ~1.5 kDa proteins, respectively, in addition to the non-shifted gene product, core protein. An A-rich sequence, located at codons 8 -14 in the HCV core coding gene, cooperates with a downstream RNA sequence to mediate both frameshifts. Increased sequence variations in this region have been reported in hepatitis C patients with liver cancer. Nonetheless, how these sequence variations and other cis- and trans-acting factors affect the frameshift efficiencies awaits further investigation, and the biological functions of HCV frameshift gene products remain almost completely unknown. The recent advent of HCV RNA replicons and an in vitro model for efficient generation of infectious HCV provides important tools and an unprecedented opportunity to study frameshifting in the context of HCV replication.

Therefore, our goal is to determine the mechanism and function of this dual frameshifting in the context of HCV replication, and to understand the significance of sequence variations in the frameshift signal that have been associated with HCC. These studies will not only enhance our understanding of HCV and translational frameshifting but may help us to identify agents that, by altering frameshift efficiencies, disrupt HCV life cycle and/or reduce its pathogenic interactions with the host.

In addition, oxidative stress has emerged as a key factor in HCV induced pathogenesis. The virus infection is characterized by a systemic oxidative stress that is most likely caused by a combination of chronic inflammation, iron overload, liver damage, and proteins encoded by HCV. The increased generation of reactive oxygen and nitrogen species, together with the decreased antioxidant defense, promotes the development and progression of hepatic and perhaps extrahepatic complications of HCV infection. Recently, we also showed that both exogenous and endogenous oxidants can specifically and rapidly suppress HCV RNA replication in human hepatocytes within 15 to 30 min in a mechanism that involved calcium signaling. The suppression was associated with the loss of HCV-replicating activity that co-fractionated with the Golgi membranes. The results further indicate that the modulation of intracellular calcium concentration might be sufficient to disable the HCV replication complex.

Therefore, through clinical collaborations and by using cell culture models that sustain continuous replication of HCV, my laboratory also studies how this virus alters the host redox status and its pathological consequence. The mechanism of HCV replication is examined, to find potential targets for antiviral therapy.