Mitochondrial Physiology Network 10.9: 78 (2005) - download pdf

Hepatitis C virus core protein binds to mitochondria and induces Ca²⁺ uptake, ROS production, complex I inhibition, and permeability transition.

Steven A Weinman, M Korenaga, T Wang, Y Li

Dept. Internal Medicine, and Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, Texas, USA. - sweinman@utmb.edu

    Hepatitis C virus replicates in hepatocytes and produces a chronic liver disease associated with oxidative stress and excess apoptosis of hepatocytes. The HCV core protein is present in endoplasmic reticulum and our lab has previously demonstrated that it also localizes to mitochondria, increases mitochondrial ROS production, and sensitizes cells to oxidant-induced apoptosis.[1,2]. The aim of this study was to examine the mechanisms by which HCV core protein affects mitochondrial function. Liver mitochondria were isolated from control and HCV transgenic (TG) mice expressing the viral proteins core, E1, E2 and p7 in the liver. Core protein was concentrated in the mitochondrial fraction and proteinase K digestion studies demonstrated its presence on the mitochondrial outer membrane. Functional abnormalities of mitochondria were also present. There was an oxidation of the mitochondrial glutathione pool that decreased GSH by 40% without changing the total content of GSH+GSSG. Mitochondria derived from transgenic liver had reduced activity of complex I NADH oxidase activity compared to that of normal liver (56.7±1.1 vs. 44.4±3.0 nmol/min mg protein , P<0.01) but normal activity of complex III. Complex I dependent ROS production was also increased. Incubation of control mitochondria in vitro with recombinant core protein also caused an oxidation of the mitochondrial GSH pool and a selective inhibition of complex I. In addition, core protein increased Ca²⁺ uptake into isolated mitochondria, measured by Rhod-2 fluorescence, and sensitized mitochondria to oxidant-induced membrane permeability transition. HCV core protein also sensitized hepatoma cells to oxidant-induced mitochondrial depolarization and cell death and this sensitization could be reversed by either antioxidants (N-acetylcysteine) or intracellular Ca²⁺ chelation (BAPTA-AM). In conclusion, these studies demonstrate that HCV core protein is a mitochondrially active protein that increases mitochondrial ROS production and sensitizes cells to oxidant-induced cell death. The results support a model in which core protein localizes to the mitochondrial outer membrane where it increases Ca²⁺ uptake. Increased mitochondrial Ca²⁺ results in an increase in ROS production, oxidation of the intramitochondrial glutathione pool, and inhibition of complex I by transgluathionylation. The resulting mitochondrial effects may contribute to liver injury and oxidative stress seen in chronic hepatitis C.

     Supported by grant AA12863 from the National Institutes of Health.

1.  Okuda M, Li K, Beard MR et al. (2002) Mitochondrial injury, oxidative stress and antioxidant gene expression are induced by hepatitis C virus core protein. Gastroenterology 122: 366-375.

2.  Otani K, Korenaga M, Beard MR, Li K, Qian T, Showalter LA, Singh AK, Wang T, Weinman SA (2005) Hepatitis C virus core protein, cytochrome P450 2E1, and alcohol produce combined mitochondrial injury and cytotoxicity in hepatoma cells. Gastroenterology 128: 96-107.