Hepatocyte NAD(P)H oxidases as an endogenous source of reactive oxygen species during hepatitis C virus infection

Abstract

Oxidative stress has been identified as a key mechanism of hepatitis C virus (HCV)-induced pathogenesis. Studies suggest that HCV increases the generation of hydroxyl radical and peroxynitrite close to the cell nucleus, inflicting DNA damage, but the source of reactive oxygen species (ROS) remains incompletely characterized. We hypothesized that HCV increased the generation of superoxide and H2O2 close to the hepatocyte nucleus and that this source of ROS was Nox4. Huh7 human hepatoma cells and telomerase-reconstituted primary human hepatocytes, transfected or infected with virus-producing HCV strains of genotype 2a and 1b, were examined for mRNA, protein, and subcellular localization of Nox proteins, along with human liver. We found that genotype 2a HCV induced persistent elevation of Nox1 and Nox4 mRNA and proteins in Huh7 cells. Genotype 1b HCV likewise elevated the levels of Nox1 and Nox4 in telomerase-reconstituted primary human hepatocytes. Furthermore, Nox1 and Nox4 proteins were increased in HCV-infected human liver compared to uninfected liver. Unlike Nox1, Nox4 was prominent in the nuclear compartment of these cells as well as human liver, particularly in the presence of HCV. HCV-induced ROS and nuclear nitrotyrosine could be decreased with siRNAs to Nox1 and Nox4. Finally, HCV increased the level of transforming growth factor beta-1 (TGFβ1). TGFβ1 could elevate Nox4 expression in the presence of infectious HCV, and HCV increased Nox4 at least in part through TGFβ1. Conclusion HCV induced a persistent elevation of Nox1 and Nox4 and increased nuclear localization of Nox4 in hepatocytes in vitro and in human liver. Hepatocyte Nox proteins are likely to act as a persistent, endogenous source of ROS during HCV-induced pathogenesis.

The NADPH oxidase inhibitor VAS2870 impairs cell growth and enhances TGF-β-induced apoptosis of liver tumor cells

“…In normal conditions, this cytokine is considered to act as a liver tumor suppressor, but many tumor cells acquire resistance to its proapoptotic effects, favoring response to this cytokine in terms of malignancy [30]. In addition to survival signals via NOX1 in hepatoma cells [8], TGF- is able to induce migration of different tumor cells via NOX proteins [31,32] and also promote oxidative damage upon hepatitis C virus, frequently associated to later HCC [33,34] . Thus, inhibiting NADPH oxidases might prevent those events and promote beneficial effects in cases of liver cancer.…”

Hypercholesterolemic diet induces hepatic steatosis and alterations in mRNA expression of NADPH oxidase in rat livers

“…A role for the NADPH oxidases in chronic liver diseases, such as fibrosis and viral hepatitis, related to chronic inflammation, has been proposed (9,10). In the pathogenesis of alcoholic liver steatosis, there is an increase in NADPH oxidase activity and predominance of pro-oxidant agents, exceeding the capacity of the organic antioxidant defense (8).…”

Control of Hepatic Nuclear Superoxide Production by Glucose 6-Phosphate Dehydrogenase and NADPH Oxidase-4

“…NOX4 has been localized in nuclei of vascular smooth muscle cells, but its subnuclear localization (such as within specific nuclear membranes) remains unclear (13). Nuclear NOX4 has also been implicated in DNA damage resulting from both hemangioendothelioma formation (14) and hepatitis C infection (15). However, NOX4 is not the only NOX localized to nuclei, because nuclear NOX1 and NOX2 have also been described (16,17).…”