Pathway in Monocytes and Hepatocytes ATM-NBS1/Mre11/Rad50 DNA Repair Nitrogen Species and by Interfering with the Repair through Reactive Oxygen and Hepatitis C Virus Inhibits DNA Damage

Hepatitis C virus (HCV) infection is associated with the development of hepatocellular carcinoma and putatively also non-Hodg-kin's B cell lymphoma. In this study, we demonstrated that PBMCs obtained from HCV-infected patients showed frequent chromosomal aberrations and that HCV infection of B cells in vitro induced enhanced chromosomal breaks and sister chromatid exchanges. HCV infection hypersensitized cells to ionizing radiation and bleomycin and inhibited nonhomologous end-joining repair. The viral core and nonstructural protein 3 proteins were shown to be responsible for the inhibition of DNA repair, mediated by NO and reactive oxygen species. Stable expression of core protein induced frequent chromosome translocations in cultured cells and in transgenic mice. HCV core protein binds to the NBS1 protein and inhibits the formation of the Mre11/NBS1/ Rad50 complex, thereby affecting ATM activation and inhibiting DNA binding of repair enzymes. Taken together, these data indicate that HCV infection inhibits multiple DNA repair processes to potentiate chromosome instability in both monocytes and hepatocytes. These effects may explain the oncogenicity and immunological perturbation of HCV infection. H epatitis C virus (HCV) infection is associated with the development of hepatocellular carcinoma (1) and causes lymphoproliferative disorders, including mixed cryog-lobulinemia and putatively non-Hodgkin's B cell lymphoma (2, 3). Chromosomal abnormalities are common in the PBMCs of hepatitis C patients as in most cancers (4). Previously, we have demonstrated that HCV infection induces a mutator phenotype by causing dsDNA breaks (DSBs) (5). We have further reported that HCV induces inducible NO synthase (iNOS) mRNA expression and enhances NO production through the action of the viral structural protein core and nonstructural protein (NS)3, and that NO is responsible for DSBs in most cellular genes (6). To identify the source of reactive oxygen species (ROS), our previous publication (7) showed that ROS is generated from mitochondrial damage-induced oxidative burst, leading to ROS generation. Accumulation of DSBs in HCV-infected cells suggests that a HCV-induced oxi-dative environment may overwhelm cellular antioxidant and DNA repair mechanisms, leading to chromosomal abnormalities. Defects in DNA repair genes cause genetic instability, gross chromosomal rearrangements, and accumulation of mutations, leading ultimately to neoplastic transformation. Both homologous recombination and nonhomologous end joining (NHEJ) play a role in the repair of DSBs in mammalian cells (8). The interaction of broken DNA with members of the Rad52 epistasis group, including Rad51, a mammalian homolog of bacterial RecA, initiates homologous recombination repair (8). Following DNA damage, Rad51 is redistributed within the nucleus …