Tumor suppressors, chromosomal instability, and hepatitis C virus-associated liver cancer.

Hepatitis C virus (HCV) is the only known RNA virus with an exclusively cytoplasmic life cycle that is associated with cancer. The mechanisms by which it causes cancer are unclear, but chronic immune-mediated inflammation and associated oxidative chromosomal DNA damage probably play a role. Compelling data suggest that the path to hepatocellular carcinoma in chronic hepatitis C shares some important features with the mechanisms of transformation employed by DNA tumor viruses. Interactions of viral proteins with key regulators of the cell cycle, the retinoblastoma-susceptibility protein, p53, and possibly DDX5 and DDX3 lead to enhanced cellular proliferation and may also compromise multiple cell-cycle checkpoints that maintain genomic integrity, thus setting the stage for carcinogenesis. Dysfunctional DNA damage and mitotic spindle checkpoints resulting from these interactions may promote chromosomal instability and leave the hepatocyte unable to control DNA damage caused by oxidative stress mediated by HCV proteins, alcohol, and immune-mediated inflammation.