Small Hepatitis Delta Antigen Selectively Binds to Target mRNA in Hepatic Cells: A Potential Mechanism by Which Hepatitis D Virus Down-Regulates Glutathione S-Transferase P1 and Induces Liver Injury and Hepatocarcinogenesis.

Liver co-infection by hepatitis B virus (HBV) and hepatitis D virus (HDV) can result in a severe form of hepatocellular carcinoma with poor prognosis. Co-infection with HDV and HBV causes more deleterious effects than infection with HBV alone. Clinical research has shown that glutathione S-transferase P1 (GSTP1), a tumor suppressor gene, is typically down-regulated in liver samples from hepatitis-infected patients. In the present study, our data indicated that small HDV antigen (s-HDAg) could specifically bind to GSTP1 mRNA and significantly down-regulate GSTP1 protein expression. For the human fetal hepatocyte cell line L-02, cells transfected with s-HDAg, along with decreased GSTP1 expression, there was a significant accumulation of reactive oxygen species (ROS) and increased apoptotic ratios. Restoring GSTP1 expression through silencing s-HDAg via RNAi or over-expressing exogenous GSTP1 could largely recover the abnormal cell status. Our results revealed a novel potential mechanism of HDV-induced liver injury and hepatocarcinogenesis: s-HDAg can inhibit GSTP1 expression by directly binding to GSTP1 mRNA, which leads to accumulation of cellular ROS, resulting in high cellular apoptotic ratios and increased selective pressure for malignant transformation. To our knowledge, this is the first study to examine s-HDAg-specific pathogenic mechanisms through potential protein-RNA interactions.