Background: Hepatitis B virus X protein is a key regulator of hepatocarcinogenesis. The pregnane X receptor is a xenobiotic nuclear receptor that plays a role in the regulation of drug-metabolizing enzymes including the cytochrome P450 3A4, an enzyme important for the bioactivation of the liver carcinogen aflatoxin B1.
Aims: To identify novel host factor that interacts with hepatitis B virus X protein and the functional interaction between hepatitis B virus X protein and pregnane X receptor in hepatocarcinogenesis.
Methods: Co-immunoprecipitation, glutathione S-transferase pull-down, and chromatin immunoprecipitation were utilized to assess the interaction between hepatitis B virus X protein and pregnane X receptor. The functional relevance of hepatitis B virus X protein-pregnane X receptor interaction was investigated in cell cultures and hepatocellular carcinoma samples.
Results: We observed that hepatitis B virus X protein and pregnane X receptor co-localize in hepatic cells. Pregnane X receptor interacted with hepatitis B virus X protein via the ligand-binding domain of pregnane X receptor. Functionally, hepatitis B virus X protein increased the transcriptional activity of pregnane X receptor. Pregnane X receptor was able to recruit hepatitis B virus X protein to the CYP3A4 gene promoter. In clinic samples, the expression of pregnane X receptor was high in hepatitis B virus-associated liver cirrhosis and stage I hepatocellular carcinoma, but low in state II and stage III hepatocellular carcinoma.
Conclusion: We revealed a novel function of hepatitis B virus X protein in co-activating pregnane X receptor. The increased expression of pregnane X receptor and its target gene CYP3A4 are potential biomarkers for the early stage of hepatitis B virus-associated hepatocarcinogenesis.
Keywords: CYP3A4; ChIP; Cytochrome P450 3A4; DMSO; GST; HBV; HBx; HCC; Hepatitis B virus X protein; Liver cancer; PCN; PXR; Pregnane X receptor; RIF; XREM; chromatin immunoprecipitation; cytochrome P450 3A4; dimethyl sulfoxide; glutathione S-transferase; hepatitis B virus; hepatitis B virus X protein; hepatocellular carcinoma; pregnane X receptor; pregnenolone 16α carbonitrile; rifampicin; xenobiotic responsive enhancer module.
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