Hepatitis B virus X protein co-activates pregnane X receptor to induce the cytochrome P450 3A4 enzyme, a potential implication in hepatocarcinogenesis

Dig Liver Dis. 2013 Dec;45(12):1041-8. doi: 10.1016/j.dld.2013.06.004. Epub 2013 Jul 26.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biomarkers, Tumor / biosynthesis*
  • Carcinogenesis / metabolism*
  • Carcinoma, Hepatocellular / metabolism*
  • Carcinoma, Hepatocellular / pathology
  • Carcinoma, Hepatocellular / virology
  • Cytochrome P-450 CYP3A / biosynthesis*
  • Cytochrome P-450 CYP3A / genetics
  • Enzyme Induction
  • Hepatitis B, Chronic / complications
  • Hepatocytes / metabolism
  • Humans
  • Liver Cirrhosis / metabolism
  • Liver Cirrhosis / virology
  • Liver Neoplasms / metabolism*
  • Liver Neoplasms / pathology
  • Liver Neoplasms / virology
  • Pregnane X Receptor
  • RNA, Messenger / metabolism
  • Receptors, Steroid / metabolism*
  • Trans-Activators / metabolism*
  • Tumor Cells, Cultured
  • Viral Regulatory and Accessory Proteins

Substances

  • Biomarkers, Tumor
  • Pregnane X Receptor
  • RNA, Messenger
  • Receptors, Steroid
  • Trans-Activators
  • Viral Regulatory and Accessory Proteins
  • hepatitis B virus X protein
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human