Insulin activates the hepatitis B virus X gene through the activating protein-1 binding site in HepG2 cells.
Insulin stimulates cellular oncogenic activators such as c-jun, c-fos, and c-myc; and hepatitis B virus (HBV) X, a viral transactivator, is known to induce liver cancer in transgenic mice. In this respect, the effect of insulin on the expression of HBx protein was investigated in HepG2 cells. Insulin-stimulated transcription from the HBV X promoter in a dose-dependent manner was assessed by chloramphenicol acetyltransferase (CAT) assay. A mutation preventing AP-1 binding to the E element abolished the activation of the HBV X promoter by insulin. In addition, insulin stimulated the minimal thymidine kinase (tk) gene promoter activity through both the HBV E element and the consensus AP-1 binding site in HepG2 cells. An electrophoretic mobility shift assay (EMSA) using insulin-treated HepG2 nuclear extracts showed that insulin actually enhanced the binding of nuclear proteins to the HBV E element as well as to the consensus AP-1 binding site. Both HBV E and AP-1 oligonucleotides were effective competitors for this binding. These results showed that insulin elevated the expression of HBx protein through the AP-1 binding site of HBV EnI. We suggest that insulin can augment the role of HBx in the development of hepatocellular carcinoma (HCC) in HBV-infected liver, probably through interaction with other cellular oncogenes.
Choi
B H
BH
Department of Molecular Biology and Research Center for Cell Differentiation, Seoul National University, Korea.
Park
C J
CJ
Rho
H M
HM
D001665:Binding Sites; D004305:Dose-Response Relationship, Drug; D004586:Electrophoresis; D004742:Enhancer Elements, Genetic; D015967:Gene Expression Regulation, Viral / Q000187:drug effects*; D005814:Genes, Viral; D006511:Hepatitis B Antigens / Q000235:genetics; D006515:Hepatitis B virus / Q000235:genetics*; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D016296:Mutagenesis; D015534:Trans-Activators / Q000235:genetics*; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D054334:Viral Regulatory and Accessory Proteins
D006511:Hepatitis B Antigens; D007328:Insulin; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein