Choi B H, Park C J, Rho H M
Department of Molecular Biology and Research Center for Cell Differentiation, Seoul National University, Korea.
DNA Cell Biol. 1998 Nov;17(11):951-6. doi: 10.1089/dna.1998.17.951.
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.
胰岛素可刺激细胞致癌激活因子，如c-jun、c-fos和c-myc；而乙肝病毒（HBV）X蛋白作为一种病毒反式激活因子，已知可在转基因小鼠中诱发肝癌。就此，我们在HepG2细胞中研究了胰岛素对HBx蛋白表达的影响。通过氯霉素乙酰转移酶（CAT）分析评估胰岛素以剂量依赖方式刺激HBV X启动子转录的情况。阻止AP-1与E元件结合的突变消除了胰岛素对HBV X启动子的激活作用。此外，胰岛素通过HBV E元件和HepG2细胞中共识AP-1结合位点刺激最小胸苷激酶（tk）基因启动子活性。使用胰岛素处理的HepG2细胞核提取物进行的电泳迁移率变动分析（EMSA）表明，胰岛素实际上增强了核蛋白与HBV E元件以及共识AP-1结合位点的结合。HBV E和AP-1寡核苷酸都是这种结合的有效竞争物。这些结果表明，胰岛素通过HBV EnI的AP-1结合位点提高了HBx蛋白的表达。我们认为，胰岛素可能通过与其他细胞癌基因相互作用，增强HBx在HBV感染肝脏中肝细胞癌（HCC）发生发展中的作用。
