Department of Cancer Research, Institute for Molecular Biology, Nankai University, Tianjin, China.
Acta Pharmacol Sin. 2010 Mar;31(3):367-74. doi: 10.1038/aps.2010.5. Epub 2010 Feb 22.
Previously, we identified a natural mutant of hepatitis B virus X gene (HBx) with a deletion from 382 to 401 base pairs (termed HBxDelta127), which could potently enhance growth of hepatoma cells. In this study, we further investigated the mechanism of increased hepatoma cell growth that was mediated by HBxDelta127.
We examined the effect of HBxDelta127 on the transcription factor sterol regulatory element-binding protein 1c (SREBP-1c) and fatty acid synthase (FAS) in a model of HepG2-XDelta127 (or H7402-XDelta127) cells, which was stably transfected with HBxDelta127 gene in a human hepatoma HepG2 (or H7402) cell line.
Relative to wild type HBx, HBxDelta127 was able to potently activate SREBP-1c at the levels of promoter activity, mRNA and protein by a luciferase reporter gene assay, RT-PCR and Western blot analysis. Then, using the treatment with MK886, a specific 5-lipoxygenases (5-LOX) inhibitor, (or 5-LOX siRNA) we identified that 5-LOX was responsible for the upregulation of SREBP-1c by luciferase reporter gene assay, RT-PCR and Western blot analysis. Because FAS was a target gene of SREBP-1c, we further showed that HBxDelta127 was able to strongly activate the promoter activity of FAS and upregulated the mRNA expression level of FAS as well, by luciferase reporter gene assay and RT-PCR. In function, flow cytometry analysis revealed that FAS contributed to the growth of hepatoma cells that was mediated by HBxDelta127, using cerulenin (a FAS inhibitor).
HBxDelta127 promotes hepatoma cell growth through activating SREBP-1c involving 5-LOX.
之前，我们发现乙型肝炎病毒 X 基因（HBx）有一个从 382 到 401 个碱基对的缺失突变（称为 HBxDelta127），它可以强烈促进肝癌细胞的生长。在这项研究中，我们进一步研究了由 HBxDelta127 介导的肝癌细胞生长增加的机制。
我们在 HepG2-XDelta127（或 H7402-XDelta127）细胞模型中，检查了 HBxDelta127 对固醇调节元件结合蛋白 1c（SREBP-1c）和脂肪酸合酶（FAS）转录因子的影响，该模型是在人肝癌 HepG2（或 H7402）细胞系中稳定转染 HBxDelta127 基因。
与野生型 HBx 相比，HBxDelta127 通过荧光素酶报告基因检测、RT-PCR 和 Western blot 分析，在启动子活性、mRNA 和蛋白水平上能够强烈激活 SREBP-1c。然后，通过使用特异性 5-脂氧合酶（5-LOX）抑制剂（或 5-LOX siRNA）MK886，我们鉴定出 5-LOX 负责通过荧光素酶报告基因检测、RT-PCR 和 Western blot 分析上调 SREBP-1c。因为 FAS 是 SREBP-1c 的靶基因，我们进一步表明，HBxDelta127 能够强烈激活 FAS 的启动子活性，并通过荧光素酶报告基因检测和 RT-PCR 上调 FAS 的 mRNA 表达水平。在功能上，通过使用 cerulenin（一种 FAS 抑制剂），流式细胞术分析表明 FAS 有助于 HBxDelta127 介导的肝癌细胞的生长。
HBxDelta127 通过激活涉及 5-LOX 的 SREBP-1c 促进肝癌细胞生长。
