A mutant of HBx (HBxDelta127) promotes hepatoma cell growth via sterol regulatory element binding protein 1c involving 5-lipoxygenase.
OBJECTIVE
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.


METHODS
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.


RESULTS
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).


CONCLUSIONS
HBxDelta127 promotes hepatoma cell growth through activating SREBP-1c involving 5-LOX.
Wang
Qi
Q
Department of Cancer Research, Institute for Molecular Biology, Nankai University, Tianjin, China.
Zhang
Wei-ying
WY
Ye
Li-hong
LH
Zhang
Xiao-dong
XD
D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000821:virology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D064429:Fatty Acid Synthases / Q000378:metabolism; D056945:Hep G2 Cells; D006515:Hepatitis B virus / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism / Q000821:virology*; D009154:Mutation; D051780:Sterol Regulatory Element Binding Protein 1 / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D054334:Viral Regulatory and Accessory Proteins
D051780:Sterol Regulatory Element Binding Protein 1; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; D001094:Arachidonate 5-Lipoxygenase; D064429:Fatty Acid Synthases