Acta Pharmacologica Sinica (2010) 31: 367–374; doi: 10.1038/aps.2010.5; published online 22 February 2010

Qi WANG¹, Wei-ying ZHANG¹, Li-hong YE^2,*, Xiao-dong ZHANG^1,*

Department of ¹Cancer Research, Key Laboratory of Molecular Microbiology and Technology of Ministry of Education, Institute for Molecular Biology, and ²Biochemistry, the Key Laboratory of Bioactive Materials, Ministry of Education, College of Life Sciences, Nankai University, Tianjin 300071, China

Aim: Previously, we identified a natural mutant of hepatitis B virus X gene (HBx) with a deletion from 382 to 401 base pairs (termed HBxΔ127), 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 HBxΔ127.

Methods: We examined the effect of HBxΔ127 on the transcription factor sterol regulatory element-binding protein 1c (SREBP-1c) and fatty acid synthase (FAS) in a model of HepG2-XΔ127 (or H7402-XΔ127) cells, which was stably transfected with HBxΔ127 gene in a human hepatoma HepG2 (or H7402) cell line.

Results: Relative to wild type HBx, HBxΔ127 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 HBxΔ127 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 HBxΔ127, using cerulenin (a FAS inhibitor).

Conclusion: HBxΔ127 promotes hepatoma cell growth through activating SREBP-1c involving 5-LOX.

Keywords: HBxΔ127; proliferation; sterol response element binding protein-1c; fatty acid synthase; 5-lipoxygenase

This work was supported by grants from the National Basic Research Program of China (No 973 Program, No 2007CB914804, No 2007CB914802, No 2009CB521702) and the National Natural Science Foundation of China (No 30670959).

The authors thank Dr Q LIU (University of Saskatchewan, Canada) for providing the plasmids: pFAS-WT-Luc, pFAS-ΔSRE–Luc, and SREBP-1c-571-Luc-WT.