Hepatitis B virus X protein regulates lipid metabolism and promotes the proliferation of liver cancer cells via the C/EBPa/SREBP-1 pathway

Abstract

Objective: To investigate the role and mechanism of hepatitis B virus (HBV)-encoded X protein (HBx) on the regulation of lipid metabolism and proliferation of human hepatoma cell line HepG2. Methods: HepG2 cells were transiently transfected with HBx expressing plasmid, and the cell proliferation was detected by MTT assay. Lipid droplet accumulation condition was stained by Oil Red O. Western blot was used to detect the protein levels of lipid metabolism-related genes, such as CCAAT/enhancer binding protein α (C/EBPα), sterol regulatory element binding protein-1 (SREBP-1), fatty acid synthetase (FASN) and acetyl-CoA carboxylase (ACC1). Methyl thiazolyl tetrazolium (MTT), Oil Red O staining and western blot were used to detect the effect of HBx on the regulation of lipid metabolism and proliferation of HepG2 cells under the conditions of overexpression and low expression of C/EBPα. Results: HBx had significantly promoted the proliferation of hepatoma cell line HepG2 in dose-and time-dependent manner (F = 32.82, P < 0.001; F = 58.21, P < 0.001). HBx had significantly promoted the lipid accumulation in HepG2 cells (F = 22.65, P < 0.001). Additionally, the protein levels of C/EBPα and SREBP-1 (key regulatory factors of lipid metabolism), and the rate-limiting enzymes FASN and ACC1 were significantly increased. C/EBPα overexpression had further strengthened the effect of HBx on HepG2 cell proliferation, lipid droplet accumulation, and lipid production-related gene expression. On the contrary, C/EBPα low expression had weakened HBx's promotional effect on cell proliferation, lipid droplet accumulation and lipid production-related gene expression. Conclusion: HBx may affect the lipid production and promote the proliferation of human hepatoma cell line HepG2 via the C/EBPa/SREBP-1 signaling pathway.