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Hepatitis B virus X protein (HBx),a 17-kd protein encoded by X gene of hepatitis B virus (HBV),has been shown to function as a transcriptional trans-activator of a variety of viral and cellular promoter/enhancer elements.The aim of the study is to investigate the extracellular regulated protein kinases (ERKs) pathway of HBx on glomerular mesangial cell (GMC) proliferation and tumor necrosis factor-α (TNF-α) expression.The HBV X gene was amplified by polymerase chain reaction (PCR),inserted into the eukaryotic expression vector pCI-neo and confirmed by restriction endonuclease digestion and sequence analysis.PCI-neo containing HBV X gene (pCI-neo-X) was then transfected into cultured GMC line via liposome.GMC proliferation,TNF-α and its mRNA expression were compared in the condition of with or without U0126 in culture media.HBx,ERK1/2 and pERK1/2 expression in GMCs was assessed by Weste blotting.TNF-α mRNA expression was assessed by semiquantitative reverse transcription-PCR (RT-PCR).TNF-α level in supeatants was measured by ELISA.GMC proliferation was detected by 3-(4,5-dimethylthiazol-2yl)2,5-diphenyltetrazolium bromide (MTT) kit.The results showed that HBx expression was found in transfected GMCs and became prominent at 36th and 48th h after transfection whether with or without U0126 in culture media.TNF-α mRNA expression was significantly decreased in U0126 group compared with U0126-free group.TNF-α levels in supeatants in PCI-neo-X transfection without U0126 group were (189.0±18.1)and (172.3±24.3) pg/mL at 36th and 48th h after transfection,respectively.In contrast,TNF-α levels in supeatants with U0126 were (65.6±11.6) and (84.0±24.6) pg/mL at 36th and 48th h,respectively.The TNF-α levels in the latter groups were significantly lower than those in the former groups (P＜ 0.05).GMCs proliferation was also lower in added U0126 group at 36th and 48th h after transfection.From above,we can conclude that HBx could induce GMC proliferation and increase TNF-α mRNA expression and its protein production.HBx upregulates TNF-α expression and induces cell proliferation of GMC line partly through ERK1/2 signal transduction pathway.