Hepatitis B virus X protein upregulates tumor necrosis factor-α expression of rat mesangial cell line via ERKs pathway

Abstract

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 p-ERK1/2 expression in GMCs was assessed by Western blotting. TNF-α mRNA expression was assessed by semiquantitative reverse transcription-PCR (RT-PCR). TNF-α level in supernatants 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 supernatants 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 supernatants 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.