Exportin 4 gene expression and DNA promoter methylation status in chronic hepatitis B virus infection

Exportin 4 (XPO4) is a novel identified candidate tumour-suppressor gene involved in the pathogenesis of hepatocellular carcinoma (HCC). This study was aimed to determine the clinical features of XPO4 mRNA expression and promoter methylation status in peripheral blood mononuclear cells (PBMCs) of patients with chronic hepatitis B virus (HBV) infection. PBMCs were isolated from 44 HCC, 38 liver cirrhosis (LC), 34 chronic hepatitis B (CHB) patients and 17 healthy controls (HCs). The mRNA level and promoter methylation status of XPO4 were determined by quantitative real-time RT-PCR and methylation-specific PCR, respectively. XPO4 mRNA level of HCC patients was significantly lower compared with LC and CHB patients as well as HCs (all P<0.01, respectively), and significant differences of the XPO4 mRNA level were found in LC and CHB group than in HCs (LC vs HCs, P<0.01; CHB vs HCs, P<0.05). Methylation rate of XPO4 promoter was significantly increased in patients with HCC than in patients with CHB and HCs (both P<0.05). DNA methylation pattern was responsible for the suppression of XPO4 transcription in the progression of HBV infection (P=0.000). Furthermore, AFP level was significantly higher in HCC patients with XPO4 methylation than in those without methylation ((8702 +/- 15635) mu m vs (1052 +/- 5370) mu m, P<0.05). In conclusion, transcription of XPO4 gene was gradually decreased and methylation rate of XPO4 promoter was increased with the progression of HBV infection. Methylation status of XPO4 in PBMCs tended to be a noninvasive biomarker to predict HCC and the progression of HBV infection.