Abstract: Objective The aim of this study was to investigate the possible mechanism of hepatitis B virus X protein (HBx) affecting cytokine signal transduction inhibitor-1 (SOCS-1) gene in vitro. Methods The expressions of HBx, DNA methyltransferase (DNMT)3A/3B and SOCS-1 in cancerous and paracancerous tissues of 22 patients with HBV-related hepatocellular carcinoma (HCC) were detected by real-time PCR. The HBx expression plasmid (pcDNA-X) or an empty plasmid (pcDNA3. 0) were transfected in L02 cells by liposome infection. The effect of 5-aza-2′-deoxycytidine(5-Aza-C) on the survival rate of L02 cells was detected by CCK8. The HBx, DNMT3A/3B and SOCS-1 mRNA as well their protein expression were assayed by real-time PCR and Western blot. Results The HBx and DNMT3A mRNA level in cancerous tissues were(65.2±3.5)and (77.2 ± 3.8), much higher than [(22.5±4.0)and(42.1± 2.9), respectively, P<0. 05], while the expression of SOCS-1 was (33.1±3.0), significantly lower than [(75.6 ±2.6),P<0. 05] in adjacent liver tissues; the activity of L02 cells expressing HBx decreased with the increase of 5-Aza-C concentration (P<0. 05); the DNMT3A mRNA level and its protein expression in L02 cells with overexpression of HBx were significantly higher than in empty plasmid-transfected cells (P< 0.05); the SOCS-1 mRNA level and its protein expression were significantly lower than in the empty plasmid-transfected cells (P< 0.05); the DNMT3A mRNA level and its protein expression in L02 cells expressing HBx after 5-Aza-C intervention were significantly lower than in the control cells (P < 0.05), while the SOCS-1 mRNA level and its protein expression were significantly higher than in the control (P < 0.05). Conclusions The present study indicates that HBx induces epigenetic down-regulation of SOCS-1 by increasing the expression of DNMT3A,which might be reversed with DNA methyltransferase inhibitor 5-Aza-C.

Key words: Hepatoma, L02 cells, Hepatitis B virus X protein, Suppressor of cytokine signaling-1, DNA methylation transferase, In vitro