OBJECTIVETo investigate the effect of hepatitis B virus-encoded X protein (HBx) on the expression of host-encoded suppressor of cytokine signaling-1 (SOCS-1) and to explore the possibility of an underlying mechanism involving modulation of CpG island methylation in the SOCS-1 gene promoter.

METHODSThe immortalized human derived non-tumor liver cell line QSG7701 was transfected with a recombinant HBx plasmid (pcDNA-X) or an empty vector control plasmid (pcDNA3.0) and stably transfected clones were selected by G418 resistance screening. Untransfected cells served as negative controls. Expression of SOCS-1 mRNA and protein was detected by real-time quantitative PCR and western blotting. The methylation status of SOCS-1 was detected by methylation-specific PCR (MSP). The significance of intergroup differences was analyzed by one-way ANOVA or pairwise comparison with post-hoc LSD test.

RESULTSSOCS-1 mRNA level was significantly lower in the pcDNA-X/QSG7701 cells compared to that in the pcDNA3.0/QSG7701 and untransfected cells (0.3249+/-0.0536 vs. 1.0543+/-0.1937 and 1.00; F = 19.6, P = 0.042). SOCS-1 protein level was similarly lower in the pcDNA-X/QSG7701 cells (0.1496+/-0.0106 vs. 0.1984+/-0.0438 and 0.2152+/-0.0816; F = 19.4, P = 0.048). The SOCS-1 promoter region showed methylation only in the pcDNA-X/QSG7701 cells.

CONCLUSIONHBx-expressing human hepatocytes have down-regulated SOCS-1 expression, both at the mRNA and protein levels, and this effect corresponds to increased methylation in the SOCS-1 promoter region harboring CpG islands.