Hepatitis B virus X protein upregulates DNA methyltransferase 3A/3B and enhances SOCS-1CpG island methylation

The aim of the present study was to investigate the effect of hepatitis B virus X protein (HBx) on the expression of DNA methyltransferase (DNMT)3A/3B and suppressors of cytokine signaling-1 (SOCS-1), as well as promoter CpG island methylation of the SOCS-1 gene. Stable hepatocyte cell lines expressing the HBx gene (pcDNA-X/QSG7701) or an empty gene (pcDNA3.0/QSG7701) were established. Reverse transcription quantitative polymerase chain reaction (PCR) was used to detect the mRNA expression levels of DNMT3A/3B and SOCS-1. Immunohistochemistry was used to detect the protein expression of DNMT3A/3B. Methylation-specific PCR (MSP) was used to detect the methylation status of the SOCS-1 gene promoter. The mRNA and protein expression levels of DNMT3A/3B were significantly higher in the pcDNA-X/QSG7701-transfected cells, compared with those in the pcDNA3.0/QSG7701 or non-transfected QSG7701 cells (P<0.05), whereas the relative mRNA expression of SOCS-1 was significantly lower in the pcDNA-X/QSG7701 cells compared with the pcDNA3.0/QSG7701 and non-transfected QSG7701 cells (F=19.6; P<0.05). Western blot analysis showed that the protein expression of SOCS-1 was significantly lower in the pcDNA-X/QSG7701 cells, compared with the pcDNA3.0/QSG7701 or non-transfected QSG7701 cells (F=19.4; P<0.05). The results of the MSP analysis showed that SOCS-1 promoter region methylation was present only in the pcDNA-X/QSG7701 cells. The HBV-X gene upregulated the mRNA and protein expression levels of DNMT3A/3B, downregulated the expression of SOCS-1 and increased SOCS-1 gene promoter CpG island methylation. This may provide a potential explanation of the mechanism underlying HBx-associated hepatocellular carcinoma.