Hepatitis B virus DNA-induced carcinogenesis of human normal liver cells by virtue of nonmethylated CpG DNA.

Hepatitis B virus has been linked to the pathogenesis and carcinogenesis of hepatocellular carcinoma. Components of viruses have been identified within pathological specimens of hepatocellular carcinoma tissue. We characterized the in vitro response of human normal liver cells (L-02 cells) to components of infectious agents related to toll-like receptors. Immortalized human normal liver cells (L-02 cells) exhibited increased proliferation in response to exposure to CpG DNA. This molecule is a well-characterized surrogate for DNA viruses, which are common in the liver. Our experiments show that L-02 cells and some hepatoma cell lines such as HepG2, HuH7, Hep3B, express TLR 9 (CpG-specific). CpG DNA, HBV DNA, DNA of HBV middle envelope protein (MP) containing a number of CpG, supernatant of HepG2.2.15 (HepG2 cells transfected HBV) excreting HBV DNA and extraction of nucleic acids from HepG2.2.15 supernatant can all activate NF-kappaB. In addition, L-02 cells were less susceptible to TNF-alpha-induced apoptosis as measured by Annexin V-FITC staining when stimulated with CpG. mRNA of DNA methyltransferase 1 (DNMT-1) and BCL-2 was increased when L-02 cells were stimulated with CpG DNA. Our study has identified a possible novel mechanism that indicates how CpG DNA of HBV DNA may contribute to the malignant transformation of benign liver cells.