Hepatitis B virus X protein upregulates expression of SMYD3 and C-MYC in HepG2 cells

The carcinogenic role of Hepatitis B X (HBX) in hepatocellular carcinoma (HCC) remains largely unknown. Histone H3 lysine 4 methyltransferase SMYD3 was found to be over-expressed and have a pro-carcinogenic effect in HCC. The role of HBX in regulating SMYD3 activity and the corresponding C-MYC gene in HCC carcinogenesis was investigated. SMYD3 and C-MYC expression in HBV-negative HepG2 and HBV-positive HepG2.2.15 were detected by real time PCR and Western blot. After transfection of HBX into HepG2, SMYD3 and C-MYC protein expression was detected and the apoptosis and proliferation of hepatoma cells were assayed. After SMYD3 expression in HepG2 with HBX transfection downregulated by siRNA, the corresponding C-MYC expression, cellular apoptosis, and proliferation were assayed by FACS. SMYD3 mRNA and protein and C-MYC protein were significantly higher in HepG2.2.15 than in HepG2. HBX transfection resulted in enhanced SMYD3 and C-MYC expressions, decreased cell apoptosis, and increased cell proliferation in HepG2 cells. Knocking down of SMYD3 in HepG2 with HBX transfection inhibited C-MYC expression and promoted apoptosis. These results suggest that HBX upregulates SMYD3 expression in HepG2, which may promote hepatoma development and progress. C-MYC may act as a down-stream gene in HBX-SMYD3-related hepatocarcinogenesis.