AIM: To study the changes of human telomerase reverse transcriptase (hTERT) mRNA expression in human hepatocarcinoma cell lines (HepG2) and cholangiocarcinoma cell lines (QBC939) after HBx gene transfection and to illustrate the significance of transcriptional regulation of hTERT gene by HBx gene in the carcinogenesis.METHODS: HepG2 and QBC939 cell lines were cultured and co-transfected with eukaryotic expression vector containing the HBx coding region and cloning vector containing enhanced green fluorescent protein (EGFP) coding sequence using lipid-mediated gene transduction technique. Thirty-six hours after transfection, EGFP expression in cells was used as the indicator of successful transfection. Flow cytometry was performed to determine the transfection efficiency.Cells were harvested and total RNA was extracted using TRIzol() reagent. The expression of hTERT mRNA in HepG2and QBC939 cell lines was assayed by reverse transcriptionpolymerase chain reaction. The expression of HBx protein in both cell lines was detected by immunocytochemical staining and West blotting.RESULTS: Flow cytometry showed that the transfection efficiency was 46.4% in HepG2 cells and 29.6% in QBC939cells for both HBx gene expression vector and blank vector. The expression of hTERT mRNA was meaningfully increased in HepG2 and QBC939 cell lines when transfected with HBx gene expression vector compared to those transfected with OPTI-MEM medium and blank vector.Immunocytochemical staining and West blotting revealed HBx protein expression in HepG2 and QBC939cells only when transfected with HBx gene.CONCLUSION: HBx gene transfection can upregulate the transcriptional expression of hTERT mRNA. The transactivation of hTERT gene by HBx gene is a newfound mechanism for pathogenesis of hepatocarcinomas and cholangiocarcinomas after HBV infection.