Effects of hepatitis B virus X protein on human telomerase reverse transcriptase expression and activity in hepatoma cells

In subjects with hepatitis B, carcinogenesis has been associated with the hepatitis B virus (HBV) X protein (HBX) and human telomerase reverse transcriptase (hTERT). In the experiments reported here, we used immunohistochemical methods to study the expression of hTERT and HBV antigens (HBsAg, HBcAg and HBxAg) in 34 cases of HCC and corresponding paratumor tissues, 30 cases of liver cirrhosis, and 6 normal livers. To examine the effect of HBX on hTERT expression and activity in hepatoma cells, we transiently and stably transfected the pCMV-X plasmid cloned HBx gene into H7402 hepatoma cells, then measured the expression of c-Myc and hTERT in these cells with the use of Western-blot analysis. Telomerase activity was detected with the use of the telomerase repeat amplification protocol (TRAP) in transiently and stably transfected cells. We found that hTERT expression was 67.6%, 73.5%, and 100% in tumor, paratumor, and cirrhosis samples, respectively, but found no hTERT positivity in samples of normal liver. HBsAg, HBcAg, and HBxAg were expressed in 58.8%, 26.5%, and 76.5% of tumor tissues, respectively; in 64.7%, 41.2%, and 85.3% of the corresponding paratumor tissues; and in 76.7%, 66.7%, and 100% of cirrhotic tissues. The χ2 test revealed no significant difference between the expression of hTERT and HBxAg in these tissues. Western-blot analysis revealed that expression of c-Myc and hTERT in the transiently transfected cells was much greater than that in the control cells. We elicited a similar result when we used the TRAP method to measure telomerase activity. Our data collectively demonstrate that HBX up-regulates the expression and activity of hTERT in hepatoma cells, suggesting that hTERT is associated with tumor development.