Modulation of human telomerase reverse transcriptase in hepatocellular carcinoma

Most cancer cells acquire immortal capability by telomerase activation. The human telomerase reverse transcriptase gene (hTERT) is considered to be the major determinant of the enzymatic activity of human telomerase, and the hTERT promoter contains several c-Myc binding sites that mediate hTERT transcriptional activation. Few studies have examined the role of hTERT in hepatocarcinogenesis, and the relationship between c-Myc and telomerase in human hepatocellular carcinoma tissue is unknown.

We measured hTERT mRNA levels and c-Myc oncoprotein expression in 57 patients with hepatocellular carcinoma using in situ hybridization and immunohistochemistry, respectively. The transcription regulation of hTERT was evaluated by transient transfection of pGL3-1375 into the human hepatocellular carcinoma cell line J5. To determine the relationship between c-Myc and the hTERT promoter, a 1375-bp DNA fragment encompassing the promoter was placed upstream of the luciferase reporter gene and transiently transfected into the cell line. Two additional hTERT promoter constructs (-776 and -100 bp region) and an hTERT promoter-LUC construct containing 2 c-Myc mutations (pGL3-181 MycMT) were also used for luciferase assays.

In 30 of 57 cases (52%), hTERT mRNA expression was associated with c-Myc protein expression. However, 16 of 57 cases (28%) showed strong hTERT mRNA detection without c-Myc protein expression, and 11 cases (19%) showed weak hTERT mRNA expression and strong c-Myc expression. Although luciferase activity was decreased between upstream 1 375 bp and 776 bp, there was no significant difference between upstream 776 bp and 100 bp. Finally, there was no significant decrease in activity after transfection of the hTERT promoter-LUC construct.

The results indicate that c-Myc does not play a major role in gene regulation of the catalytic subunit of telomerase (hTERT) in human hepatocellular carcinoma. Other regulatory elements or epigenetic phenomena should be further investigated to understand hTERT gene regulation in human hepatocellular carcinoma.