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X protein of hepatitis B virus functions as a transcriptional corepressor on the human telomerase promoter
Author(s) -
Su JiunMing,
Lai XiangMe,
Lan KengHsin,
Li ChungPin,
Chao Yee,
Yen SangHue,
Chang FullYoung,
Lee ShouDong,
Lee WeiPing
Publication year - 2007
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.21675
Subject(s) - corepressor , telomerase , virology , hepatitis b virus , promoter , biology , hepatitis b virus pre beta , cancer research , microbiology and biotechnology , virus , hepatitis b virus dna polymerase , genetics , repressor , gene , transcription factor , gene expression
The X protein of hepatitis B virus (HBx) is essential for transactivation of hepatitis B viral and host cellular genes. It has been specifically implicated in the development of hepatocellular carcinoma; however, the molecular mechanism remains unknown. Telomeres, the DNA‐protein complexes at the ends of eukaryotic chromosomes, protect chromosomes from degradation at the terminal regions, fusion with a broken DNA end, and inappropriate recombination. The shortening of telomeres that occurs during hepatocellular carcinogenesis has been well studied. In the present study, we isolated an HBx isoform that resulted in telomere shortening in hepatoma cell lines. We found that this HBx isoform down‐regulated the expression of human telomerase by transcriptionally repressing its promoter. To further determine the molecular mechanism, we examined human telomerase promoter and identified myc‐associated zinc finger protein (MAZ) as a transcriptional repressor of the promoter. We found that the HBx isoform achieved transcriptional suppression of human telomerase by enhancing MAZ binding to its consensus sequence in the promoter through physical association with MAZ. Conclusion: The data suggest that HBx can induce telomere shortening by acting as a transcriptional corepressor of MAZ on the human telomerase promoter. (H EPATOLOGY 2007.)