Effects of histone deacetylase inhibitor FR901228 on expression level of telomerase reverse transcriptase in oral cancer

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Abstract

We speculated whether or not the expression level of telomerase reverse transcriptase (hTERT) would be modulated by agents targeting epigenetics in oral cancer cell lines. Although hTERT is known to be targeted by epigenetic changes, it remains unclear how chemoagents targeting epigenetics work on hTERT transcription. In the present study, the epigenetic effects of histone deacetylase (HDAC) inhibitor FR901228 on hTERT transcription were analysed by RT-PCR in oral cancer cell lines. The mRNA expression of hTERT was upregulated after exposure to FR901228 in hTERT-negative Hep2 cells, even in the hTERT highly expressed SAS and KB cells. Moreover, co-treatment of protein synthesis inhibitor cycloheximide (CHX) resulted in the induction of hTERT transcription by FR901228. This suggests that the induction of hTERT by FR901228 requires de novo protein synthesis to some extent and is more likely a direct than an indirect effect on epigenetic changes such as histone acetylation / deacetylation. We further examined the effect of FR901228 on c-myc protein, which is one of the main hTERT transcription activators. FR901228 repressed c-myc protein only in the absence of CHX, dependent of the enhancement of de novo protein synthesis. Our results indicate that c-myc protein is repressed indirectly by FR901228 but may not contribute FR901228-induced hTERT transcription. The present study showed that the HDAC inhibitor FR901228 induced the hTERT gene by a complex mechanism that involved other transcription factors except for c-myc, in addition to the inhibition of histone deacetylation.

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