Abstract
BackgroundLysine-specific demethylase 1 (LSD1), catalysing demethylation of mono- and di-methylated histone H3-K4 or K9, exhibits diverse transcriptional activities by mediating chromatin reconfiguration. The telomerase reverse transcriptase (hTERT) gene, encoding an essential component for telomerase activity that is involved in cellular immortalization and transformation, is silent in most normal human cells while activated in up to 90% of human cancers. It remains to be defined how exactly the transcriptional activation of the hTERT gene occurs during the oncogenic process.Methodology/Principal FindingsIn the present study, we determined the effect of LSD1 on hTERT transcription. In normal human fibroblasts with a tight hTERT repression, a pharmacological inhibition of LSD1 led to a weak hTERT expression, and a robust induction of hTERT mRNA was observed when LSD1 and histone deacetylases (HDACs) were both inhibited. Small interference RNA-mediated depletion of both LSD1 and CoREST, a co-repressor in HDAC-containing complexes, synergistically activated hTERT transcription. In cancer cells, inhibition of LSD1 activity or knocking-down of its expression led to significant increases in levels of hTERT mRNA and telomerase activity. Chromatin immunoprecipitation assay showed that LSD1 occupied the hTERT proximal promoter, and its depletion resulted in elevated di-methylation of histone H3-K4 accompanied by increased H3 acetylation locally in cancer cells. Moreover, during the differentiation of leukemic HL60 cells, the decreased hTERT expression was accompanied by the LSD1 recruitment to the hTERT promoter.Conclusions/SignificanceLSD1 represses hTERT transcription via demethylating H3-K4 in normal and cancerous cells, and together with HDACs, participates in the establishment of a stable repression state of the hTERT gene in normal or differentiated malignant cells. The findings contribute to better understandings of hTERT/telomerase regulation, which may be implicated in the development of therapeutic strategies for telomerase dysregulation-associated human diseases including cancers.
Highlights
The post-translational modification of nucleosomal histones, including acetylation, phosphorylation, methylation, ubiquitination and sumoylation, plays a key role in the regulation of gene transcription through remodelling chromatin structure [1]
To rule out possible Lysine-specific demethylase 1 (LSD1)-independent, non-specific effects of tranylcypromine, we knocked-down LSD1 expression by using the specific LSD1 siRNA. siRNA treatment of MRC5 cells resulted in silencing of LSD1 expression, and consistent with the finding described above, hTERT mRNA was induced in these LSD1-depleted cells (Fig. 1B)
We provide evidence that LSD1 is required for transcriptional repression of the hTERT gene in both normal and cancerous human cell lines
Summary
The post-translational modification of nucleosomal histones, including acetylation, phosphorylation, methylation, ubiquitination and sumoylation, plays a key role in the regulation of gene transcription through remodelling chromatin structure [1]. Lysine-specific demethylase 1 (LSD1), catalysing demethylation of mono- and di-methylated histone H3-K4 or K9, exhibits diverse transcriptional activities by mediating chromatin reconfiguration. The telomerase reverse transcriptase (hTERT) gene, encoding an essential component for telomerase activity that is involved in cellular immortalization and transformation, is silent in most normal human cells while activated in up to 90% of human cancers. It remains to be defined how exactly the transcriptional activation of the hTERT gene occurs during the oncogenic process. Chromatin immunoprecipitation assay showed that LSD1 occupied the hTERT proximal promoter, and its depletion resulted in elevated di-methylation of histone H3-K4 accompanied by increased H3 acetylation locally in cancer cells. The findings contribute to better understandings of hTERT/telomerase regulation, which may be implicated in the development of therapeutic strategies for telomerase dysregulation-associated human diseases including cancers
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