CTCF binds the proximal exonic region of hTERT and inhibits its transcription

The expression of the catalytic subunit (hTERT) represents the limiting factor for telomerase activity. Previously, we detected a transcriptional repressor effect of the proximal exonic region (first two exons) of the hTERT gene. To better understand the mechanism involved and to identify a potentia...

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Bibliographic Details
Published in:Nucleic acids research 2005-01, Vol.33 (21), p.6850-6860
Main Authors: Renaud, Stéphanie, Loukinov, Dmitri, Bosman, Fred T., Lobanenkov, Victor, Benhattar, Jean
Format: Article
Language:English
Subjects:
Binding Sites
CCCTC-Binding Factor
Cell Line, Tumor
Cells, Cultured
DNA-Binding Proteins - biosynthesis
DNA-Binding Proteins - genetics
DNA-Binding Proteins - metabolism
Exons
Gene Silencing
Humans
Promoter Regions, Genetic
Repressor Proteins - metabolism
Telomerase - biosynthesis
Telomerase - genetics
Transcription, Genetic
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Summary:The expression of the catalytic subunit (hTERT) represents the limiting factor for telomerase activity. Previously, we detected a transcriptional repressor effect of the proximal exonic region (first two exons) of the hTERT gene. To better understand the mechanism involved and to identify a potential repressor, we further characterized this region. The addition of the hTERT proximal exonic region downstream of the hTERT minimal promoter strongly reduced promoter transcriptional activity in all cells tested (tumor, normal and immortalized). This exonic region also significantly inhibited the transcriptional activity of the CMV and CDKN2A promoters, regardless of the cell type. Therefore, the repressor effect of hTERT exonic region is neither cell nor promoter-dependent. However, the distance between the promoter and the exonic region can modulate this repressor effect, suggesting that nucleosome positioning plays a role in transcriptional repression. We showed by electrophoretic mobility shift assay that CCCTC-binding factor (CTCF) binds to the proximal exonic region of hTERT. Chromatin immunoprecipitaion assays confirmed the binding of CTCF to this region. CTCF is bound to hTERT in cells in which hTERT is not expressed, but not in telomerase-positive ones. Moreover, the transcriptional downregulation of CTCF by RNA interference derepressed hTERT gene expression in normal telomerase-negative cells. Our results suggest that CTCF participates in key cellular mechanisms underlying immortality by regulating hTERT gene expression.
ISSN:0305-1048
1362-4962
DOI:10.1093/nar/gki989