title: Transcriptional repression by the proximal exonic region at the human TERT gene.
abstract: In humans, the enzyme telomerase (hTERT) is responsible for the synthesis of new repeat sequences at the telomeres of chromosomes. Although active in early embryogenesis, the hTERT gene is transcriptionally silenced in almost all somatic cells in the adult, but is aberrantly re-activated in over 90% of human cancers. The molecular mechanisms responsible for repression of this gene are thought to involve the transcription factor CTCF. In this study, we bioinformatically identify putative CTCF binding sites in the hTERT proximal exonic region (PER) and determine their functional relevance in mediating transcriptional silencing at this gene. Tests using a reporter gene assay in HeLa cancer cells demonstrate that a sub-region of the PER exhibits strong transcriptional repressive activity. This repression is independent of the previously identified CTCF binding site near the transcriptional start site of the hTERT gene. In addition, site directed mutagenesis of three predicted CTCF binding sites, including a previously characterized in vivo site in exon 2, does not result in a loss of the repression mediated by the PER. The results from this study indicate that expression of the hTERT gene in HeLa cells is regulated by sequences in the PER. This transcriptional control is mediated through additional regulatory molecular mechanisms, independent of CTCF binding.
authors.affiliation: Biology Department, Harvey Mudd College, Claremont, CA 91711, USA.
authors.forename: Terence C
authors.initials: TC
authors.lastname: Wong
authors.forename: Ethan S
authors.initials: ES
authors.lastname: Sokol
authors.forename: Alicia N
authors.initials: AN
authors.lastname: Schep
authors.forename: Meera
authors.initials: M
authors.lastname: Punjiya
authors.forename: Diana A
authors.initials: DA
authors.lastname: Tran
authors.forename: Divina
authors.initials: D
authors.lastname: Allan
authors.forename: Robert A
authors.initials: RA
authors.lastname: Drewell
mesh_terms: D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D000076246:CCCTC-Binding Factor; D019295:Computational Biology; D017124:Conserved Sequence; D017931:DNA Primers / Q000235:genetics; D005091:Exons; D055785:Gene Knockdown Techniques; D053263:Gene Regulatory Networks; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010957:Plasmids / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019098:Telomerase / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D000076246:CCCTC-Binding Factor; C000619697:CTCF protein, human; D017931:DNA Primers; D034741:RNA, Small Interfering; D012097:Repressor Proteins; C509186:TERT protein, human; D019098:Telomerase