title: Sp1 and Sp3 recruit histone deacetylase to repress transcription of human telomerase reverse transcriptase (hTERT) promoter in normal human somatic cells.
abstract: Activation of telomerase is crucial for cells to gain immortality. In human cells, telomerase activity is tightly regulated by the expression of its catalytic subunit, human telomerase reverse transcriptase (hTERT). In most normal human somatic cells, hTERT is not expressed, and its suppression acts as an important gatekeeper against tumorigenesis. Here we describe the systematic analyses of hTERT promoter to understand the transcriptional repression mechanism of the hTERT gene in normal human somatic cells. Through the serial deletion analysis of hTERT promoter in normal human fibroblasts, we identified a critical repressive element on the hTERT promoter. The repressive element formed DNA-protein complexes with Sp1 and Sp3 in nuclear extracts. Using formaldehyde cross-linked chromatin immunoprecipitation analysis, we found that Sp1 and Sp3 were associated with the endogenously repressed hTERT promoter in human fibroblasts. Furthermore, Sp1 and Sp3 interacted with histone deacetylase (HDAC) in these cells. Overexpression of dominant-negative mutants of Sp1 and Sp3, which contained mainly the HDAC2-binding domain, relieved the HDAC-mediated repression of the hTERT promoter. Taken together, these results suggest that Sp1 and Sp3 associate with the hTERT promoter, recruiting HDAC for the localized deacetylation of nucleosomal histones and transcriptional silencing of the hTERT gene in normal human somatic cells.
authors.affiliation: National Creative Research Initiative Center for Genetic Reprogramming, Institute for Molecular Biology and Genetics, Seoul National University, Seoul 151-742, Korea.
authors.forename: Jaejoon
authors.initials: J
authors.lastname: Won
authors.forename: Jeongbin
authors.initials: J
authors.lastname: Yim
authors.forename: Tae Kook
authors.initials: TK
authors.lastname: Kim
mesh_terms: D001483:Base Sequence; D002478:Cells, Cultured; D002843:Chromatin / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000378:metabolism; D004268:DNA-Binding Proteins; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D020868:Gene Silencing; D017930:Genes, Reporter; D006655:Histone Deacetylases / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D020218:Response Elements / Q000235:genetics; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D002843:Chromatin; D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D016329:Sp1 Transcription Factor; D019098:Telomerase; D006655:Histone Deacetylases