title: Chromatin dynamics at the hTERT promoter during transcriptional activation and repression by c-Myc and Mnt in Xenopus leavis oocytes.
abstract: The transcription factors c-Myc and Mnt regulate gene expression through dimerization with Max and binding to E-boxes in target genes. While c-Myc activates gene expression via recruitment of histone modifying complexes, Mnt acts as a transcriptional repressor. Here, we used the Xenopus leavis oocyte system to address the effect of c-Myc and Mnt on transcription and chromatin remodeling over the E-box region in the human telomerase reverse transcriptase (hTERT) promoter. As expected we found elevated and decreased levels of hTERT transcription upon exogenously expressed c-Myc/Max and Mnt/Max, respectively. In addition, we confirmed binding of these heterodimers to both E-boxes already enriched with H3K9ac and H4K16ac. These chromatin marks were further enhanced upon c-Myc/Max binding followed by increased DNA accessibility in the E-box region. In contrast, Mnt/Max inhibited Myc-induced transcription and mediated repression through complete chromatin condensation and deacetylation of H3K9 and H4K16 across the E-box region. Importantly, Mnt was able to counteract c-Myc mediated activation even when expressed at low levels, suggesting Mnt to act as a strong repressor by closing the chromatin structure. Collectively our data demonstrate that the balance between c-Myc and Mnt activity determines the transcriptional outcome of the hTERT promoter by modulation of the chromatin architecture.
authors.affiliation: Department of Microbiology, Tumor and Cell Biology (MTC), Karolinska Institutet, Box 280, SE-171 77 Stockholm, Sweden.
authors.forename: Therese
authors.initials: T
authors.lastname: Wahlström
authors.forename: Sergey
authors.initials: S
authors.lastname: Belikov
authors.forename: Marie
authors.initials: M
authors.lastname: Arsenian Henriksson
mesh_terms: D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002843:Chromatin / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D019098:Telomerase / Q000235:genetics*; D014158:Transcription, Genetic / Q000235:genetics*; D014982:Xenopus laevis
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D002843:Chromatin; C106465:MNT protein, human; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D012097:Repressor Proteins; C509186:TERT protein, human; D019098:Telomerase
keywords: AU; Ac; ChIP; Chromatin remodeling; DMS; DNase I; EMSA; HAT; HDAC; HEK293T; Histone modification; Mnt; Transcription; WB; Western Blot; acetylation; arbitrary units; bHLHZip; basepair; basic helix loop helix leucine zipper; bp; c-Myc; chromatin immunoprecipitation; deoxyribonuclease I; dimethylsulfate; double stranded DNA; dsDNA; electrophoretic mobility shift assay; hTERT; hTERT promoter; histone acetylase; histone deacetylase; human embryonic kidney 293T; human telomerase reverse transcriptase; single stranded DNA; ssDNA