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.
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.
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