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Promoter G-quadruplex folding precedes transcription and is controlled by chromatin

ABSTRACT: Four stranded DNA G-quadruplex (G4) structures are common features of the human genome that are primarily found in active promoters associated with elevated transcription. Here, we explore the relationship between the folding of G4s in promoters, transcription and chromatin state. Transcriptional inhibition by DRB or by triptolide reveals that promoter G4 formation, as assessed G4 ChIP-seq, is not reliant on transcriptional activity. Establishing a link between G4 formation and chromatin accessibility, we demonstrate that chromatin compaction leads to loss of promoter G4s accompanied by a corresponding loss of RNA polymerase II (Pol II). Furthermore, pre-treatment of cells with a G4-stabilising ligand can mitigate Pol II loss at promoters induced by chromatin compaction. Overall, our findings show that G4 formation is fostered in accessible chromatin and does not require active transcription. Furthermore, our findings suggest that G4s have a role to recruit Pol II to promote transcription.

ORGANISM(S): Homo sapiens

PROVIDER: GSE162299 | GEO | 2021/03/31

REPOSITORIES: GEO

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Project description:DNA secondary structures are important for fundamental genome functions such as transcription and replication1. The G-quadruplex (G4) structural motif has been linked to gene regulation2,3 and genome instability4,5 and may be important to cancer development and other diseases6-8. Recently, ~700,000 discrete G4s have been observed in naked human single-stranded genomic DNA using G4-seq, a high-throughput sequencing technique that detects structural features in vitro.9 It is of vital importance to investigate G4 structures within an endogenous chromatin context, which until now remained elusive10,11. Herein, we address this via the development of G4 ChIP-seq, an antibody-based G4 chromatin immunoprecipitation and high-throughput sequencing approach. We identified ~10,000 endogenous G4 structures and show that G4s are predominantly seen in regulatory, nucleosome-depleted, chromatin regions. G4s were enriched in the promoters and 5âUTR regions of highly transcribed genes, particularly in genes related to cancer and in somatic copy number amplifications, such as MYC. Reorganization of the chromatin landscape using a histone deacetylase inhibitor, resulted in de novo G4 formation in new and more prominent regulatory, nucleosome-depleted regions associated with increased transcriptional output. Our findings suggest a striking relationship between promoter nucleosome-depleted regions, G4 formation and elevated transcriptional activity. Comparison between normal human epidermal keratinocytes and their immortalized counterparts revealed a ï¾7-fold greater G4 abundance in immortalized cells, of which 80 % were found in regulatory, nucleosome-depleted regions common to both cell types. Consequently, cells exhibiting more G4s displayed significantly increased transcriptional output and were more sensitive to growth inhibition by a small molecule G4 ligand. Overall, our results provide new mechanistic insights into where and when DNA adopts G4 structure in vivo. Our findings show for the first time that regulatory, nucleosome-depleted chromatin and transcriptional states predominantly shape the endogenous G4 DNA landscape. Two cell lines, treated with entinostat or untreated, analyzed to detect gene expression differences, presence of G-Qudruplexes and chromatin state. Each combination of conditions replicated in duplicates or triplicates.

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Promoter G-quadruplex folding precedes transcription and is controlled by chromatin

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