Chromatin immunoprecipitation for genome-wide mapping of endogenous G-quadruplex DNA structures
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE99205 | GEO | 2017/11/15
SECONDARY ACCESSION(S): PRJNA387558
REPOSITORIES: GEO
Similar Datasets
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.
2016-08-05 | E-GEOD-76688 | biostudies-arrayexpress
Project description:Four-stranded G-quadruplex (G4) structures form guanine-rich tracts, but their role in RNA biology remains poorly defined. Herein, we first delineate the presence of endogenous RNA G4s in the human cellular transcriptome by proxy of their binding to interacting proteins, DHX36, GRSF1 and DDX3X. We then demonstrate that a sub-population of these RNA G4s are reliably detected as folded structures in cross-linked cellular lysates using the G4 structure-specific antibody BG4. The 5' UTRs of protein-coding mRNAs show significant enrichment in such folded RNA G4s, particularly within mRNA for ribosomal proteins. As G4s in ribosomal mRNA are evolutionarily conserved in higher vertebrates this points to a common mode for translational co-regulation mediated by RNA G4 structures. Supporting this we find that G4-stabilising small molecules inhibit the translation of ribosomal protein mRNA and significantly down-regulate cellular translation.
2021-11-10 | GSE154570 | GEO
Project description:G-quadruplexes (G4s) are alternative DNA secondary structures of the human genome with key roles in transcription, replication and genome stability. Structure-specific small molecules and antibodies, such as BG4, have facilitated the detection of G4s in cells and chromatin. The availability of an alternative probe to BG4 would help to address some of its potential limitations in mapping G4 structures and would independently confirm and/or extend our earlier findings. Herein, we describe the development of SG4, a camelid single-chain only derived nanobody raised against the human MycG4 promoter structure. SG4 is small, easily expressed and demonstrates low nanomolar affinity for folded G4 structures in vitro. Clues to SG4 binding were obtained experimentally by mutating single amino acids. Moreover, AlphaFold2 protein predictions combined with molecular dynamics/docking simulations generated a de novo binding model of SG4-G4 interactions that identifies key amino acids with significant contributions to G4 binding. Using SG4 in G4 ChIP-seq, we also demonstrate the detection of G4 structures in two cancer cell lines. SG4 thus provides an alternative tool for G4 genome mapping and independently verifies our earlier findings.
2023-03-06 | GSE207567 | GEO
Project description:Four-stranded G-quadruplexes (G4s) are prevalent secondary structural features of the human genome. They are formed through stacking of Hoogsteen hydrogen-bonded G-tetrads connected by loops of variable length and sequence. G4 structures are found widely in genome control elements including gene promoters and are tightly linked to active gene expression and the recruitment of transcription factors and chromatin remodellers. To systematically investigate how G4 structures modulate transcription, we have developed a strategy in which different G4 sequences are engineered into the promoter of a synthetic reporter gene and ectopically into the same endogenous position in the genome of human cells. Here, we show that G4 sequences introduced into the host genome can fold into an G4 structure. Crucially, we demonstrate that G4 formation within a gene promoter stimulates transcription compared to G4-negative promoters and that this is not due to inherent G-richness. Finally, we provide robust evidence that transcriptional levels are directly related to the degree of thermodynamic stability of the G4 structure. Taken together, our results provide compelling evidence that G4 structures have a direct and positive regulatory role in gene transcription.
2024-02-21 | GSE241008 | GEO
Project description:Nucleic acid secondary structures play a critical role in the regulation of biological processes. Genome-wide detection of DNA and RNA secondary structures is essential to identify pathways that are regulated by nucleic acid folding. There are no methods to interrogate DNA secondary structure formation on a genome-wide scale. We present G4-Seq, a method that applies the concept of polymerase interference at G-quadruplex (G4) DNA secondary structures to a human genome scale by massively parallel array-sequencing. Our approach generated a high-resolution map of more than 700,000 distinct G4s in the human genome, including non-canonical structural variants with bulges or extended loops, which are difficult to predict by classical approaches. This experimental map reveals many previously uncharacterized G4 structures in functional genomic regions, of which we highlight those associated with cancer, that include oncogenes, tumor suppressors and somatic copy-number alterations.
2015-07-19 | GSE63874 | GEO
Project description:Control of DNA methylation level is critical for gene regulation, and the factors that govern hypomethylation at CpG islands (CGIs) are still being uncovered. Here, we provide evidence that G-quadruplex (G4) DNA secondary structures are genomic features that influence methylation at CGIs. We show that the presence of G4 structure is tightly associated with CGI hypomethylation. Surprisingly, we find that these G4 sites are enriched for DNA methyltransferase 1 (DNMT1) occupancy, which is consistent with our biophysical observations that DNMT1 exhibits higher binding affinity for G4s as compared to duplex, hemi-methylated or single-stranded DNA. The biochemical assays also show that the G4 structure itself, rather than sequence, inhibits DNMT1 enzymatic activity. Based on these data, we propose that G4 formation sequesters DNMT1 thereby protecting certain CGIs from methylation and inhibiting local methylation.
2018-07-16 | GSE107690 | GEO
Project description:In the presence of monovalent alkali metal ions, G-rich DNA sequences containing four runs of contiguous guanines can fold into G-quadruplex (G4) structures. Recent studies showed that these structures are located in critical regions of the human genome and assume important functions in many essential DNA metabolic processes, including replication, transcription and repair. However, not all potential G4-forming sequences are actually folded into G4 structures in cells, where G4 structures are known to be dynamic and modulated by G4-binding proteins as well as helicases. It remains unclear whether there are other factors influencing the formation and stability of G4 structures in cells. Herein, we showed that DNA G4s can undergo phase separation in vitro. In addition, immunofluorescence microscopy and ChIP-Seq experiments with the use of BG4, a G4 structure-specific antibody, revealed that disruption of phase separation in cells could result in global destabilization of G4 structures. Together, our work revealed phase separation as a new determinant in regulating the formation and stability of G4 structures in human cells.
2023-07-05 | GSE225772 | GEO
Project description:Homologous recombination (HR) is a key process for repairing DNA double strand breaks and for promoting genetic diversity, and it occurs unevenly throughout the genome. G-quadruplexes (G4s) are stable secondary structures widely present across the genome, which function in regulating gene transcription and maintaining genome stability. However, elevated G4 levels by BLM (RecQ like helicase unwinding G4) depletion can significantly drive HR at these G4 sites, which may threaten genome stability. Here, we investigated the role of Yin Yang-1 (YY1) in modulating HR at G4 sites. To elucidate G4 sites on the genome, cleavage under targets and tagmentation (CUT&Tag) of BG4, a G4 specific antibody, was conducted.
2024-05-29 | GSE254872 | GEO
Project description:G-quadruplexes (G4s) are noncanonical DNA secondary structures formed through the self-association of guanines, and they are distributed widely across the genome. G4 participates in multiple biological processes including gene transcription, and G4-targeted ligands serve as potential therapeutic agents for DNA-targeted therapies. However, genome-wide studies of the exact roles of G4s in transcriptional regulation are still lacking. We found that drug-induced promoter-proximal RNA polymerase II pausing promotes nearby G4 formation, and oppositely, G4 stabilization by G4-targeted ligands globally reduces RNA polymerase II occupancy at gene promoters as well as nascent RNA synthesis. To study the underlying mechanisms by which native G4 affects transcriptional regulation, we annealed the biotin-labeled core promoter DNA to form G4s and performed pull-down assays with nuclear extraction proteins in the presence or absence of TMPyP4. Mass spectrometry analysis was performed to identify the interacting proteins with G4-forming core promoter DNA.
2021-07-19 | PXD026830 | Pride
Project description: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.
2021-03-31 | GSE162299 | GEO