Direct mapping of G-quadruplex anchored 3D chromatin structure via ViCAR
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ABSTRACT:
ORGANISM(S): Mus musculus Homo sapiens
PROVIDER: GSE250219 | GEO | 2024/08/12
REPOSITORIES: GEO
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Project description:DNA structure can regulate genome function. Four-stranded DNA G-quadruplex (G4) structures have been implicated in transcriptional regulation; however, previous studies have not directly addressed the role of an individual G4 within its endogenous cellular context. Using CRISPR to genetically abrogate endogenous G4 structure folding, we directly interrogate the G4 found within the upstream regulatory region of the critical human MYC oncogene. G4 loss leads to suppression of MYC transcription from the P1 promoter that is mediated by the deposition of a de novo nucleosome alongside alterations in RNA polymerase recruitment. We also show that replacement of the endogenous MYC G4 with a different G4 structure from the KRAS oncogene restores G4 folding and MYC transcription. Moreover, we demonstrate that the MYC G4 structure itself, rather than its sequence, recruits transcription factors and histone modifiers. Overall, our work establishes that G4 structures are important features of transcriptional regulation that coordinate recruitment of key chromatin proteins and the transcriptional machinery through interactions with DNA secondary structure, rather than primary sequence.
2024-02-06 | GSE223370 | 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: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: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:G-quadruplex structure (G4) is a type of DNA secondary structure that widely exists in the genomes of many organisms. G4s are believed to participate in multiple biological processes. Acyl- CoA binding protein (ACBP), a ubiquitously expressed and highly conserved protein in eukaryotic cells, plays important roles in lipid metabolism by transporting and protecting acyl-CoA esters. Here, we report the functional identification of a G4 in the promoter of the ACBP gene in silkworm and human cancer cells. We found that G4 exists as a conserved element in the promoters of ACBP genes in invertebrates and vertebrates. The BmACBP G4 bound with G4-binding protein LARK regulated BmACBP transcription, which was blocked by the G4 stabilizer pyridostatin (PDS) and G4 antisense oligonucleotides. PDS treatment with 5 th instar silkworm larvae decreased the BmACBP expression and triacylglycerides (TAG) level, resulting in reductions in fat body mass, body size and weight and growth and metamorphic rates. PDS treatment and knocking out of the HsACBP G4 in human hepatic adenocarcinoma HepG2 cells inhibited the expression of HsACBP and decreased the TAG level and cell proliferation. Altogether, our findings suggest that G4 of the ACBP genes is involved in regulation of lipid metabolism processes in invertebrates and vertebrates.
2022-05-04 | GSE201939 | 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:DNA-protein interactions regulate critical biological processes. Identifying proteins that bind to specific, functional genomic loci is essential for understanding the underlying regulatory mechanisms on a molecular level. Here, we describe a novel co-binding-mediated protein profiling (CMPP) strategy to investigate the interactome of DNA G-quadruplexes (G4s) in cellular chromatin. CMPP involves cell-permeable, functionalized G4-ligand probes that bind endogenous G4s and subsequently crosslink to co-binding G4-interacting proteins in situ. We show the robustness of CMPP on proximity labelling of a G4 binding protein in vitro. Employing this approach in live cells, we identify hundreds of putative G4-interacting proteins from various functional classes. Next, we observe high G4 binding affinity and selectivity for several G4 interactors in vitro and confirm direct G4 interactions for one of the top candidates in chromatin. Our studies provide a chemical approach to map protein interactions of specific nucleic acid features in living cells.
2021-06-28 | GSE165124 | GEO
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
Project description:The effect of bisquinolinium compounds PhenDC3 and 360A genome wide gene expression changes modulated via promoter based G-quadruplex (G4) motifs. The total RNA was extracted after treating HeLa S3 cells with 10 µM of no molecule (DMSO), 8979A (control molecule), PhenDC3 (G4 specific molecule) or 360A (G4 specific molecule) for 48 hrs in triplicate.
2012-05-29 | E-GEOD-32170 | biostudies-arrayexpress
Project description:G-quadruplex (G4) structural motifs have been linked to transcription, replication and genome instability and are implicated in cancer and other diseases. However, it is crucial to demonstrate the bona fide formation of G4 structures within an endogenous chromatin context. Herein we address this through the development of G4 ChIP-seq, an antibody-based G4 chromatin immunoprecipitation and high-throughput sequencing approach. We find ∼10,000 G4 structures in human chromatin, predominantly in regulatory, nucleosome-depleted regions. G4 structures are enriched in the promoters and 5' UTRs of highly transcribed genes, particularly in genes related to cancer and in somatic copy number amplifications, such as MYC. Strikingly, de novo and enhanced G4 formation are associated with increased transcriptional activity, as shown by HDAC inhibitor-induced chromatin relaxation and observed in immortalized as compared to normal cellular states. Our findings show that regulatory, nucleosome-depleted chromatin and elevated transcription shape the endogenous human G4 DNA landscape.
2016-08-05 | GSE76688 | GEO