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Biological relevance and therapeutic potential of G-quadruplex structures in the human noncoding transcriptome.

ABSTRACT: Noncoding RNAs are functional transcripts that are not translated into proteins. They represent the largest portion of the human transcriptome and have been shown to regulate gene expression networks in both physiological and pathological cell conditions. Research in this field has made remarkable progress in the comprehension of how aberrations in noncoding RNA drive relevant disease-associated phenotypes; however, the biological role and mechanism of action of several noncoding RNAs still need full understanding. Besides fulfilling its function through sequence-based mechanisms, RNA can form complex secondary and tertiary structures which allow non-canonical interactions with proteins and/or other nucleic acids. In this context, the presence of G-quadruplexes in microRNAs and long noncoding RNAs is increasingly being reported. This evidence suggests a role for RNA G-quadruplexes in controlling microRNA biogenesis and mediating noncoding RNA interaction with biological partners, thus ultimately regulating gene expression. Here, we review the state of the art of G-quadruplexes in the noncoding transcriptome, with their structural and functional characterization. In light of the existence and further possible development of G-quadruplex binders that modulate G-quadruplex conformation and protein interactions, we also discuss the therapeutic potential of G-quadruplexes as targets to interfere with disease-associated noncoding RNAs.

SUBMITTER: Tassinari M

PROVIDER: S-EPMC8053107 | biostudies-literature |

REPOSITORIES: biostudies-literature

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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.

Project description:RNA structures are of crucial importance for biological function and gene regulation. Guanine (G)-rich sequences in RNA can assemble to form RNA G-quadruplex (rG4) structures; specific rG4s have been shown to regulate gene expression, and are associated with human diseases. However, no transcriptome-wide method has been reported to map rG4s, limiting our understanding of the rG4 structure and its relationship with function and regulation. Here we introduce a transcriptome-wide rG4 profiling method, rG4-Seq, in which the rG4-mediated reverse transcriptase stalling is read out by next-generation sequencing at nucleotide resolution. We apply this method to human RNA and report the first global map of rG4 structures for any organism. Our analysis identifies over 3,000 rG4s, and increases to over 11,000 upon addition of a rG4 stabilizing ligand Pyridostatin (PDS). Notably, we discover that besides canonical rG4s, many rG4s are non-canonical with novel structural features such as long-loops, bulges, and 2-quartet. We also find that rG4 formation is associated with its stability, Cytosine (C)-content, and the stability of alternative RNA structures. Our data reveals that rG4s can be found in messenger RNAs (mRNAs) and long intergenic noncoding RNAs (lincRNAs). In mRNAs, rG4s are enriched in untranslated regions, and are significantly correlated with microRNA target sites and polyadenylation signals. Remarkably, we found that majority of our in vitro identified rG4s can change the in silico predicted RNA structure to uncover alternative RNA conformation.. Futhermore, the rG4s that have analogues in many ortholog genes across different species show a preferential association with RNA processing and stability. rG4-seq is a broadly applicable method that enables the RNA G4 structurome and its biological roles to be interrogated and can be readily applied in other organisms on a transcriptome-wide scale. 12 samples, 150 bp single-ended RNA-Seq libraries from cell extracts after performing RTS reaction in different buffers (Li, K and K+PDS rich buffer). Each of the 3 conditions has 4 libraries from independent biological replicates.

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Biological relevance and therapeutic potential of G-quadruplex structures in the human noncoding transcriptome.

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