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Promoter R-loops Recruit U2AF1 to Modulate Its Phase Separation and RNA Splicing

ABSTRACT: R-loops and guanine quadruplexes (G4s) are secondary structures of nucleic acids that are ubiquitously present in cells, and are enriched in promoter regions of genes. By employing a bioinformatic approach based on overlap analysis of transcription factor ChIP-seq datasets, we found that many splicing factors, including U2AF1 whose recognition of 3¢ splicing site is crucial for pre-mRNA splicing, exhibit pronounced enrichment at endogenous R-loop- and DNA G4-structure loci in promoter regions of human genes. We revealed that U2AF1 can bind directly to R-loops and DNA G4 structures at low nM binding affinity. Additionally, we showed the ability of U2AF1 to undergo phase separation, which could be stimulated by binding with R-loops, but not duplex DNA, RNA/DNA hybrid, DNA G4, or single-stranded RNA. We also demonstrated that U2AF1 binds to promoter R-loops in human cells, and this binding competes with U2AF1’s interaction with 3¢-splicing site, thereby modulating pre-mRNA splicing. Together, we uncovered a group of candidate proteins that can bind to both R-loops and DNA G4s, revealed the direct and strong interaction of U2AF1 with these nucleic acid structures, and unveiled new functions of this interaction, i.e., promotion of phase separation of U2AF1 and modulation of mRNA splicing. Our work also established, for the first time, a biochemical basis for U2AF1’s occupancy in gene promoters.

ORGANISM(S): Homo sapiens

PROVIDER: GSE230254 | GEO | 2023/10/12

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 R-loops Recruit U2AF1 to Modulate Its Phase Separation and RNA Splicing

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