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Topoisomerase 1 prevents replication stress at R-loop-enriched transcription termination sites

ABSTRACT: R-loops have both positive and negative impacts on chromosome functions. To identify toxic R-loops in the human genome, we have mapped RNA:DNA hybrids, replication stress markers and DNA double strand breaks (DSBs) in cells depleted for Topoisomerase I (Top1), an enzyme that relaxes DNA supercoiling and prevents R-loop formation. RNA:DNA hybrids were found at both promoters (TSS) and terminators (TTS) of highly expressed genes. In contrast, the phosphorylation of RPA by ATR was only detected at TTS, which are preferentially replicated in a head-on orientation relative to the direction of transcription. In Top1-depleted cells, DSBs also cumulated at TTS, leading to persistent checkpoint activation, spreading of -H2AX on chromatin and global replication fork slowdown. These data indicate that fork pausing at the TTS of highly expressed genes containing R-loops prevents head-on conflicts between replication and transcription and maintains genome integrity in a Top1-dependent manner.

ORGANISM(S): Homo sapiens

PROVIDER: GSE108172 | GEO | 2020/06/20

REPOSITORIES: GEO

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Topoisomerase I suppresses genomic instability by preventing interference between replication and transcription

Project description:Topoisomerase I (Top1) is a key enzyme acting at the interface between DNA replication, transcription and mRNA maturation. Here, we show that Top1 suppresses genomic instability in mammalian cells by preventing conflicts between transcription and DNA replication. Using DNA combing and ChIP-on-chip, we found that Top1-deficient cells accumulate stalled replication forks and chromosome breaks in S phase and that breaks occur preferentially at gene-rich regions of the genome. Strikingly, these phenotypes were suppressed by preventing the formation of RNA-DNA hybrids (R-loops) during transcription. Moreover, these defects could be mimicked by depletion of the splicing factor ASF/SF2, which interacts functionally with Top1. Taken together, these data indicate that Top1 prevents replication fork collapse by suppressing the formation of R-loops in an ASF/SF2-dependent manner. We propose that interference between replication and transcription represents a major source of spontaneous replication stress, which could drive genomic instability during early stages of tumorigenesis. Bed files contain the gamma-H2AX enrichment sites described in the paper

2009-08-08 | GSE17552 | GEO

Topoisomerase 1 dependent R-loop deficiency drives accelerated replication and genomic instability

Project description:DNA replication is a complex process tightly regulated to ensure faithful genome duplication, and its perturbation leads to DNA damage and genomic instability. Replication stress is commonly associated with slow and stalled replication forks. Recently, accelerated replication has emerged as a non-canonical form of replication stress. However, the molecular basis underlying fork acceleration is largely unknown. Here we show that mutated HRAS activation leads to increased topoisomerase 1 (TOP1) expression leading to aberrant replication fork acceleration and DNA damage by decreasing RNA-DNA hybrids or R-loops. In these cells, restoration of TOP1 expression or mild replication inhibition rescues the perturbed replication and reduces DNA damage. Furthermore, TOP1 or RNaseH1 overexpression induces accelerated replication and DNA damage, highlighting the importance of TOP1 equilibrium in regulating R-loop homeostasis to ensure faithful DNA replication and genome integrity. Altogether, our results reveal a novel mechanism of oncogene-induced DNA damage induced by aberrant replication fork acceleration.

2022-09-08 | GSE168738 | GEO

DDX17 helicase promotes resolution of R-loop-mediated transcription-replication conflicts in human cells

Project description:R-loops are three-stranded nucleic acid structures composed of an RNA:DNA hybrid and displaced DNA strand. These structures can halt DNA replication when formed co- transcriptionally in the opposite orientation to replication fork progression. Recent studies have shown that replication forks stalled by co-transcription R-loops can be restarted by a mechanism involving fork cleavage by MUS81 endonuclease, followed by reactivation of transcription, and fork religation by the DNA ligase IV (LIG4)/XRCC4 complex. However, how R-loops are eliminated to allow the sequential restart of transcription and replication in this pathway remains elusive. Here, we identified the human DDX17 helicase as a factor that associates with R-loops and counteracts R-loop-mediated replication stress to preserve genome stability. We show that DDX17 unwinds RNA:DNA hybrids in vitro and promotes MUS81-dependent restart of R-loop-stalled forks in human cells in a manner dependent on its helicase activity. Loss of DDX17 helicase induces accumulation of R-loops and the formation of R-loop-dependent anaphase bridges and micronuclei. These findings establish DDX17 as a component of the MUS81-LIG4 pathway for resolution of R-loop-mediated transcription- replication conflicts, which may be involved in R-loop unwinding.

2022-11-02 | PXD034331 | Pride

Sen1 and Rrm3 ensure permissive topological conditions for replication termination [ChIP-seq]

Project description:Replication forks terminate at TERs and telomeres. Forks that converge or encounter transcription generate topological stress. Combining genetic, genomic and imaging approaches we found that Rrm3hPif1 and Sen1hSenataxin helicases assist termination at TERs, Sen1 at telomeres. rrm3 and sen1 are synthetic lethal, fail to terminate replication exhibiting lagging chromosomes and fragility at TERs and telomeres. sen1 rrm3 build up RNA-DNA hybrids at TERs, sen1 accumulates RNPII at TERs and telomeres. Double mutants exhibit X-shaped gapped or reversed converging forks. Rrm3 and Sen1 restrain Top1 and Top2 activities, preventing toxic accumulation of positive supercoil at TERs and telomeres. We suggest that Rrm3 and Sen1 coordinate the activities of fork-associated Top1 and Top2 with those of gene loop-associated Top1 and Top2 by preventing DNA and RNA polymerases slowing down when forks encounter transcription head-on or codirectionally, respectively. Hence Rrm3 and Sen1 are essential to generate permissive topological conditions for replication termination.

2022-10-11 | GSE214925 | GEO

Sen1 and Rrm3 ensure permissive topological conditions for replication termination [ChIP-chip]

2022-10-11 | GSE214908 | GEO

Linear interaction between transcription and replication shapes DNA break dynamics

Project description:Recurrent DNA break clusters (RDCs) are replication and transcription collision hotspots. Through high-resolution replication sequencing and a capture-ligation assay in mouse neural progenitor cells experiencing replication stress, we unraveled the replication fork architecture dictating RDC location and orientation. Most RDC occurs at the replication forks traversing timing transition regions (TTRs), where sparse replication origins connect unidirectional forks. Leftward-moving forks generate telomere-connected DNA double-strand breaks (DSB) while rightward-moving forks lead to centromere-connected DSBs. Strand-specific mapping for DNA-bounded RNA revealed transient DNA:RNA hybrids present at a higher density in RDC than in other actively transcribed long genes. In addition, mapping nascent RNA and RNA polymerase activity revealed that head-to-head interactions between replication and transcription machinery slow down DNA replication, resulting in 60% DSB contribution to the head-on as compared to 60% for co-directional . Our findings revealed TTR as a novel fragile class and highlighted how the linear interaction between transcription and replication impacts genome stability.

2024-03-18 | GSE254765 | GEO

Genome wide DRIP-seq in control knockdown HeLa cells

Project description:We mapped the location of RNA:DNA hybrids in HeLa cells that had been knocked down with a control siRNA. We found that the levels of RNA:DNA hybrids around origins of replication (defined from data from Pretyk et al, Nat Commun 2016) strongly correlated to the directionality of transcription around these origins (defined from GRO-seq data from GEO dataset GSM1518913.) Specifically, in regions where the replication fork travels antiparallel (Head-On) to the direction of transcription we find elevated RNA:DNA hybrids, and in regions where the replication fork travels parallel to the direction of replication (Co-directional) we find reduced RNA:DNA hybrids. These results imply that the relative directions of replication and transcription have an effect on the levels of RNA:DNA hybrids across the genome.

2017-07-27 | GSE93368 | GEO

RNase H2 degrades toxic RNA:DNA hybrids behind stalled forks to promote replication restart

Project description:R-loops represent a major source of replication stress but the mechanism by which these structures impede fork progression remains unclear. To address this question, we monitored fork progression, arrest and restart in S. cerevisiae cells lacking RNase H1 and H2, two enzymes responsible for degrading RNA:DNA hybrids. We found that while RNase H-deficient cells could replicate normally their chromosomes under unchallenged growth conditions, their replication was impaired when exposed to hydroxyurea (HU) or methyl methanesulfonate (MMS). Indeed, these cells exhibited increased levels of RNA:DNA hybrids at stalled forks and were unable to generate RPA-coated single-stranded (ssDNA), an important postreplicative step in resuming replication. Similar impairments in nascent DNA resection at HU-arrested forks were observed in human cells lacking RNase H2. However, the addition of triptolide, an inhibitor of transcription that induces RNA polymerase degradation, fully restored fork resection. Taken together, these data indicate that RNA:DNA hybrids not only act as barriers to replication forks, but also interfere with postreplicative fork repair mechanisms if not promptly degraded by RNase H.

2023-10-14 | GSE215896 | GEO

A role for the Saccharomyces cerevisiae Rtt109 histone acetyltransferase in R-loop homeostasis and associated genome instability

Project description:The stability of the genome is occasionally challenged by the formation of DNA-RNA hybrids and R-loops, which can be influenced by the chromatin context. This is mainly due to the fact that DNA-RNA hybrids hamper the progression of replication forks, leading to fork stalling and, ultimately, DNA breaks. Through a specific screening of chromatin modifiers performed in the yeast Saccharomyces cerevisiae, we have found that the Rtt109 histone acetyltransferase is involved in several steps of R-loop-metabolism and their associated genetic instability. On one hand, Rtt109 prevents DNA-RNA hybridization by the acetylation of histone H3 lysines 14 and 23, and on the other hand, it is involved in the repair of replication-born DNA breaks, such as those that can be caused by R-loops, by acetylating lysines 14 and 56. In addition, Rtt109 loss renders cells highly sensitive to replication stress in combination with R-loop-accumulating THO-complex mutants. Our data evidence that the chromatin context simultaneously influences the occurrence of DNA-RNA hybrid-associated DNA damage and its repair, adding complexity to the source of R-loop-associated genetic instability.

2022-07-13 | GSE192701 | GEO

UAP56/DDX39b is a major co-transcriptional RNA-DNA helicase that unwinds harmful R loops genome-wide

Project description:Non-scheduled R loops represent a major source of DNA damage and replication stress. Cells have different ways to prevent R loop accumulation. One mechanism relies on the conserved THO complex in association with co-transcriptional RNA processing factors including the RNA-dependent ATPase UAP56/DDX39B and histone modifiers such as the SIN3 deacetylase in humans. We investigated the function of UAP56/DDX39B in R loop removal. We show that UAP56 depletion causes R loop accumulation, R loop-mediated genome instability and replication fork stalling. We demonstrate an RNA-DNA helicase activity in UAP56 and that its overexpression suppresses R loops and genome instability induced by depleting 5 different unrelated factors. UAP56/DDX39B localizes to active chromatin and prevents the accumulation of RNA-DNA hybrids over the entire genome. We propose that, in addition to its RNA processing role, UAP56/DDX39B is a key helicase required to eliminate harmful co-transcriptional RNA structures that otherwise would block transcription and replication.

2020-05-25 | GSE127979 | GEO

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