Replication forks stalled at co-transcriptional R-loops can be restarted by a mechanism involving fork cleavage-religation cycles mediated by MUS81 endonuclease and DNA ligase IV (LIG4), which presumably relieve the topological barrier generated by the transcription-replication conflict (TRC) and facilitate ELL-dependent reactivation of transcription. Here, we report that the restart of R-loop-stalled replication forks via the MUS81-LIG4-ELL pathway requires senataxin (SETX), a helicase that can unwind RNA:DNA hybrids. We found that SETX promotes replication fork progression by preventing R-loop accumulation during S-phase. Interestingly, loss of SETX helicase activity leads to nascent DNA degradation upon induction of R-loop-mediated fork stalling by hydroxyurea. This fork degradation phenotype is independent of replication fork reversal and results from DNA2-mediated resection of MUS81-cleaved replication forks that accumulate due to defective replication restart. Finally, we demonstrate that SETX acts in a common pathway with the DEAD-box helicase DDX17 to suppress R-loop-mediated replication stress in human cells. A possible cooperation between these RNA/DNA helicases in R-loop unwinding at TRC sites is discussed.

• MeSH
• Flap Endonucleases metabolism   genetics   MeSH
• DEAD-box RNA Helicases * metabolism   genetics   MeSH
• DNA-Binding Proteins * metabolism   genetics   MeSH
• DNA Helicases * metabolism   genetics   MeSH
• DNA Ligase ATP metabolism   genetics   MeSH
• DNA metabolism   genetics   MeSH
• Endonucleases * metabolism   genetics   MeSH
• Transcription, Genetic MeSH
• Humans MeSH
• Multifunctional Enzymes * metabolism   genetics   MeSH
• R-Loop Structures * MeSH
• DNA Replication * MeSH
• RNA Helicases * metabolism   genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Flap Endonucleases MeSH
• DEAD-box RNA Helicases * MeSH
• DNA-Binding Proteins * MeSH
• DNA Helicases * MeSH
• DNA Ligase ATP MeSH
• DNA MeSH
• Endonucleases * MeSH
• Multifunctional Enzymes * MeSH
• MUS81 protein, human MeSH Browser
• RNA Helicases * MeSH
• SETX protein, human MeSH Browser

Transcription-replication conflicts (TRCs) induce formation of cotranscriptional RNA:DNA hybrids (R-loops) stabilized by G-quadruplexes (G4s) on the displaced DNA strand, which can cause fork stalling. Although it is known that these stalled forks can resume DNA synthesis in a process initiated by MUS81 endonuclease, how TRC-associated G4/R-loops are removed to allow fork passage remains unclear. Here, we identify the mismatch repair protein MutSβ, an MLH1-PMS1 heterodimer termed MutLβ, and the G4-resolving helicase FANCJ as factors that are required for MUS81-initiated restart of DNA replication at TRC sites in human cells. This DNA repair process depends on the G4-binding activity of MutSβ, the helicase activity of FANCJ, and the binding of FANCJ to MLH1. Furthermore, we show that MutSβ, MutLβ, and MLH1-FANCJ interaction mediate FANCJ recruitment to G4s. These data suggest that MutSβ, MutLβ, and FANCJ act in conjunction to eliminate G4/R-loops at TRC sites, allowing replication restart.

• MeSH
• DNA Helicases genetics   metabolism   MeSH
• DNA genetics   MeSH
• Humans MeSH
• Fanconi Anemia Complementation Group Proteins * genetics   metabolism   MeSH
• R-Loop Structures * MeSH
• DNA Replication MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Helicases MeSH
• DNA MeSH
• Fanconi Anemia Complementation Group Proteins * MeSH

Oncogene-induced replication stress has been recognized as a major cause of genome instability in cancer cells. Increased expression of cyclin E1 caused by amplification of the CCNE1 gene is a common cause of replication stress in various cancers. Protein phosphatase magnesium-dependent 1 delta (PPM1D) is a negative regulator of p53 and has been implicated in termination of the cell cycle checkpoint. Amplification of the PPM1D gene or frameshift mutations in its final exon promote tumorigenesis. Here, we show that PPM1D activity further increases the replication stress caused by overexpression of cyclin E1. In particular, we demonstrate that cells expressing a truncated mutant of PPM1D progress faster from G1 to S phase and fail to complete licensing of the replication origins. In addition, we show that transcription-replication collisions and replication fork slowing caused by CCNE1 overexpression are exaggerated in cells expressing the truncated PPM1D. Finally, replication speed and accumulation of focal DNA copy number alterations caused by induction of CCNE1 expression was rescued by pharmacological inhibition of PPM1D. We propose that increased activity of PPM1D suppresses the checkpoint function of p53 and thus promotes genome instability in cells expressing the CCNE1 oncogene.

• Keywords
• PPM1D phosphatase, cancer, cell cycle, cyclin E1, replication stress,
• MeSH
• Cyclin E genetics   metabolism   MeSH
• Humans MeSH
• Tumor Suppressor Protein p53 * genetics   metabolism   MeSH
• Neoplasms * MeSH
• Genomic Instability MeSH
• Protein Phosphatase 2C genetics   metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cyclin E MeSH
• Tumor Suppressor Protein p53 * MeSH
• PPM1D protein, human MeSH Browser
• Protein Phosphatase 2C MeSH

Prolonged pausing of the transcription machinery may lead to the formation of three-stranded nucleic acid structures, called R-loops, typically resulting from the annealing of the nascent RNA with the template DNA. Unscheduled persistence of R-loops and RNA polymerases may interfere with transcription itself and other essential processes such as DNA replication and repair. Senataxin (SETX) is a putative helicase, mutated in two neurodegenerative disorders, which has been implicated in the control of R-loop accumulation and in transcription termination. However, understanding the precise role of SETX in these processes has been precluded by the absence of a direct characterisation of SETX biochemical activities. Here, we purify and characterise the helicase domain of SETX in parallel with its yeast orthologue, Sen1. Importantly, we show that SETX is a bona fide helicase with the ability to resolve R-loops. Furthermore, SETX has retained the transcription termination activity of Sen1 but functions in a species-specific manner. Finally, subsequent characterisation of two SETX variants harbouring disease-associated mutations shed light into the effect of such mutations on SETX folding and biochemical properties. Altogether, these results broaden our understanding of SETX function in gene expression and the maintenance of genome integrity and provide clues to elucidate the molecular basis of SETX-associated neurodegenerative diseases.

• MeSH
• DNA Helicases * genetics   metabolism   MeSH
• Transcription, Genetic MeSH
• Humans MeSH
• Multifunctional Enzymes genetics   metabolism   MeSH
• Neurodegenerative Diseases MeSH
• R-Loop Structures MeSH
• Gene Expression Regulation MeSH
• RNA Helicases * metabolism   MeSH
• Saccharomyces cerevisiae Proteins metabolism   MeSH
• Saccharomyces cerevisiae metabolism   MeSH
• Transcription Termination, Genetic * MeSH
• Transcription Factors genetics   metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Helicases * MeSH
• Multifunctional Enzymes MeSH
• RNA Helicases * MeSH
• Saccharomyces cerevisiae Proteins MeSH
• SEN1 protein, S cerevisiae MeSH Browser
• SETX protein, human MeSH Browser
• Transcription Factors MeSH

Elevated levels of reactive oxygen species (ROS) reduce replication fork velocity by causing dissociation of the TIMELESS-TIPIN complex from the replisome. Here, we show that ROS generated by exposure of human cells to the ribonucleotide reductase inhibitor hydroxyurea (HU) promote replication fork reversal in a manner dependent on active transcription and formation of co-transcriptional RNA:DNA hybrids (R-loops). The frequency of R-loop-dependent fork stalling events is also increased after TIMELESS depletion or a partial inhibition of replicative DNA polymerases by aphidicolin, suggesting that this phenomenon is due to a global replication slowdown. In contrast, replication arrest caused by HU-induced depletion of deoxynucleotides does not induce fork reversal but, if allowed to persist, leads to extensive R-loop-independent DNA breakage during S-phase. Our work reveals a link between oxidative stress and transcription-replication interference that causes genomic alterations recurrently found in human cancer.

• MeSH
• DNA-Binding Proteins * metabolism   MeSH
• DNA MeSH
• Hydroxyurea pharmacology   MeSH
• Humans MeSH
• Reactive Oxygen Species MeSH
• DNA Replication * MeSH
• S Phase genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA-Binding Proteins * MeSH
• DNA MeSH
• Hydroxyurea MeSH
• Reactive Oxygen Species MeSH

An elevated frequency of DNA replication defects is associated with diabetes and cancer. However, data linking these nuclear perturbations to the onset or progression of organ complications remained unexplored. Here, we report that RAGE (Receptor for Advanced Glycated Endproducts), previously believed to be an extracellular receptor, upon metabolic stress localizes to the damaged forks. There it interacts and stabilizes the minichromosome-maintenance (Mcm2-7) complex. Accordingly, RAGE deficiency leads to slowed fork progression, premature fork collapse, hypersensitivity to replication stress agents and reduction of viability, which was reversed by the reconstitution of RAGE. This was marked by the 53BP1/OPT-domain expression and the presence of micronuclei, premature loss-of-ciliated zones, increased incidences of tubular-karyomegaly, and finally, interstitial fibrosis. More importantly, the RAGE-Mcm2 axis was selectively compromised in cells expressing micronuclei in human biopsies and mouse models of diabetic nephropathy and cancer. Thus, the functional RAGE-Mcm2/7 axis is critical in handling replication stress in vitro and human disease.

• MeSH
• Diabetes Mellitus * MeSH
• Humans MeSH
• Minichromosome Maintenance Complex Component 2 * genetics   metabolism   MeSH
• Minichromosome Maintenance Proteins metabolism   MeSH
• Mice MeSH
• Neoplasms * MeSH
• Cell Cycle Proteins metabolism   MeSH
• Receptor for Advanced Glycation End Products * metabolism   MeSH
• DNA Replication genetics   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Minichromosome Maintenance Complex Component 2 * MeSH
• Minichromosome Maintenance Proteins MeSH
• MCM2 protein, human MeSH Browser
• Cell Cycle Proteins MeSH
• Receptor for Advanced Glycation End Products * MeSH

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. A recent study has shown that replication forks stalled by co-transcriptional R-loops can be restarted by a mechanism involving fork cleavage by MUS81 endonuclease, followed by ELL-dependent 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 R-loops 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-ELL pathway for resolution of R-loop-mediated transcription-replication conflicts, which may be involved in R-loop unwinding.

• MeSH
• DEAD-box RNA Helicases genetics   metabolism   MeSH
• DNA Helicases metabolism   MeSH
• DNA metabolism   MeSH
• Endonucleases metabolism   MeSH
• Humans MeSH
• R-Loop Structures * MeSH
• DNA Replication * genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DDX17 protein, human MeSH Browser
• DEAD-box RNA Helicases MeSH
• DNA Helicases MeSH
• DNA MeSH
• Endonucleases MeSH

RECQ5 belongs to the RecQ family of DNA helicases. It is conserved from Drosophila to humans and its deficiency results in genomic instability and cancer susceptibility in mice. Human RECQ5 is known for its ability to regulate homologous recombination by disrupting RAD51 nucleoprotein filaments. It also binds to RNA polymerase II (RNAPII) and negatively regulates transcript elongation by RNAPII. Here, we summarize recent studies implicating RECQ5 in the prevention and resolution of transcription-replication conflicts, a major intrinsic source of genomic instability during cancer development.

• Keywords
• DNA repair, R-loops, RECQ5, genomic instability, replication stress, transcription-replication conflicts,
• MeSH
• DNA genetics   metabolism   MeSH
• Transcription, Genetic genetics   MeSH
• RecQ Helicases genetics   metabolism   physiology   MeSH
• Humans MeSH
• Genomic Instability MeSH
• DNA Replication MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• DNA MeSH
• RecQ Helicases MeSH