PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “stalled replication fork”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

18 recordsLinked to original sources
PubMed2024

PARP1 UFMylation ensures the stability of stalled replication forks.

The S-phase checkpoint involving CHK1 is essential for fork stability in response to fork stalling. PARP1 acts as a sensor of replication stress and is required for CHK1 activation. However, it is unclear how the activity of PARP1 is regulated. Here, we found that UFMylation is required for the efficient activation of CHK1 by UFMylating PARP1 at K548 during replication stress. Inactivation of UFL1, the E3 enzyme essential for UFMylation, delayed CHK1 activation and inhibits nascent DNA degradation during replication blockage as seen in PARP1-deficient cells. An in vitro study indicated that PARP1 is UFMylated at K548, which enhances its catalytic activity. Correspondingly, a PARP1 UFMylation-deficient mutant (K548R) and pathogenic mutant (F553L) compromised CHK1 activation, the restart of stalled replication forks following replication blockage, and chromosome stability. Defective PARP1 UFMylation also resulted in excessive nascent DNA degradation at stalled replication forks. Finally, we observed that PARP1 UFMylation-deficient knock-in mice exhibited increased sensitivity to replication stress caused by anticancer treatments. Thus, we demonstrate that PARP1 UFMylation promotes CHK1 activation and replication fork stability during replication stress, thus safeguarding genome integrity.

DNA Replication↗
PubMed2025

The DNA replication checkpoint limits Okazaki fragment accumulation to protect and restart stalled forks.

Understanding how DNA replication forks stall and restart and how the DNA replication checkpoint prevents irreversible fork collapse in molecular detail are crucial for understanding how cells maintain stable genomes and how they prevent the genetic instability that drives cancer. Here, we describe the reconstitution of fork stalling and restart with purified budding yeast proteins. After nucleotide depletion, leading-strand DNA synthesis quickly stops but CMG helicase continues to unwind, and Okazaki fragments continue to initiate on the lagging strand. Incomplete Okazaki fragments sequester PCNA, RFC, and DNA polymerases δ and ε, which prevents normal DNA synthesis restart and exposes nascent DNA to nuclease attack. The DNA replication checkpoint restrains fork progression, which limits this sequestration, protecting stalled forks from collapse and ensuring restart.

DNA Replication↗
PubMed2026

STN1 upregulation promotes PARPi resistance in BRCA2-deficient cancer cells via replication fork protection and suppression of ssDNA gap formation.

PARPi are effective therapy for BRCA1/2 mutant cancers, yet recurrent PARPi resistance frequently develops. The underlying mechanism of PARPi resistance remains largely unresolved. Here, we identify STN1, a component of the CTC1/STN1/TEN1 (CST) complex, as a modulator of PARPi resistance in BRCA2-deficient cells. RNA-seq analysis of PARPi-resistant cancer cells from BRCA2-mutated backgrounds shows largely distinct transcriptomic profiles with limited overlap, suggesting multiple routes to resistance. Notably, STN1 is consistently upregulated in resistant cells. We observe that overexpression of STN1 enhances Olaparib resistance in multiple BRCA2-deficient cell lines and alleviates DNA damage under replication stress. Mechanistically, we find that STN1 overexpression increases RAD51 loading to stalled replication forks while restricting MRE11 recruitment in BRCA2-deficient cells, thereby protecting stalled forks from nascent-strand degradation. Furthermore, STN1 overexpression rescues the accumulation of ssDNA gaps, a major determinant of PARPi sensitivity in BRCA2-deficient cells. Taken together, these findings suggest that elevated STN1 levels can partially compensate for BRCA2 loss by stabilizing stalled replication forks and limiting ssDNA gap accumulation. Our study uncovers a STN1-dependent pathway of replication stress tolerance that promotes PARPi resistance independently of homologous recombination restoration, highlighting STN1 as a potential biomarker and mechanistic contributor to therapeutic resistance in BRCA2-mutated cancers.

PARPi resistance↗
PubMed2026

R-loops and D-loops: a delicate balance in genomic stability and instability.

R-loops and D-loops are three-stranded nucleic acid structures that have emerged as central regulators of genome stability, gene expression, and DNA metabolism. R-loops form co-transcriptionally or post-transcriptionally when nascent RNA re-anneals with the template DNA strand, generating an RNA: DNA hybrid that displaces the non-template strand into a single-stranded state. These structures are enriched at CpG island promoters, transcription termination sites, and immunoglobulin class-switch regions, where they coordinate transcription regulation, chromatin remodeling, and DNA damage signaling. D-loops are formed when a single-stranded DNA segment pairs with one strand of a duplex and displaces the other, arising through context-dependent mechanisms that include RAD51- or DMC1-mediated strand invasion in homologous recombination, shelterin-assisted invasion at telomeres, and replication-coupled strand displacement at the mitochondrial DNA origin. They serve as indispensable intermediates in double-strand break repair, telomere maintenance, and mitochondrial DNA replication. Recent cryo-electron microscopy studies have resolved the stepwise RAD51-mediated strand exchange mechanism at near-atomic resolution, substantially advancing structural understanding of D-loop biogenesis. Despite their differences in molecular composition, both structures remodel Watson-Crick base pairing and, when dysregulated, are associated with replication fork stalling, transcription-replication conflicts, and aberrant recombination. This review systematically compares the structural features, formation mechanisms, regulatory networks, and biological functions of R-loops and D-loops, with emphasis on their convergent roles in safeguarding genome integrity. We further discuss rapidly evolving detection technologies and emerging therapeutic strategies targeting these structures in cancer and neurodegeneration, identifying key unresolved questions for future investigation.

Genomic Instability↗
PubMed2020

Distinct roles of BRCA2 in replication fork protection in response to hydroxyurea and DNA interstrand cross-links.

DNA interstrand cross-links (ICLs) are a form of DNA damage that requires the interplay of a number of repair proteins including those of the Fanconi anemia (FA) and the homologous recombination (HR) pathways. Pathogenic variants in the essential gene BRCA2/FANCD1, when monoallelic, predispose to breast and ovarian cancer, and when biallelic, result in a severe subtype of Fanconi anemia. BRCA2 function in the FA pathway is attributed to its role as a mediator of the RAD51 recombinase in HR repair of programmed DNA double-strand breaks (DSB). BRCA2 and RAD51 functions are also required to protect stalled replication forks from nucleolytic degradation during response to hydroxyurea (HU). While RAD51 has been shown to be necessary in the early steps of ICL repair to prevent aberrant nuclease resection, the role of BRCA2 in this process has not been described. Here, based on the analysis of BRCA2 DNA-binding domain (DBD) mutants (c.8488-1G>A and c.8524C>T) discovered in FA patients presenting with atypical FA-like phenotypes, we establish that BRCA2 is necessary for the protection of DNA at ICLs. Cells carrying BRCA2 DBD mutations are sensitive to ICL-inducing agents but resistant to HU treatment consistent with relatively high HR repair in these cells. BRCA2 function at an ICL protects against DNA2-WRN nuclease-helicase complex and not the MRE11 nuclease that is implicated in the resection of HU-induced stalled replication forks. Our results also indicate that unlike the processing at HU-induced stalled forks, the function of the SNF2 translocases (SMARCAL1, ZRANB3, or HLTF), implicated in fork reversal, are not an integral component of the ICL repair, pointing to a different mechanism of fork protection at different DNA lesions.

BRCA2 Protein↗
PubMed2022

DNA polymerase delta interacting protein 3 facilitates the activation and maintenance of DNA damage checkpoint in response to replication stress.

BACKGROUND: Replication stress response is crucial for the maintenance of a stable genome. POLDIP3 (DNA polymerase delta interacting protein 3) was initially identified as one of the DNA polymerase δ (Pol δ) interacting proteins almost 20 years ago. Using a variety of in vitro biochemical assays, we previously established that POLDIP3 is a key regulator of the enzymatic activity of Pol δ. However, the in vivo function of POLDIP3 in DNA replication and DNA damage response has been elusive. METHODS: We first generated POLDIP3 knockout (KO) cells using the CRISPR/Cas9 technology. We then investigated its biological functions in vivo using a variety of biochemical and cell biology assays. RESULTS: We showed that although the POLDIP3-KO cells manifest no pronounced defect in global DNA synthesis under nonstress conditions, they are sensitive to a variety of replication fork blockers. Intriguingly, we found that POLDIP3 plays a crucial role in the activation and maintenance of the DNA damage checkpoint in response to exogenous as well as endogenous replication stress. CONCLUSION: Our results indicate that when the DNA replication fork is blocked, POLDIP3 can be recruited to the stalled replication fork and functions to bridge the early DNA damage checkpoint response and the later replication fork repair/restart.

DNA Polymerase III↗
PubMed2026

The function of Mgs1/WRNIP1 in genome maintenance.

Preservation of genomic integrity during replication is challenging, because replication forks are often stalled by several forms of DNA damage or stable secondary DNA structures. Prolonged stalling of the replication fork can lead to incomplete replication, which may induce double strand breaks, genome rearrangements and cell death. Therefore, several DNA repair mechanisms evolved to rescue stalled replication forks, which can elaborate in error-free or error-prone manners. The pathway selection and the fine tuning of the collaboration between different DNA repair proteins involved in the rescue of the stalled replication fork are very important. Based on our recent knowledge, yeast Mgs1 and its human homologue WRNIP1 proteins can be excellent candidates for this fine-tuning regulator function. In this review we summarize our current knowledge about them and try to point out the most important future steps to prove this hypothesis.

DNA repair↗
PubMed2026

G-quadruplex structures as regulators of cellular processes and drivers of genome instability in cancer.

G-quadruplexes (G4s) are essential regulatory structures whose biological functions are inseparable from their potential to destabilize the genome. They play critical roles in transcription, replication and chromatin architecture, yet they also contribute to the genomic instability that fuels cancer. This dual role is an inherent consequence of where G4s form in the genome. G4s are enriched at highly active regulatory regions, including promoters, replication origins and topologically associated domain boundaries, where their controlled formation and resolution by helicases and topoisomerases support normal genome function. When this control is lost, the same features that make G4s functional become harmful, leading to R-loop and G-loop accumulation, replication fork stalling and increased conflicts between transcription and replication. Topoisomerase activity, which normally relieves supercoiling stress, can instead generate the DNA double-strand breaks that characterize cancer genomes. Persistent G4 structures also promote micronuclei formation and cytoplasmic DNA accumulation, activating the cGAS-STING innate immune signaling pathway. Here, we discuss these mechanisms and present pan-cancer genomic analyses showing that these processes operate broadly across human tumors. Therapeutically targeting G4s requires balancing their essential regulatory roles with their pathological effects. Understanding this tension is therefore essential for exploiting G4s as therapeutic targets across cancer types.

DEAH-box helicases↗
PubMed2016

A mechanism for 1,4-Benzoquinone-induced genotoxicity.

Benzene is a common environmental toxin and its metabolite, 1-4-Benzoquinone (BQ) causes hematopoietic cancers like myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). BQ has not been comprehensively assessed for its impact on genome maintenance, limiting our understanding of the true health risks associated with benzene exposure and our ability to identify people with increased sensitivity to this genotoxin. Here we analyze the impact BQ exposure has on wild type and DNA repair-defective mouse embryonic stem (ES) cells and wild type human cells. We find that double strand break (DSB) repair and replication fork maintenance pathways including homologous recombination (HR) and Fanconi anemia (FA) suppress BQ toxicity. BQ-induced damage efficiently stalls replication forks, yet poorly induces ATR/DNA-PKCS responses. Furthermore, the pattern of BQ-induced γH2AX and 53BP1foci is consistent with the formation of poly(ADP-ribose) polymerase 1 (PARP1)-stabilized regressed replication forks. At a biochemical level, BQ inhibited topoisomerase 1 (topo1)-mediated DNA ligation and nicking in vitro; thus providing mechanism for the cellular phenotype. These data are consistent with a model that proposes BQ interferes with type I topoisomerase's ability to maintain replication fork restart and progression leading to chromosomal instability that has the potential to cause hematopoietic cancers like MDS and AML.

Animals↗
PubMed2025

Pathogenic variants in MAEA disrupt DNA replication fork stability and are associated with developmental abnormalities in humans.

Replication stress (RS) poses a threat to genome stability and drives genomic rearrangements. The homologous recombination (HR) pathway repairs stalled replication forks (RFs) and prevents such instability. Through an E3 ubiquitin ligase screen aimed at identifying regulators of RAD51, we identified macrophage erythroblast attacher (MAEA), a core component of C-terminal to Lish (CTLH) E3 ubiquitin ligase complex, as a regulator of the HR pathway. Loss of MAEA impairs RAD51 recruitment at stalled RFs, leading to increased sensitivity to RS-inducing agents and excessive degradation of nascent DNA strands. Mechanistically, MAEA associates with and mediates the ubiquitylation of Ku80, enabling its removal from RF ends and facilitating the loading of RAD51. Notably, MAEA deficiency is associated with a developmental disorder involving microcephaly, craniofacial abnormalities, ocular defects, and heart malformations. Functional assays show that disease-linked MAEA variants (R34C, E349G, Y394D, and M396R) are defective in RS response. These findings establish MAEA as an essential factor in RF protection and genome integrity.

Humans↗
PubMed2026

Cohesin reshapes replication fork contacts to aid fork slowing and reversal.

DNA replication forks can be challenged by cancer chemotherapeutic treatments, leading to accumulation of single-stranded DNA and slowdown of DNA synthesis. The marked plasticity of replication forks under replication stress ensures fork stability, damage tolerance and complete genome duplication1. Initiation and progression of replication forks occur in a three-dimensionally organized genome. DNA loop extrusion by the cohesin complex organizes the genome2 and regulates the initiation and positioning of DNA replication origins3,4. Although transient interaction of sister forks was recently reported during unperturbed replication5, the functional relevance of fork contacts during replication stress and the role of cohesin in this context remain unknown. Here we show that cohesin-mediated loop extrusion rearranges nascent DNA contacts at stressed replication forks to promote genome stability. Using auxin-inducible degron6, separation-of-function mutants7-9 and a newly developed Micro-C-based technique to capture chromatin contacts at nascent DNA (Repli-C), we found that loop-extruding cohesin accumulates at stalled replication forks, limiting sister-fork coupling in favour of inter-replicon contacts. This process promotes active fork slowing and reversal by preventing PRIMPOL action on single-stranded DNA1. These findings show that the replication stress response is not merely an accumulation of individual regulatory events, but is topologically integrated across the genome through cohesin loop extrusion. While providing a new function for loop-extruding cohesin, our results indicate the potential impact on cancer therapy of frequent cohesin mutations in tumours10.

Journal Article↗
PubMed2023

Structural basis for stabilisation of the RAD51 nucleoprotein filament by BRCA2.

The BRCA2 tumour suppressor protein preserves genomic integrity via interactions with the DNA-strand exchange RAD51 protein in homology-directed repair. The RAD51-binding TR2 motif at the BRCA2 C-terminus is essential for protection and restart of stalled replication forks. Biochemical evidence shows that TR2 recognises filamentous RAD51, but existing models of TR2 binding to RAD51 lack a structural basis. Here we used cryo-electron microscopy and structure-guided mutagenesis to elucidate the mechanism of TR2 binding to nucleoprotein filaments of human RAD51. We find that TR2 binds across the protomer interface in the filament, acting as a brace for adjacent RAD51 molecules. TR2 targets an acidic-patch motif on human RAD51 that serves as a recruitment hub in fission yeast Rad51 for recombination mediators Rad52 and Rad55-Rad57. Our findings provide a structural rationale for RAD51 filament stabilisation by BRCA2 and reveal a common recruitment mechanism of recombination mediators to the RAD51 filament.

Humans↗
PubMed2024

Sen1: The Varied Virtues of a Multifaceted Helicase.

Several machineries concurrently work on the DNA, but among them RNA Polymerases (RNAPs) are the most widespread and active users. The homeostasis of such a busy genomic environment relies on the existence of mechanisms that allow limiting transcription to a functional level, both in terms of extent and rate. Sen1 is a central player in this sense: using its translocase activity this protein has evolved the specific function of dislodging RNAPs from the DNA template, thus ending the transcription cycle. Over the years, studies have shown that Sen1 uses this same mechanism in a multitude of situations, allowing termination of all three eukaryotic RNAPs in different contexts. In virtue of its helicase activity, Sen1 has also been proposed to have a prominent function in the resolution of co-transcriptional genotoxic R-loops, which can cause the stalling of replication forks. In this review, we provide a synopsis of past and recent findings on the functions of Sen1 in yeast and of its human homologue Senataxin (SETX).

Humans↗
PubMed2025

The TONSL-MMS22L complex and FANCM form an interdependent complex on chromatin to counter replication stress.

FANCM is branchpoint DNA translocase essential for cellular response to replication stress. Here, we show that replication stress stimulates FANCM and the TONSL-MMS22L heterodimer bound to histones H3-H4 to form an interdependent complex on chromatin. TONSL-MMS22L recruits FANCM and Fanconi anemia (FA) core complex to stalled and collapsed forks, maintains FANCM on replication-stressed chromatin, promotes FANCD2 monoubiquitination, facilitates both repair and replication traverse of DNA interstrand crosslinks (ICLs), and suppresses sister chromatid exchanges, through its interactions with FANCM and H3-H4. Reciprocally, both DNA translocase activity and phosphorylation of FANCM facilitate recruitment of TONSL-MMS22L and RAD51 to perturbed forks. Moreover, TONSL-MMS22L and FANCM function together to promote activation of the FA pathway, ICL repair, homologous recombination and replication traverse. Cancer patients with tumors with wildtype FANCM and low expression of TONSL-MMS22L have a more favorable prognosis than those with high expression. Thus, FANCM-TONSL-MMS22L acts coordinately as a complex on chromatin that resolves replication stress, and this complex may present a therapeutic target for wildtype FANCM-linked cancer.

FANCM↗
PubMed2021

Mechanism, cellular functions and cancer roles of polymerase-theta-mediated DNA end joining.

Cellular pathways that repair chromosomal double-strand breaks (DSBs) have pivotal roles in cell growth, development and cancer. These DSB repair pathways have been the target of intensive investigation, but one pathway - alternative end joining (a-EJ) - has long resisted elucidation. In this Review, we highlight recent progress in our understanding of a-EJ, especially the assignment of DNA polymerase theta (Polθ) as the predominant mediator of a-EJ in most eukaryotes, and discuss a potential molecular mechanism by which Polθ-mediated end joining (TMEJ) occurs. We address possible cellular functions of TMEJ in resolving DSBs that are refractory to repair by non-homologous end joining (NHEJ), DSBs generated following replication fork collapse and DSBs present owing to stalling of repair by homologous recombination. We also discuss how these context-dependent cellular roles explain how TMEJ can both protect against and cause genome instability, and the emerging potential of Polθ as a therapeutic target in cancer.

Animals↗
PubMed2026

PARG inhibition reduces ssDNA levels and limits RPA loading upon replication fork collapse.

Poly(ADP-ribosyl)ation (PARylation) is a transient post-translational modification catalyzed by PARP enzymes and reversed by PARG. PARG inhibition causes sustained PARylation and is being explored as an anticancer strategy, but its cellular consequences remain incompletely understood. Here, we examine how persistent PARylation influences cellular responses to replication stress and DNA damage. We show that sustained PARylation reduces phosphorylated and chromatin-bound RPA most strongly under fork-stalling conditions that progress toward fork collapse. This effect requires PARP1 activity and is restrained by intact ATR-CHK1 signaling, as checkpoint inhibition renders otherwise resistant cells permissive for PARG inhibitor-associated phosphorylated RPA loss from the chromatin. The reduction of RPA phosphorylation is not dependent on BRCA1 and it is not accompanied by increased RAD51 loading. Instead, reduced chromatin-bound RPA coincides with decreased exposed ssDNA. Our results identify a checkpoint-dependent fork-collapse state in which sustained PARylation limits ssDNA and RPA levels.

Replication Protein A↗
PubMed2026

The role of CHAMP1 in chromatin-mediated DNA damage repair.

Defects in the replication stress response are major drivers of cancer development and present key targetable vulnerabilities that can be exploited for anti-cancer therapy. Recent studies have identified CHAMP1 as a novel DNA damage repair factor with roles in double-strand break repair and the replication stress response. Mutations in CHAMP1 are associated with the neurodevelopmental disorder CHAMP1 Syndrome. More recently, children with CHAMP1 Syndrome have developed leukemia, suggesting that CHAMP1 mutations are a potential cancer risk factor. CHAMP1 is part of two DNA damage repair complexes: CHAMP1-POGZ-REV7 (Complex I) and CHAMP1-POGZ-HP1α (Complex II). Complex I promotes homologous recombination by removing the Shieldin complex from the ends of double strand breaks and allowing DSB end resection to occur. Complex II enriches heterochromatin content through the recruitment of the methyltransferase SETDB1 to DNA damage sites. Increased heterochromatin at stalled forks is associated with proper fork stability and restart, demonstrating the importance of CHAMP1 in maintaining genomic integrity. Loss of CHAMP1 leads to increased sensitivity to DNA damaging agents and increased dependence on other DNA damage repair pathways, such as the DNA damage checkpoint and the Fanconi Anemia pathway. CHAMP1 is overexpressed in breast and ovarian cancer cells with high levels of replication stress, providing a molecular mechanism for the tolerance of replication stress. These new findings on the relationship of CHAMP1 with well-established DNA damage repair pathways, suggest that targeting CHAMP1 could present a new synthetic lethality opportunity for cancer cells with high levels of replication stress.

CHAMP1↗