Checkpoint-mediated DNA polymerase e exonuclease activity curbing counteracts resection-driven fork collapse
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PROVIDER: PRJNA658081 | ENA |
REPOSITORIES: ENA
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Project description:DNA polymerase epsilon (Pole) carries out leading strand synthesis with high fidelity owing to its exonuclease activity. Pole polymerase and exonuclease activities are in balance, due to partitioning of nascent strands between catalytic sites, so that net end resection occurs when synthesis is impaired. Stalling of chromosomal DNA synthesis activates replication checkpoint kinases, required to preserve the functional integrity of replication forks. We found that Pole is phosphorylated in a Rad53CHK1-dependent manner upon fork stalling, likely to limit Pole-driven nascent strand resection that causes replication fork collapse. In stress conditions Pole phosphorylation occurs on serine 430 of the Pol2 catalytic subunit. A S430 phosphomimic limits strand partitioning and exonucleolytic processivity, while non-phosphorylatable Pol2-S430A bypasses checkpoint regulation causing stalled fork resection and collapse. We propose that checkpoint kinases switch Pole to an exonuclease-safe mode by curbing active site partitioning thus preventing nascent strand resection and stabilizing stalled replication forks.
2021-04-30 | GSE156480 | GEO
Project description:DNA polymerase ε (Polε) carries out high-fidelity leading strand synthesis owing to its exonuclease activity. Polε polymerase and exonuclease activities are balanced, because of partitioning of nascent DNA strands between catalytic sites, so that net resection occurs when synthesis is impaired. In vivo, DNA synthesis stalling activates replication checkpoint kinases, which act to preserve the functional integrity of replication forks. We show that stalled Polε drives nascent strand resection causing fork functional collapse, averted via checkpoint-dependent phosphorylation. Polε catalytic subunit Pol2 is phosphorylated on serine 430, influencing partitioning between polymerase and exonuclease active sites. A phosphormimetic S430D change reduces exonucleolysis in vitro and counteracts fork collapse. Conversely, non-phosphorylatable pol2-S430A expression causes resection-driven stressed fork defects. Our findings reveal that checkpoint kinases switch Polε to an exonuclease-safe mode preventing nascent strand resection and stabilizing stalled replication forks. Elective partitioning suppression has implications for the diverse Polε roles in genome integrity maintenance.
| S-EPMC7612761 | biostudies-literature
Project description:Leading-strand DNA replication by polymerase epsilon (Polϵ) across single-strand breaks (SSBs) causes single-ended double-strand breaks (seDSBs), which are repaired via homology-directed repair (HDR) and suppressed by fork reversal (FR). Although previous studies identified many molecules required for hydroxyurea-induced FR, FR at seDSBs is poorly understood. Here, we identified molecules that specifically mediate FR at seDSBs. Because FR at seDSBs requires poly(ADP ribose)polymerase 1 (PARP1), we hypothesized that seDSB/FR-associated molecules would increase tolerance to camptothecin (CPT) but not the PARP inhibitor olaparib, even though both anti-cancer agents generate seDSBs. Indeed, we uncovered that Polϵ exonuclease and CTF18, a Polϵ cofactor, increased tolerance to CPT but not olaparib. To explore potential functional interactions between Polϵ exonuclease, CTF18, and PARP1, we created exonuclease-deficient POLE1exo-/-, CTF18-/-, PARP1-/-, CTF18-/-/POLE1exo-/-, PARP1-/-/POLE1exo-/-, and CTF18-/-/PARP1-/- cells. Epistasis analysis indicated that Polϵ exonuclease and CTF18 were interdependent and required PARP1 for CPT tolerance. Remarkably, POLE1exo-/- and HDR-deficient BRCA1-/- cells exhibited similar CPT sensitivity. Moreover, combining POLE1exo-/- with BRCA1-/- mutations synergistically increased CPT sensitivity. In conclusion, the newly identified PARP1-CTF18-Polϵ exonuclease axis and HDR act independently to prevent fork collapse at seDSBs. Olaparib inhibits this axis, explaining the pronounced cytotoxic effects of olaparib on HDR-deficient cells.
| S-EPMC10711444 | biostudies-literature
Project description:During genome replication, the leading strand DNA polymerase conducts continuous synthesis over long stretches of DNA within each replicon. Processive DNA synthesis supports symmetric progression of sister replication forks and efficient genome duplication. To address the mechanisms underlying leading strand polymerase-mediated synthesis, we examine one of its conserved domains, referred to as POPS, in the budding yeast Pol2 enzyme. We provide evidence that POPS supports replication fork symmetry and efficient genome replication via balancing the function of the Pol2 exonuclease domain. We found that the defective growth, slow S phase progression, and impaired genome synthesis associated with a POPS mutation were rescued by abolishing the Pol2 exonuclease activity. The suppressive effects further extended to the increased DNA re-arrangements in the POPS mutant and its negative genetic interactions with mutants of other genome maintenance factors. Significantly, our single molecule replicon-seq data demonstrate that the POPS mutant exhibited genome-wide replication fork asymmetry, and this defect was improved by eliminating the Pol2 exonuclease activity, thus providing a basis for its rescuing of a range of POPS mutant phenotypes. Collectively, these data suggest a model in which balanced activity between a unique Pol2 catalytic domain, and its exonuclease domain facilitates replication fork symmetry and genome maintenance.
2022-09-02 | GSE212101 | GEO
Project description:Problems during DNA replication underlie genomic instability and drive malignant transformation. The DNA damage checkpoint stabilizes stalled replication forks thus counteracting aberrant fork transitions, DNA breaks and chromosomal rearrangements. We analyzed fork processing in checkpoint deficient cells by coupling psoralen crosslinking with replication intermediate two-dimensional gel analysis. This revealed a novel role for Exo1 nuclease in resecting reversed replication fork structures and counteracting the accumulation of aberrant intermediates resembling fork cleavage products. Genetic analyses demonstrated a functional interplay of Exo1 with Mus81, Dna2 and Sae2 nucleases in promoting cell survival following replication stress, suggestive of concerted nucleolytic processing of stalled forks. While Mus81 and other Structure Specific Endonucleases do not contribute to obvious collapsed fork transitions, Dna2 promotes reversed fork resection likely by facilitating Exo1 access to nascent strands. Instead, Sae2 cooperates with Exo1 in counteracting putative fork cleavage events linked to double strand breaks formation and increased gross chromosomal rearrangement rates. Our data indicate that in checkpoint deficient cells diverse nuclease activities interface to eliminate aberrant replication intermediates and prevent chromosome instability.
| S-EPMC5159547 | biostudies-literature
Project description:Genome-wide fork-collapse sites in MEFs from ATR inhibition [mouse]
| PRJNA475584 | ENA
Project description:The S phase checkpoint is crucial to maintain genome stability under conditions that threaten DNA replication. One of its critical functions is to prevent Exo1-dependent fork degradation, and Exo1 is phosphorylated in response to different genotoxic agents. Exo1 seemed to be regulated by several post-translational modifications in the presence of replicative stress, but the specific contribution of checkpoint-dependent phosphorylation to Exo1 control and fork stability is not clear. We show here that Exo1 phosphorylation is Dun1-independent and Rad53-dependent in response to DNA damage or dNTP depletion, and in both situations Exo1 is similarly phosphorylated at multiple sites. To investigate the correlation between Exo1 phosphorylation and fork stability, we have generated phospho-mimic exo1 alleles that rescue fork collapse in rad53 mutants as efficiently as exo1-nuclease dead mutants or the absence of Exo1, arguing that Rad53-dependent phosphorylation is the mayor requirement to preserve fork stability. We have also shown that this rescue is Bmh1-2 independent, arguing that the 14-3-3 proteins are dispensable for fork stabilization, at least when Exo1 is downregulated. Importantly, our results indicated that phosphorylation specifically inhibits the 5' to 3'exo-nuclease activity, suggesting that this activity of Exo1 and not the flap-endonuclease, is the enzymatic activity responsible of the collapse of stalled replication forks in checkpoint mutants.
| S-EPMC7102976 | biostudies-literature
Project description:Nascent strand were purified with either the BrdU or the lambda exonuclease methods from culture human basophilic erythroblasts and sequenced/ Two methods were compared to isolated the Nascent strand, lambda exonuclease digestion or immunoprecipitation after pulse labelling with BrdU The following files were generated by combining round 1 and 2 sample files; FNY01_2_2_Ery_NS_BrdU_macs_summits.bed FNY01_2_2_Ery_NS_BrdU_macs_peaks.bed FNY01_2_2_Ery_NS_lexo_macs_peaks.bed FNY01_2_2_Ery_NS_lexo_macs_summits.bed
2014-05-01 | E-GEOD-50976 | biostudies-arrayexpress
Project description:Cellular proteostasis collapse in mammalian senescence
| PRJNA512837 | ENA
Project description:Dual Roles of Poly(dA:dT) Tracts in Replication Initiation and Fork Collapse
| PRJNA478131 | ENA