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Replication fork

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https://www.readbyqxmd.com/read/28334891/rad51-interconnects-between-dna-replication-dna-repair-and-immunity
#1
Souparno Bhattacharya, Kalayarasan Srinivasan, Salim Abdisalaam, Fengtao Su, Prithvi Raj, Igor Dozmorov, Ritu Mishra, Edward K Wakeland, Subroto Ghose, Shibani Mukherjee, Aroumougame Asaithamby
RAD51, a multifunctional protein, plays a central role in DNA replication and homologous recombination repair, and is known to be involved in cancer development. We identified a novel role for RAD51 in innate immune response signaling. Defects in RAD51 lead to the accumulation of self-DNA in the cytoplasm, triggering a STING-mediated innate immune response after replication stress and DNA damage. In the absence of RAD51, the unprotected newly replicated genome is degraded by the exonuclease activity of MRE11, and the fragmented nascent DNA accumulates in the cytosol, initiating an innate immune response...
February 21, 2017: Nucleic Acids Research
https://www.readbyqxmd.com/read/28334766/crystal-structure-of-the-n-terminal-domain-of-human-timeless-and-its-interaction-with-tipin
#2
Sandro Holzer, Gianluca Degliesposti, Mairi L Kilkenny, Sarah L Maslen, Dijana Matak-Vinkovíc, Mark Skehel, Luca Pellegrini
Human Timeless is involved in replication fork stabilization, S-phase checkpoint activation and establishment of sister chromatid cohesion. In the cell, Timeless forms a constitutive heterodimeric complex with Tipin. Here we present the 1.85 Å crystal structure of a large N-terminal segment of human Timeless, spanning amino acids 1-463, and we show that this region of human Timeless harbours a partial binding site for Tipin. Furthermore, we identify minimal regions of the two proteins that are required for the formation of a stable Timeless-Tipin complex and provide evidence that the Timeless-Tipin interaction is based on a composite binding interface comprising different domains of Timeless...
February 25, 2017: Nucleic Acids Research
https://www.readbyqxmd.com/read/28325102/building-up-and-breaking-down-mechanisms-controlling-recombination-during-replication
#3
Dana Branzei, Barnabas Szakal
The complete and faithful duplication of the genome is an essential prerequisite for proliferating cells to maintain genome integrity. This objective is greatly challenged by DNA damage encountered during replication, which causes fork stalling and in certain cases, fork breakage. DNA damage tolerance (DDT) pathways mitigate the effects on fork stability induced by replication fork stalling by mediating damage-bypass and replication fork restart. These DDT mechanisms, largely relying on homologous recombination (HR) and specialized polymerases, can however contribute to genome rearrangements and mutagenesis...
March 22, 2017: Critical Reviews in Biochemistry and Molecular Biology
https://www.readbyqxmd.com/read/28320884/replication-restart-in-bacteria
#4
Bénédicte Michel, Steven J Sandler
In bacteria replication forks assembled at a replication origin travel to the terminus, often a few megabases away. They may encounter obstacles that trigger replisome disassembly, rendering replication restart from abandoned forks crucial for cell viability. During the past 25 years the genes that encode replication restart proteins have been identified and genetically characterized. In parallel, the enzymes were purified and analyzed in vitro, where they can catalyze replication initiation in a sequence-independent manner from fork-like DNA structures...
March 20, 2017: Journal of Bacteriology
https://www.readbyqxmd.com/read/28314779/an-atr-dependent-function-for-the-ddx19-rna-helicase-in-nuclear-r-loop-metabolism
#5
Dana Hodroj, Bénédicte Recolin, Kamar Serhal, Susan Martinez, Nikolay Tsanov, Raghida Abou Merhi, Domenico Maiorano
Coordination between transcription and replication is crucial in the maintenance of genome integrity. Disturbance of these processes leads to accumulation of aberrant DNA:RNA hybrids (R-loops) that, if unresolved, generate DNA damage and genomic instability. Here we report a novel, unexpected role for the nucleopore-associated mRNA export factor Ddx19 in removing nuclear R-loops formed upon replication stress or DNA damage. We show, in live cells, that Ddx19 transiently relocalizes from the nucleopore to the nucleus upon DNA damage, in an ATR/Chk1-dependent manner, and that Ddx19 nuclear relocalization is required to clear R-loops...
March 17, 2017: EMBO Journal
https://www.readbyqxmd.com/read/28301743/eukaryotic-dna-replication-fork
#6
Peter M J Burgers, Thomas A Kunkel
This review focuses on the biogenesis and composition of the eukaryotic DNA replication fork, with an emphasis on the enzymes that synthesize DNA and repair discontinuities on the lagging strand of the replication fork. Physical and genetic methodologies aimed at understanding these processes are discussed. The preponderance of evidence supports a model in which DNA polymerase ε (Pol ε) carries out the bulk of leading strand DNA synthesis at an undisturbed replication fork. DNA polymerases α and δ carry out the initiation of Okazaki fragment synthesis and its elongation and maturation, respectively...
March 1, 2017: Annual Review of Biochemistry
https://www.readbyqxmd.com/read/28294450/initiation-of-drosophila-chorion-gene-amplification-requires-claspin-and-mus101-whereas-claspin-but-not-mus101-plays-a-major-role-during-elongation
#7
Seung Ho Choi, Ji-Hong Park, Tram Thi Ngoc Nguyen, Hee Jin Shim, Young-Han Song
BACKGROUND: Claspin and TopBP1 are checkpoint mediators that are required for the phosphorylation of Chk1 by ATR to maintain genomic stability. Here, we investigated the functions of Drosophila Claspin and mus101 (TopBP1 ortholog) during chorion (eggshell component) gene amplification, which occurs in follicle cells in the absence of global genomic DNA replication. RESULTS: Unlike Drosophila mei-41 (ATR ortholog) mutant embryos, Claspin and mus101 mutant embryos showed severe eggshell defects resulting from defects in chorion gene amplification...
March 14, 2017: Developmental Dynamics: An Official Publication of the American Association of Anatomists
https://www.readbyqxmd.com/read/28290553/slx4-prevents-gen1-dependent-dsbs-during-dna-replication-arrest-under-pathological-conditions-in-human-cells
#8
Eva Malacaria, Annapaola Franchitto, Pietro Pichierri
SLX4 is a versatile protein serving as docking for multiple structure-specific endonucleases during DNA repair, however, little is known about its function at demised replication forks. Using RNAi or FA-P cells complemented with SLX4 mutants that abrogate interaction with MUS81 or SLX1, we show that SLX4 cooperates with MUS81 to introduce DSBs after replication stress but also counteracts pathological targeting of demised forks by GEN1. Such unexpected function of SLX4 is unrelated to interaction with endonucleases, but concerns the physical presence of the protein...
March 14, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28276523/homozygosity-for-the-wrn-helicase-inactivating-variant-r834c-does-not-confer-a-werner-syndrome-clinical-phenotype
#9
Ashwini S Kamath-Loeb, Diego G Zavala-van Rankin, Jeny Flores-Morales, Mary J Emond, Julia M Sidorova, Alessandra Carnevale, Maria Del Carmen Cárdenas-Cortés, Thomas H Norwood, Raymond J Monnat, Lawrence A Loeb, Gabriela E Mercado-Celis
Loss-of-function mutations in the WRN helicase gene cause Werner syndrome- a progeroid syndrome with an elevated risk of cancer and other age-associated diseases. Large numbers of single nucleotide polymorphisms have been identified in WRN. We report here the organismal, cellular, and molecular phenotypes of variant rs3087425 (c. 2500C > T) that results in an arginine to cysteine substitution at residue 834 (R834C) and up to 90% reduction of WRN helicase activity. This variant is present at a high (5%) frequency in Mexico, where we identified 153 heterozygous and three homozygous individuals among 3,130 genotyped subjects...
March 9, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28273463/reversal-of-ddk-mediated-mcm-phosphorylation-by-rif1-pp1-regulates-replication-initiation-and-replisome-stability-independently-of-atr-chk1
#10
Robert C Alver, Gaganmeet Singh Chadha, Peter J Gillespie, J Julian Blow
Dbf4-dependent kinases (DDKs) are required for the initiation of DNA replication, their essential targets being the MCM2-7 proteins. We show that, in Xenopus laevis egg extracts and human cells, hyper-phosphorylation of DNA-bound Mcm4, but not phosphorylation of Mcm2, correlates with DNA replication. These phosphorylations are differentially affected by the DDK inhibitors PHA-767491 and XL413. We show that DDK-dependent MCM phosphorylation is reversed by protein phosphatase 1 (PP1) targeted to chromatin by Rif1...
March 7, 2017: Cell Reports
https://www.readbyqxmd.com/read/28272375/regulation%C3%A2-of%C3%A2-dna%C3%A2-replication%C3%A2-through%C3%A2-natural%C3%A2-impediments%C3%A2-in%C3%A2-the%C3%A2-eukaryotic%C3%A2-genome
#11
REVIEW
Mariana C Gadaleta, Eishi Noguchi
All living organisms need to duplicate their genetic information while protecting it from unwanted mutations, which can lead to genetic disorders and cancer development. Inaccuracies during DNA replication are the major cause of genomic instability, as replication forks are prone to stalling and collapse, resulting in DNA damage. The presence of exogenous DNA damaging agents as well as endogenous difficult-to-replicate DNA regions containing DNA-protein complexes, repetitive DNA, secondary DNA structures, or transcribing RNA polymerases, increases the risk of genomic instability and thus threatens cell survival...
March 7, 2017: Genes
https://www.readbyqxmd.com/read/28270495/the-checkpoint-kinase-1-inhibitor-prexasertib-induces-regression-of-preclinical-models-of-human-neuroblastoma
#12
Caitlin D Lowery, Alle B VanWye, Michele Dowless, Wayne Blosser, Beverly L Falcon, Julie Stewart, Jennifer Stephens, Richard P Beckmann, Aimee Bence Lin, Louis F Stancato
PURPOSE: Checkpoint kinase 1 (CHK1) is a key regulator of the DNA damage response and a mediator of replication stress through modulation of replication fork licensing and activation of S and G2/M cell cycle checkpoints. We evaluated prexasertib (LY2606368), a small molecule CHK1 inhibitor currently in clinical testing, in multiple preclinical models of pediatric cancer. Following an initial assessment of prexasertib activity, this study focused on preclinical models of neuroblastoma...
March 7, 2017: Clinical Cancer Research: An Official Journal of the American Association for Cancer Research
https://www.readbyqxmd.com/read/28270450/ssb1-and-ssb2-cooperate-to-regulate-mouse-hematopoietic-stem-and-progenitor-cells-by-resolving-replicative-stress
#13
Wei Shi, Therese Vu, Didier Boucher, Anna Biernacka, Jules Nde, Raj K Pandita, Jasmin Straube, Glen M Boyle, Fares Al-Ejeh, Purba Nag, Jessie Jeffery, Janelle L Harris, Amanda L Bain, Marta Grzelak, Magdalena Skrzypczak, Abhishek Mitra, Norbert Dojer, Nicola Crosetto, Nicole Cloonan, Olivier J Becherel, John Finnie, Jeffrey R Skaar, Carl R Walkley, Tej K Pandita, Maga Rowicka, Krzysztof Ginalski, Steven W Lane, Kum Kum Khanna
Hematopoietic stem and progenitor cells (HSPCs) are vulnerable to endogenous damage and defects in DNA repair can limit their function. The two single-stranded DNA binding proteins SSB1 and SSB2 are crucial regulators of the DNA damage response; however their overlapping roles during normal physiology are incompletely understood. We generated mice where both Ssb1 and Ssb2 were constitutively or conditionally deleted. Constitutive Ssb1/Ssb2 double knockout (DKO) caused early embryonic lethality, while conditional Ssb1/Ssb2 double knockout (cDKO) in adult mice resulted in acute lethality due to bone marrow failure and intestinal atrophy featuring stem and progenitor cell depletion, a phenotype unexpected from the previously reported single knockout models of Ssb1 or Ssb2 Mechanistically, cDKO HSPCs showed altered replication fork dynamics, massive accumulation of DNA damage, genome-wide double strand breaks (DSBs) enriched at Ssb binding regions and CpG islands, together with the accumulation of R-loops and cytosolic ssDNA...
March 7, 2017: Blood
https://www.readbyqxmd.com/read/28262582/a-role-for-the-base-excision-repair-enzyme-neil3-in-replication-dependent-repair-of-interstrand-dna-cross-links-derived-from-psoralen-and-abasic-sites
#14
REVIEW
Zhiyu Yang, Maryam Imani Nejad, Jacqueline Gamboa Varela, Nathan E Price, Yinsheng Wang, Kent S Gates
Interstrand DNA-DNA cross-links are highly toxic lesions that are important in medicinal chemistry, toxicology, and endogenous biology. In current models of replication-dependent repair, stalling of a replication fork activates the Fanconi anemia pathway and cross-links are "unhooked" by the action of structure-specific endonucleases such as XPF-ERCC1 that make incisions flanking the cross-link. This process generates a double-strand break, which must be subsequently repaired by homologous recombination. Recent work provided evidence for a new, incision-independent unhooking mechanism involving intrusion of a base excision repair (BER) enzyme, NEIL3, into the world of cross-link repair...
April 2017: DNA Repair
https://www.readbyqxmd.com/read/28257701/the-smx-dna-repair-tri-nuclease
#15
Haley D M Wyatt, Rob C Laister, Stephen R Martin, Cheryl H Arrowsmith, Stephen C West
The efficient removal of replication and recombination intermediates is essential for the maintenance of genome stability. Resolution of these potentially toxic structures requires the MUS81-EME1 endonuclease, which is activated at prometaphase by formation of the SMX tri-nuclease containing three DNA repair structure-selective endonucleases: SLX1-SLX4, MUS81-EME1, and XPF-ERCC1. Here we show that SMX tri-nuclease is more active than the three individual nucleases, efficiently cleaving replication forks and recombination intermediates...
March 2, 2017: Molecular Cell
https://www.readbyqxmd.com/read/28255082/pten-regulates-glutamine-flux-to-pyrimidine-synthesis-and-sensitivity-to-dihydroorotate-dehydrogenase-inhibition
#16
Deepti Mathur, Elias Stratikopoulos, Sait Ozturk, Nicole Steinbach, Sarah Pegno, Sarah Schoenfeld, Raymund Yong, Vundavalli V Murty, John M Asara, Lewis C Cantley, Ramon Parsons
Metabolic changes induced by oncogenic drivers of cancer contribute to tumor growth and are attractive targets for cancer treatment. Here, we found that increased growth of PTEN-mutant cells was dependent on glutamine flux through the de novo pyrimidine synthesis pathway, which created sensitivity to the inhibition of dihydroorotate dehydrogenase, a rate-limiting enzyme for pyrimidine ring synthesis. S-phase PTEN-mutant cells showed increased numbers of replication forks, and inhibitors of dihydroorotate dehydrogenase led to chromosome breaks and cell death due to inadequate ATR activation and DNA damage at replication forks...
March 2, 2017: Cancer Discovery
https://www.readbyqxmd.com/read/28254358/specific-killing-of-dna-damage-response-deficient-cells-with-inhibitors-of-poly-adp-ribose-glycohydrolase
#17
Polly Gravells, Emma Grant, Kate M Smith, Dominic I James, Helen E Bryant
Poly(ADP-ribosylation) of proteins following DNA damage is well studied and the use of poly(ADP-ribose) polymerase (PARP) inhibitors as therapeutic agents is an exciting prospect for the treatment of many cancers. Poly(ADP-ribose) glycohydrolase (PARG) has endo- and exoglycosidase activities which can cleave glycosidic bonds, rapidly reversing the action of PARP enzymes. Like addition of poly(ADP-ribose) (PAR) by PARP, removal of PAR by PARG is also thought to be required for repair of DNA strand breaks and for continued replication at perturbed forks...
February 17, 2017: DNA Repair
https://www.readbyqxmd.com/read/28246327/monoubiquitylation-of-histone-h2b-contributes-to-the-bypass-of-dna-damage-during-and-after-dna-replication
#18
Shih-Hsun Hung, Ronald P Wong, Helle D Ulrich, Cheng-Fu Kao
DNA lesion bypass is mediated by DNA damage tolerance (DDT) pathways and homologous recombination (HR). The DDT pathways, which involve translesion synthesis and template switching (TS), are activated by the ubiquitylation (ub) of PCNA through components of the RAD6-RAD18 pathway, whereas the HR pathway is independent of RAD18 However, it is unclear how these processes are coordinated within the context of chromatin. Here we show that Bre1, an ubiquitin ligase specific for histone H2B, is recruited to chromatin in a manner coupled to replication of damaged DNA...
February 28, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28244221/genomic-rearrangements-induced-by-unscheduled-dna-double-strand-breaks-in-somatic-mammalian-cells
#19
REVIEW
Ayeong So, Tangui Le Guen, Bernard S Lopez, Josée Guirouilh-Barbat
DNA double-strand breaks (DSBs) are highly toxic lesions that can lead to profound genome rearrangements and/or cell death. DSBs routinely occur in genomes due to endogenous or exogenous stresses. Efficient repair systems, canonical non-homologous end-joining and homologous recombination, exist in the cell and not only ensure the maintenance of genome integrity but also, via specific programmed DNA double-strand breaks, permit its diversity and plasticity. However, these repair systems need to be tightly controlled because they can also generate genomic rearrangements...
February 28, 2017: FEBS Journal
https://www.readbyqxmd.com/read/28242626/atr-inhibition-disrupts-rewired-homologous-recombination-and-fork-protection-pathways-in-parp-inhibitor-resistant-brca-deficient-cancer-cells
#20
Stephanie A Yazinski, Valentine Comaills, Rémi Buisson, Marie-Michelle Genois, Hai Dang Nguyen, Chu Kwen Ho, Tanya Todorova Kwan, Robert Morris, Sam Lauffer, André Nussenzweig, Sridhar Ramaswamy, Cyril H Benes, Daniel A Haber, Shyamala Maheswaran, Michael J Birrer, Lee Zou
Poly-(ADP-ribose) polymerase (PARP) inhibitors (PARPis) selectively kill BRCA1/2-deficient cells, but their efficacy in BRCA-deficient patients is limited by drug resistance. Here, we used derived cell lines and cells from patients to investigate how to overcome PARPi resistance. We found that the functions of BRCA1 in homologous recombination (HR) and replication fork protection are sequentially bypassed during the acquisition of PARPi resistance. Despite the lack of BRCA1, PARPi-resistant cells regain RAD51 loading to DNA double-stranded breaks (DSBs) and stalled replication forks, enabling two distinct mechanisms of PARPi resistance...
February 27, 2017: Genes & Development
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