scholarly journals Holliday junction trap shows how cells use recombination and a junction-guardian role of RecQ helicase

2016 ◽  
Vol 2 (11) ◽  
pp. e1601605 ◽  
Author(s):  
Jun Xia ◽  
Li-Tzu Chen ◽  
Qian Mei ◽  
Chien-Hui Ma ◽  
Jennifer A. Halliday ◽  
...  
Keyword(s):  
Dna Damage ◽  
Genome Instability ◽  
Human Cancer ◽  
Single Cells ◽  
Strand Break ◽  
Holliday Junctions ◽  
Dna Breaks ◽  
E Coli ◽  
Dna Replication And Repair ◽  
The Many

DNA repair by homologous recombination (HR) underpins cell survival and fuels genome instability, cancer, and evolution. However, the main kinds and sources of DNA damage repaired by HR in somatic cells and the roles of important HR proteins remain elusive. We present engineered proteins that trap, map, and quantify Holliday junctions (HJs), a central DNA intermediate in HR, based on catalytically deficient mutant RuvC protein ofEscherichia coli. We use RuvCDefGFP (RDG) to map genomic footprints of HR at defined DNA breaks inE. coliand demonstrate genome-scale directionality of double-strand break (DSB) repair along the chromosome. Unexpectedly, most spontaneous HR-HJ foci are instigated, not by DSBs, but rather by single-stranded DNA damage generated by replication. We show that RecQ, theE. coliortholog of five human cancer proteins, nonredundantly promotes HR-HJ formation in single cells and, in a novel junction-guardian role, also prevents apparent non-HR–HJs promoted by RecA overproduction. We propose that one or more human RecQ orthologs may act similarly in human cancers overexpressing the RecA orthologRAD51and find that cancer genome expression data implicate the orthologs BLM and RECQL4 in conjunction with EME1 and GEN1 as probable HJ reducers in such cancers. Our results support RecA-overproducingE. colias a model of the many human tumors with up-regulatedRAD51and provide the first glimpses of important, previously elusive reaction intermediates in DNA replication and repair in single living cells.

scholarly journals Two mechanisms of chromosome fragility at replication-termination sites in bacteria

2021 ◽  
Vol 7 (25) ◽  
pp. eabe2846
Author(s):  
Qian Mei ◽  
Devon M. Fitzgerald ◽  
Jingjing Liu ◽  
Jun Xia ◽  
John P. Pribis ◽  
...  
Keyword(s):  
Replication Fork ◽  
Genome Instability ◽  
Neurological Diseases ◽  
Strand Break ◽  
Fragile Sites ◽  
Holliday Junctions ◽  
Dna Breaks ◽  
Dna Damage And Repair ◽  
Chromosome Fragility ◽  
Chromosomal Fragile Sites

Chromosomal fragile sites are implicated in promoting genome instability, which drives cancers and neurological diseases. Yet, the causes and mechanisms of chromosome fragility remain speculative. Here, we identify three spontaneous fragile sites in the Escherichia coli genome and define their DNA damage and repair intermediates at high resolution. We find that all three sites, all in the region of replication termination, display recurrent four-way DNA or Holliday junctions (HJs) and recurrent DNA breaks. Homology-directed double-strand break repair generates the recurrent HJs at all of these sites; however, distinct mechanisms of DNA breakage are implicated: replication fork collapse at natural replication barriers and, unexpectedly, frequent shearing of unsegregated sister chromosomes at cell division. We propose that mechanisms such as both of these may occur ubiquitously, including in humans, and may constitute some of the earliest events that underlie somatic cell mosaicism, cancers, and other diseases of genome instability.

scholarly journals Biology before the SOS Response—DNA Damage Mechanisms at Chromosome Fragile Sites

Cells ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 2275
Author(s):  
Devon M. Fitzgerald ◽  
Susan M Rosenberg
Keyword(s):  
Dna Damage ◽  
Genome Instability ◽  
Human Cancer ◽  
Sos Response ◽  
Fragile Sites ◽  
Holliday Junctions ◽  
Cancer Evolution ◽  
Dna Damage Tolerance ◽  
Chromosome Fragility ◽  
Species Evolution

The Escherichia coli SOS response to DNA damage, discovered and conceptualized by Evelyn Witkin and Miroslav Radman, is the prototypic DNA-damage stress response that upregulates proteins of DNA protection and repair, a radical idea when formulated in the late 1960s and early 1970s. SOS-like responses are now described across the tree of life, and similar mechanisms of DNA-damage tolerance and repair underlie the genome instability that drives human cancer and aging. The DNA damage that precedes damage responses constitutes upstream threats to genome integrity and arises mostly from endogenous biology. Radman’s vision and work on SOS, mismatch repair, and their regulation of genome and species evolution, were extrapolated directly from bacteria to humans, at a conceptual level, by Radman, then many others. We follow his lead in exploring bacterial molecular genomic mechanisms to illuminate universal biology, including in human disease, and focus here on some events upstream of SOS: the origins of DNA damage, specifically at chromosome fragile sites, and the engineered proteins that allow us to identify mechanisms. Two fragility mechanisms dominate: one at replication barriers and another associated with the decatenation of sister chromosomes following replication. DNA structures in E. coli, additionally, suggest new interpretations of pathways in cancer evolution, and that Holliday junctions may be universal molecular markers of chromosome fragility.

scholarly journals Monohydrazone Based G-Quadruplex Selective Ligands Induce DNA Damage and Genome Instability in Human Cancer Cells

2020 ◽  
Vol 63 (6) ◽  
pp. 3090-3103 ◽  
Author(s):  
Jussara Amato ◽  
Giulia Miglietta ◽  
Rita Morigi ◽  
Nunzia Iaccarino ◽  
Alessandra Locatelli ◽  
...  
Keyword(s):  
Dna Damage ◽  
Cancer Cells ◽  
Genome Instability ◽  
Human Cancer ◽  
Human Cancer Cells ◽  
G Quadruplex ◽  
Selective Ligands

scholarly journals TDP-43 mutations link Amyotrophic Lateral Sclerosis with R-loop homeostasis and R loop-mediated DNA damage

PLoS Genetics ◽  
2020 ◽  
Vol 16 (12) ◽  
pp. e1009260
Author(s):  
Marta Giannini ◽  
Aleix Bayona-Feliu ◽  
Daisy Sproviero ◽  
Sonia I. Barroso ◽  
Cristina Cereda ◽  
...  
Keyword(s):  
Dna Damage ◽  
Amyotrophic Lateral Sclerosis ◽  
Rna Binding ◽  
Neurodegenerative Disorder ◽  
Genome Instability ◽  
Neuronal Model ◽  
Dna Breaks ◽  
Dna And Rna ◽  
Double Strand Dna Breaks ◽  
Lateral Sclerosis

TDP-43 is a DNA and RNA binding protein involved in RNA processing and with structural resemblance to heterogeneous ribonucleoproteins (hnRNPs), whose depletion sensitizes neurons to double strand DNA breaks (DSBs). Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disorder, in which 97% of patients are familial and sporadic cases associated with TDP-43 proteinopathies and conditions clearing TDP-43 from the nucleus, but we know little about the molecular basis of the disease. After showing with the non-neuronal model of HeLa cells that TDP-43 depletion increases R loops and associated genome instability, we prove that mislocalization of mutated TDP-43 (A382T) in transfected neuronal SH-SY5Y and lymphoblastoid cell lines (LCLs) from an ALS patient cause R-loop accumulation, R loop-dependent increased DSBs and Fanconi Anemia repair centers. These results uncover a new role of TDP-43 in the control of co-transcriptional R loops and the maintenance of genome integrity by preventing harmful R-loop accumulation. Our findings thus link TDP-43 pathology to increased R loops and R loop-mediated DNA damage opening the possibility that R-loop modulation in TDP-43-defective cells might help develop ALS therapies.

scholarly journals The Dystonia Gene THAP1 Controls DNA Double Strand Break Repair Choice

2020 ◽  
Author(s):  
Kenta Shinoda ◽  
Dali Zong ◽  
Elsa Callen ◽  
Wei Wu ◽  
Lavinia C. Dumitrache ◽  
...  
Keyword(s):  
Dna Damage ◽  
Genome Instability ◽  
Parp Inhibitor ◽  
Progression Free Survival ◽  
Strand Break ◽  
Transcriptional Network ◽  
Cross Resistance ◽  
Dna Double Strand Breaks ◽  
Dsb Repair ◽  
Protein Levels

AbstractThe Shieldin complex, consisting of SHLD1, SHLD2, SHLD3 and REV7, shields DNA double strand breaks (DSBs) from nucleolytic resection. The end-protecting activity of Shieldin promotes productive non-homologous end joining (NHEJ) in G1 but can threaten genome integrity during S-phase by blocking homologous recombination (HR). Curiously, the penultimate Shieldin component, SHLD1 is one of the least abundant mammalian proteins. Here, we report that the transcription factors THAP1, YY1 and HCF1 bind directly to the SHLD1 promoter, where they cooperatively maintain the low basal expression of SHLD1. Functionally, this transcriptional network ensures that SHLD1 protein levels are kept in check to enable a proper balance between end protection and end resection during physiological DSB repair. In the context of BRCA1 deficiency, loss of THAP1 dependent SHLD1 expression confers cross resistance to PARP inhibitor and cisplatin, and shorter progression free survival in ovarian cancer patients. In contrast, loss of THAP1 in BRCA2 deficient cells increases genome instability and correlates with improved responses to chemotherapy. Pathogenic THAP1 mutations are causatively linked to the adult-onset torsion dystonia type 6 (DYT6) movement disorder, but the critical disease targets are unknown. We further demonstrate that murine models of Thap1-associated dystonia show reduced Shld1 expression concomitant with elevated levels of unresolved DNA damage in the brain. In summary, our study provides the first example of a transcriptional network that directly controls DSB repair choice and reveals a previously unsuspected link between DNA damage and dystonia.

scholarly journals Single-Strand Break End Resection in Genome Integrity: Mechanism and Regulation by APE2

2018 ◽  
Vol 19 (8) ◽  
pp. 2389 ◽  
Author(s):  
Md. Hossain ◽  
Yunfeng Lin ◽  
Shan Yan
Keyword(s):  
Dna Damage ◽  
Genome Instability ◽  
Strand Break ◽  
Single Strand ◽  
Genome Integrity ◽  
Single Strand Break ◽  
Strand Breaks ◽  
Single Strand Breaks ◽  
Damage Response ◽  
End Resection

DNA single-strand breaks (SSBs) occur more than 10,000 times per mammalian cell each day, representing the most common type of DNA damage. Unrepaired SSBs compromise DNA replication and transcription programs, leading to genome instability. Unrepaired SSBs are associated with diseases such as cancer and neurodegenerative disorders. Although canonical SSB repair pathway is activated to repair most SSBs, it remains unclear whether and how unrepaired SSBs are sensed and signaled. In this review, we propose a new concept of SSB end resection for genome integrity. We propose a four-step mechanism of SSB end resection: SSB end sensing and processing, as well as initiation, continuation, and termination of SSB end resection. We also compare different mechanisms of SSB end resection and DSB end resection in DNA repair and DNA damage response (DDR) pathways. We further discuss how SSB end resection contributes to SSB signaling and repair. We focus on the mechanism and regulation by APE2 in SSB end resection in genome integrity. Finally, we identify areas of future study that may help us gain further mechanistic insight into the process of SSB end resection. Overall, this review provides the first comprehensive perspective on SSB end resection in genome integrity.

scholarly journals Mechanistic insight into the role of Poly(ADP-ribosyl)ation in DNA topology modulation and response to DNA damage

Mutagenesis ◽  
2019 ◽  
Vol 35 (1) ◽  
pp. 107-118
Author(s):  
Bakhyt T Matkarimov ◽  
Dmitry O Zharkov ◽  
Murat K Saparbaev
Keyword(s):  
Dna Damage ◽  
Dna Repair ◽  
Genotoxic Stress ◽  
Strand Break ◽  
Dna Supercoiling ◽  
Dna Strand Breaks ◽  
Chromosomal Dna ◽  
Dna Breaks ◽  
Strand Breaks ◽  
Dna Strand

Abstract Genotoxic stress generates single- and double-strand DNA breaks either through direct damage by reactive oxygen species or as intermediates of DNA repair. Failure to detect and repair DNA strand breaks leads to deleterious consequences such as chromosomal aberrations, genomic instability and cell death. DNA strand breaks disrupt the superhelical state of cellular DNA, which further disturbs the chromatin architecture and gene activity regulation. Proteins from the poly(ADP-ribose) polymerase (PARP) family, such as PARP1 and PARP2, use NAD+ as a substrate to catalyse the synthesis of polymeric chains consisting of ADP-ribose units covalently attached to an acceptor molecule. PARP1 and PARP2 are regarded as DNA damage sensors that, upon activation by strand breaks, poly(ADP-ribosyl)ate themselves and nuclear acceptor proteins. Noteworthy, the regularly branched structure of poly(ADP-ribose) polymer suggests that the mechanism of its synthesis may involve circular movement of PARP1 around the DNA helix, with a branching point in PAR corresponding to one complete 360° turn. We propose that PARP1 stays bound to a DNA strand break end, but rotates around the helix displaced by the growing poly(ADP-ribose) chain, and that this rotation could introduce positive supercoils into damaged chromosomal DNA. This topology modulation would enable nucleosome displacement and chromatin decondensation around the lesion site, facilitating the access of DNA repair proteins or transcription factors. PARP1-mediated DNA supercoiling can be transmitted over long distances, resulting in changes in the high-order chromatin structures. The available structures of PARP1 are consistent with the strand break-induced PAR synthesis as a driving force for PARP1 rotation around the DNA axis.

scholarly journals DNA polymerase X from Deinococcus radiodurans implicated in bacterial tolerance to DNA damage is characterized as a short patch base excision repair polymerase

Microbiology ◽  
2009 ◽  
Vol 155 (9) ◽  
pp. 3005-3014 ◽  
Author(s):  
Nivedita P. Khairnar ◽  
Hari S. Misra
Keyword(s):  
Dna Damage ◽  
Dna Polymerase ◽  
Base Excision Repair ◽  
Deinococcus Radiodurans ◽  
Excision Repair ◽  
Strand Break ◽  
Klenow Fragment ◽  
E Coli ◽  
Base Excision

The Deinococcus radiodurans R1 genome encodes an X-family DNA repair polymerase homologous to eukaryotic DNA polymerase β. The recombinant deinococcal polymerase X (PolX) purified from transgenic Escherichia coli showed deoxynucleotidyltransferase activity. Unlike the Klenow fragment of E. coli, this enzyme showed short patch DNA synthesis activity on heteropolymeric DNA substrate. The recombinant enzyme showed 5′-deoxyribose phosphate (5′-dRP) lyase activity and base excision repair function in vitro, with the help of externally supplied glycosylase and AP endonuclease functions. A polX disruption mutant of D. radiodurans expressing 5′-dRP lyase and a truncated polymerase domain was comparatively less sensitive to γ-radiation than a polX deletion mutant. Both mutants showed higher sensitivity to hydrogen peroxide. Excision repair mutants of E. coli expressing this polymerase showed functional complementation of UV sensitivity. These results suggest the involvement of deinococcal polymerase X in DNA-damage tolerance of D. radiodurans, possibly by contributing to DNA double-strand break repair and base excision repair.

scholarly journals Role of Lamin B1 in Chromatin Instability

2014 ◽  
Vol 35 (5) ◽  
pp. 884-898 ◽  
Author(s):  
Veronika Butin-Israeli ◽  
Stephen A. Adam ◽  
Nikhil Jain ◽  
Gabriel L. Otte ◽  
Daniel Neems ◽  
...  
Keyword(s):  
Dna Damage ◽  
Dna Replication ◽  
S Phase ◽  
Dna Breaks ◽  
End Joining ◽  
Nuclear Lamins ◽  
Lamin B1 ◽  
Dna Damage Signaling ◽  
Double Strand Dna Breaks ◽  
Dna Replication And Repair

Nuclear lamins play important roles in the organization and structure of the nucleus; however, the specific mechanisms linking lamin structure to nuclear functions are poorly defined. We demonstrate that reducing nuclear lamin B1 expression by short hairpin RNA-mediated silencing in cancer cell lines to approximately 50% of normal levels causes a delay in the cell cycle and accumulation of cells in early S phase. The S phase delay appears to be due to the stalling and collapse of replication forks. The double-strand DNA breaks resulting from replication fork collapse were inefficiently repaired, causing persistent DNA damage signaling and the assembly of extensive repair foci on chromatin. The expression of multiple factors involved in DNA replication and repair by both nonhomologous end joining and homologous repair is misregulated when lamin B1 levels are reduced. We further demonstrate that lamin B1 interacts directly with the promoters of some genes associated with DNA damage response and repair, includingBRCA1andRAD51. Taken together, the results suggest that the maintenance of lamin B1 levels is required for DNA replication and repair through regulation of the expression of key factors involved in these essential nuclear functions.

scholarly journals Role of Base Excision Repair Pathway in the Processing of Complex DNA Damage Generated by Oxidative Stress and Anticancer Drugs

2021 ◽  
Vol 8 ◽  
Author(s):  
Yeldar Baiken ◽  
Damira Kanayeva ◽  
Sabira Taipakova ◽  
Regina Groisman ◽  
Alexander A. Ishchenko ◽  
...  
Keyword(s):  
Dna Damage ◽  
Base Excision Repair ◽  
Genome Instability ◽  
Excision Repair ◽  
Chromosomal Rearrangements ◽  
Strand Break ◽  
Dna Lesions ◽  
Complex Nature ◽  
Base Excision

Chemical alterations in DNA induced by genotoxic factors can have a complex nature such as bulky DNA adducts, interstrand DNA cross-links (ICLs), and clustered DNA lesions (including double-strand breaks, DSB). Complex DNA damage (CDD) has a complex character/structure as compared to singular lesions like randomly distributed abasic sites, deaminated, alkylated, and oxidized DNA bases. CDD is thought to be critical since they are more challenging to repair than singular lesions. Although CDD naturally constitutes a relatively minor fraction of the overall DNA damage induced by free radicals, DNA cross-linking agents, and ionizing radiation, if left unrepaired, these lesions cause a number of serious consequences, such as gross chromosomal rearrangements and genome instability. If not tightly controlled, the repair of ICLs and clustered bi-stranded oxidized bases via DNA excision repair will either inhibit initial steps of repair or produce persistent chromosomal breaks and consequently be lethal for the cells. Biochemical and genetic evidences indicate that the removal of CDD requires concurrent involvement of a number of distinct DNA repair pathways including poly(ADP-ribose) polymerase (PARP)-mediated DNA strand break repair, base excision repair (BER), nucleotide incision repair (NIR), global genome and transcription coupled nucleotide excision repair (GG-NER and TC-NER, respectively), mismatch repair (MMR), homologous recombination (HR), non-homologous end joining (NHEJ), and translesion DNA synthesis (TLS) pathways. In this review, we describe the role of DNA glycosylase-mediated BER pathway in the removal of complex DNA lesions.

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