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Bansal A, Kaushik S, Kukreti S. Non-canonical DNA structures: Diversity and disease association. Front Genet 2022; 13:959258. [PMID: 36134025 PMCID: PMC9483843 DOI: 10.3389/fgene.2022.959258] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Accepted: 07/25/2022] [Indexed: 11/18/2022] Open
Abstract
A complete understanding of DNA double-helical structure discovered by James Watson and Francis Crick in 1953, unveil the importance and significance of DNA. For the last seven decades, this has been a leading light in the course of the development of modern biology and biomedical science. Apart from the predominant B-form, experimental shreds of evidence have revealed the existence of a sequence-dependent structural diversity, unusual non-canonical structures like hairpin, cruciform, Z-DNA, multistranded structures such as DNA triplex, G-quadruplex, i-motif forms, etc. The diversity in the DNA structure depends on various factors such as base sequence, ions, superhelical stress, and ligands. In response to these various factors, the polymorphism of DNA regulates various genes via different processes like replication, transcription, translation, and recombination. However, altered levels of gene expression are associated with many human genetic diseases including neurological disorders and cancer. These non-B-DNA structures are expected to play a key role in determining genetic stability, DNA damage and repair etc. The present review is a modest attempt to summarize the available literature, illustrating the occurrence of non-canonical structures at the molecular level in response to the environment and interaction with ligands and proteins. This would provide an insight to understand the biological functions of these unusual DNA structures and their recognition as potential therapeutic targets for diverse genetic diseases.
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Affiliation(s)
- Aparna Bansal
- Nucleic Acid Research Lab, Department of Chemistry, University of Delhi, Delhi, India
- Department of Chemistry, Hansraj College, University of Delhi, Delhi, India
| | - Shikha Kaushik
- Nucleic Acid Research Lab, Department of Chemistry, University of Delhi, Delhi, India
- Department of Chemistry, Rajdhani College, University of Delhi, New Delhi, India
| | - Shrikant Kukreti
- Nucleic Acid Research Lab, Department of Chemistry, University of Delhi, Delhi, India
- *Correspondence: Shrikant Kukreti,
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2
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Bergquist H, Rocha CSJ, Álvarez-Asencio R, Nguyen CH, Rutland MW, Smith CIE, Good L, Nielsen PE, Zain R. Disruption of Higher Order DNA Structures in Friedreich's Ataxia (GAA)n Repeats by PNA or LNA Targeting. PLoS One 2016; 11:e0165788. [PMID: 27846236 PMCID: PMC5112992 DOI: 10.1371/journal.pone.0165788] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 10/07/2016] [Indexed: 01/08/2023] Open
Abstract
Expansion of (GAA)n repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich’s ataxia. (GAA)n expansions form non-canonical structures, including intramolecular triplex (H-DNA), and R-loops and are associated with epigenetic modifications. With the aim of interfering with higher order H-DNA (like) DNA structures within pathological (GAA)n expansions, we examined sequence-specific interaction of peptide nucleic acid (PNA) with (GAA)n repeats of different lengths (short: n=9, medium: n=75 or long: n=115) by chemical probing of triple helical and single stranded regions. We found that a triplex structure (H-DNA) forms at GAA repeats of different lengths; however, single stranded regions were not detected within the medium size pathological repeat, suggesting the presence of a more complex structure. Furthermore, (GAA)4-PNA binding of the repeat abolished all detectable triplex DNA structures, whereas (CTT)5-PNA did not. We present evidence that (GAA)4-PNA can invade the DNA at the repeat region by binding the DNA CTT strand, thereby preventing non-canonical-DNA formation, and that triplex invasion complexes by (CTT)5-PNA form at the GAA repeats. Locked nucleic acid (LNA) oligonucleotides also inhibited triplex formation at GAA repeat expansions, and atomic force microscopy analysis showed significant relaxation of plasmid morphology in the presence of GAA-LNA. Thus, by inhibiting disease related higher order DNA structures in the Frataxin gene, such PNA and LNA oligomers may have potential for discovery of drugs aiming at recovering Frataxin expression.
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Affiliation(s)
- Helen Bergquist
- Department of Medical Biochemistry and Microbiology, Microbiology-Immunology, Uppsala University, Uppsala, Sweden
- Department of Laboratory Medicine, Clinical Research Center, Karolinska Institutet, SE-141 86, Huddinge, Sweden
| | - Cristina S. J. Rocha
- Department of Laboratory Medicine, Clinical Research Center, Karolinska Institutet, SE-141 86, Huddinge, Sweden
| | - Rubén Álvarez-Asencio
- KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry, Stockholm, Sweden
| | - Chi-Hung Nguyen
- Laboratoire de Pharmacochimie, Institut Curie, PSL Research University, UMR 9187 – U 1196 CNRS-Institut Curie, INSERM, Centre Universitaire, Orsay, France
| | - Mark. W. Rutland
- KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry, Stockholm, Sweden
| | - C. I. Edvard Smith
- Department of Laboratory Medicine, Clinical Research Center, Karolinska Institutet, SE-141 86, Huddinge, Sweden
| | - Liam Good
- Department of Pathology and Infectious Diseases, Royal Veterinary College, University of London, United Kingdom
| | - Peter E. Nielsen
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, The Panum Institute, Copenhagen, Denmark
| | - Rula Zain
- Department of Laboratory Medicine, Clinical Research Center, Karolinska Institutet, SE-141 86, Huddinge, Sweden
- Department of Clinical Genetics, Centre for Rare Diseases, Karolinska University Hospital, SE-171 76, Stockholm, Sweden
- * E-mail:
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3
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Govan JM, Uprety R, Hemphill J, Lively MO, Deiters A. Regulation of transcription through light-activation and light-deactivation of triplex-forming oligonucleotides in mammalian cells. ACS Chem Biol 2012; 7:1247-56. [PMID: 22540192 DOI: 10.1021/cb300161r] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Triplex-forming oligonucleotides (TFOs) are efficient tools to regulate gene expression through the inhibition of transcription. Here, nucleobase-caging technology was applied to the temporal regulation of transcription through light-activated TFOs. Through site-specific incorporation of caged thymidine nucleotides, the TFO:DNA triplex formation is blocked, rendering the TFO inactive. However, after a brief UV irradiation, the caging groups are removed, activating the TFO and leading to the inhibition of transcription. Furthermore, the synthesis and site-specific incorporation of caged deoxycytidine nucleotides within TFO inhibitor sequences was developed, allowing for the light-deactivation of TFO function and thus photochemical activation of gene expression. After UV-induced removal of the caging groups, the TFO forms a DNA dumbbell structure, rendering it inactive, releasing it from the DNA, and activating transcription. These are the first examples of light-regulated TFOs and their application in the photochemical activation and deactivation of gene expression. In addition, hairpin loop structures were found to significantly increase the efficacy of phosphodiester DNA-based TFOs in tissue culture.
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Affiliation(s)
- Jeane M. Govan
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina
27695, United States
| | - Rajendra Uprety
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina
27695, United States
| | - James Hemphill
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina
27695, United States
| | - Mark O. Lively
- Center
for Structural Biology, Wake Forest University School of Medicine, Winston-Salem,
North Carolina 27157, United States
| | - Alexander Deiters
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina
27695, United States
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4
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Eick A, Riechert-Krause F, Weisz K. Binding and NMR structural studies on indoloquinoline-oligonucleotide conjugates targeting duplex DNA. Bioconjug Chem 2012; 23:1127-37. [PMID: 22571630 DOI: 10.1021/bc200582u] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
An 11-phenyl-indolo[3,2-b]quinoline (PIQ) was tethered through an aminoalkyl linker to the 5'-end of four pyrimidine oligonucleotides with T/C scrambled sequences at their two 5'-terminal positions. Binding to different double-helical DNA targets formed parallel triple helices with a PIQ-mediated stabilization that strongly depends on pH and the terminal base triad at the 5'-triplex-duplex junction. The most effective stabilization was observed with a TAT triplet at the 5'-junction under low pH conditions, pointing to a protonated ligand with a high triplex binding affinity and unfavorable charge repulsions in the case of a terminal C(+)GC triplet at the junction. The latter preference of the PIQ ligand for TAT over CGC is alleviated yet still preserved at higher pH. Intercalation of PIQ at the 5'-triplex-duplex junction as suggested by the triplex melting experiments was confirmed by homonuclear and heteronuclear NMR structural studies on a specifically isotope-labeled triplex. The NMR analysis revealed two coexisting species that only differ by a 180° rotation of the indoloquinoline within the intercalation pocket. NOE-derived molecular models indicate extensive stacking interactions of the indoloquinoline moiety with the TAT base triplet and CG base pair at the junction and a phenyl substituent that is positioned in the major groove and oriented almost perpendicular to the plane of the indoloquinoline.
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Affiliation(s)
- Andrea Eick
- Institute of Biochemistry, Ernst-Moritz-Arndt University Greifswald , Felix-Hausdorff-Strasse 4, D-17487 Greifswald, Germany
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5
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Mukherjee A, Vasquez KM. Triplex technology in studies of DNA damage, DNA repair, and mutagenesis. Biochimie 2011; 93:1197-208. [PMID: 21501652 DOI: 10.1016/j.biochi.2011.04.001] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2011] [Accepted: 04/01/2011] [Indexed: 12/18/2022]
Abstract
Triplex-forming oligonucleotides (TFOs) can bind to the major groove of homopurine-homopyrimidine stretches of double-stranded DNA in a sequence-specific manner through Hoogsteen hydrogen bonding to form DNA triplexes. TFOs by themselves or conjugated to reactive molecules can be used to direct sequence-specific DNA damage, which in turn results in the induction of several DNA metabolic activities. Triplex technology is highly utilized as a tool to study gene regulation, molecular mechanisms of DNA repair, recombination, and mutagenesis. In addition, TFO targeting of specific genes has been exploited in the development of therapeutic strategies to modulate DNA structure and function. In this review, we discuss advances made in studies of DNA damage, DNA repair, recombination, and mutagenesis by using triplex technology to target specific DNA sequences.
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Affiliation(s)
- Anirban Mukherjee
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Dell Pediatric Research Institute, 1400 Barbara Jordan Blvd., Austin, TX 78723, USA
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Sargent RG, Kim S, Gruenert DC. Oligo/polynucleotide-based gene modification: strategies and therapeutic potential. Oligonucleotides 2011; 21:55-75. [PMID: 21417933 DOI: 10.1089/oli.2010.0273] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Oligonucleotide- and polynucleotide-based gene modification strategies were developed as an alternative to transgene-based and classical gene targeting-based gene therapy approaches for treatment of genetic disorders. Unlike the transgene-based strategies, oligo/polynucleotide gene targeting approaches maintain gene integrity and the relationship between the protein coding and gene-specific regulatory sequences. Oligo/polynucleotide-based gene modification also has several advantages over classical vector-based homologous recombination approaches. These include essentially complete homology to the target sequence and the potential to rapidly engineer patient-specific oligo/polynucleotide gene modification reagents. Several oligo/polynucleotide-based approaches have been shown to successfully mediate sequence-specific modification of genomic DNA in mammalian cells. The strategies involve the use of polynucleotide small DNA fragments, triplex-forming oligonucleotides, and single-stranded oligodeoxynucleotides to mediate homologous exchange. The primary focus of this review will be on the mechanistic aspects of the small fragment homologous replacement, triplex-forming oligonucleotide-mediated, and single-stranded oligodeoxynucleotide-mediated gene modification strategies as it relates to their therapeutic potential.
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Affiliation(s)
- R Geoffrey Sargent
- Department of Otolaryngology-Head and Neck Surgery, University of California , San Francisco, California 94115, USA
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7
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Nakanishi K, Cavallo F, Perrouault L, Giovannangeli C, Moynahan ME, Barchi M, Brunet E, Jasin M. Homology-directed Fanconi anemia pathway cross-link repair is dependent on DNA replication. Nat Struct Mol Biol 2011; 18:500-3. [PMID: 21423196 PMCID: PMC3273992 DOI: 10.1038/nsmb.2029] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2010] [Accepted: 01/18/2011] [Indexed: 12/30/2022]
Abstract
Homologous recombination (also termed homology-directed repair, HDR) is a major pathway for the repair of DNA interstrand cross-links (ICLs) in mammalian cells. Cells from individuals with Fanconi anemia (FA) are characterized by extreme ICL sensitivity, but their reported defect in HDR is mild. Here we examined ICL-induced HDR using a GFP reporter and observed a profound defect in ICL-induced HDR in FA cells, but only when the reporter could replicate.
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Affiliation(s)
- Koji Nakanishi
- Developmental Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York, USA
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8
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Kolevzon N, Yavin E. Site-Specific DNA Photocleavage and Photomodulation by Oligonucleotide Conjugates. Oligonucleotides 2010; 20:263-75. [DOI: 10.1089/oli.2010.0247] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Netanel Kolevzon
- The School of Pharmacy, The Institute for Drug Research, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Eylon Yavin
- The School of Pharmacy, The Institute for Drug Research, The Hebrew University of Jerusalem, Jerusalem, Israel
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9
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Tsai TL, Shieh DB, Yeh CS, Tzeng Y, Htet K, Chuang KS, Hwu JR, Su WC. The down regulation of target genes by photo activated DNA nanoscissors. Biomaterials 2010; 31:6545-54. [DOI: 10.1016/j.biomaterials.2010.04.058] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2010] [Accepted: 04/29/2010] [Indexed: 01/24/2023]
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10
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Vasquez KM. Targeting and processing of site-specific DNA interstrand crosslinks. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2010; 51:527-39. [PMID: 20196133 PMCID: PMC2895014 DOI: 10.1002/em.20557] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
DNA interstrand crosslinks (ICLs) are among the most cytotoxic types of DNA damage, and thus ICL-inducing agents such as cyclophosphamide, melphalan, cisplatin, psoralen, and mitomycin C have been used clinically as anticancer drugs for decades. ICLs can also be formed endogenously as a consequence of cellular metabolic processes. ICL-inducing agents continue to be among the most effective chemotherapeutic treatments for many cancers; however, treatment with these agents can lead to secondary malignancies, in part due to mutagenic processing of the DNA lesions. The mechanisms of ICL repair have been characterized more thoroughly in bacteria and yeast than in mammalian cells. Thus, a better understanding of the molecular mechanisms of ICL processing offers the potential to improve the efficacy of these drugs in cancer therapy. In mammalian cells, it is thought that ICLs are repaired by the coordination of proteins from several pathways, including nucleotide excision repair (NER), base excision repair (BER), mismatch repair (MMR), homologous recombination (HR), translesion synthesis (TLS), and proteins involved in Fanconi anemia (FA). In this review, we focus on the potential functions of NER, MMR, and HR proteins in the repair of and response to ICLs in human cells and in mice. We will also discuss a unique approach, using psoralen covalently linked to triplex-forming oligonucleotides to direct ICLs to specific sites in the mammalian genome.
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Affiliation(s)
- Karen M Vasquez
- Department of Carcinogenesis, The University of Texas M.D. Anderson Cancer Center, Science Park-Research Division, Smithville, Texas 78957, USA.
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Chan SH, Yu AM, McVey M. Dual roles for DNA polymerase theta in alternative end-joining repair of double-strand breaks in Drosophila. PLoS Genet 2010; 6:e1001005. [PMID: 20617203 PMCID: PMC2895639 DOI: 10.1371/journal.pgen.1001005] [Citation(s) in RCA: 178] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2009] [Accepted: 05/27/2010] [Indexed: 11/25/2022] Open
Abstract
DNA double-strand breaks are repaired by multiple mechanisms that are roughly grouped into the categories of homology-directed repair and non-homologous end joining. End-joining repair can be further classified as either classical non-homologous end joining, which requires DNA ligase 4, or “alternative” end joining, which does not. Alternative end joining has been associated with genomic deletions and translocations, but its molecular mechanism(s) are largely uncharacterized. Here, we report that Drosophila melanogaster DNA polymerase theta (pol theta), encoded by the mus308 gene and previously implicated in DNA interstrand crosslink repair, plays a crucial role in DNA ligase 4-independent alternative end joining. In the absence of pol theta, end joining is impaired and residual repair often creates large deletions flanking the break site. Analysis of break repair junctions from flies with mus308 separation-of-function alleles suggests that pol theta promotes the use of long microhomologies during alternative end joining and increases the likelihood of complex insertion events. Our results establish pol theta as a key protein in alternative end joining in Drosophila and suggest a potential mechanistic link between alternative end joining and interstrand crosslink repair. DNA double-strand breaks, in which both strands of the DNA double helix are cut, must be recognized and accurately repaired in order to promote cell survival and prevent the accumulation of mutations. However, error-prone repair occasionally occurs, even when accurate repair is possible. We have investigated the genetic requirements of an error-prone break-repair mechanism called alternative end joining. We have previously shown that alternative end joining is frequently used in the fruit fly, Drosophila melanogaster. Here, we demonstrate that a fruit fly protein named DNA polymerase theta is a key player in this inaccurate repair mechanism. Genetic analysis suggests that polymerase theta may be important for two processes associated with alternative end joining: (1) annealing at short, complementary DNA sequences, and (2) DNA synthesis that creates small insertions at break-repair sites. In the absence of polymerase theta, a backup repair mechanism that frequently results in large chromosome deletions is revealed. Because DNA polymerase theta is highly expressed in many types of human cancers, our findings lay the groundwork for further investigations into how polymerase theta is involved in repair processes that may promote the development of cancer.
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Affiliation(s)
- Sze Ham Chan
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
| | - Amy Marie Yu
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
| | - Mitch McVey
- Department of Biology, Tufts University, Medford, Massachusetts, United States of America
- Program in Genetics, Tufts Sackler School of Graduate Biomedical Sciences, Boston, Massachusetts, United States of America
- * E-mail:
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12
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Hinz JM. Role of homologous recombination in DNA interstrand crosslink repair. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2010; 51:582-603. [PMID: 20658649 DOI: 10.1002/em.20577] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Homologous recombination repair (HRR) encompasses mechanisms that employ homologous DNA sequences as templates for repair or tolerance of a wide range of DNA lesions that inhibit DNA replication in S phase. Arguably the most imposing of these DNA lesions is that of the interstrand crosslink (ICL), consisting of a covalently attached chemical bridge between opposing DNA strands. ICL repair requires the coordinated activities of HRR and a number of proteins from other DNA repair and damage response systems, including nucleotide excision repair, base excision repair, mismatch repair, and translesion DNA synthesis (TLS). Interestingly, different organisms favor alternative methods of HRR in the ICL repair process. E. coli perform ICL repair using a homology-driven damage bypass mechanism analogous to daughter strand gap repair. Eukaryotes from yeast to humans initiate ICL repair primarily during DNA replication, relying on HRR activity to restart broken replication forks associated with double-strand break intermediates induced by nucleolytic activities of other excision repair factors. Higher eukaryotes also employ several additional factors, including members of the Fanconi anemia damage-response network, which further promote replication-associated ICL repair through the activation and coordination of various DNA excision repair, TLS, and HRR proteins. This review focuses on the proteins and general mechanisms of HRR associated with ICL repair in different model organisms.
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Affiliation(s)
- John M Hinz
- School of Molecular Biosciences, Washington State University, Pullman, Washington, USA.
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Smeaton MB, Hlavin EM, Noronha AM, Murphy SP, Wilds CJ, Miller PS. Effect of cross-link structure on DNA interstrand cross-link repair synthesis. Chem Res Toxicol 2009; 22:1285-97. [PMID: 19580249 DOI: 10.1021/tx9000896] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
DNA interstrand cross-links (ICLs) are products of chemotherapeutic agents and cellular metabolic processes that block both replication and transcription. If left unrepaired, ICLs are extremely toxic to cells, and ICL repair mechanisms contribute to the survival of certain chemotherapeutic resistance tumors. A critical step in ICL repair involves unhooking the cross-link. In the absence of a homologous donor sequence, the resulting gap can be filled in by a repair synthesis step involving bypass of the cross-link remnant. Here, we examine the effect of cross-link structure on the ability of unhooked DNA substrates to undergo repair synthesis in mammalian whole cell extracts. Using 32P incorporation assays, we found that repair synthesis occurs efficiently past the site of damage when a DNA substrate containing a single N4C-ethyl-N4C cross-link is incubated in HeLa or Chinese hamster ovary cell extracts. This lesion, which can base pair with deoxyguanosine, is readily bypassed by both Escherichia coli DNA polymerase I and T7 DNA polymerase in a primer extension assay. In contrast, bypass was not observed in the primer extension assay or in mammalian cell extracts when DNA substrates containing a N3T-ethyl-N3T or N1I-ethyl-N3T cross-link, whose linkers obstruct the hydrogen bond face of the bases, were used. A modified phosphorothioate sequencing method was used to analyze the ICL repair patches created in the mammalian cell extracts. In the case of the N4C-ethyl-N4C substrate, the repair patch spanned the site of the cross-link, and the lesion was bypassed in an error-free manner. However, although the N3T-ethyl-N3T and N1I-ethyl-N3T substrates were unhooked in the extracts, bypass was not detected. These and our previous results suggest that although the chemical structure of an ICL may not affect initial cross-link unhooking, it can play a significant role in subsequent processing of the cross-link. Understanding how the physical and chemical differences of ICLs affect repair may provide a better understanding of the cytotoxic and mutagenic potential of specific ICLs.
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Affiliation(s)
- Michael B Smeaton
- Department of Biochemistry and Molecular Biology, Johns Hopkins Bloomberg School of Public Health, Johns Hopkins University, 615 North Wolfe Street, Baltimore, Maryland 21205, USA
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14
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Liu Y, Nairn RS, Vasquez KM. Targeted gene conversion induced by triplex-directed psoralen interstrand crosslinks in mammalian cells. Nucleic Acids Res 2009; 37:6378-88. [PMID: 19726585 PMCID: PMC2770658 DOI: 10.1093/nar/gkp678] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Correction of a defective gene is a promising approach for both basic research and clinical gene therapy. However, the absence of site-specific targeting and the low efficiency of homologous recombination in human cells present barriers to successful gene targeting. In an effort to overcome these barriers, we utilized triplex-forming oligonucleotides (TFOs) conjugated to a DNA interstrand crosslinking (ICL) agent, psoralen (pTFO-ICLs), to improve the gene targeting efficiency at a specific site in DNA. Gene targeting events were monitored by the correction of a deletion on a recipient plasmid with the homologous sequence from a donor plasmid in human cells. The mechanism underlying this event is stimulation of homologous recombination by the pTFO-ICL. We found that pTFO-ICLs are efficient in inducing targeted gene conversion (GC) events in human cells. The deletion size in the recipient plasmid influenced both the recombination frequency and spectrum of recombinants; i.e. plasmids with smaller deletions had a higher frequency and proportion of GC events. The polarity of the pTFO-ICL also had a prominent effect on recombination. Our results suggest that pTFO-ICL induced intermolecular recombination provides an efficient method for targeted gene correction in mammalian cells.
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Affiliation(s)
- Yaobin Liu
- Department of Carcinogenesis, University of Texas MD Anderson Cancer Center, Science Park-Research Division, Smithville, Texas, USA
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