scholarly journals DNA-PK Promotes DNA End Resection at DNA Double Strand Breaks in G0 cells

2021 ◽  
Author(s):  
Jessica K Tyler ◽  
Faith C Fowler ◽  
Chelsea Peart ◽  
Bo-Ruei Chen ◽  
Barry Sleckman ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Strand Break ◽  
Dna Double Strand Breaks ◽  
Proliferating Cells ◽  
Dsb Repair ◽  
Extensive Resection ◽  
Key Factor ◽  
Dna End Resection ◽  
End Resection

DNA double-strand break (DSB) repair by homologous recombination is confined to the S and G2 phases of the cell cycle partly due to 53BP1 antagonizing DNA end resection in G1 phase and non-cycling quiescent (G0) cells where DSBs are predominately repaired by non-homologous end joining (NHEJ). Unexpectedly, we uncovered extensive MRE11- and CtIP-dependent DNA end resection at DSBs in G0 mammalian cells. A whole genome CRISPR/Cas9 screen revealed the DNA-dependent kinase (DNA-PK) complex as a key factor in promoting DNA end resection in G0 cells. In agreement, depletion of FBXL12, which promotes ubiquitylation and removal of the KU70/KU80 subunits of DNA-PK from DSBs, promotes even more extensive resection in G0 cells. In contrast, a requirement for DNA-PK in promoting DNA end resection in proliferating cells at the G1 or G2 phase of the cell cycle was not observed. Our findings establish that DNA-PK uniquely promotes DNA end resection in G0, but not in G1 or G2 phase cells, and has important implications for DNA DSB repair in quiescent cells.

scholarly journals Repair of G1 induced DNA double-strand breaks in S-G2/M by alternative NHEJ

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Wei Yu ◽  
Chloé Lescale ◽  
Loelia Babin ◽  
Marie Bedora-Faure ◽  
Hélène Lenden-Hasse ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Strand Break ◽  
Cancer Therapies ◽  
Dna Double Strand Breaks ◽  
Dna Breaks ◽  
Dsb Repair ◽  
Chromosome Translocations ◽  
Dna End Resection ◽  
G1 Cells ◽  
Alternative Nhej

Abstract The alternative non-homologous end-joining (NHEJ) pathway promotes DNA double-strand break (DSB) repair in cells deficient for NHEJ or homologous recombination, suggesting that it operates at all stages of the cell cycle. Here, we use an approach in which DNA breaks can be induced in G1 cells and their repair tracked, enabling us to show that joining of DSBs is not functional in G1-arrested XRCC4-deficient cells. Cell cycle entry into S-G2/M restores DSB repair by Pol θ-dependent and PARP1-independent alternative NHEJ with repair products bearing kilo-base long DNA end resection, micro-homologies and chromosome translocations. We identify a synthetic lethal interaction between XRCC4 and Pol θ under conditions of G1 DSBs, associated with accumulation of unresolved DNA ends in S-G2/M. Collectively, our results support the conclusion that the repair of G1 DSBs progressing to S-G2/M by alternative NHEJ drives genomic instability and represent an attractive target for future DNA repair-based cancer therapies.

Repair pathway choice for double-strand breaks

2020 ◽  
Vol 64 (5) ◽  
pp. 765-777 ◽  
Author(s):  
Yixi Xu ◽  
Dongyi Xu
Keyword(s):  
Cell Cycle ◽  
Double Strand Breaks ◽  
Homologous Region ◽  
Gene Repair ◽  
Repair Pathway ◽  
Dna Double Strand Breaks ◽  
Environmental Radiation ◽  
Strand Breaks ◽  
Dna End Resection ◽  
End Resection

Abstract Deoxyribonucleic acid (DNA) is at a constant risk of damage from endogenous substances, environmental radiation, and chemical stressors. DNA double-strand breaks (DSBs) pose a significant threat to genomic integrity and cell survival. There are two major pathways for DSB repair: nonhomologous end-joining (NHEJ) and homologous recombination (HR). The extent of DNA end resection, which determines the length of the 3′ single-stranded DNA (ssDNA) overhang, is the primary factor that determines whether repair is carried out via NHEJ or HR. NHEJ, which does not require a 3′ ssDNA tail, occurs throughout the cell cycle. 53BP1 and the cofactors PTIP or RIF1-shieldin protect the broken DNA end, inhibit long-range end resection and thus promote NHEJ. In contrast, HR mainly occurs during the S/G2 phase and requires DNA end processing to create a 3′ tail that can invade a homologous region, ensuring faithful gene repair. BRCA1 and the cofactors CtIP, EXO1, BLM/DNA2, and the MRE11–RAD50–NBS1 (MRN) complex promote DNA end resection and thus HR. DNA resection is influenced by the cell cycle, the chromatin environment, and the complexity of the DNA end break. Herein, we summarize the key factors involved in repair pathway selection for DSBs and discuss recent related publications.

scholarly journals Human SIRT6 Promotes DNA End Resection Through CtIP Deacetylation

Science ◽  
2010 ◽  
Vol 329 (5997) ◽  
pp. 1348-1353 ◽  
Author(s):  
Abderrahmane Kaidi ◽  
Brian T. Weinert ◽  
Chunaram Choudhary ◽  
Stephen P. Jackson
Keyword(s):  
Homologous Recombination ◽  
Genome Stability ◽  
Protein A ◽  
Strand Break ◽  
Dsb Repair ◽  
Interacting Protein ◽  
Dna Double Strand Break ◽  
Dna End Resection ◽  
Lysine Deacetylases ◽  
End Resection

SIRT6 belongs to the sirtuin family of protein lysine deacetylases, which regulate aging and genome stability. We found that human SIRT6 has a role in promoting DNA end resection, a crucial step in DNA double-strand break (DSB) repair by homologous recombination. SIRT6 depletion impaired the accumulation of replication protein A and single-stranded DNA at DNA damage sites, reduced rates of homologous recombination, and sensitized cells to DSB-inducing agents. We identified the DSB resection protein CtIP [C-terminal binding protein (CtBP) interacting protein] as a SIRT6 interaction partner and showed that SIRT6-dependent CtIP deacetylation promotes resection. A nonacetylatable CtIP mutant alleviated the effect of SIRT6 depletion on resection, thus identifying CtIP as a key substrate by which SIRT6 facilitates DSB processing and homologous recombination. These findings further clarify how SIRT6 promotes genome stability.

scholarly journals Evidence for DNA-PK-dependent and -independent DNA double-strand break repair pathways in mammalian cells as a function of the cell cycle.

1997 ◽  
Vol 17 (3) ◽  
pp. 1425-1433 ◽  
Author(s):  
S E Lee ◽  
R A Mitchell ◽  
A Cheng ◽  
E A Hendrickson
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Cellular Response ◽  
Strand Break ◽  
S Phase ◽  
Dependent Manner ◽  
Severe Combined Immune Deficiency ◽  
Dsb Repair ◽  
G2 Checkpoint ◽  
G2 Phase

Mice homozygous for the scid (severe combined immune deficiency) mutation are defective in the repair of DNA double-strand breaks (DSBs) and are consequently very X-ray sensitive and defective in the lymphoid V(D)J recombination process. Recently, a strong candidate for the scid gene has been identified as the catalytic subunit of the DNA-dependent protein kinase (DNA-PK) complex. Here, we show that the activity of the DNA-PK complex is regulated in a cell cycle-dependent manner, with peaks of activity found at the G1/early S phase and again at the G2 phase in wild-type cells. Interestingly, only the deficit of the G1/early S phase DNA-PK activity correlated with an increased hypersensitivity to X-irradiation and a DNA DSB repair deficit in synchronized scid pre-B cells. Finally, we demonstrate that the DNA-PK activity found at the G2 phase may be required for exit from a DNA damage-induced G2 checkpoint arrest. These observations suggest the presence of two pathways (DNA-PK-dependent and -independent) of illegitimate mammalian DNA DSB repair and two distinct roles (DNA DSB repair and G2 checkpoint traversal) for DNA-PK in the cellular response to ionizing radiation.

Double-strand-break-induced homologous recombination in mammalian cells

2001 ◽  
Vol 29 (2) ◽  
pp. 196-201 ◽  
Author(s):  
R. D. Johnson ◽  
M. Jasin
Keyword(s):  
Homologous Recombination ◽  
Sister Chromatid ◽  
Mammalian Cells ◽  
Indirect Evidence ◽  
Strand Break ◽  
Double Strand Breaks ◽  
Crossing Over ◽  
Dna Double Strand Breaks ◽  
Dsb Repair ◽  
Strand Breaks

In mammalian cells, the repair of DNA double-strand breaks (DSBs) occurs by both homologous and non-homologous mechanisms. Indirect evidence, including that from gene targeting and random integration experiments, had suggested that non-homologous mechanisms were significantly more frequent than homologous ones. However, more recent experiments indicate that homologous recombination is also a prominent DSB repair pathway. These experiments show that mammalian cells use homologous sequences located at multiple positions throughout the genome to repair a DSB. However, template preference appears to be biased, with the sister chromatid being preferred by 2–3 orders of magnitude over a homologous or heterologous chromosome. The outcome of homologous recombination in mammalian cells is predominantly gene conversion that is not associated with crossing-over. The preference for the sister chromatid and the bias against crossing-over seen in mitotic mammalian cells may have developed in order to reduce the potential for genome alterations that could occur when other homologous repair templates are utilized. In attempts to understand further the mechanism of homologous recombination, the proteins that promote this process are beginning to be identified. To date, four mammalian proteins have been demonstrated conclusively to be involved in DSB repair by homologous recombination: Rad54, XRCC2, XRCC3 and BRCAI. This paper summarizes results from a number of recent studies.

scholarly journals RNF169 limits 53BP1 deposition at DSBs to stimulate single-strand annealing repair

2018 ◽  
Vol 115 (35) ◽  
pp. E8286-E8295 ◽  
Author(s):  
Liwei An ◽  
Chao Dong ◽  
Junshi Li ◽  
Jie Chen ◽  
Jingsong Yuan ◽  
...  
Keyword(s):  
Single Strand ◽  
Fine Tuning ◽  
Dna Double Strand Breaks ◽  
Dsb Repair ◽  
Strand Breaks ◽  
Single Strand Annealing ◽  
Molecular Rheostat ◽  
Dna End Resection ◽  
Strand Annealing ◽  
End Resection

Unrestrained 53BP1 activity at DNA double-strand breaks (DSBs) hampers DNA end resection and upsets DSB repair pathway choice. RNF169 acts as a molecular rheostat to limit 53BP1 deposition at DSBs, but how this fine balance translates to DSB repair control remains undefined. In striking contrast to 53BP1, ChIP analyses of AsiSI-induced DSBs unveiled that RNF169 exhibits robust accumulation at DNA end-proximal regions and preferentially targets resected, RPA-bound DSBs. Accordingly, we found that RNF169 promotes CtIP-dependent DSB resection and favors homology-mediated DSB repair, and further showed that RNF169 dose-dependently stimulates single-strand annealing repair, in part, by alleviating the 53BP1-imposed barrier to DSB end resection. Our results highlight the interplay of RNF169 with 53BP1 in fine-tuning choice of DSB repair pathways.

scholarly journals Nucleosome disassembly during human non-homologous end joining followed by concerted HIRA- and CAF-1-dependent reassembly

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Xuan Li ◽  
Jessica K Tyler
Keyword(s):  
Strand Break ◽  
End Joining ◽  
Efficient Removal ◽  
Dsb Repair ◽  
Dna Double Strand Break ◽  
Dna End Resection ◽  
Non Homologous End Joining ◽  
Nucleosome Disassembly ◽  
End Resection ◽  
Assembly Pathways

The cell achieves DNA double-strand break (DSB) repair in the context of chromatin structure. However, the mechanisms used to expose DSBs to the repair machinery and to restore the chromatin organization after repair remain elusive. Here we show that induction of a DSB in human cells causes local nucleosome disassembly, apparently independently from DNA end resection. This efficient removal of histone H3 from the genome during non-homologous end joining was promoted by both ATM and the ATP-dependent nucleosome remodeler INO80. Chromatin reassembly during DSB repair was dependent on the HIRA histone chaperone that is specific to the replication-independent histone variant H3.3 and on CAF-1 that is specific to the replication-dependent canonical histones H3.1/H3.2. Our data suggest that the epigenetic information is re-established after DSB repair by the concerted and interdependent action of replication-independent and replication-dependent chromatin assembly pathways.

scholarly journals The Role of Drosophila CtIP in Homology-Directed Repair of DNA Double-Strand Breaks

Genes ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1430
Author(s):  
Ian Yannuzzi ◽  
Margaret A. Butler ◽  
Joel Fernandez ◽  
Jeannine R. LaRocque
Keyword(s):  
Direct Repeat ◽  
Double Strand Breaks ◽  
Dna Double Strand Breaks ◽  
Dsb Repair ◽  
Strand Breaks ◽  
Homology Directed Repair ◽  
Dna End Resection ◽  
The Impact ◽  
End Resection

DNA double-strand breaks (DSBs) are a particularly genotoxic type of DNA damage that can result in chromosomal aberrations. Thus, proper repair of DSBs is essential to maintaining genome integrity. DSBs can be repaired by non-homologous end joining (NHEJ), where ends are processed before joining through ligation. Alternatively, DSBs can be repaired through homology-directed repair, either by homologous recombination (HR) or single-strand annealing (SSA). Both types of homology-directed repair are initiated by DNA end resection. In cultured human cells, the protein CtIP has been shown to play a role in DNA end resection through its interactions with CDK, BRCA1, DNA2, and the MRN complex. To elucidate the role of CtIP in a multicellular context, CRISPR/Cas9 genome editing was used to create a DmCtIPΔ allele in Drosophila melanogaster. Using the DSB repair reporter assay direct repeat of white (DR-white), a two-fold decrease in HR in DmCtIPΔ/Δ mutants was observed when compared to heterozygous controls. However, analysis of HR gene conversion tracts (GCTs) suggests DmCtIP plays a minimal role in determining GCT length. To assess the function of DmCtIP on both short (~550 bp) and long (~3.6 kb) end resection, modified homology-directed SSA repair assays were implemented, resulting in a two-fold decrease in SSA repair in both short and extensive end resection requirements in the DmCtIPΔ/Δ mutants compared to heterozygote controls. Through these analyses, we affirmed the importance of end resection on DSB repair pathway choice in multicellular systems, described the function of DmCtIP in short and extensive DNA end resection, and determined the impact of end resection on GCT length during HR.

scholarly journals A Novel Set of Cas9 Fusion Proteins to stimulate Homologous Recombination: Cas9-HRs

2020 ◽  
Author(s):  
Chris R. Hackley
Keyword(s):  
Homologous Recombination ◽  
Long Range ◽  
Mammalian Cells ◽  
Strand Break ◽  
Dsb Repair ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Attractive Option ◽  
End Resection ◽  
Rate Limiting

AbstractCRISPR/Cas9 has revolutionized genetic engineering, however, the inability to control double strand break (DSB) repair has severely limited both therapeutic and academic applications. Many attempts have been made to control DSB repair choice, however particularly in the case of larger edits, none have been able to bypass the rate-limiting step of Homologous Recombination (HR): long-range 5’ end resection. Here we describe a novel set of Cas9 fusions, Cas9-HRs, designed to bypass the rate-limiting step of HR repair by simultaneously coupling initial and long-range end resection. Cas9-HRs can increase the rate HR by 2-2.5 fold and decrease cellular toxicity by 2-4 fold compared to Cas9 in mammalian cells with minimal apparent editing site bias, thus making Cas9-HRs an attractive option for applications demanding increased HDR rates for long inserts and/or reduced p53 pathway activation.SummaryA novel Cas9 fusion protein designed to increase HDR rates through bypassing the rate limiting step of homologous recombination repair.

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