scholarly journals Nonhomologous End-Joining Repair Plays a More Important Role than Homologous Recombination Repair in Defining Radiosensitivity after Exposure to High-LET Radiation

2014 ◽  
Vol 182 (3) ◽  
pp. 338-344 ◽  
Author(s):  
Akihisa Takahashi ◽  
Makoto Kubo ◽  
Hongyu Ma ◽  
Akiko Nakagawa ◽  
Yukari Yoshida ◽  
...  
Keyword(s):  
Homologous Recombination ◽  
Nonhomologous End Joining ◽  
Homologous Recombination Repair ◽  
End Joining ◽  
High Let Radiation ◽  
Recombination Repair ◽  
High Let

scholarly journals Inhibition of the ATR kinase enhances 5-FU sensitivity independently of nonhomologous end-joining and homologous recombination repair pathways

2020 ◽  
Vol 295 (37) ◽  
pp. 12946-12961
Author(s):  
Soichiro S. Ito ◽  
Yosuke Nakagawa ◽  
Masaya Matsubayashi ◽  
Yoshihiko M. Sakaguchi ◽  
Shinko Kobashigawa ◽  
...  
Keyword(s):  
Homologous Recombination ◽  
Mammalian Cells ◽  
Cell Cycle Checkpoint ◽  
Nonhomologous End Joining ◽  
Homologous Recombination Repair ◽  
Dna Breaks ◽  
End Joining ◽  
Nucleotide Synthesis ◽  
Recombination Repair ◽  
Repair Pathways

The anticancer agent 5-fluorouracil (5-FU) is cytotoxic and often used to treat various cancers. 5-FU is thought to inhibit the enzyme thymidylate synthase, which plays a role in nucleotide synthesis and has been found to induce single- and double-strand DNA breaks. ATR Ser/Thr kinase (ATR) is a principal kinase in the DNA damage response and is activated in response to UV– and chemotherapeutic drug–induced DNA replication stress, but its role in cellular responses to 5-FU is unclear. In this study, we examined the effect of ATR inhibition on 5-FU sensitivity of mammalian cells. Using immunoblotting, we found that 5-FU treatment dose-dependently induced the phosphorylation of ATR at the autophosphorylation site Thr-1989 and thereby activated its kinase. Administration of 5-FU with a specific ATR inhibitor remarkably decreased cell survival, compared with 5-FU treatment combined with other major DNA repair kinase inhibitors. Of note, the ATR inhibition enhanced induction of DNA double-strand breaks and apoptosis in 5-FU–treated cells. Using gene expression analysis, we found that 5-FU induced the activation of the intra-S cell-cycle checkpoint. Cells lacking BRCA2 were sensitive to 5-FU in the presence of ATR inhibitor. Moreover, ATR inhibition enhanced the efficacy of the 5-FU treatment, independently of the nonhomologous end-joining and homologous recombination repair pathways. These findings suggest that ATR could be a potential therapeutic target in 5-FU–based chemotherapy.

scholarly journals Proton Irradiation Increases the Necessity for Homologous Recombination Repair Along with the Indispensability of Non-Homologous End Joining

Cells ◽  
2020 ◽  
Vol 9 (4) ◽  
pp. 889 ◽  
Author(s):  
Klaudia Szymonowicz ◽  
Adam Krysztofiak ◽  
Jansje van der Linden ◽  
Ajvar Kern ◽  
Simon Deycmar ◽  
...  
Keyword(s):  
Dna Damage ◽  
Homologous Recombination ◽  
Proton Irradiation ◽  
Negative Impact ◽  
Particle Therapy ◽  
Homologous Recombination Repair ◽  
End Joining ◽  
X Ray ◽  
Recombination Repair ◽  
Non Homologous End Joining

Technical improvements in clinical radiotherapy for maximizing cytotoxicity to the tumor while limiting negative impact on co-irradiated healthy tissues include the increasing use of particle therapy (e.g., proton therapy) worldwide. Yet potential differences in the biology of DNA damage induction and repair between irradiation with X-ray photons and protons remain elusive. We compared the differences in DNA double strand break (DSB) repair and survival of cells compromised in non-homologous end joining (NHEJ), homologous recombination repair (HRR) or both, after irradiation with an equal dose of X-ray photons, entrance plateau (EP) protons, and mid spread-out Bragg peak (SOBP) protons. We used super-resolution microscopy to investigate potential differences in spatial distribution of DNA damage foci upon irradiation. While DNA damage foci were equally distributed throughout the nucleus after X-ray photon irradiation, we observed more clustered DNA damage foci upon proton irradiation. Furthermore, deficiency in essential NHEJ proteins delayed DNA repair kinetics and sensitized cells to both, X-ray photon and proton irradiation, whereas deficiency in HRR proteins sensitized cells only to proton irradiation. We assume that NHEJ is indispensable for processing DNA DSB independent of the irradiation source, whereas the importance of HRR rises with increasing energy of applied irradiation.

141 INDICATIONS FOR DNA DOUBLE-STRAND BREAK REPAIR IN EARLY BOVINE EMBRYOS

2007 ◽  
Vol 19 (1) ◽  
pp. 188
Author(s):  
A. Brero ◽  
D. Koehler ◽  
T. Cremer ◽  
E. Wolf ◽  
V. Zakhartchenko
Keyword(s):  
Dna Repair ◽  
Homologous Recombination ◽  
Strand Break ◽  
Dna Lesions ◽  
Homologous Recombination Repair ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Male And Female ◽  
Γh2ax Foci ◽  
Recombination Repair

DNA double-strand breaks (DSBs) are considered the most severe type of DNA lesions, because such lesions, if unrepaired, lead to a loss of genome integrity. Soon after induction of DSBs, chromatin surrounding the damage is modified by phosphorylation of the histone variant H2AX, generating so-called γH2AX, which is a hallmark of DSBs (Takahashi et al. 2005 Cancer Lett. 229, 171–179). γH2AX appears to be a signal for the recruitment of proteins constituting the DNA repair machinery. Depending on the type of damage and the cell cycle stage of the affected cell, DSBs are repaired either by nonhomologous end joining or by homologous recombination using the sister chromatid DNA as template (Hoeijmakers 2001 Nature 411, 366–374). We used immunofluorescence to analyze chromatin composition during bovine development and found γH2AX foci in both male and female pronuclei of IVF embryos. The number and size of foci varied considerably between embryos and between the male and female pronuclei. To test whether the observed γH2AX foci represented sites of active DNA repair, we co-stained IVF zygotes for γH2AX and 3 different proteins involved in homologous recombination repair of DSBs: NBS1 (phosphorylated at amino acid serine 343), 53BP1, and Rad51. We found co-localization of γH2AX foci with phosphorylated NBS1 as well as with Rad51 but did not observe the presence of 53BP1 at γH2AX foci in IVF zygotes. Our finding shows the presence of DSBs in IVF zygotes and suggests the capability of homologous recombination repair. The lack of 53BP1, a component of homologous recombination repair, which usually co-localizes with γH2AX foci at exogenously induced DSBs (Schultz et al. 2000 J. Cell. Biol. 151, 1381–1390) poses the possibility that the mechanism present in early embryos differs substantially from that involved in DNA repair of DSBs in somatic cells.

scholarly journals ATR inhibition enhances 5-fluorouracil sensitivity independent of non-homologous end-joining and homologous recombination repair pathway

2020 ◽  
Author(s):  
Soichiro S. Ito ◽  
Yosuke Nakagawa ◽  
Masaya Matsubayashi ◽  
Yoshihiko M. Sakaguchi ◽  
Shinko Kobashigawa ◽  
...  
Keyword(s):  
Homologous Recombination ◽  
Homologous Recombination Repair ◽  
Dna Double Strand Breaks ◽  
Dna Breaks ◽  
End Joining ◽  
Drug Induced ◽  
Nucleotide Synthesis ◽  
Double Strand Dna Breaks ◽  
Recombination Repair ◽  
Non Homologous End Joining

ABSTRACTThe anticancer agent, 5-fluorouracil (5-FU), is typically applied in the treatment of various types of cancers because of its properties. Thought to be an inhibitor of the enzyme thymidylate synthase which plays a role in nucleotide synthesis, 5-FU has been found to induce single- and double-strand DNA breaks. The activation of ATR occurs as a reaction to UV- and chemotherapeutic drug-induced replication stress. In this study, we examined the effect of ATR inhibition on 5-FU sensitivity. Using western blotting, we found that 5-FU treatment led to the phosphorylation of ATR. Surviving fractions were remarkably decreased in 5-FU with ATR inhibitor (ATRi) compared to 5-FU with other major DNA repair kinases inhibitors. ATR inhibition enhanced induction of DNA double-strand breaks and apoptosis in 5-FU-treated cells. Using gene expression analysis, we found that 5-FU could induce the activation of intra-S checkpoint. Surprisingly, BRCA2-deficient cells were sensitive to 5-FU in the presence of ATRi. In addition, ATR inhibition enhanced the efficacy of 5-FU treatment, independent of non-homologous end-joining and homologous recombination repair pathways. Findings from the present study suggest ATR as a potential therapeutic target for 5-FU chemotherapy.

scholarly journals XRN2 Links RNA:DNA Hybrid Resolution to Double Strand Break Repair Pathway Choice

Cancers ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1821
Author(s):  
Tuyen T. Dang ◽  
Julio C. Morales
Keyword(s):  
Homologous Recombination ◽  
Strand Break ◽  
Double Strand Break Repair ◽  
Homologous Recombination Repair ◽  
Repair Pathway ◽  
End Joining ◽  
Recombination Repair ◽  
Rna:Dna Hybrid ◽  
Break Repair ◽  
Non Homologous End Joining

It was recently shown that the 5’ to 3’ exoribonuclease XRN2 is involved in the DNA damage response. Importantly, loss of XRN2 abrogates DNA double stranded break repair via the non-homologous end-joining pathway. However, the mechanistic details of how XRN2 functions in the non-homologous end-joining repair process are unknown. In this study, we elucidated that XRN2-mediated RNA:DNA hybrid resolution is required to allow Ku70 binding to DNA ends. These data suggest that XRN2 is required for the initiation of non-homologous end-joining repair. Interestingly, we uncovered a role for XRN2 in the homologous recombination repair pathway. Loss of XRN2 lead to a decrease in the repair of double strand breaks by homologous recombination. Strikingly, when we removed RNA:DNA hybrids by RNaseH1 over-expression, homologous recombination was not restored. We found RNA:DNA hybrid formation at and downstream of the DSB site, suggesting that unregulated transcription inhibits homologous recombination repair. In summary, our results indicate a relation between RNA:DNA hybrid resolution and double strand break repair pathway choice.

Sign in / Sign up

Export Citation Format

Share Document