{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,31]],"date-time":"2026-10-31T10:30:11Z","timestamp":1793442611508,"version":"4.5.0"},"reference-count":57,"publisher":"Radiation Research Society","issue":"5","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Radiation Research"],"published-print":{"date-parts":[[2021,3,23]]},"abstract":"<jats:p>Alternative end-joining (alt-EJ) is a DNA end resection-dependent, error-prone pathway utilized by vertebrate cells to repair DNA double-strand breaks (DSBs), but its engagement is linked to chromosomal translocations and genomic instability. Here, we report that when proliferating cells are exposed to ionizing radiation, treatment with nucleoside analogs (NAs) causes strong radiosensitization by increasing engagement of alt-EJ, while at the same time suppressing homologous recombination (HR) in S- and G2phase cells. This NA-mediated pathway shift may reflect a passive compensatory engagement of alt-EJ following HR suppression that is specific for S- and G2-phase cells, and\/or the direct activation of alt-EJ throughout the cell cycle. To distinguish between these possibilities, we utilize here a cell culture model that exploits genetic and cell cycle-dependent inactivation of DSB repair pathways, to exclusively study alt-EJ and its modulation by NAs in murine and human cell lines. To this end, we allow LIG4\u2013\/\u2013-deficient cells to accumulate in G1\/G0 phase by transfer to serum-deprived media and obtain cells deficient in c-NHEJ owing to the genetic LIG4 knockout, deficient in HR owing to the absence of S- or G2-phase cells, and compromised in their ability to carry out alt-EJ owing to their accumulation in G0. We find that in these cells irradiation and treatment with the NA, \u03b2-arabinofuranosyladenine (araA), and to a lesser degree with other NAs, promptly activates suppressed alt-EJ that now functions at levels approximating those of c-NHEJ in wild-type cells. Results at high dose (20 Gy) generated using pulsed-field gel electrophoresis (PFGE) are corroborated by results at low dose (1 Gy) generated by scoring 53BP1 foci. Strikingly, araA treatment activates a normally undetectable DNA-end-resection at DSBs, which requires ATR activity, but proceeds unimpeded after CtIP knockdown. Treatment with araA increases the formation of chromosomal aberrations and enhances radiation-induced cell killing. The results support direct stimulation of resection by NAs and alt-EJ as a mechanism of their documented radiosensitizing potential. We propose that this stimulation also occurs in repair-proficient cells and that it occurs throughout the cell cycle. It may therefore be harnessed to develop protocols combining NAs with radiation to treat human cancer.<\/jats:p>","DOI":"10.1667\/rade-20-00195.1","type":"journal-article","created":{"date-parts":[[2021,5,3]],"date-time":"2021-05-03T01:27:00Z","timestamp":1620005220000},"page":"412-426","source":"Crossref","is-referenced-by-count":3,"title":["Nucleoside Analogs Radiosensitize G0 Cells by Activating DNA End Resection and Alternative End-Joining"],"prefix":"10.1667","volume":"195","author":[{"given":"Simon","family":"Magin","sequence":"first","affiliation":[{"name":"Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Prabodha Kumar","family":"Meher","sequence":"additional","affiliation":[{"name":"Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"George","family":"Iliakis","sequence":"additional","affiliation":[{"name":"Institute of Medical Radiation Biology, University of Duisburg-Essen Medical School, Essen, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1243","reference":[{"key":"45","doi-asserted-by":"crossref","unstructured":"EP Rogakou, DR Pilch, AH Orr, et al.  \"J Biol Chem.\"  273, \"DNA double-stranded breaks induce histone H2AX phosphorylation on serine 139.\" 5858 (1998)","DOI":"10.1074\/jbc.273.10.5858"},{"key":"3","doi-asserted-by":"crossref","unstructured":"WD Heyer, KT Ehmsen, J Liu,  \"Annu Rev Genet.\"  44, \"Regulation of homologous recombination in eukaryotes.\" 113 (2010)","DOI":"10.1146\/annurev-genet-051710-150955"},{"key":"1","doi-asserted-by":"crossref","unstructured":"KD Miller, L Nogueira, AB Mariotto, et al.  \"CA Cancer J Clin.\"  69, \"Cancer treatment and survivorship statistics, 2019.\" 363 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SC Watkins, et al.  \"Nucleic Acids Res.\"  41, \"ATR kinase activation in G1 phase facilitates the repair of ionizing radiation-induced DNA damage.\" 10334 (2013)","DOI":"10.1093\/nar\/gkt833"},{"key":"51","doi-asserted-by":"crossref","unstructured":"G Iliakis, T Murmann, A Soni,  \"Mutat Res Genet Toxicol Environ Mutagen.\"  793, \"Alternative end-joining repair pathways are the ultimate backup for abrogated classical non-homologous end-joining and homologous recombination repair: Implications for the formation of chromosome translocations.\" 166 (2015)","DOI":"10.1016\/j.mrgentox.2015.07.001"},{"key":"52","doi-asserted-by":"crossref","unstructured":"MN Cornforth  and JS Bedford  \"Radiat Res.\"  111, \"A quantitative comparison of potentially lethal damage repair and the rejoining of interphase chromosome breaks in low passage normal human-fibroblasts.\" 385 (1987)","DOI":"10.2307\/3576926"},{"key":"53","doi-asserted-by":"crossref","unstructured":"WC Dewey, SC Furman, HH Miller,  \"Radiat Res.\"  43, \"Comparison of lethality and chromosomal damage induced by x-rays in synchronized Chinese hamster cells in vitro.\" 561 (1970)","DOI":"10.2307\/3573230"},{"key":"54","doi-asserted-by":"crossref","unstructured":"N Tsesmetzis, CBJ Paulin, SG Rudd, et al.  \"Cancers.\"  10, \"Nucleobase and nucleoside analogues: Resistance and re-sensitisation at the level of pharmacokinetics, pharmacodynamics and metabolism.\" 240 (2018)","DOI":"10.3390\/cancers10070240"},{"key":"55","doi-asserted-by":"crossref","unstructured":"X Zhao, C Wei, J Li, et al.  \"Acta Biochim Biophys Sin (Shanghai).\"  49, \"Cell cycle-dependent control of homologous recombination.\" 655 (2017)","DOI":"10.1093\/abbs\/gmx055"},{"key":"56","doi-asserted-by":"crossref","unstructured":"GG Jones, PM Reaper, AR Pettitt, et al.  \"Oncogene.\"  23, \"The ATR-p53 pathway is suppressed in noncycling normal and malignant lymphocytes.\" 1911 (2004)","DOI":"10.1038\/sj.onc.1207318"},{"key":"57","doi-asserted-by":"crossref","unstructured":"KE Adams, AL Medhurst, DA Dart, et al.  \"Oncogene.\"  25, \"Recruitment of ATR to sites of ionising radiation-induced DNA damage requires ATM and components of the MRN protein complex.\" 3894 (2006)","DOI":"10.1038\/sj.onc.1209426"}],"container-title":["Radiation Research"],"original-title":[],"deposited":{"date-parts":[[2026,10,31]],"date-time":"2026-10-31T09:33:10Z","timestamp":1793439190000},"score":1,"resource":{"primary":{"URL":"https:\/\/bioone.org\/journals\/radiation-research\/volume-195\/issue-5\/RADE-20-00195.1\/Nucleoside-Analogs-Radiosensitize-G0-Cells-by-Activating-DNA-End-Resection\/10.1667\/RADE-20-00195.1.full"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,3,23]]},"references-count":57,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2021,5,1]]}},"URL":"https:\/\/doi.org\/10.1667\/rade-20-00195.1","relation":{},"ISSN":["0033-7587","1938-5404"],"issn-type":[{"value":"0033-7587","type":"print"},{"value":"1938-5404","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,3,23]]}}}