title: CtIP and MRN promote non-homologous end-joining of etoposide-induced DNA double-strand breaks in G1.
abstract: Topoisomerases class II (topoII) cleave and re-ligate the DNA double helix to allow the passage of an intact DNA strand through it. Chemotherapeutic drugs such as etoposide target topoII, interfere with the normal enzymatic cleavage/re-ligation reaction and create a DNA double-strand break (DSB) with the enzyme covalently bound to the 5'-end of the DNA. Such DSBs are repaired by one of the two major DSB repair pathways, non-homologous end-joining (NHEJ) or homologous recombination. However, prior to repair, the covalently bound topoII needs to be removed from the DNA end, a process requiring the MRX complex and ctp1 in fission yeast. CtIP, the mammalian ortholog of ctp1, is known to promote homologous recombination by resecting DSB ends. Here, we show that human cells arrested in G0/G1 repair etoposide-induced DSBs by NHEJ and, surprisingly, require the MRN complex (the ortholog of MRX) and CtIP. CtIP's function for repairing etoposide-induced DSBs by NHEJ in G0/G1 requires the Thr-847 but not the Ser-327 phosphorylation site, both of which are needed for resection during HR. This finding establishes that CtIP promotes NHEJ of etoposide-induced DSBs during G0/G1 phase with an end-processing function that is distinct to its resection function.
authors.affiliation: Radiation Biology and DNA Repair, Darmstadt University of Technology, 64287 Darmstadt, Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Quennet
authors.forename: Andrea
authors.initials: A
authors.lastname: Beucher
authors.forename: Olivia
authors.initials: O
authors.lastname: Barton
authors.forename: Shunichi
authors.initials: S
authors.lastname: Takeda
authors.forename: Markus
authors.initials: M
authors.lastname: Löbrich
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000633:toxicity*; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000502:physiology; D002478:Cells, Cultured; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000502:physiology*; D004706:Endodeoxyribonucleases; D005047:Etoposide / Q000633:toxicity*; D016193:G1 Phase / Q000187:drug effects / Q000235:genetics; D006801:Humans; D000076228:MRE11 Homologue Protein; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D013912:Threonine / Q000378:metabolism
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C121766:MRE11 protein, human; C112156:NBN protein, human; D009687:Nuclear Proteins; D013912:Threonine; D005047:Etoposide; D004706:Endodeoxyribonucleases; D000076228:MRE11 Homologue Protein; C410741:RBBP8 protein, human