The role of the Mre11-Rad50-Nbs1 complex in double-strand break repair-facts and myths.
Homologous recombination (HR) initiates double-strand break (DSB) repair by digesting 5'-termini at DSBs, the biochemical reaction called DSB resection, during which DSBs are processed by nucleases to generate 3' single-strand DNA. Rad51 recombinase polymerizes along resected DNA, and the resulting Rad51-DNA complex undergoes homology search. Although DSB resection by the Mre11 nuclease plays a critical role in HR in Saccharomyces cerevisiae, it remains elusive whether DSB resection by Mre11 significantly contributes to HR-dependent DSB repair in mammalian cells. Depletion of Mre11 decreases the efficiency of DSB resection only by 2- to 3-fold in mammalian cells. We show that although Mre11 is required for efficient HR-dependent repair of ionizing-radiation-induced DSBs, Mre11 is largely dispensable for DSB resection in both chicken DT40 and human TK6 B cell lines. Moreover, a 2- to 3-fold decrease in DSB resection has virtually no impact on the efficiency of HR. Thus, although a large number of researchers have reported the vital role of Mre11-mediated DSB resection in HR, the role may not explain the very severe defect in HR in Mre11-deficient cells, including their lethality. We here show experimental evidence for the additional roles of Mre11 in (i) elimination of chemical adducts from DSB ends for subsequent DSB repair, and (ii) maintaining HR intermediates for their proper resolution.
Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshida Konoe, Sakyo-ku, Kyoto 606-8501, Japan stakeda@rg.med.kyoto-u.ac.jp.
Shunichi
S
Takeda
Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshida Konoe, Sakyo-ku, Kyoto 606-8501, Japan.
Nguyen Ngoc
NN
Hoa
Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshida Konoe, Sakyo-ku, Kyoto 606-8501, Japan.
Hiroyuki
H
Sasanuma
D017766:Acid Anhydride Hydrolases; D000818:Animals; D030161:Avian Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D002645:Chickens; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000378:metabolism*; D045566:DNA, Cruciform; D004268:DNA-Binding Proteins / Q000378:metabolism*; D059765:Homologous Recombination / Q000235:genetics; D006801:Humans; D000076228:MRE11 Homologue Protein; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism*; D051135:Rad51 Recombinase / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism
D030161:Avian Proteins; D018797:Cell Cycle Proteins; D045566:DNA, Cruciform; D004268:DNA-Binding Proteins; C121766:MRE11 protein, human; C112156:NBN protein, human; D009687:Nuclear Proteins; D051135:Rad51 Recombinase; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D045643:DNA Repair Enzymes
Mre11; double-strand break repair; double-strand break resection; etoposide; homologous recombination; ionizing radiation; non-homologous end joining; topoisomerase