title: Microhomology-mediated End Joining and Homologous Recombination share the initial end resection step to repair DNA double-strand breaks in mammalian cells.
abstract: Microhomology-mediated end joining (MMEJ) is a major pathway for Ku-independent alternative nonhomologous end joining, which contributes to chromosomal translocations and telomere fusions, but the underlying mechanism of MMEJ in mammalian cells is not well understood. In this study, we demonstrated that, distinct from Ku-dependent classical nonhomologous end joining, MMEJ--even with very limited end resection--requires cyclin-dependent kinase activities and increases significantly when cells enter S phase. We also showed that MMEJ shares the initial end resection step with homologous recombination (HR) by requiring meiotic recombination 11 homolog A (Mre11) nuclease activity, which is needed for subsequent recruitment of Bloom syndrome protein (BLM) and exonuclease 1 (Exo1) to DNA double-strand breaks (DSBs) to promote extended end resection and HR. MMEJ does not require S139-phosphorylated histone H2AX (γ-H2AX), suggesting that initial end resection likely occurs at DSB ends. Using a MMEJ and HR competition repair substrate, we demonstrated that MMEJ with short end resection is used in mammalian cells at the level of 10-20% of HR when both HR and nonhomologous end joining are available. Furthermore, MMEJ is used to repair DSBs generated at collapsed replication forks. These studies suggest that MMEJ not only is a backup repair pathway in mammalian cells, but also has important physiological roles in repairing DSBs to maintain cell viability, especially under genomic stress.
authors.affiliation: Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: Lan N
authors.initials: LN
authors.lastname: Truong
authors.forename: Yongjiang
authors.initials: Y
authors.lastname: Li
authors.forename: Linda Z
authors.initials: LZ
authors.lastname: Shi
authors.forename: Patty Yi-Hwa
authors.initials: PY
authors.lastname: Hwang
authors.forename: Jing
authors.initials: J
authors.lastname: He
authors.forename: Hailong
authors.initials: H
authors.lastname: Wang
authors.forename: Niema
authors.initials: N
authors.lastname: Razavian
authors.forename: Michael W
authors.initials: MW
authors.lastname: Berns
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Wu
mesh_terms: D000818:Animals; D034961:Antigens, Nuclear / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D059766:DNA End-Joining Repair; D045643:DNA Repair Enzymes / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D059765:Homologous Recombination; D006801:Humans; D000072200:Ku Autoantigen; D000076228:MRE11 Homologue Protein; D008540:Meiosis; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism; D053484:RecQ Helicases / Q000378:metabolism; D016196:S Phase
chemical_list: D034961:Antigens, Nuclear; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; C121766:MRE11 protein, human; D009687:Nuclear Proteins; D049452:Green Fluorescent Proteins; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; C114331:EXO1 protein, human; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; D000076228:MRE11 Homologue Protein; C410741:RBBP8 protein, human; C097151:Bloom syndrome protein; D053484:RecQ Helicases; C000606509:Xrcc6 protein, human; C000606510:Xrcc6 protein, mouse; D000072200:Ku Autoantigen; D045643:DNA Repair Enzymes
keywords: BLM/Exo1; CtIP; DNA damage; DNA repair pathway; genome stability