title: APE1 is dispensable for S-region cleavage but required for its repair in class switch recombination.
abstract: Activation-induced cytidine deaminase (AID) is essential for antibody diversification, namely somatic hypermutation (SHM) and class switch recombination (CSR). The deficiency of apurinic/apyrimidinic endonuclease 1 (Ape1) in CH12F3-2A B cells reduces CSR to ∼20% of wild-type cells, whereas the effect of APE1 loss on SHM has not been examined. Here we show that, although APE1's endonuclease activity is important for CSR, it is dispensable for SHM as well as IgH/c-myc translocation. Importantly, APE1 deficiency did not show any defect in AID-induced S-region break formation, but blocked both the recruitment of repair protein Ku80 to the S region and the synapse formation between Sμ and Sα. Knockdown of end-processing factors such as meiotic recombination 11 homolog (MRE11) and carboxy-terminal binding protein (CtBP)-interacting protein (CtIP) further reduced the remaining CSR in Ape1-null CH12F3-2A cells. Together, our results show that APE1 is dispensable for SHM and AID-induced DNA breaks and may function as a DNA end-processing enzyme to facilitate the joining of broken ends during CSR.
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Jianliang
authors.initials: J
authors.lastname: Xu
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Afzal
authors.initials: A
authors.lastname: Husain
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Wenjun
authors.initials: W
authors.lastname: Hu
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan honjo@mfour.med.kyoto-u.ac.jp.
authors.forename: Tasuku
authors.initials: T
authors.lastname: Honjo
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Maki
authors.initials: M
authors.lastname: Kobayashi
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D003564:Cytidine Deaminase / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics / Q000378:metabolism; D016393:Lymphoma, B-Cell / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D000076228:MRE11 Homologue Protein; D051379:Mice; D009154:Mutation; D021381:Protein Transport; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D011995:Recombination, Genetic; D027041:Somatic Hypermutation, Immunoglobulin / Q000235:genetics*; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D003564:Cytidine Deaminase; D045643:DNA Repair Enzymes; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D004268:DNA-Binding Proteins; D007143:Immunoglobulin Heavy Chains; D000076228:MRE11 Homologue Protein; D016271:Proto-Oncogene Proteins c-myc; D000098830:AICDA (Activation-Induced Cytidine Deaminase); C501070:RBBP8 protein, mouse; C512689:Mre11a protein, mouse; C486216:Apex1 protein, mouse
keywords: DNA cleavage; DNA synapse formation; class switch recombination; end processing; somatic hypermutation