The C-terminal region of activation-induced cytidine deaminase is responsible for a recombination function other than DNA cleavage in class switch recombination.
Activation-induced cytidine deaminase (AID) is an essential factor for the class switch recombination (CSR) and somatic hypermutation (SHM) of Ig genes. CSR and SHM are initiated by AID-induced DNA breaks in the S and V regions, respectively. Because truncation or frame-shift mutations at the carboxyl (C)-terminus of AID abolishes CSR but not SHM, the C-terminal region of AID likely is required for the targeting of DNA breaks in the S region. To test this hypothesis, we determined the precise location and relative amounts of AID-induced DNA cleavage using an in situ DNA end-labeling method. We established CH12F3-2 cell transfectants expressing the estrogen receptor (ER) fused with wild-type (WT) AID or a deletion mutant lacking the C-terminal 16 aa, JP8Bdel. We found that AID-ER, but not JP8Bdel-ER, caused a CSR to IgA from the addition of 4-hydroxy tamoxifen. In contrast, both WT AID and JP8Bdel induced DNA breaks in both the V and S regions. In addition, JP8Bdel enhanced c-myc/IgH translocations. Our findings indicate that the C-terminal domain of AID is not required for S-region DNA breaks but is required for S-region recombination after DNA cleavage. Therefore, AID does not distinguish between the V and S regions for cleavage, but carries another function specific to CSR.
Doi
Tomomitsu
T
Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan.
Kato
Lucia
L
Ito
Satomi
S
Shinkura
Reiko
R
Wei
Min
M
Nagaoka
Hitoshi
H
Wang
Jishu
J
Honjo
Tasuku
T
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D003564:Cytidine Deaminase / Q000737:chemistry / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004249:DNA Damage; D005822:Genetic Vectors; D006801:Humans; D017578:Immunoglobulin Class Switching; D007075:Immunoglobulin M / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011995:Recombination, Genetic; D017386:Sequence Homology, Amino Acid; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D007075:Immunoglobulin M; D004247:DNA; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase