The C-terminal region of activation-induced cytidine deaminase is responsible for a recombination function other than DNA cleavage in class switch recombination
The C-terminal region of activation-induced cytidine deaminase is responsible for a recombination function other than DNA cleavage in class switch recombination
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DOI：
10.1073/pnas.0813253106
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发表时间：
2009-02-24
影响因子：
11.1
通讯作者：
Honjo, Tasuku
中科院分区：
文献类型：
--
作者：
Doi, Tomomitsu;Kato, Lucia;Honjo, Tasuku
激活诱导的胞苷脱氨酶 (AID) 是 Ig 基因类别转换重组 (CSR) 和体细胞超突变 (SHM) 的重要因素。 CSR 和 SHM 分别由 AID 诱导的 S 区和 V 区 DNA 断裂启动。由于 AID 羧基 (C) 末端的截短或移码突变会消除 CSR，但不会消除 SHM，因此 AID 的 C 末端区域可能是靶向 S 区域 DNA 断裂所必需的。为了检验这一假设，我们使用原位 DNA 末端标记方法确定了 AID 诱导的 DNA 裂解的精确位置和相对量。我们建立了表达雌激素受体 (ER) 的 CH12F3-2 细胞转染子，该受体与野生型 (WT) AID 或缺乏 C 端 16 个氨基酸的缺失突变体 JP8Bdel 融合。我们发现，AID-ER（而非 JP8Bdel-ER）因添加 4-羟基他莫昔芬而引起 IgA 的 CSR。相比之下，WT AID 和 JP8Bdel 均诱导 V 区和 S 区 DNA 断裂。此外，JP8Bdel 增强了 c-myc/IgH 易位。我们的研究结果表明，AID 的 C 末端结构域不是 S 区 DNA 断裂所必需的，而是 DNA 切割后 S 区重组所必需的。因此，AID不区分V区和S区进行切割，而是携带CSR特有的另一种功能。
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.