Xu Jianliang, Husain Afzal, Hu Wenjun, Honjo Tasuku, Kobayashi Maki
Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan.
Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan
Proc Natl Acad Sci U S A. 2014 Dec 2;111(48):17242-7. doi: 10.1073/pnas.1420221111. Epub 2014 Nov 17.
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.
活化诱导的胞苷脱氨酶（AID）对于抗体多样化至关重要，即体细胞超突变（SHM）和类别转换重组（CSR）。CH12F3-2A B细胞中无嘌呤/无嘧啶内切核酸酶1（Ape1）的缺陷将CSR降低至野生型细胞的约20%，而APE1缺失对SHM的影响尚未得到研究。在这里我们表明，虽然APE1的内切核酸酶活性对CSR很重要，但它对于SHM以及IgH/c-myc易位是可有可无的。重要的是，APE1缺陷在AID诱导的S区域断裂形成中未显示任何缺陷，但阻断了修复蛋白Ku80向S区域的募集以及Sμ和Sα之间的突触形成。敲低诸如减数分裂重组11同源物（MRE11）和羧基末端结合蛋白（CtBP）相互作用蛋白（CtIP）等末端加工因子进一步降低了Ape1缺失的CH12F3-2A细胞中剩余的CSR。总之，我们的结果表明，APE1对于SHM和AID诱导的DNA断裂是可有可无的，并且可能作为一种DNA末端加工酶，在CSR过程中促进断裂末端的连接。
