Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA 01655, USA.
J Immunol. 2011 Sep 1;187(5):2464-75. doi: 10.4049/jimmunol.1101406. Epub 2011 Jul 29.
Activation-induced cytidine deaminase (AID) is induced in B cells during an immune response and is essential for both class-switch recombination (CSR) and somatic hypermutation of Ab genes. The C-terminal 10 aa of AID are required for CSR but not for somatic hypermutation, although their role in CSR is unknown. Using retroviral transduction into mouse splenic B cells, we show that the C terminus is not required for switch (S) region double-strand breaks (DSBs) and therefore functions downstream of DSBs. Using chromatin immunoprecipitation, we show that AID binds cooperatively with UNG and the mismatch repair proteins Msh2-Msh6 to Ig Sμ and Sγ3 regions, and this depends on the C terminus and the deaminase activity of AID. We also show that mismatch repair does not contribute to the efficiency of CSR in the absence of the AID C terminus. Although it has been demonstrated that both UNG and Msh2-Msh6 are important for introduction of S region DSBs, our data suggest that the ability of AID to recruit these proteins is important for DSB resolution, perhaps by directing the S region DSBs toward accurate and efficient CSR via nonhomologous end joining.
激活诱导胞嘧啶脱氨酶 (AID) 在免疫反应期间在 B 细胞中诱导，对于类别转换重组 (CSR) 和抗体基因的体细胞超突变都是必不可少的。AID 的 C 端 10 个氨基酸残基对于 CSR 是必需的，但对于体细胞超突变则不是必需的，尽管它们在 CSR 中的作用尚不清楚。通过逆转录病毒转导到小鼠脾脏 B 细胞中，我们表明 C 末端对于开关 (S) 区双链断裂 (DSB) 不是必需的，因此其功能位于 DSB 之后。通过染色质免疫沉淀，我们表明 AID 与 UNG 和错配修复蛋白 Msh2-Msh6 协同结合到 Ig Sμ 和 Sγ3 区域，这取决于 AID 的 C 末端和脱氨酶活性。我们还表明，在没有 AID C 末端的情况下，错配修复不会影响 CSR 的效率。尽管已经证明 UNG 和 Msh2-Msh6 对于引入 S 区 DSB 都很重要，但我们的数据表明，AID 招募这些蛋白的能力对于 DSB 分辨率很重要，可能通过将 S 区 DSB 导向通过非同源末端连接的准确和有效的 CSR。
