Alternative end-joining catalyzes robust IgH locus deletions and translocations in the combined absence of ligase 4 and Ku70
Alternative end-joining catalyzes robust IgH locus deletions and translocations in the combined absence of ligase 4 and Ku70
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DOI：
10.1073/pnas.0915067107
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发表时间：
2010-02-16
影响因子：
11.1
通讯作者：
Alt, Frederick W.
中科院分区：
文献类型：
--
作者：
Boboila, Cristian;Jankovic, Mila;Alt, Frederick W.
B淋巴细胞中的类别转换重组（CSR）是由在免疫球蛋白重链（IgH）恒定区外显子侧翼的转换（S）区引入多个DNA双链断裂（DSB）而启动的。CSR通过末端连接将供体Sμ中的一个DSB与下游受体S区（例如Sγ1）中的一个DSB连接起来而完成。在正常细胞中，许多CSR连接是由经典的非同源末端连接（C - NHEJ）介导的，它利用Ku70/80复合物进行DSB识别，并利用XRCC4/DNA连接酶4进行连接。在缺乏C - NHEJ的情况下，替代末端连接（A - EJ）以较低水平介导CSR，即使在Ku70和连接酶4同时缺失的情况下也是如此，这表明A - EJ途径与C - NHEJ完全不同。在CSR过程中，多个DSB被引入到Sμ中，其中一些被重新连接或相互连接以产生内部转换缺失（ISD）。此外，S区的DSB可以与其他染色体连接以产生易位，在缺乏单个C - NHEJ成分（例如XRCC4）时，易位水平会增加。我们询问在完全缺乏C - NHEJ的情况下（例如在Ku70/连接酶4双缺陷的B细胞中）是否会发生ISD和S区易位。我们意外地发现，用于CSR的B细胞活化在Sμ和Sγ1中都会产生大量的ISD，并且在缺乏C - NHEJ的情况下，两者中的ISD都会大大增加。在Ku70和连接酶4同时缺失的情况下，IgH染色体到c - myc癌基因的易位也会增加。我们讨论了这些发现对正常和异常DSB修复中A - EJ的影响。
Class switch recombination (CSR) in B lymphocytes is initiated by introduction of multiple DNA double-strand breaks (DSBs) into switch (S) regions that flank immunoglobulin heavy chain (IgH) constant region exons. CSR is completed by joining a DSB in the donor S mu to a DSB in a downstream acceptor S region (e. g., S gamma 1) by end-joining. In normal cells, many CSR junctions are mediated by classical nonhomologous end-joining (C-NHEJ), which employs the Ku70/80 complex for DSB recognition and XRCC4/DNA ligase 4 for ligation. Alternative end-joining (A-EJ) mediates CSR, at reduced levels, in the absence of C-NHEJ, even in combined absence of Ku70 and ligase 4, demonstrating an A-EJ pathway totally distinct from C-NHEJ. Multiple DSBs are introduced into S mu during CSR, with some being rejoined or joined to each other to generate internal switch deletions (ISDs). In addition, S-region DSBs can be joined to other chromosomes to generate translocations, the level of which is increased by absence of a single C-NHEJ component (e. g., XRCC4). We asked whether ISD and S-region translocations occur in the complete absence of C-NHEJ (e. g., in Ku70/ligase 4 double-deficient B cells). We found, unexpectedly, that B-cell activation for CSR generates substantial ISD in both S mu and S gamma 1 and that ISD in both is greatly increased by the absence of C-NHEJ. IgH chromosomal translocations to the c-myc oncogene also are augmented in the combined absence of Ku70 and ligase 4. We discuss the implications of these findings for A-EJ in normal and abnormal DSB repair.