IgH class switching and translocations use a robust non-classical end-joining pathway
IgH class switching and translocations use a robust non-classical end-joining pathway
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DOI：
10.1038/nature06020
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发表时间：
2007-09-27
期刊：
影响因子：
64.8
通讯作者：
Alt, Frederick W.
中科院分区：
文献类型：
--
作者：
Yan, Catherine T.;Boboila, Cristian;Alt, Frederick W.
免疫球蛋白可变区外显子通过V(D)J重组在发育中的B细胞中组装。一旦成熟，当这些细胞被抗原激活时，就会经历类切换重组(CSR)。CSR将用给定可变区外显子表达的重链恒定区外显子(CH)从Cm改变为下游CH(例如，C Gamma、C epsilon或Cα)，从而将表达从IgM转换为Ig G、Ig E或Ig A。V(D)J重组和CSR都涉及DNA双链断裂的引入和末端连接(1，2)修复。对于CSR，双链断裂被引入到CM和下游CH两侧的开关区，随后融合断开的开关区(1)。在哺乳动物细胞中，“经典的”非同源末端连接(C-NHEJ)途径修复普通DNA双链断裂和V(D)J重组产生的程序性双链断裂(2，3)。如在V(D)J重组过程中观察到的，C-NHEJ连接缺乏同源性的末端以形成直接连接，并且也连接具有几个碱基对同源性的末端以形成微同源连接(3，4)。CSR连接也表现为直接连接和微同源连接，CSR被建议使用C-NHEJ(5-8)。Xrcc4和DNA连接酶IV(Lig4)协同催化C-NHEJ的连接步骤，是最特异的C-NHEJ因子；它们是V(D)J重组所必需的，除了C-NHEJ(2)之外没有已知的功能。在这里，我们通过分析Xrcc4或Lig4缺陷的小鼠B细胞中的CSR来评估C-NHEJ是否也对CSR至关重要。C-NHEJ确实催化CSR连接，因为C-NHEJ缺陷的B细胞降低了CSR和大量的IgH位点(免疫球蛋白重链，由IGH编码)染色体断裂。然而，另一种明显偏向于微同源连接的替代末端连接途径，在C-NHEJ缺陷的B细胞中以出人意料的强健水平支持CSR。在没有C-NHEJ的情况下，这种可选的末端连接途径也经常将IGH基因座断裂连接到其他染色体上，从而产生易位。
Immunoglobulin variable region exons are assembled in developing B cells by V(D)J recombination. Once mature, these cells undergo class-switch recombination (CSR) when activated by antigen. CSR changes the heavy chain constant region exons (CH) expressed with a given variable region exon from Cm to a downstream CH (for example, C gamma, C epsilon or C alpha), thereby switching expression from IgM to IgG, IgE or IgA. Both V(D)J recombination and CSR involve the introduction of DNA double-strand breaks and their repair by means of end joining(1,2). For CSR, double-strand breaks are introduced into switch regions that flank Cm and a downstream CH, followed by fusion of the broken switch regions(1). In mammalian cells, the 'classical' non-homologous end joining (C-NHEJ) pathway repairs both general DNA double-strand breaks and programmed double-strand breaks generated by V(D)J recombination(2,3). C-NHEJ, as observed during V(D)J recombination, joins ends that lack homology to form 'direct' joins, and also joins ends with several base-pair homologies to form microhomology joins(3,4). CSR joins also display direct and microhomology joins, and CSR has been suggested to use C-NHEJ(5-8). Xrcc4 and DNA ligase IV (Lig4), which cooperatively catalyse the ligation step of C-NHEJ, are the most specific C-NHEJ factors; they are absolutely required for V(D)J recombination and have no known functions other than C-NHEJ(2). Here we assess whether C-NHEJ is also critical for CSR by assaying CSR in Xrcc4- or Lig4-deficient mouse B cells. C-NHEJ indeed catalyses CSR joins, because C-NHEJ-deficient B cells had decreased CSR and substantial levels of IgH locus (immunoglobulin heavy chain, encoded by Igh) chromosomal breaks. However, an alternative end-joining pathway, which is markedly biased towards microhomology joins, supports CSR at unexpectedly robust levels in C-NHEJ-deficient B cells. In the absence of C-NHEJ, this alternative end-joining pathway also frequently joins Igh locus breaks to other chromosomes to generate translocations.