Further evidence for involvement of a noncanonical function of uracil DNA glycosylase in class switch recombination
Further evidence for involvement of a noncanonical function of uracil DNA glycosylase in class switch recombination
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DOI：
10.1073/pnas.0813252106
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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：
Begum, Nasim A.;Stanlie, Andre;Honjo, Tasuku
激活诱导的胞苷脱氨酶（AID）在IG基因座中引入DNA切割以启动B细胞中的体细胞超突变（SHM）和类别转换重组（CSR）。DNA脱氨基模型假设AID使DNA上的胞苷（C）脱氨基并产生尿苷（U），导致尿嘧啶DNA糖基化酶（UNG）去除U后DNA裂解。虽然UNG缺陷减少CSR效率的十分之一，我们报告说，催化失活的UNG突变体完全精通CSR和几个突变体在非催化位点失去CSR活性，表明酶活性的UNG是不需要CSR。在这份报告中，我们表明，许多UNG突变体的CSR活动严重依赖于其N-末端结构域，无论其酶活性。在另一个UNG家族成员SMUG 1及其突变体中也发现了催化和CSR活性的解离。我们还表明，Ugi，一种特异性的肽抑制剂的UNG，抑制CSR，而不减少DNA切割的S（开关）区域，确认UNG在CSR中的DNA切割的可分配性。因此，UNG可能参与CSR中DNA切割后的修复步骤。此外，对于CSR，UNG突变体需要N末端而不是酶活性，这表明UNG蛋白结构是关键的。目前的研究结果支持了我们早期的建议，即CSR取决于UNG蛋白的非典型功能（例如。例如，在一个实施例中，作为修复酶的支架），其可能是DNA切割后重组反应所需的。
Activation-induced cytidine deaminase (AID) introduces DNA cleavage in the Ig gene locus to initiate somatic hypermutation (SHM) and class switch recombination (CSR) in B cells. The DNA deamination model assumes that AID deaminates cytidine (C) on DNA and generates uridine (U), resulting in DNA cleavage after removal of U by uracil DNA glycosylase (UNG). Although UNG deficiency reduces CSR efficiency to one tenth, we reported that catalytically inactive mutants of UNG were fully proficient in CSR and that several mutants at noncatalytic sites lost CSR activity, indicating that enzymatic activity of UNG is not required for CSR. In this report we show that CSR activity by many UNG mutants critically depends on its N-terminal domain, irrespective of their enzymatic activities. Dissociation of the catalytic and CSR activity was also found in another UNG family member, SMUG1, and its mutants. We also show that Ugi, a specific peptide inhibitor of UNG, inhibits CSR without reducing DNA cleavage of the S (switch) region, confirming dispensability of UNG in DNA cleavage in CSR. It is therefore likely that UNG is involved in a repair step after DNA cleavage in CSR. Furthermore, requirement of the N terminus but not enzymatic activity of UNG mutants for CSR indicates that the UNG protein structure is critical. The present findings support our earlier proposal that CSR depends on a noncanonical function of the UNG protein (e. g., as a scaffold for repair enzymes) that might be required for the recombination reaction after DNA cleavage.