Ubiquitylated PCNA plays a role in somatic hypermutation and class-switch recombination and is required for meiotic progression
Ubiquitylated PCNA plays a role in somatic hypermutation and class-switch recombination and is required for meiotic progression
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DOI：
10.1073/pnas.0808182105
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发表时间：
2008-10-21
影响因子：
11.1
通讯作者：
Scharff, Matthew D.
中科院分区：
文献类型：
--
作者：
Roa, Sergio;Avdievich, Elena;Scharff, Matthew D.
免疫球蛋白（Ig）基因的体细胞高频突变（SHM）和类别转换重组（CSR）依赖于激活诱导的胞苷脱氨酶（AID）诱导的突变。增殖细胞核抗原（PCNA）的支架特性及其K164残基的泛素化被认为在组织易错修复事件中起重要作用，这些事件有助于AID诱导的Ig基因座多样化。我们构建了PCNA基因敲除小鼠（Pcna^{-/-}），其在胚胎期致死。表达具有K164R突变的PCNA挽救了致死表型，但这些小鼠（Pcna^{-/-}tg(K164R)）在粗线期早期表现出减数分裂缺陷且不育。在Pcna^{-/-}tg(K164R)小鼠中，B细胞正常增殖，但PCNA - K164R突变导致体外向IgG1和IgG3的类别转换重组受损，这与转换区突变频率降低以及倾向于平端连接有关。在NP免疫后对重链V186.2区域的分析显示，在Pcna^{-/-}tg(K164R)小鼠中，聚合酶η（Pol η）偏好的WA基序中A:T残基的突变频率显著降低，并且G残基的突变频率呈链偏向性增加，尤其在AID靶向的GYW基序的情况下。Pcna^{-/-}tg(K164R)小鼠的表型支持这样的观点：PCNA的泛素化直接参与减数分裂过程以及通过类别转换重组（CSR）和体细胞高频突变（SHM）实现Ig基因座的多样化。
Somatic hypermutation (SHM) and class-switch recombination (CSR) of Ig genes are dependent upon activation-induced cytidine deaminase (AID)-induced mutations. The scaffolding properties of proliferating cell nuclear antigen (PCNA) and ubiquitylation of its residue K164 have been suggested to play an important role organizing the error-prone repair events that contribute to the AID-induced diversification of the Ig locus. We generated knockout mice for PCNA (Pcna(-/-)), which were embryonic lethal. Expression of PCNA with the K164R mutation rescued the lethal phenotype, but the mice (Pcna(-/-)tg(K164R)) displayed a meiotic defect in early pachynema and were sterile. B cells proliferated normally in Pcna(-/-)tg(K164R) mice, but a PCNA-K164R mutation resulted in impaired ex vivo CSR to IgG1 and IgG3, which was associated with reduced mutation frequency at the switch regions and a bias toward blunt junctions. Analysis of the heavy chain V186.2 region after NP-immunization showed in Pcna(-/-)tgK(164R) mice a significant reduction in the mutation frequency of A:T residues in WA motifs preferred by polymerase-eta (Pol eta), and a strand-biased increase in the mutation frequency of G residues, preferentially in the context of AID-targeted GYW motifs. The phenotype of Pcna(-/-)tg(K164R) mice supports the idea that ubiquitylation of PCNA participates directly in the meiotic process and the diversification of the Ig locus through class-switch recombination (CSR) and somatic hypermutation (SHM).