Activation-induced cytidine deaminase (AID)-dependent somatic hypermutation requires a splice isoform of the serine/arginine-rich (SR) protein SRSF1
Activation-induced cytidine deaminase (AID)-dependent somatic hypermutation requires a splice isoform of the serine/arginine-rich (SR) protein SRSF1
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DOI：
10.1073/pnas.1120368109
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发表时间：
2012-01-24
影响因子：
11.1
通讯作者：
Kanayama, Naoki
中科院分区：
文献类型：
--
作者：
Kanehiro, Yuichi;Todo, Kagefumi;Kanayama, Naoki
Ig可变区（IgV）基因的体细胞超突变（SHM）需要IgV转录和酶激活诱导胞苷脱氨酶（AID）。鉴定IgV基因对艾滋病诱导的突变比其他基因更敏感的辅助因子是免疫学中的一个关键问题。在这里，我们描述了典型的富含丝氨酸/精氨酸（SR）蛋白SRSF1的剪接异构体，称为SRSF1-3，在艾滋病诱导的DT40鸡b细胞系SHM中发挥重要作用。出乎意料的是，我们发现SHM不发生在缺乏SRSF1-3 （DT40- asf）的DT40细胞系中，尽管它在亲代DT40细胞中很容易检测到。引人注目的是，在DT40-ASF细胞中AID的过表达导致非特异性（脱靶）突变的大量增加。相反，将SRSF1-3而不是SRSF1引入这些细胞中，可以特异性地恢复SHM，而不会增加脱靶突变。此外，我们发现SRSF1-3优先结合IgV基因并抑制Ig转录物的加工，这提供了SRSF1-3使IgV基因可用于艾滋病依赖性SHM的机制。SRSF1不仅是必不可少的剪接因子，而且还调节mRNA代谢的各个方面，维持基因组的稳定性。因此，我们的研究结果确定了SRSF1，特别是其剪接变体，在使AID在SHM期间特异性地作用于其天然底物中的一个意想不到的重要作用。
Somatic hypermutation (SHM) of Ig variable region (IgV) genes requires both IgV transcription and the enzyme activation-induced cytidine deaminase (AID). Identification of a cofactor responsible for the fact that IgV genes are much more sensitive to AID-induced mutagenesis than other genes is a key question in immunology. Here, we describe an essential role for a splice isoform of the prototypical serine/arginine-rich (SR) protein SRSF1, termed SRSF1-3, in AID-induced SHM in a DT40 chicken B-cell line. Unexpectedly, we found that SHM does not occur in a DT40 line lacking SRSF1-3 (DT40-ASF), although it is readily detectable in parental DT40 cells. Strikingly, overexpression of AID in DT40-ASF cells led to a large increase in nonspecific (off-target) mutations. In contrast, introduction of SRSF1-3, but not SRSF1, into these cells specifically restored SHM without increasing off-target mutations. Furthermore, we found that SRSF1-3 binds preferentially to the IgV gene and inhibits processing of the Ig transcript, providing a mechanism by which SRSF1-3 makes the IgV gene available for AID-dependent SHM. SRSF1 not only acts as an essential splicing factor but also regulates diverse aspects of mRNA metabolism and maintains genome stability. Our findings, thus, define an unexpected and important role for SRSF1, particularly for its splice variant, in enabling AID to function specifically on its natural substrate during SHM.