Kawaguchi Yuka, Nariki Hiroaki, Kawamoto Naoko, Kanehiro Yuichi, Miyazaki Satoshi, Suzuki Mari, Magari Masaki, Tokumitsu Hiroshi, Kanayama Naoki
Department of Medical Bioengineering, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan.
Department of Medical Bioengineering, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan.
Biochem Biophys Res Commun. 2017 Apr 1;485(2):261-266. doi: 10.1016/j.bbrc.2017.02.097. Epub 2017 Feb 21.
Activation-induced cytidine deaminase (AID) is essential for diversification of the Ig variable region (IgV). AID is excluded from the nucleus, where it normally functions. However, the molecular mechanisms responsible for regulating AID localization remain to be elucidated. The SR-protein splicing factor SRSF1 is a nucleocytoplasmic shuttling protein, a splicing isoform of which called SRSF1-3, has previously been shown to contribute to IgV diversification in chicken DT40 cells. In this study, we examined whether SRSF1-3 functions in IgV diversification by promoting nuclear localization of AID. AID expressed alone was localized predominantly in the cytoplasm. In contrast, co-expression of AID with SRSF1-3 led to the nuclear accumulation of both AID and SRSF1-3 and the formation of a protein complex that contained them both, although SRSF1-3 was dispensable for nuclear import of AID. Expression of either SRSF1-3 or a C-terminally-truncated AID mutant increased IgV diversification in DT40 cells. However, overexpression of exogenous SRSF1-3 was unable to further enhance IgV diversification in DT40 cells expressing the truncated AID mutant, although SRSF1-3 was able to form a protein complex with the AID mutant. These results suggest that SRSF1-3 promotes nuclear localization of AID probably by forming a nuclear protein complex, which might stabilize nuclear AID and induce IgV diversification in an AID C-terminus-dependent manner.
活化诱导的胞苷脱氨酶（AID）对于Ig可变区（IgV）的多样化至关重要。AID通常在细胞核中发挥作用，但它会被排除在细胞核之外。然而，负责调节AID定位的分子机制仍有待阐明。SR蛋白剪接因子SRSF1是一种穿梭于核质之间的蛋白，其一种剪接异构体SRSF1-3先前已被证明有助于鸡DT40细胞中的IgV多样化。在本研究中，我们研究了SRSF1-3是否通过促进AID的核定位在IgV多样化中发挥作用。单独表达的AID主要定位于细胞质中。相反，AID与SRSF1-3共表达导致AID和SRSF1-3在细胞核中积累，并形成包含它们两者的蛋白复合物，尽管SRSF1-3对于AID的核输入并非必需。SRSF1-3或C末端截短的AID突变体的表达均增加了DT40细胞中的IgV多样化。然而，尽管SRSF1-3能够与AID突变体形成蛋白复合物，但外源性SRSF1-3的过表达无法进一步增强表达截短AID突变体的DT40细胞中的IgV多样化。这些结果表明，SRSF1-3可能通过形成核蛋白复合物促进AID的核定位，该复合物可能稳定核内AID并以AID C末端依赖的方式诱导IgV多样化。
