Department of Biochemistry, Graduate School of Medicine, Osaka University, 1-3 Yamada-oka, Suita, Osaka 565-0871, Japan.
J Biol Chem. 2011 Apr 29;286(17):15126-31. doi: 10.1074/jbc.M110.213579. Epub 2011 Mar 17.
Snail, a zinc finger-containing transcriptional regulator, migrates into the nucleus where it controls gene expression. We demonstrated previously that importin β1 directly recognizes the zinc finger domain of Snail and transports it into the nucleus. Here, using in vitro and in vivo assays, we show that importin α, an adaptor protein for importin β1, negatively regulates the nuclear import of Snail mediated by importin β1. In vitro binding assays indicated that importin α interacted with the zinc finger domain of Snail to compete with the binding of importin β1 and that Snail did not form a ternary complex with importin α/importin β1. Overexpression of importin α in A549 cells reduced the endogenous Snail protein level, which was restored by inhibitors of the proteasome and glycogen synthase kinase 3β. Furthermore, knockdown of importin α by siRNA treatment increased the endogenous Snail protein level in several cancer cell lines. This study provides a novel regulatory mechanism of the nuclear protein import process by importin α and gives an implication to control Snail activity by inhibiting its nuclear localization.
蜗牛，一种含锌指的转录调控因子，迁移到细胞核内，在那里它控制基因表达。我们之前已经证明，importin β1 可以直接识别 Snail 的锌指结构域，并将其运输到细胞核内。在这里，我们使用体外和体内实验，表明 importin α（importin β1 的衔接蛋白）通过 importin β1 负调控 Snail 的核输入。体外结合实验表明，importin α 与 Snail 的锌指结构域相互作用，与 importin β1 的结合竞争，并且 Snail 没有与 importin α/importin β1 形成三元复合物。在 A549 细胞中过表达 importin α 会降低内源性 Snail 蛋白水平，而蛋白酶体和糖原合酶激酶 3β 的抑制剂可使其恢复。此外，通过 siRNA 处理敲低 importin α 会增加几种癌细胞系中的内源性 Snail 蛋白水平。本研究提供了 importin α 调节核蛋白输入过程的新机制，并暗示通过抑制其核定位来控制 Snail 的活性。
