Importin α Protein Acts as a Negative Regulator for Snail Protein Nuclear Import

Toshihiro Sekimoto,Yoshihiro Yoneda,Yoshimi Miyamoto,Shouko Arai

doi:10.1074/jbc.m110.213579

Toshihiro Sekimoto, Yoshihiro Yoneda + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m110.213579

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Abstract

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.

Highlights

Additional genes should be regulated to diminish the epithelial characteristics and to provoke the mesenchymal transition [4]
We found that three importin ␣ family members, importin ␣1/Rch1, importin ␣3/Qip1, and importin ␣5/NPI-1, directly bound to Snail in vitro (Fig. 1A), suggesting the possibility that, in addition to the importin ␤1-mediated pathway, the classical importin ␣/␤1 transport machinery plays some role in Snail nuclear import
We found that inhibition of proteasome function increased the nuclear fluorescence intensity of Snail (Fig. 4A). These results suggest that importin ␣ can negatively regulate Snail nuclear import to facilitate its degradation in the cytoplasm, whereas a proportion of the Snail proteins escape from the importin ␣-mediated suppression of nuclear import and degradation by the proteasome to enter the nucleus

Summary

Introduction

Additional genes should be regulated to diminish the epithelial characteristics and to provoke the mesenchymal transition [4]. Importin ␣ Inhibits Nuclear Import of Snail in Vitro and in Vivo—It has been shown that importin ␤1 directly recognizes and transports Snail into the nucleus [20].

Results

Conclusion