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

• Published in: The Journal of biological chemistry 2011-04, Vol.286 (17), p.15126-15131
• Main Authors: Sekimoto, Toshihiro, Miyamoto, Yoshimi, Arai, Shouko, Yoneda, Yoshihiro
• Format: Article
• Language: English
• Subjects: Active Transport, Cell Nucleus; alpha Karyopherins - physiology; beta Karyopherins - metabolism; Binding Sites; Cell Biology; Cell Line, Tumor; Cell Nucleus - metabolism; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Importin; Nuclear Transport; Proteasome Endopeptidase Complex; Protein Binding; Protein Degradation; Protein Stability; Protein Targeting; Protein Translocation; Snail; Snail Family Transcription Factors; Transcription Factors - metabolism; Tumor; Zinc Fingers
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.213579

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.