title: Nucleocytoplasmic shuttling of the zinc finger protein EZI Is mediated by importin-7-dependent nuclear import and CRM1-independent export mechanisms.
abstract: Nucleocytoplasmic translocation constitutes a foundation for nuclear proteins to exert their proper functions and hence for various biological reactions to occur normally in eukaryotic cells. We reported previously that EZI/Zfp467, a 12 zinc finger motif-containing protein, localizes predominantly in the nucleus, yet the underlying mechanism still remains elusive. Here we constructed a series of mutant forms of EZI and examined their subcellular localization. The results delineated a non-canonical nuclear localization signal in the region covering the 9th to the 12th zinc fingers, which was necessary for nuclear accumulation of EZI as well as sufficient to confer nuclear localizing ability to a heterologous protein. We also found that the N-terminal domain of EZI is necessary for its nuclear export, the process of which was not sensitive to the CRM1 inhibitor leptomycin B. An interaction proteomics approach and the following co-immunoprecipitation experiments identified the nuclear import receptor importin-7 as a molecule that associated with EZI and, importantly, short interfering RNA-mediated knockdown of importin-7 expression completely abrogated nuclear accumulation of EZI. Taken together, these results identify EZI as a novel cargo protein for importin-7 and demonstrate a nucleocytoplasmic shuttling mechanism that is mediated by importin-7-dependent nuclear localization and CRM1-independent nuclear export.
authors.affiliation: Laboratory of Cell Growth and Differentiation, Institute of Molecular and Cellular Biosciences, the University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: Eiko
authors.initials: E
authors.lastname: Saijou
authors.forename: Tohru
authors.initials: T
authors.lastname: Itoh
authors.forename: Kyung-Woon
authors.initials: KW
authors.lastname: Kim
authors.forename: Shun-ichiro
authors.initials: S
authors.lastname: Iemura
authors.forename: Tohru
authors.initials: T
authors.lastname: Natsume
authors.forename: Atsushi
authors.initials: A
authors.lastname: Miyajima
mesh_terms: D000818:Animals; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism*; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D006822:Hybrid Cells; D028884:Karyopherins / Q000378:metabolism*; D051379:Mice; D041681:NIH 3T3 Cells; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D035165:Transcription Factors, General
chemical_list: D004268:DNA-Binding Proteins; C466996:IPO7 protein, human; D028884:Karyopherins; D018160:Receptors, Cytoplasmic and Nuclear; D035165:Transcription Factors, General; C524849:ZNF467 protein, human