title: Importin alpha1 (Rch1) mediates nuclear translocation of thioredoxin-binding protein-2/vitamin D(3)-up-regulated protein 1.
abstract: Thioredoxin-binding protein-2 (TBP-2)/vitamin D(3) up-regulated protein 1 is an endogenous molecule interacting with thioredoxin (TRX), negatively regulating TRX function, and being implicated in the suppression of tumor development and metastasis. We found that TBP-2 ectopically expressed in the breast cancer cell line MCF-7 was localized predominantly in the nucleus exhibiting growth suppressive activity. The nuclear accumulation of endogenous TBP-2 protein was also demonstrated when the cells were treated with an anti-cancer drug, suberoylanilide hydroxamic acid. To investigate the mechanism underlying the nuclear localization, we performed a yeast two-hybrid screening and identified importin alpha(1) (Rch1) as a protein interacting with TBP-2. The physical interaction between TBP-2 and Rch1 was confirmed with a glutathione S-transferase pull-down assay. The interaction of TBP-2 was specific to Rch1 among other importin alpha subfamilies (Qip1 and NPI-1), and amino acids 1-227 of TBP-2 were sufficient for both the interaction with Rch1 and the nuclear localization, although there is no typical nuclear localization signal in this sequence. The expression of short interfering RNA of Rch1 suppressed suberoylanilide hydroxamic acid-induced nuclear accumulation of TBP-2. Collectively, our results strongly suggest that an interaction with importin system is required for TBP-2 nuclear translocation and growth control tightly associated with TRX-dependent redox regulation of transcription factors.
authors.affiliation: Department of Biological Responses, Institute for Virus Research, Kyoto University, 53 Shogoin-Kawaharacho, Sakyo, Kyoto 606-8507, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Nishinaka
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Masutani
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Oka
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Matsuo
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: Keiko
authors.initials: K
authors.lastname: Nishio
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Ishii
authors.forename: Junji
authors.initials: J
authors.lastname: Yodoi
mesh_terms: D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism* / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D017931:DNA Primers; D006801:Humans; D021381:Protein Transport; D013879:Thioredoxins / Q000378:metabolism*; D028901:alpha Karyopherins / Q000502:physiology*
chemical_list: D002352:Carrier Proteins; D017931:DNA Primers; C486715:TXNIP protein, human; D028901:alpha Karyopherins; C087978:karyopherin alpha 2; D013879:Thioredoxins