title: Chromosomal region maintenance 1 (CRM1)-dependent nuclear export of Smad ubiquitin regulatory factor 1 (Smurf1) is essential for negative regulation of transforming growth factor-beta signaling by Smad7.
abstract: Smad ubiquitin regulatory factor 1 (Smurf1), a HECT type E3 ubiquitin ligase, interacts with inhibitory Smad7 and induces translocation of Smad7 to the cytoplasm. Smurf1 then associates with the transforming growth factor (TGF)-beta type I receptor, TbetaR-I, enhancing turnover. However, the mechanism of nuclear export of Smad7 by Smurf1 has not been elucidated. Here we identified a functional nuclear export signal (NES) in a C-terminal region of Smurf1. In transfected cells, the Smurf1-Smad7 complex was accumulated in the cytoplasm by the nuclear export receptor, CRM1; this action was prevented by treatment with leptomycin B, a specific inactivator of CRM1 function. A green fluorescence protein fusion protein containing the C-terminal NES motif of Smurf1, located in the cytoplasm, accumulated in the nucleus following treatment with leptomycin B. Moreover, Smurf1 was shown to bind physically to CRM1 through NES, and nuclear export of the Smurf1-Smad7 complex was prevented by mutations of Smurf1 within the NES. Finally, the Smurf1 NES mutant reduced inhibition by Smad7 of the transcriptional activation induced by TGF-beta. These results thus suggest that CRM1-dependent nuclear export of Smurf1 is essential for the negative regulation of TGF-beta signaling by Smad7.
authors.affiliation: Department of Biochemistry, The Cancer Institute of the Japanese Foundation for Cancer Research, 1-37-1 Kami-ikebukuro, Toshima-ku, Tokyo 170-8455, Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Tajima
authors.forename: Kouichiro
authors.initials: K
authors.lastname: Goto
authors.forename: Minoru
authors.initials: M
authors.lastname: Yoshida
authors.forename: Kenichi
authors.initials: K
authors.lastname: Shinomiya
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Sekimoto
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Yoneda
authors.forename: Kohei
authors.initials: K
authors.lastname: Miyazono
authors.forename: Takeshi
authors.initials: T
authors.lastname: Imamura
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins / Q000502:physiology*; D008025:Ligases / Q000378:metabolism*; D008969:Molecular Sequence Data; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear; D051906:Smad7 Protein; D015534:Trans-Activators / Q000737:chemistry / Q000502:physiology*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases; D000097606:Exportin 1 Protein
chemical_list: D004268:DNA-Binding Proteins; D028884:Karyopherins; D008025:Ligases; D018160:Receptors, Cytoplasmic and Nuclear; D051906:Smad7 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D044767:Ubiquitin-Protein Ligases; D000097606:Exportin 1 Protein; C497806:SMAD7 protein, human; C471641:SMURF2 protein, human