title: Smurf1 regulates the inhibitory activity of Smad7 by targeting Smad7 to the plasma membrane.
abstract: Smad ubiquitin regulatory factor 1 (Smurf1), a HECT-type E3 ubiquitin ligase, interacts with inhibitory Smad7 and induces cytoplasmic localization of Smad7. Smurf1 then associates with transforming growth factor-beta type I receptor (TbetaR-I) and enhances the turnover of this receptor. However, the mechanisms of the nuclear export and plasma membrane localization of the Smurf1.Smad7 complex have not been elucidated. We show here that Smurf1 targets Smad7 to the plasma membrane through its N-terminal conserved 2 (C2) domain. Both wild-type Smurf1 (Smurf1(WT)) and Smurf1 lacking the C2 domain (Smurf1(deltaC2)) bound to Smad7 and translocated nuclear Smad7 to the cytoplasm. However, unlike Smurf1(WT), Smurf1(deltaC2) did not move to the plasma membrane and failed to recruit Smad7 to the cell surface TbetaR-II.TbetaR-I complex. Moreover, although Smurf1(deltaC2) induced ubiquitination of Smad7, it failed to induce the ubiquitination and degradation of TbetaR-I and did not enhance the inhibitory activity of Smad7. Thus, these results suggest that the plasma membrane localization of Smad7 by Smurf1 requires the C2 domain of Smurf1 and is essential for the inhibitory effect of Smad7 in the transforming growth factor-beta signaling pathway.
authors.affiliation: Department of Molecular Pathology, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Chie
authors.initials: C
authors.lastname: Suzuki
authors.forename: Gyo
authors.initials: G
authors.lastname: Murakami
authors.forename: Minoru
authors.initials: M
authors.lastname: Fukuchi
authors.forename: Tomomasa
authors.initials: T
authors.lastname: Shimanuki
authors.forename: Yuko
authors.initials: Y
authors.lastname: Shikauchi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Imamura
authors.forename: Kohei
authors.initials: K
authors.lastname: Miyazono
mesh_terms: D030201:Activin Receptors, Type I / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D008025:Ligases / Q000502:physiology*; D008156:Luciferases / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009154:Mutation; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D015398:Signal Transduction; D051906:Smad7 Protein; D015534:Trans-Activators / Q000378:metabolism*; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
chemical_list: D004268:DNA-Binding Proteins; D018125:Receptors, Transforming Growth Factor beta; C497806:SMAD7 protein, human; D051906:Smad7 Protein; D015534:Trans-Activators; D025801:Ubiquitin; D004247:DNA; D008156:Luciferases; C471641:SMURF2 protein, human; D044767:Ubiquitin-Protein Ligases; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D008025:Ligases; D002118:Calcium