title: The N domain of Smad7 is essential for specific inhibition of transforming growth factor-beta signaling.
abstract: Inhibitory Smads (I-Smads) repress signaling by cytokines of the transforming growth factor-beta (TGF-beta) superfamily. I-Smads have conserved carboxy-terminal Mad homology 2 (MH2) domains, whereas the amino acid sequences of their amino-terminal regions (N domains) are highly divergent from those of other Smads. Of the two different I-Smads in mammals, Smad7 inhibited signaling by both TGF-beta and bone morphogenetic proteins (BMPs), whereas Smad6 was less effective in inhibiting TGF-beta signaling. Analyses using deletion mutants and chimeras of Smad6 and Smad7 revealed that the MH2 domains were responsible for the inhibition of both TGF-beta and BMP signaling by I-Smads, but the isolated MH2 domains of Smad6 and Smad7 were less potent than the full-length Smad7 in inhibiting TGF-beta signaling. The N domains of I-Smads determined the subcellular localization of these molecules. Chimeras containing the N domain of Smad7 interacted with the TGF-beta type I receptor (TbetaR-I) more efficiently, and were more potent in repressing TGF-beta signaling, than those containing the N domain of Smad6. The isolated N domain of Smad7 physically interacted with the MH2 domain of Smad7, and enhanced the inhibitory activity of the latter through facilitating interaction with TGF-beta receptors. The N domain of Smad7 thus plays an important role in the specific inhibition of TGF-beta signaling.
authors.affiliation: Department of Biochemistry, The Cancer Institute of the Japanese Foundation for Cancer Research, Tokyo 170-8455, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Hanyu
authors.forename: Y
authors.initials: Y
authors.lastname: Ishidou
authors.forename: T
authors.initials: T
authors.lastname: Ebisawa
authors.forename: T
authors.initials: T
authors.lastname: Shimanuki
authors.forename: T
authors.initials: T
authors.lastname: Imamura
authors.forename: K
authors.initials: K
authors.lastname: Miyazono
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D030201:Activin Receptors, Type I / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D008025:Ligases / Q000378:metabolism; D008907:Mink; D016296:Mutagenesis / Q000502:physiology; D010766:Phosphorylation; 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; D011993:Recombinant Fusion Proteins; D020545:Respiratory Mucosa / Q000166:cytology; D015398:Signal Transduction / Q000502:physiology*; D051899:Smad2 Protein; D051905:Smad6 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases
chemical_list: D004268:DNA-Binding Proteins; D018125:Receptors, Transforming Growth Factor beta; D011993:Recombinant Fusion Proteins; D051899:Smad2 Protein; D051905:Smad6 Protein; D051906:Smad7 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D044767:Ubiquitin-Protein Ligases; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D008025:Ligases