title: Dissection of inhibitory Smad proteins: both N- and C-terminal domains are necessary for full activities of Xenopus Smad6 and Smad7.
abstract: Smad6 and Smad7 comprise a subclass of vertebrate Smads that antagonize, rather than transduce, TGF-beta family signaling. These Anti-Smads can block BMP signaling, as evidenced by their ability to induce a secondary dorsal axis when misexpressed ventrally in Xenopus embryos. Smad7 inhibits additional TGF-beta related pathways, and causes spina bifida when misexpressed dorsally. We have performed structure-function analyses to identify domains of Anti-Smads that are responsible for their shared and unique activities. We find that the C-terminal domain of Smad7 displays strong axis inducing activity but cannot induce spina bifida. The isolated N-terminal domain of Smad7 is inactive but restores the ability of the C-terminus to cause spina bifida when the two are co-expressed. By contrast, the N- and C-terminal domains of Smad6 have weak axis inducing activity when expressed individually, but show full activity when co-expressed. Chimeric analysis demonstrates that the C-terminal domain of Smad7, but not Smad6, can induce spina bifida when fused to the N-terminal domain of either Smad6 or Smad7. Thus, although the C-terminal domain is the primary determinant of the intrinsic activity of Xenopus Anti-Smads, the N-terminal domain is essential for full activity, is interchangeable between Smad6 and 7, and can function in trans.
authors.affiliation: Department of Cell and Developmental Biology, L215, School of Medicine, Oregon Health Sciences University, Portland 97201-3098, USA.
authors.forename: T
authors.initials: T
authors.lastname: Nakayama
authors.forename: L K
authors.initials: LK
authors.lastname: Berg
authors.forename: J L
authors.initials: JL
authors.lastname: Christian
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019485:Bone Morphogenetic Proteins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D008957:Models, Genetic; D009154:Mutation; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D051905:Smad6 Protein; D051906:Smad7 Protein; D016135:Spinal Dysraphism / Q000378:metabolism; D013329:Structure-Activity Relationship; D013997:Time Factors; D015534:Trans-Activators / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D014981:Xenopus; D029867:Xenopus Proteins
chemical_list: D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; D051905:Smad6 Protein; C497805:Smad6 protein, Xenopus; D051906:Smad7 Protein; C497809:Smad7 protein, Xenopus; D015534:Trans-Activators; D029867:Xenopus Proteins; D012313:RNA