Promoting bone morphogenetic protein signaling through negative regulation of inhibitory Smads.
Inhibitory Smads, i.e. Smad6 and Smad7, are potent antagonists of the BMP-Smad pathway by interacting with activated bone morphogenetic protein (BMP) type I receptors and thereby preventing the activation of receptor-regulated Smads, or by competing with activated R-Smads for heteromeric complex formation with Smad4. The molecular mechanisms that underlie the regulation of I-Smad activity have remained elusive. Here we report the identification of a cytoplasmic protein, previously termed associated molecule with the SH3 domain of STAM (AMSH), as a direct binding partner for Smad6. AMSH interacts with Smad6, but not with R- and Co-Smads, upon BMP receptor activation in cultured cells. Consistent with this finding, stimulation of cells with BMP induces a co-localization of Smad6 with AMSH in the cytoplasm. Ectopic expression of AMSH prolongs BMP-induced Smad1 phosphorylation, and potentiates BMP-induced activation of transcriptional reporter activity, growth arrest and apoptosis. The data strongly suggest that the molecular mechanism by which AMSH exerts its action is by inhibiting the binding of Smad6 to activated type I receptors or activated R-Smads.
Itoh
F
F
Division of Cellular Biochemistry, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands.
Asao
H
H
Sugamura
K
K
Heldin
C H
CH
ten Dijke
P
P
Itoh
S
S
D029404:Activin Receptors; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000378:metabolism*; D019556:COS Cells; D002455:Cell Division; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D056827:Endosomal Sorting Complexes Required for Transport; D017930:Genes, Reporter; D006801:Humans; D008156:Luciferases / Q000235:genetics; D051379:Mice; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051785:Smad Proteins; D051898:Smad1 Protein; D051901:Smad4 Protein; D051902:Smad5 Protein; D051905:Smad6 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta; D014407:Tumor Cells, Cultured
D048868:Adaptor Proteins, Signal Transducing; C525819:BMP7 protein, human; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D010750:Phosphoproteins; D018125:Receptors, Transforming Growth Factor beta; D011993:Recombinant Fusion Proteins; C497399:SMAD1 protein, human; C497796:SMAD4 protein, human; C497797:SMAD5 protein, human; C497802:SMAD6 protein, human; C497806:SMAD7 protein, human; C109775:STAM protein, human; D051785:Smad Proteins; D051898:Smad1 Protein; C497401:Smad1 protein, mouse; D051901:Smad4 Protein; C490810:Smad4 protein, mouse; D051902:Smad5 Protein; C497798:Smad5 protein, mouse; D051905:Smad6 Protein; C497803:Smad6 protein, mouse; D051906:Smad7 Protein; C497807:Smad7 protein, mouse; C491648:Stam protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D008156:Luciferases; D017346:Protein Serine-Threonine Kinases; D029404:Activin Receptors