Roles of pathway-specific and inhibitory Smads in activin receptor signaling.
Activins and other members of the transforming growth factor-beta-like superfamily of growth factors transduce their signals by interacting with two types of receptor serine/threonine kinases. The Smad proteins, a new family of intracellular mediators are involved in the signaling pathways of these receptors, but the initial stages of their activation as well as their specific functions remain to be defined. We report here that the pathway-specific Smad2 and 3 can form a complex with the activin receptor in a ligand-dependent manner. This complex formation is rapid but also transient. Indeed, soon after their association with the activin receptor, Smad2 and Smad3 are released into the cytoplasm where they interact with the common partner Smad4. These Smad complexes then mediate activin-induced transcription. Finally, we show that the inhibitory Smad7 can prevent the association of the two pathway-specific Smads with the activin receptor complex, thereby blocking the activin signal.
Lebrun
J J
JJ
Clayton Foundation Laboratories for Peptide Biology, Salk Institute for Biological Studies, La Jolla, California 92037, USA.
Takabe
K
K
Chen
Y
Y
Vale
W
W
D030201:Activin Receptors, Type I; D028341:Activins; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000939:Epitopes; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D007265:Inhibins / Q000378:metabolism / Q000494:pharmacology; D007544:Isopropyl Thiogalactoside / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000276:immunology; D017978:Receptors, Growth Factor / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; D000939:Epitopes; D016271:Proto-Oncogene Proteins c-myc; D017978:Receptors, Growth Factor; D011994:Recombinant Proteins; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; C497806:SMAD7 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D051906:Smad7 Protein; D015534:Trans-Activators; D028341:Activins; D007544:Isopropyl Thiogalactoside; D007265:Inhibins; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I