TGF-beta receptor-mediated signalling through Smad2, Smad3 and Smad4

EMBO J. 1997 Sep 1;16(17):5353-62. doi: 10.1093/emboj/16.17.5353.

Abstract

Smad family members are newly identified essential intracellular signalling components of the transforming growth factor-beta (TGF-beta) superfamily. Smad2 and Smad3 are structurally highly similar and mediate TGF-beta signals. Smad4 is distantly related to Smads 2 and 3, and forms a heteromeric complex with Smad2 after TGF-beta or activin stimulation. Here we show that Smad2 and Smad3 interacted with the kinase-deficient TGF-beta type I receptor (TbetaR)-I after it was phosphorylated by TbetaR-II kinase. TGF-beta1 induced phosphorylation of Smad2 and Smad3 in Mv1Lu mink lung epithelial cells. Smad4 was found to be constitutively phosphorylated in Mv1Lu cells, the phosphorylation level remaining unchanged upon TGF-beta1 stimulation. Similar results were obtained using HSC4 cells, which are also growth-inhibited by TGF-beta. Smads 2 and 3 interacted with Smad4 after TbetaR activation in transfected COS cells. In addition, we observed TbetaR-activation-dependent interaction between Smad2 and Smad3. Smads 2, 3 and 4 accumulated in the nucleus upon TGF-beta1 treatment in Mv1Lu cells, and showed a synergistic effect in a transcriptional reporter assay using the TGF-beta-inducible plasminogen activator inhibitor-1 promoter. Dominant-negative Smad3 inhibited the transcriptional synergistic response by Smad2 and Smad4. These data suggest that TGF-beta induces heteromeric complexes of Smads 2, 3 and 4, and their concomitant translocation to the nucleus, which is required for efficient TGF-beta signal transduction.

MeSH terms

  • Activin Receptors, Type I*
  • Amino Acid Sequence
  • Animals
  • Antibody Specificity
  • Biological Transport
  • COS Cells
  • Cell Nucleus / metabolism
  • DNA-Binding Proteins / immunology
  • DNA-Binding Proteins / metabolism*
  • Epithelial Cells
  • Genes, Reporter
  • Humans
  • Lung / cytology
  • Mink
  • Models, Biological
  • Molecular Sequence Data
  • Phosphorylation
  • Protein Binding
  • Protein-Serine-Threonine Kinases / metabolism
  • Receptor, Transforming Growth Factor-beta Type I
  • Receptor, Transforming Growth Factor-beta Type II
  • Receptors, Transforming Growth Factor beta / metabolism*
  • Signal Transduction
  • Smad2 Protein
  • Smad3 Protein
  • Smad4 Protein
  • Trans-Activators / immunology
  • Trans-Activators / metabolism*
  • Transcription, Genetic
  • Tumor Cells, Cultured

Substances

  • DNA-Binding Proteins
  • Receptors, Transforming Growth Factor beta
  • SMAD2 protein, human
  • SMAD3 protein, human
  • SMAD4 protein, human
  • Smad2 Protein
  • Smad3 Protein
  • Smad4 Protein
  • Trans-Activators
  • Protein-Serine-Threonine Kinases
  • Activin Receptors, Type I
  • Receptor, Transforming Growth Factor-beta Type I
  • Receptor, Transforming Growth Factor-beta Type II