Lefty inhibits receptor-regulated Smad phosphorylation induced by the activated transforming growth factor-beta receptor

J Biol Chem. 2001 Jun 15;276(24):21397-404. doi: 10.1074/jbc.M010783200. Epub 2001 Feb 20.


Transforming growth factor-beta (TGF-beta) is a pleiotropic cytokine that regulates growth and differentiation of diverse types of cells. TGF-beta actions are directed by ligand-induced activation of TGF-beta receptors with intrinsic serine/threonine kinase activity that trigger phosphorylation of receptor-regulated Smad (R-Smad) protein. Phosphorylated R-Smad proteins bind to Smad4, and the complexes formed move into the nucleus, where they act as components of a transcriptional complex. Here, we show that TGF-beta signaling is inhibited by lefty, a novel member of the TGF-beta superfamily. Lefty perturbed TGF-beta signaling by inhibiting the phosphorylation of Smad2 following activation of the TGF-beta receptor. Moreover, lefty inhibited the events that lie downstream from R-Smad phosphorylation, including heterodimerization of R-Smad proteins with Smad4 and nuclear translocation of the R-Smad.Smad4 complex. Lefty repressed TGF-beta-induced expression of reporter genes for the p21, cdc25, and connective tissue growth factor promoters and of a reporter gene driven by the Smad-binding element. Similarly, lefty inhibited both BMP-mediated Smad5 phosphorylation and gene transcription. The action of lefty does not appear to depend on protein synthesis, including synthesis of inhibitory Smad proteins. Thus, lefty provides a repressed state of TGF-beta- or BMP-responsive genes and participates in negative modulation of TGF-beta and BMP signaling by inhibition of phosphorylation of R-Smad proteins.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Binding Sites
  • Cell Line
  • DNA-Binding Proteins / metabolism*
  • Gene Expression Regulation / drug effects
  • Genes, Reporter
  • Humans
  • Kinetics
  • Left-Right Determination Factors
  • Luciferases / genetics
  • Luciferases / metabolism
  • Phosphates / metabolism
  • Phosphoproteins / metabolism*
  • Phosphorylation
  • Promoter Regions, Genetic
  • Receptors, Transforming Growth Factor beta / physiology*
  • Recombinant Proteins / metabolism
  • Signal Transduction / physiology*
  • Smad2 Protein
  • Smad5 Protein
  • Trans-Activators / metabolism*
  • Transcription, Genetic* / drug effects
  • Transfection
  • Transforming Growth Factor beta / genetics
  • Transforming Growth Factor beta / metabolism*
  • Transforming Growth Factor beta / pharmacology


  • DNA-Binding Proteins
  • LEFTY1 protein, human
  • Left-Right Determination Factors
  • Phosphates
  • Phosphoproteins
  • Receptors, Transforming Growth Factor beta
  • Recombinant Proteins
  • SMAD2 protein, human
  • SMAD5 protein, human
  • Smad2 Protein
  • Smad5 Protein
  • Trans-Activators
  • Transforming Growth Factor beta
  • Luciferases