Smad4 and FAST-1 in the assembly of activin-responsive factor

Nature. 1997 Sep 4;389(6646):85-9. doi: 10.1038/38008.

Abstract

Members of the TGF-beta superfamily of signalling molecules work by activating transmembrane receptors with phosphorylating activity (serine-threonine kinase receptors); these in turn phosphorylate and activate SMADs, a class of signal transducers. Activins are growth factors that act primarily through Smad2, possibly in partnership with Smad4, which forms heteromeric complexes with different ligand-specific SMADs after activation. In frog embryos, Smad2 participates in an activin-responsive factor (ARF), which then binds to a promoter element of the Mix.2 gene. The principal DNA-binding component of ARF is FAST-1, a transcription factor with a novel winged-helix structure. We now report that Smad4 is present in ARF, and that FAST-1, Smad4 and Smad2 co-immunoprecipitate in a ligand-regulated fashion. We have mapped the site of interaction between FAST-1 and Smad2/Smad4 to a novel carboxy-terminal domain of FAST-1, and find that overexpression of this domain specifically inhibits activin signalling. In a yeast two-hybrid assay, the FAST-1 carboxy terminus interacts with Smad2 but not Smad4. Deletion mutants of the FAST-1 carboxy terminus that still participate in ligand-regulated Smad2 binding no longer associated with Smad4 or ARF. These results indicate that Smad4 stabilizes a ligand-stimulated Smad2-FAST-1 complex as an active DNA-binding factor.

Publication types

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

MeSH terms

  • Activins
  • Animals
  • Binding Sites
  • DNA / metabolism
  • DNA-Binding Proteins / metabolism*
  • Electrophoresis
  • Embryo, Nonmammalian / metabolism
  • Epitopes
  • Forkhead Transcription Factors
  • Humans
  • Inhibins / antagonists & inhibitors
  • Inhibins / metabolism*
  • Macromolecular Substances
  • Mice
  • Molecular Sequence Data
  • Nerve Growth Factors
  • Precipitin Tests
  • Signal Transduction
  • Smad Proteins
  • Smad2 Protein
  • Smad4 Protein
  • Trans-Activators / metabolism*
  • Transcription Factors / metabolism*
  • Xenopus
  • Xenopus Proteins*

Substances

  • DNA-Binding Proteins
  • Epitopes
  • FOXH1 protein, Xenopus
  • FOXH1 protein, human
  • Forkhead Transcription Factors
  • Foxh1 protein, mouse
  • Macromolecular Substances
  • Nerve Growth Factors
  • SMAD2 protein, human
  • SMAD4 protein, human
  • Smad Proteins
  • Smad2 Protein
  • Smad2 protein, Xenopus
  • Smad2 protein, mouse
  • Smad4 Protein
  • Smad4 protein, mouse
  • Trans-Activators
  • Transcription Factors
  • Xenopus Proteins
  • smad4.1 protein, Xenopus
  • smad4.2 protein, Xenopus
  • Activins
  • Inhibins
  • DNA

Associated data

  • GENBANK/U70980