A Smad3 and TTF-1/NKX2-1 complex regulates Smad4-independent gene expression

Cell Res. 2014 Aug;24(8):994-1008. doi: 10.1038/cr.2014.97. Epub 2014 Jul 25.


Thyroid transcription factor-1 (TTF-1, also known as NKX2-1) is a tissue-specific transcription factor in lung epithelial cells. Although TTF-1 inhibits the epithelial-to-mesenchymal transition induced by transforming growth factor-β (TGF-β) in lung adenocarcinoma cells, the mechanism through which TTF-1 inhibits the functions of TGF-β is unknown. Here we show that TTF-1 disrupts the nuclear Smad3-Smad4 complex without affecting the nuclear localization of phospho-Smad3. Genome-wide analysis by chromatin immunoprecipitation followed by sequencing revealed that TTF-1 colocalizes with Smad3 on chromatin and alters Smad3-binding patterns throughout the genome, while TTF-1 generally inhibits Smad4 binding to chromatin. Moreover, Smad3 binds to chromatin together with TTF-1, but not with Smad4, at some Smad3-binding regions when TGF-β signaling is absent, and knockdown of Smad4 expression does not attenuate Smad3 binding in these regions. Thus, TTF-1 may compete with Smad4 for interaction with Smad3, and in the presence of TTF-1, Smad3 regulates the transcription of certain genes independently of Smad4. These findings provide a new model of regulation of TGF-β-Smad signaling by TTF-1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line, Tumor
  • Chromatin / metabolism
  • Chromatin Immunoprecipitation
  • DNA-Binding Proteins / antagonists & inhibitors
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Gene Expression / drug effects
  • Humans
  • Protein Binding
  • RNA Interference
  • RNA, Small Interfering / metabolism
  • Signal Transduction / drug effects
  • Smad3 Protein / metabolism*
  • Smad4 Protein / antagonists & inhibitors
  • Smad4 Protein / genetics
  • Smad4 Protein / metabolism*
  • Transcription Factors
  • Transforming Growth Factor beta / pharmacology


  • Chromatin
  • DNA-Binding Proteins
  • RNA, Small Interfering
  • Smad3 Protein
  • Smad4 Protein
  • TTF1 protein, human
  • Transcription Factors
  • Transforming Growth Factor beta