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Negative feedback regulation of TGF-beta signaling by the SnoN oncoprotein

S L Stroschein1, W Wang, S Zhou

  • 1Life Sciences Division, Lawrence Berkeley National Laboratory, and Department of Molecular and Cell Biology, University of California, Berkeley, 229 Stanley Hall, Mail Code 3206, Berkeley, CA 94720, USA.

Science (New York, N.Y.)
|October 26, 1999
PubMed

Insights

SnoN oncoprotein represses transforming growth factor-beta (TGF-beta) signaling by interacting with Smad proteins. TGF-beta stimulation initially degrades SnoN, enabling gene activation, but later increases SnoN to terminate signaling.

Area of Science:

  • Molecular biology
  • Cell signaling
  • Cancer research

Background:

  • Smad proteins are key mediators of transforming growth factor-beta (TGF-beta) signaling.
  • TGF-beta signaling regulates critical cellular processes like growth and differentiation.
  • The oncoprotein SnoN is known to interact with Smad proteins.

Purpose of the Study:

  • To elucidate the role of SnoN oncoprotein in TGF-beta signaling.
  • To understand the mechanism by which SnoN regulates Smad-mediated transcription.
  • To investigate the dynamic regulation of SnoN during TGF-beta stimulation.

Main Methods:

  • Co-immunoprecipitation assays to detect protein interactions.
  • Reporter gene assays to measure transcriptional activity.
  • Western blotting to assess protein levels and degradation.
  • Analysis of gene expression following TGF-beta stimulation.

Main Results:

  • SnoN interacts with Smad2 and Smad4, recruiting the corepressor N-CoR to inhibit transcription.
  • TGF-beta stimulation leads to rapid degradation of SnoN via Smad3, permitting target gene activation.
  • Sustained TGF-beta stimulation (2 hours) increases SnoN expression, terminating Smad-mediated transactivation.
  • SnoN functions to maintain TGF-beta-responsive genes in a repressed state in the absence of ligand.

Conclusions:

  • SnoN acts as a critical repressor of TGF-beta signaling.
  • The dynamic regulation of SnoN levels is essential for controlling the duration and amplitude of TGF-beta responses.
  • SnoN plays a dual role in TGF-beta signaling: repression in the absence of ligand and negative feedback termination upon stimulation.

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