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Smad7 Protein Interacts with Receptor-regulated Smads (R-Smads) to Inhibit Transforming Growth Factor-β (TGF-β)/Smad

Xiaohua Yan1, Hongwei Liao2, Minzhang Cheng2

  • 1From the State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, 100084 China, yanxiaohua06@126.com.

The Journal of Biological Chemistry
|November 12, 2015
PubMed

Insights

Smad7 inhibits Transforming Growth Factor-beta (TGF-β) signaling by directly binding to R-Smads, preventing Smad4 interaction and promoting R-Smad degradation via NEDD4L. This reveals a novel Smad-level regulatory mechanism for TGF-β.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Signal Transduction

Background:

  • Transforming Growth Factor-beta (TGF-β) is a cytokine regulating diverse cellular processes.
  • Smad7 is a known negative regulator of TGF-β signaling, but its precise mechanisms are not fully elucidated.

Purpose of the Study:

  • To investigate novel molecular mechanisms by which Smad7 antagonizes TGF-β signaling at the Smad level.

Main Methods:

  • Gal4-luciferase reporter assays were used to assess Smad7's inhibitory effects.
  • Investigated protein-protein interactions between Smad7, R-Smads, Smad4, and NEDD4L.
  • Utilized domain mapping to identify critical regions for Smad7-R-Smad interaction.

Main Results:

  • Smad7 oligomerizes with R-Smads upon TGF-β signaling, directly inhibiting R-Smad activity.
  • Smad7 competes with Smad4 for R-Smad binding and recruits NEDD4L for R-Smad polyubiquitination and proteasomal degradation.
  • The Mad homology 2 (MH2) domain of Smad7, particularly a basic region within the L3/β8 loop-strand module, is crucial for R-Smad interaction.

Conclusions:

  • Smad7 employs a novel mechanism to inhibit TGF-β signaling by directly targeting R-Smads.
  • This interaction leads to R-Smad inactivation and degradation, offering new insights into TGF-β pathway regulation.
Keywords:
SMAD transcription factorSmad7cell signalingprotein degradationprotein-protein interactionsignaling regulationtransforming growth factor beta (TGF-B)ubiquitylation (ubiquitination)

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