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Comparative Strategies for Ubiquitination Detection in Mammalian Cell Lysates Using SMAD2/SMURF2 as a Model
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FAM/USP9x, a deubiquitinating enzyme essential for TGFbeta signaling, controls Smad4 monoubiquitination

Sirio Dupont1, Anant Mamidi, Michelangelo Cordenonsi

  • 1Department of Histology, Microbiology, and Medical Biotechnologies, University of Padua School of Medicine, viale Colombo 3, 35131 Padua, Italy.

Cell
|January 13, 2009
PubMed

Insights

The deubiquitinase FAM (USP9x) is crucial for TGF-beta signaling by reversing Smad4 monoubiquitination, a key step in regulating cellular responses.

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Ubiquitination and deubiquitination

Background:

  • Smad complex assembly is vital for TGFbeta signaling.
  • Mechanisms controlling nuclear Smad complex activity remain unclear.

Purpose of the Study:

  • Identify novel regulators of Smad complex function.
  • Elucidate the role of ubiquitination in TGFbeta signaling control.

Main Methods:

  • siRNA screening to identify key proteins.
  • In vivo ubiquitination analysis of Smad4.
  • Investigating protein-protein interactions.

Main Results:

  • FAM (USP9x) identified as a conserved deubiquitinase essential for TGFbeta and BMP signaling.
  • Smad4 is monoubiquitinated at Lysine 519, inhibiting its function.
  • FAM counteracts Smad4 monoubiquitination, restoring Smad4 activity.
  • Ectodermin/Tif1gamma (Ecto) functions as a Smad4 monoubiquitin ligase.

Conclusions:

  • Smad4 monoubiquitination/deubiquitination regulates TGFbeta responsiveness.
  • FAM's deubiquitinase activity is critical for Smad4 function.
  • This ubiquitination-based regulation is parallel to R-Smad phosphorylation.

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