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The tumor suppressor Smad4/DPC4 is regulated by phosphorylations that integrate FGF, Wnt, and TGF-β signaling

Hadrien Demagny1, Tatsuya Araki1, Edward M De Robertis1

  • 1Howard Hughes Medical Institute and Department of Biological Chemistry, University of California, Los Angeles, Los Angeles, CA 90095-1662, USA.

Cell Reports
|November 7, 2014
PubMed

Insights

Smad4 tumor suppressor activity is regulated by Wnt and FGF signaling pathways via phosphorylation. This integration impacts key developmental processes and cancer, revealing cross-talk between major signaling cascades.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Developmental Biology

Background:

  • Smad4 is a key tumor suppressor in the transforming growth factor β (TGF-β) pathway.
  • Its constitutive function has been the prevailing model in cancer research.

Purpose of the Study:

  • To investigate the regulatory mechanisms of Smad4 activity beyond the canonical TGF-β pathway.
  • To elucidate how Wnt and fibroblast growth factor (FGF) signaling pathways intersect with Smad4 function.

Main Methods:

  • Phosphorylation site analysis of Smad4.
  • Investigating the roles of glycogen synthase kinase 3 (GSK3) and mitogen-activated protein kinase (MAPK).
  • Utilizing Xenopus embryo models to study developmental implications.

Main Results:

  • Smad4 activity is modulated by Wnt and FGF pathways through specific phosphorylation sites.
  • FGF-activated MAPK primes Smad4 for Wnt-dependent ubiquitination via GSK3 and β-TrCP.
  • This cross-talk regulates TGF-β signaling, germ-layer specification, and Spemann organizer formation in Xenopus.

Conclusions:

  • Smad4 integrates Wnt, FGF, and TGF-β signaling pathways through phosphorylation-dependent mechanisms.
  • This integration is crucial for normal development and has implications for understanding cancer.
  • The findings challenge the notion of constitutive Smad4 function, highlighting dynamic regulation.

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