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Tgf-beta induced Erk phosphorylation of smad linker region regulates smad signaling

Chris Hough1, Maria Radu, Jules J E Doré

  • 1BioMedical Sciences, Memorial University, St. John's, Newfoundland, Canada.

Plos One
|August 11, 2012
PubMed

Insights

Transforming Growth Factor-Beta (TGF-β) activates Extracellular Signal Regulated Kinase (Erk) in mesenchymal cells via a novel pathway. This Erk activation is crucial for TGF-β-induced cell growth and enhances Smad signaling duration.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Signal Transduction

Background:

  • The Transforming Growth Factor-Beta (TGF-β) family regulates crucial cellular functions, including apoptosis, differentiation, and proliferation.
  • TGF-β signaling typically involves receptor binding, Smad protein activation, and subsequent nuclear gene expression regulation.

Purpose of the Study:

  • To identify and characterize a novel TGF-β signaling pathway involving Extracellular Signal Regulated Kinase (Erk).
  • To investigate the cell-type specificity of TGF-β-induced Erk activation.
  • To elucidate the role of Erk in TGF-β-mediated cellular processes and its interaction with Smad signaling.

Main Methods:

  • Investigated TGF-β induced Erk activation in different cell types (mesenchymal vs. epithelial).
  • Utilized phosphotidylinositol 3-kinase (PI3K) and p21-activated kinase2 (Pak2) pathway components to understand Erk activation mechanism.
  • Assessed the necessity of Erk activation for fibroblast replication and its effect on Smad protein stability and transcription duration.

Main Results:

  • TGF-β induced Erk activation in mesenchymal cells but not epithelial cells, indicating cell-type specificity.
  • A pathway involving PI3K, Pak2, and c-Raf was identified as responsible for TGF-β-induced Erk activation.
  • Erk activation was essential for TGF-β-induced fibroblast proliferation.
  • Erk was found to phosphorylate nuclear Smad proteins, increasing their stability and prolonging Smad target gene transcription.

Conclusions:

  • A novel TGF-β signaling pathway (TGF-β/PI3K/Pak2/Raf/MEK/Erk) exists in mesenchymal cells, distinct from canonical Smad pathways.
  • This Erk pathway is critical for TGF-β-induced cell growth and modulates Smad signaling duration.
  • Cellular TGF-β signaling involves an integrated network of interacting pathways rather than isolated Smad or non-Smad pathways.

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