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TSC1 activates TGF-β-Smad2/3 signaling in growth arrest and epithelial-to-mesenchymal transition

Antje Thien1, Mirja Tamara Prentzell2, Birgit Holzwarth3

  • 1Bioinformatics and Molecular Genetics (Faculty of Biology), Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany; Renal Division, University Hospital Freiburg, 79106 Freiburg, Germany.

Developmental Cell
|March 3, 2015
PubMed

Insights

Tuberous sclerosis protein 1 (TSC1) integrates growth factor signaling by inhibiting mTORC1. This study reveals TSC1 also regulates transforming growth factor β (TGF-β) signaling independently of TSC2, impacting cell growth and cancer progression.

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Cancer research

Background:

  • Tuberous sclerosis proteins TSC1 and TSC2 form a complex that inhibits mTORC1, a key regulator of cell growth and proliferation.
  • Growth factor signaling pathways, such as transforming growth factor β (TGF-β), play critical roles in cellular processes and disease.

Purpose of the Study:

  • To investigate the role of TSC1 in TGF-β signaling independently of TSC2.
  • To elucidate the mechanism by which TSC1 interacts with and regulates the TGF-β-Smad2/3 pathway.
  • To determine the functional consequences of TSC1's involvement in TGF-β signaling, including its impact on cell growth and epithelial-to-mesenchymal transition (EMT).

Main Methods:

  • Co-immunoprecipitation assays to assess protein interactions between TSC1, TGF-β receptor components, and Smad2/3.
  • Western blotting to analyze Smad2/3 phosphorylation and target gene expression.
  • Cell-based assays to evaluate TGF-β-induced growth arrest and EMT.
  • Studies involving hyperactive Akt signaling to investigate its interplay with TSC1-dependent pathways.

Main Results:

  • TSC1 functions as a component of the TGF-β-Smad2/3 pathway, independent of TSC2.
  • TSC1 directly interacts with the TGF-β receptor complex and Smad2/3, facilitating their association.
  • TSC1 is essential for TGF-β-induced Smad2/3 phosphorylation, target gene expression, growth arrest, and EMT.
  • Hyperactive Akt specifically activates TSC1-dependent cytostatic Smad signaling, leading to growth arrest.

Conclusions:

  • TSC1 acts as a crucial link between Akt activity and TGF-β-Smad2/3 signaling.
  • The findings have significant implications for cancer therapies targeting phosphoinositide 3-kinases and Akt, as these treatments may inadvertently inhibit tumor-suppressive TGF-β signaling.
  • Targeting the TSC1-Akt-TGF-β axis could offer novel therapeutic strategies for cancers exhibiting dysregulated growth factor signaling.

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