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Interaction between Smad7 and beta-catenin: importance for transforming growth factor beta-induced apoptosis

Sofia Edlund1, So Young Lee, Susanne Grimsby

  • 1Ludwig Institute for Cancer Research, Box 595, Biomedical Center, SE 751 24 Uppsala, Sweden.

Molecular and Cellular Biology
|February 3, 2005
PubMed

Insights

Transforming growth factor beta (TGF-beta) signaling regulates cell fate. Smad7 protein is crucial for TGF-beta to increase beta-catenin and LEF1, impacting apoptosis in cancer and skin cells.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • Transforming growth factor beta (TGF-beta) and Wnt/wingless signaling pathways are critical regulators of cell fate during development and tissue homeostasis.
  • Beta-catenin and lymphoid enhancer binding factor 1/T-cell-specific factor (LEF1/TCF) are key transcriptional regulators within the Wnt signaling pathway.

Purpose of the Study:

  • To investigate the interaction between Smad7, a component of TGF-beta signaling, and beta-catenin/LEF1, components of Wnt signaling.
  • To determine the role of Smad7 in TGF-beta-induced Wnt pathway activation and its downstream effects on cell fate, including apoptosis.

Main Methods:

  • Utilized small interfering RNA (siRNA) to repress endogenous Smad7 expression in human prostate cancer (PC-3U) cells and human keratinocytes (HaCaT cells).
  • Assessed the impact of Smad7 repression on TGF-beta-induced changes in beta-catenin and LEF1 levels, phosphorylation of signaling molecules (p38, Akt, GSK3beta), and protein-protein interactions.
  • Evaluated the role of Smad7-beta-catenin association in TGF-beta-induced apoptosis by suppressing beta-catenin expression via siRNA.

Main Results:

  • Smad7 was found to interact with beta-catenin and LEF1 in a TGF-beta-dependent manner.
  • Smad7 is essential for TGF-beta1-induced accumulation of beta-catenin and LEF1 in both PC-3U and HaCaT cells.
  • Repression of Smad7 blocked TGF-beta-induced activation of p38, Akt, and GSK3beta, and prevented the association between beta-catenin and LEF1.
  • Physical association between Smad7 and beta-catenin was critical for TGF-beta-induced apoptosis, as beta-catenin suppression reduced the apoptotic response.

Conclusions:

  • Smad7 acts as a crucial mediator linking TGF-beta signaling to Wnt pathway activation.
  • The interaction between Smad7 and beta-catenin is vital for executing TGF-beta-mediated apoptosis, highlighting a novel cross-talk mechanism between these pathways with implications for cancer and tissue biology.

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