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Akt interacts directly with Smad3 to regulate the sensitivity to TGF-beta induced apoptosis

Andrew R Conery1, Yanna Cao, E Aubrey Thompson

  • 1Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA.

Nature Cell Biology
|April 24, 2004
PubMed

Insights

Transforming growth factor beta (TGF-beta) triggers apoptosis or growth arrest. Akt kinase interacts with Smad3, regulating TGF-beta-induced apoptosis sensitivity independent of Akt

Area of Science:

  • Cellular biology
  • Molecular signaling pathways
  • Cancer research

Background:

  • Transforming growth factor beta (TGF-beta) elicits diverse cellular responses, including apoptosis and cell-cycle arrest, varying by cell type.
  • Smad proteins (Smad2, Smad3, Smad4) are key mediators of TGF-beta signaling, regulating gene expression after nuclear translocation.
  • The precise mechanisms determining differential cellular sensitivity to TGF-beta remain incompletely understood.

Purpose of the Study:

  • To elucidate the molecular mechanisms underlying differential cellular responses to TGF-beta, specifically focusing on apoptosis.
  • To investigate the role of crosstalk between TGF-beta signaling and other key cellular pathways in modulating TGF-beta's effects.
  • To identify factors that dictate whether cells undergo apoptosis or growth arrest in response to TGF-beta.

Main Methods:

  • Investigated the interaction between Akt/PKB kinase and Smad3 in response to TGF-beta stimulation.
  • Utilized biochemical assays to assess Smad3 phosphorylation, nuclear translocation, and transcriptional activity.
  • Manipulated the ratio of Smad3 to Akt to evaluate its impact on cellular sensitivity to TGF-beta-induced apoptosis and growth inhibition.

Main Results:

  • Akt/PKB kinase directly interacts with unphosphorylated Smad3, sequestering it in the cytoplasm and preventing nuclear translocation.
  • This Akt-Smad3 interaction inhibits Smad3-mediated transcription and suppresses TGF-beta-induced apoptosis, independent of Akt kinase activity.
  • The ratio of Smad3 to Akt levels correlates with cellular sensitivity to TGF-beta-induced apoptosis, but not growth inhibition.

Conclusions:

  • Crosstalk between the Akt/PKB and Smad3 pathways is a critical determinant of sensitivity to TGF-beta-induced apoptosis.
  • The Akt-Smad3 interaction provides a mechanism for regulating apoptosis independently of growth inhibition in response to TGF-beta.
  • Findings highlight the interplay between the TGF-beta and phosphatidylinositol-3-OH kinase (PI(3)K) pathways in controlling cell fate decisions.

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