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Live Cell Imaging of the TGF- β/Smad3 Signaling Pathway In Vitro and In Vivo Using an Adenovirus Reporter System
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Internalization-dependent and -independent requirements for transforming growth factor beta receptor signaling via

Sumedha G Penheiter1, Hugh Mitchell, Nandor Garamszegi

  • 1Thoracic Diseases Research Unit and Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota 55905, USA.

Molecular and Cellular Biology
|June 8, 2002
PubMed

Insights

Transforming growth factor beta (TGF-beta) receptor internalization is essential for Smad protein activation and downstream signaling. Endocytosis is required to propagate TGF-beta signals, not just dampen them.

Area of Science:

  • Cell biology
  • Molecular signaling
  • Receptor trafficking

Background:

  • Transforming growth factor beta (TGF-beta) signaling is mediated by type I and type II serine/threonine kinase receptors.
  • Signal transduction involves phosphorylation of Smad proteins by the type I receptor.
  • The role of endocytosis in TGF-beta receptor (TGF-beta R) signaling initiation and maintenance remains unclear.

Purpose of the Study:

  • To investigate the role of TGF-beta R internalization in the endocytic pathway.
  • To determine if endocytosis modulates type I receptor activation, receptor/Smad/SARA complex formation, and Smad2/3 phosphorylation.
  • To assess the impact of endocytosis on TGF-beta-dependent reporter gene activity.

Main Methods:

  • Investigated TGF-beta R internalization and its effect on signaling components.
  • Examined receptor phosphorylation, Smad association, and Smad phosphorylation.
  • Assessed Smad nuclear translocation and reporter gene activity.

Main Results:

  • Type I receptor phosphorylation and SARA/Smad2 association with the TGF-beta R complex occur independently of clathrin.
  • Smad2 or Smad3 activation and downstream signaling require endocytic vesicle formation.
  • TGF-beta R endocytosis is crucial for Smad pathway propagation.

Conclusions:

  • TGF-beta receptor endocytosis is a necessary step for propagating Smad-mediated signaling.
  • Endocytosis is not solely a mechanism for signal attenuation but actively contributes to signal transduction.
  • This finding highlights the importance of receptor trafficking in TGF-beta pathway regulation.

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