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Molecular Analysis of Endothelial-mesenchymal Transition Induced by Transforming Growth Factor-β Signaling
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Down-regulation of transforming growth factor-beta receptors: cooperativity between the types I, II, and III

J C Zwaagstra1, Z Kassam, M D O'Connor-Mccourt

  • 1Biotechnology Research Institute, National Research Council Canada, Montreal, Quebec, H4P 2R2, Canada. john.zwaagstra@nrc.ca

Experimental Cell Research
|October 21, 1999
PubMed

Insights

Transforming growth factor-beta (TGF-beta) receptors I, II, and III down-regulate upon ligand binding. This process involves cell surface aggregation and internalization, requiring all three receptor types for efficient TGF-beta signaling modulation.

Area of Science:

  • Cell biology
  • Molecular signaling
  • Receptor biology

Background:

  • Transforming growth factor-beta (TGF-beta) receptors mediate crucial cellular processes.
  • Receptor down-regulation is a key mechanism for modulating TGF-beta signaling.
  • The specific roles of TGF-beta receptor types I, II, and III in down-regulation are not fully elucidated.

Purpose of the Study:

  • To investigate the down-regulation mechanisms of TGF-beta receptor types I, II, and III.
  • To determine the necessity of each receptor type for efficient down-regulation.
  • To explore the role of temperature in TGF-beta receptor down-regulation.

Main Methods:

  • Utilized cell lines endogenously and transiently expressing TGF-beta receptors.
  • Administered TGF-beta1 at varying concentrations and temperatures (4°C and 37°C).
  • Employed microscopy with fluorescently tagged receptors (RI-GFP) to visualize cellular localization.

Main Results:

  • Down-regulation of TGF-beta receptors I, II, and III occurred rapidly (within 2 hours) and showed a dose-dependent response to TGF-beta1.
  • All three receptor types were necessary for efficient down-regulation; RI was crucial for maximal RII down-regulation.
  • Receptors RII and RIII showed partial down-regulation when coexpressed without RI.
  • TGF-beta receptors exhibited partial down-regulation even at 4°C, with RI-GFP forming surface aggregates.
  • At 37°C, RI-GFP was internalized, not detected at the cell surface.

Conclusions:

  • TGF-beta receptor down-regulation follows a two-phase mechanism: initial receptor aggregation at the cell surface followed by internalization.
  • The presence and interaction of all three TGF-beta receptor types are critical for effective signal modulation.
  • Temperature plays a significant role in the distinct stages of TGF-beta receptor down-regulation.

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