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Molecular Analysis of Endothelial-mesenchymal Transition Induced by Transforming Growth Factor-β Signaling
07:49

Molecular Analysis of Endothelial-mesenchymal Transition Induced by Transforming Growth Factor-β Signaling

Published on: August 3, 2018

Smad-mediated transcription is required for transforming growth factor-beta 1-induced p57(Kip2) proteolysis in

S Nishimori1, Y Tanaka, T Chiba

  • 1Department of Molecular Oncology, and the Department of Tumor Biochemistry, The Tokyo Metropolitan Institute of Medical Science, 3-18-22 Honkomagome, Bunkyo-ku, Tokyo 113-8613, Japan.

The Journal of Biological Chemistry
|January 22, 2001
PubMed

Insights

Transforming growth factor-beta1 (TGF-β1) triggers the degradation of p57Kip2, an essential cell cycle regulator, via the Smad pathway. This degradation requires new protein synthesis, highlighting a novel regulatory mechanism in osteoblastic cells.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Cyclin-dependent kinase inhibitory proteins (CKIs) are crucial negative regulators of the cell cycle.
  • p57Kip2 is a unique CKI essential for embryonic development, with functions not compensated by other CKIs.
  • Previous research indicated p57Kip2 degradation via the ubiquitin-proteasome pathway in TGF-β1-stimulated osteoblastic cells.

Purpose of the Study:

  • To elucidate the mechanism of TGF-β1-induced p57Kip2 proteolysis.
  • To investigate the role of the Smad pathway in regulating p57Kip2 degradation.
  • To identify potential factors involved in the accelerated degradation of p57Kip2.

Main Methods:

  • Ectopic expression of constitutively active TGF-β type I receptor (ALK-5(TD)) in osteoblastic cells.
  • Analysis of p57Kip2 degradation following serum starvation and TGF-β1 stimulation.
  • Investigating the effect of Smad2, Smad3, Smad4, and Smad7 on p57Kip2 proteolysis.
  • Utilizing transcription inhibitors (actinomycin D, α-amanitin) to assess the role of new protein synthesis.

Main Results:

  • TGF-β1-induced p57Kip2 proteolysis is mediated by the Smad pathway.
  • Ectopic expression of ALK-5(TD) mimicked TGF-β1 effects, causing rapid p57Kip2 degradation.
  • Co-expression of Smad2 or Smad3 with Smad4 enhanced p57Kip2 proteolysis.
  • Degradation was blocked by Smad7, actinomycin D, or α-amanitin, indicating dependence on new transcription.

Conclusions:

  • TGF-β1 signaling, via the Smad pathway, accelerates p57Kip2 degradation in osteoblastic cells.
  • This process requires the synthesis of new factors that target p57Kip2 or the ubiquitin-proteasome system.
  • The findings reveal a novel regulatory mechanism involving TGF-β1, Smads, and proteasomal degradation of p57Kip2.

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