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Transforming growth factor-beta inhibition of proteasomal activity: a potential mechanism of growth arrest

Laura Tadlock1, Yoko Yamagiwa, James Hawker

  • 1Department of Internal Medicine, Scott and White Clinic, Texas A&M University System Health Science Center College of Medicine, Temple, TX 76508, USA.

American Journal of Physiology. Cell Physiology
|March 21, 2003
PubMed

Insights

Transforming growth factor-beta (TGF-β) selectively inhibits proteasome activity, specifically degrading Cbz-Leu-Leu-Leu-7-amido-4-methyl-coumarin (z-LLL-AMC). This growth inhibition mechanism, independent of heat shock protein 90 (HSP90), impacts cell cycle regulators like p27KIP1.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The proteasome is crucial for degrading cell cycle regulatory proteins.
  • Direct links between growth signaling and proteasome function remain unclear.

Purpose of the Study:

  • To investigate the impact of transforming growth factor-beta (TGF-β) on proteasome activity.
  • To elucidate the mechanism by which TGF-β affects proteasomal function and cell growth.

Main Methods:

  • Assessed proteasomal substrate hydrolysis using specific fluorogenic peptides (z-LLL-AMC, suc-LLVY-AMC, z-LLE-AMC).
  • Measured intracellular oxidative injury and heat shock protein 90 (HSP90) expression.
  • Analyzed the expression of cyclin-dependent kinase inhibitors (p27KIP1, p21WAF1, p16INK4A) and cell proliferation.

Main Results:

  • TGF-β selectively decreased z-LLL-AMC hydrolysis in a concentration-dependent manner.
  • Increased intracellular oxidative injury was observed with TGF-β treatment.
  • TGF-β treatment led to increased p27KIP1 expression and decreased cell proliferation, independent of HSP90.

Conclusions:

  • TGF-β inhibits a specific proteasomal activity, potentially via oxidative inactivation or altered subunit composition.
  • This mechanism contributes to growth inhibition by modulating key cell cycle regulators like p27KIP1.

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