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Transforming growth factor-beta (TGF-beta)-induced down-regulation of cyclin A expression requires a functional

X H Feng1, E H Filvaroff, R Derynck

  • 1Department of Growth and Development, University of California, San Francisco 94143, USA.

The Journal of Biological Chemistry
|October 13, 1995
PubMed

Insights

Transforming growth factor-beta (TGF-beta) inhibits epithelial cell proliferation by downregulating cyclin A. A functional TGF-beta receptor complex, particularly the juxtamembrane domain, is essential for this growth inhibition and gene expression regulation.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • Transforming growth factor-beta (TGF-beta) is a key regulator of cell proliferation, particularly inhibiting epithelial cell growth.
  • TGF-beta exerts its effects by modulating cell cycle machinery, including the downregulation of cyclin A expression.
  • Understanding the TGF-beta signaling pathway and its receptor requirements is crucial for developing targeted therapies.

Purpose of the Study:

  • To identify the specific domains of TGF-beta type I (RI) and type II (RII) receptors essential for TGF-beta-mediated growth inhibition.
  • To elucidate the role of the TGF-beta receptor complex in regulating cyclin A gene expression.
  • To establish a reporter assay for quantifying TGF-beta's antiproliferative effects.

Main Methods:

  • Cloning and functional analysis of a TGF-beta-responsive human cyclin A gene promoter fragment.
  • Development of a cyclin A-luciferase reporter assay for TGF-beta responsiveness.
  • Construction and testing of chimeric and mutant TGF-beta receptors (RI, RII) in Mv1Lu cells.
  • Analysis of TGF-beta effects on gene expression using a plasminogen activator inhibitor type 1 (PAI-1) promoter reporter assay.

Main Results:

  • A 760-bp human cyclin A promoter fragment conferred TGF-beta responsiveness.
  • TGF-beta-induced inhibition of cyclin A expression was restored in RI or RII-deficient cells by wild-type receptor expression.
  • A functional TGF-beta receptor complex, comprising both RI and RII, was necessary for cyclin A regulation.
  • The juxtamembrane domain of the receptors was essential, while the cytoplasmic tail was dispensable for TGF-beta signaling.
  • Mutant receptors lacking cytoplasmic domains or kinase activity exhibited dominant-negative inhibition.

Conclusions:

  • A complete TGF-beta receptor complex is indispensable for TGF-beta-dependent downregulation of cyclin A gene expression.
  • The juxtamembrane domain of TGF-beta receptors plays a critical role in mediating antiproliferative signals.
  • The findings highlight conserved receptor requirements for both TGF-beta-induced growth inhibition and gene expression changes.

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