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TGF beta-induced growth inhibition in primary fibroblasts requires the retinoblastoma protein

R E Herrera1, T P Mäkelä, R A Weinberg

  • 1Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142, USA.

Molecular Biology of the Cell
|September 1, 1996
PubMed

Insights

Transforming growth factor beta (TGF-β) normally inhibits cell proliferation. However, the retinoblastoma protein (pRb) is crucial, as its absence can make TGF-β growth-stimulatory, impacting tumorigenesis.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Cancer Research

Background:

  • Transforming growth factor beta (TGF-β) is known to inhibit cell proliferation via G1 cell-cycle arrest.
  • Cyclin-dependent kinase (CDK) complexes are implicated in this arrest, as TGF-β treatment reduces their activity.

Purpose of the Study:

  • To investigate the role of the retinoblastoma protein (pRb) in TGF-β-induced growth arrest.
  • To understand how pRb status influences cellular responses to TGF-β.

Main Methods:

  • Utilized wild-type (RB+/+) and retinoblastoma protein-deficient (RB-/-) primary mouse embryo fibroblasts.
  • Assessed CDK4 and CDK2-associated kinase activities following TGF-β treatment.
  • Observed cell proliferation and growth responses at high cell density.

Main Results:

  • TGF-β inhibited CDK4 kinase activity in both RB+/+ and RB-/- cells.
  • TGF-β completely inhibited CDK2 kinase activity in RB+/+ cells but only slightly in RB-/- cells.
  • RB-/- cells showed a loss of TGF-β-mediated growth inhibition at high cell density, with TGF-β promoting their growth.

Conclusions:

  • The retinoblastoma protein (pRb) is essential for the G1 cell-cycle arrest induced by TGF-β.
  • Elimination of pRb can convert TGF-β's growth-inhibitory effects into growth-stimulatory effects under specific conditions.
  • These findings may explain TGF-β's role in enhancing tumorigenicity and the link between RB gene inactivation and tumorigenesis.

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