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Deficient R-smad/smad4 complex formation in fibroblasts growth-stimulated by TGF-beta 1
1Laboratoire de Radiobiologie et Etude du Génome, INRA/CEA, Domaine de Vilvert, 78352 Jouy-en-Josas, France. lawrence@dsvidf.cea.fr
Abstract:
Although most cell types are inhibited by TGF-beta 1 some mesenchymal cells are growth-stimulated by TGF-beta 1. Here, using two cell models, in which the normal untransformed cells (WI38 human embryo and NIH3T3 mouse fibroblasts) are stimulated to proliferate by TGF-beta 1 and their SV40 Large T-transformed counterparts are inhibited, we show that the two former cells are deficient in smad2-smad4 and smad3-smad4 complex formation, whereas these complexes are present in the two latter cells. In addition, endogenous smad4 levels in total cell extracts are lower in WI38 and NIH3T3 fibroblasts than in their Large T-expressing counterparts. In WI38 fibroblasts smad4 is, at best, inefficiently translocated to the nucleus. TGF-beta 1-mediated growth-stimulation of these normal fibroblasts does not appear to involve the presently known smads, but this situation is reversed in the Large T-transformed cells inhibited by TGF-beta 1.
Insights
Normal fibroblasts are growth-stimulated by transforming growth factor-beta 1 (TGF-β1), unlike most cells. This study reveals deficiencies in smad complex formation in these cells, suggesting a novel TGF-β1 signaling pathway.
Area of Science:
- Cell biology
- Molecular biology
- Cancer research
Background:
- Transforming growth factor-beta 1 (TGF-β1) typically inhibits cell proliferation.
- Some mesenchymal cells exhibit paradoxical growth stimulation by TGF-β1.
- The underlying molecular mechanisms for differential TGF-β1 responses remain incompletely understood.
Purpose of the Study:
- To investigate the role of Smad proteins in TGF-β1-mediated growth regulation in normal versus transformed fibroblasts.
- To elucidate the molecular basis for TGF-β1-induced proliferation in normal fibroblasts and inhibition in transformed cells.
Main Methods:
- Utilized two cell models: normal fibroblasts (WI38, NIH3T3) and their SV40 Large T-transformed counterparts.
- Assessed Smad2-Smad4 and Smad3-Smad4 complex formation.
- Quantified endogenous Smad4 protein levels.
- Examined Smad4 nuclear translocation.
Main Results:
- Normal fibroblasts (WI38, NIH3T3) showed impaired Smad2-Smad4 and Smad3-Smad4 complex formation and lower endogenous Smad4 levels compared to transformed cells.
- Smad4 nuclear translocation was inefficient in normal WI38 fibroblasts.
- TGF-β1-induced growth stimulation in normal fibroblasts did not involve known Smad pathways, contrasting with the inhibition in transformed cells.
Conclusions:
- Deficiencies in Smad complex formation and Smad4 nuclear translocation correlate with TGF-β1-induced proliferation in normal fibroblasts.
- Transformed cells exhibit intact Smad complex formation, leading to TGF-β1-mediated growth inhibition.
- These findings suggest a novel TGF-β1 signaling pathway in normal fibroblasts that bypasses canonical Smad signaling.