Related Experiment Videos
Hepatocyte growth factor releases mink epithelial cells from transforming growth factor beta1-induced growth arrest
M Tsubari1, J Taipale, E Tiihonen
1Department of Virology, Haartman Institute, University of Helsinki, Helsinki, Finland.
Abstract:
Transforming growth factor beta (TGF-beta) potently suppresses Mv1Lu mink epithelial cell growth, whereas hepatocyte growth factor (HGF) counteracts TGF-beta-mediated growth inhibition and induces Mv1Lu cell proliferation (J. Taipale and J. Keski-Oja, J. Biol. Chem. 271:4342-4348, 1996). By addressing the cell cycle regulatory mechanisms involved in HGF-mediated release of Mv1Lu cells from TGF-beta inhibition, we show that increased DNA replication is accompanied by phosphorylation of the retinoblastoma protein and alternative regulation of cyclin-Cdk-inhibitor complexes. While TGF-beta treatment decreased the expression of Cdk6, this effect was counteracted by HGF, followed by partial restoration of cyclin D2-associated kinase activity. Notably, HGF failed to prevent TGF-beta induction of p15 and its association with Cdk6. However, HGF reversed the TGF-beta-mediated decrease in Cdk6-associated p27 and cyclin D2-associated Cdk6, suggesting that HGF modifies the TGF-beta response at the level of G1 cyclin complex formation. Counteraction of TGF-beta regulation of Cdk6 by HGF may in turn affect the association of p27 with Cdk2-cyclin E complexes. Though HGF did not differentially regulate the total levels of p27 in TGF-beta-treated cells, p27 immunodepletion experiments suggested that upon treatment with both growth factors, less p27 is associated with Cdk2-cyclin E complexes, in parallel with restoration of the active form of Cdk2 and the associated kinase activity. The results demonstrate that HGF intercepts TGF-beta cell cycle regulation at multiple points, affecting both G1 and G1-S cyclin kinase activities.
Insights
Hepatocyte growth factor (HGF) counteracts TGF-beta's cell growth inhibition by altering cell cycle regulators. HGF modifies cyclin-Cdk complexes, restoring kinase activity and promoting cell proliferation.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Transforming growth factor beta (TGF-beta) inhibits Mv1Lu mink epithelial cell growth.
- Hepatocyte growth factor (HGF) opposes TGF-beta's inhibitory effects and promotes cell proliferation.
- Understanding the cell cycle mechanisms underlying HGF's counteraction of TGF-beta is crucial.
Purpose of the Study:
- To investigate the cell cycle regulatory mechanisms by which HGF releases Mv1Lu cells from TGF-beta-induced growth inhibition.
- To elucidate how HGF affects cyclin-Cdk complexes and their associated kinase activities in the context of TGF-beta signaling.
Main Methods:
- Mv1Lu mink epithelial cells were treated with TGF-beta and HGF.
- Analysis of DNA replication, retinoblastoma protein phosphorylation, and cyclin-Cdk-inhibitor complexes.
- Western blotting, immunoprecipitation, and kinase assays were employed.
Main Results:
- HGF counteracted TGF-beta-induced decrease in Cdk6 expression and restored cyclin D2-associated kinase activity.
- HGF reversed TGF-beta-mediated decreases in Cdk6-associated p27 and cyclin D2-associated Cdk6.
- HGF reduced p27 association with Cdk2-cyclin E complexes, restoring active Cdk2 kinase activity.
Conclusions:
- HGF interferes with TGF-beta-mediated cell cycle regulation at multiple points.
- HGF affects both G1 and G1-S phase cyclin kinase activities, promoting cell proliferation.
- These findings highlight HGF as a key modulator of TGF-beta signaling in cell cycle control.