Hepatocyte growth factor releases mink epithelial cells from transforming growth factor beta1-induced growth arrest by restoring Cdk6 expression and cyclin E-associated Cdk2 activity.
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.
Tsubari
M
M
Department of Virology, Haartman Institute, University of Helsinki, Helsinki, Finland.
Taipale
J
J
Tiihonen
E
E
Keski-Oja
J
J
Laiho
M
M
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D019927:Cyclin E / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D004847:Epithelial Cells / Q000187:drug effects*; D005434:Flow Cytometry; D017228:Hepatocyte Growth Factor / Q000494:pharmacology*; D006657:Histones / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D008907:Mink; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D019927:Cyclin E; D006657:Histones; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; D016212:Transforming Growth Factor beta; D017228:Hepatocyte Growth Factor; D018844:Cyclin-Dependent Kinases