title: Ectopic expression of Cdk6 circumvents transforming growth factor-beta mediated growth inhibition.
abstract: Transforming growth factor-beta (TGF-beta) induced growth arrest of cells involves regulation of the activities of both D- and E-type cyclin kinase complexes thought to be mediated primarily by the regulation of p15(Ink4b) and p27(Kip1) cyclin kinase inhibitors. We show here that TGF-beta downregulates Cdk6 and that transient and stable expression of Cdk6 in Mv1Lu mink epithelial cells overrides TGF-beta mediated arrest. The main effect of the ectopic Cdk6 expression was to sequester TGF-beta induced p15(Ink4b) and to maintain more p27(Kip1) in cyclin D-complexes preventing the complete shift of p27(Kip1) to Cdk2 invoked by TGF-beta. This led to the presence of an active cyclinD-Cdk6-p27(Kip1) complex and partially active cyclin E-Cdk2 complex and resulted in the failure of TGF-beta to fully arrest Mv1Lu cell growth. Though dominant negative Cdk6, expressed similarly in the cells, sequestered both p15(Ink4b) and p27(Kip1), it lacks kinase activity and was unable to override the TGF-beta arrest. The results demonstrate that downregulation of Cdk6 kinase is required for the enforcement of the G(1)-phase arrest by TGF-beta and results in changes in association of the p15(Ink4b) and p27(Kip1) inhibitors with D- and E-type cyclin kinase complexes.
authors.affiliation: Haartman Institute, Department of Virology, University of Helsinki, FIN-00014 Helsinki, Finland.
authors.forename: F
authors.initials: F
authors.lastname: Zhang
authors.forename: M
authors.initials: M
authors.lastname: Taipale
authors.forename: A
authors.initials: A
authors.lastname: Heiskanen
authors.forename: M
authors.initials: M
authors.lastname: Laiho
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D050762:Cyclin-Dependent Kinase Inhibitor p15; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D004261:DNA Replication; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D025521:Tumor Suppressor Proteins
chemical_list: D018797:Cell Cycle Proteins; D050762:Cyclin-Dependent Kinase Inhibitor p15; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases