title: Mutual requirement of CDK4 and Myc in malignant transformation: evidence for cyclin D1/CDK4 and p16INK4A as upstream regulators of Myc.
abstract: We demonstrate in this paper that CDK4 which is a G1 phase specific cell cycle regulator and catalytic subunit of D-type cyclins has oncogenic activity similar to D-type cyclins themselves and is able to provoke focus formation when cotransfected with activated Ha-ras into primary rat embryo fibroblasts. Surprisingly, using two different mutants we show that CDK4's ability to bind to p16INK4a and not its kinase activity is important for its transforming potential. In addition, p16INK4a but not a mutant form that is found in human tumours can completely abrogate focus formation by CDK4 suggesting that CDK4 can malignantly transform cells by sequestering p16INK4a or other CKIs. We demonstrate that both cyclin D1 and CDK4 functionally depend on active Myc to exert their potential as oncogenes and vice versa that the transforming ability of Myc requires functional cyclin D/CDK complexes. Moreover, we find that p16INK4a and the Rb related protein p107 which releases Myc after phosphorylation by cyclin D1/CDK4 efficiently block Myc's activity as a transcriptional transactivator and as an oncogene. We conclude that both p16INK4a and cyclin D/CDK4 complexes are upstream regulators of Myc and directly govern Myc function in transcriptional transactivation and transformation via the pocket protein p107.
authors.affiliation: Institut für Zellbiologie (Tumorforschung), IFZ, Universitätsklinikum Essen, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Haas
authors.forename: P
authors.initials: P
authors.lastname: Staller
authors.forename: C
authors.initials: C
authors.lastname: Geisen
authors.forename: J
authors.initials: J
authors.lastname: Bartek
authors.forename: M
authors.initials: M
authors.lastname: Eilers
authors.forename: T
authors.initials: T
authors.lastname: Möröy
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D002471:Cell Transformation, Neoplastic; D019938:Cyclin D1; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16; D018844:Cyclin-Dependent Kinases / Q000502:physiology*; D016213:Cyclins / Q000502:physiology*; D016259:Genes, myc / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D015513:Oncogene Proteins / Q000502:physiology*; D011518:Proto-Oncogene Proteins; D051381:Rats; D011916:Rats, Inbred F344; D016160:Retinoblastoma Protein / Q000502:physiology; D015533:Transcriptional Activation
chemical_list: D002352:Carrier Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D016213:Cyclins; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D019938:Cyclin D1; C495900:CDK4 protein, human; C495902:Cdk4 protein, mouse; C495903:Cdk4 protein, rat; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases