title: Activation of cyclin D1-kinase in murine fibroblasts lacking both p21(Cip1) and p27(Kip1).
abstract: Deregulation of D-type cyclin-dependent kinases (CDK4 and 6) is widely observed in various human cancers, illustrating their importance in cell cycle control. Like other cyclin-dependent kinases (CDKs), assembly with cyclins is the most critical step for activation of CDK4/6. As previously reported elsewhere, we observed that the level of cyclinD1-CDK4 complex and its associated kinase activity were significantly low in asynchronously proliferating mouse embryo fibroblasts lacking both p21(Cip1) and p27(Kip1) (p21/p27-null MEFs). These evidences imply that p21(Cip1) and p27(Kip1) CDK inhibitors are 'essential activators' of cyclin D-kinases. We, however, discovered here that both the assembly and activation of cyclin D1-CDK4 complex occur when quiescent p21/p27-null MEFs were stimulated to re-enter the cell cycle. This mitogen-induced cyclin D1-kinase activity was blocked by overexpression of p16(INK4a) and resulted in the inhibition of S phase entry in p21/p27-null MEFs. Furthermore, ectopic expression of p34(SEI-1), a mitogen-induced CDK4 binding protein, increased the levels of active cyclinD1-CDK4 complex in asynchronously proliferating p21/p27-null MEFs. Together, our results suggest that there are several independent ways to stimulate the assembly of cyclin D1-CDK4 kinases. Although p21(Cip1) and p27(Kip1) play a role in this process, our results demonstrate that additional mechanisms must occur in G0 to S phase transition.
authors.affiliation: Cancer Research UK, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester M20 4BX, UK.
authors.forename: Masataka
authors.initials: M
authors.lastname: Sugimoto
authors.forename: Nicholas
authors.initials: N
authors.lastname: Martin
authors.forename: Deepti P
authors.initials: DP
authors.lastname: Wilks
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Tamai
authors.forename: Thomas J G
authors.initials: TJ
authors.lastname: Huot
authors.forename: Cristina
authors.initials: C
authors.lastname: Pantoja
authors.forename: Ko
authors.initials: K
authors.lastname: Okumura
authors.forename: Manuel
authors.initials: M
authors.lastname: Serrano
authors.forename: Eiji
authors.initials: E
authors.lastname: Hara
mesh_terms: D000818:Animals; D002417:Cattle; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000502:physiology; D003260:Contact Inhibition; D003470:Culture Media / Q000494:pharmacology; D016895:Culture Media, Serum-Free; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000172:deficiency* / Q000502:physiology; D004622:Embryo, Mammalian / Q000166:cytology; D004789:Enzyme Activation / Q000187:drug effects; D005312:Fetal Blood / Q000502:physiology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018390:Gene Targeting; D006133:Growth Substances / Q000494:pharmacology; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D008934:Mitogens / Q000494:pharmacology; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D016192:Resting Phase, Cell Cycle; D016196:S Phase; D015534:Trans-Activators / Q000502:physiology; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins / Q000172:deficiency* / Q000502:physiology; D000092468:Bromodomain Containing Proteins
chemical_list: D018797:Cell Cycle Proteins; D003470:Culture Media; D016895:Culture Media, Serum-Free; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases; D016213:Cyclins; D006133:Growth Substances; D046911:Macromolecular Substances; D008934:Mitogens; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; C493961:Cdkn1b protein, mouse; C402464:SERTAD1 protein, human; C485730:Sertad1 protein, mouse; D000092468:Bromodomain Containing Proteins; C495900:CDK4 protein, human; C495902:Cdk4 protein, mouse