title: Inhibition of Cdk4 activity enhances translation of p27kip1 in quiescent Rb-negative cells.
abstract: We show in this work that the inhibition of Cdk4 (6) in Rb(-/-) 3T3 cells enhances the accumulation of the p27(kip1) cyclin-dependent kinase inhibitor when these cells are induced into quiescence. Two different forms of inhibition of Cdk4 (6), namely overexpression of the Cdk4 (6) inhibitor p16 and overexpression of a dominant negative mutant of Cdk4 (Cdk4(N158)), result in this effect. This suggests that the relevant activity of Cdk4 (6) that has to be inactivated in this setting is its kinase activity. The accumulation of p27(kip1) is due to enhanced translation of the protein, mediated by the 3'-untranslated region of the p27(kip1) mRNA. Moreover, the cells that overexpress p16(ink4a) or Cdk4(N158) show a delay in G(1) when made quiescent and restimulated to proliferate. This delay is overcome by transfection of a plasmid expressing antisense p27(kip1), which shows that the accumulation of p27(kip1) in these cells is related to their G(1) delay. In summary, we report a new functional link between two important cell cycle regulators, Cdk4 and p27(kip1), and provide a mechanistic explanation to the previously reported epistatic relations between these two proteins.
authors.affiliation: Departamento de Fisiología, Facultad de Medicina, University of Santiago de Compostela, 1 Calle San Francisco, Santiago de Compostela, 15705 A Coruña, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: González
authors.forename: Marcos
authors.initials: M
authors.lastname: Seoane
authors.forename: Pilar
authors.initials: P
authors.lastname: Caamaño
authors.forename: Juan
authors.initials: J
authors.lastname: Viñuela
authors.forename: Fernando
authors.initials: F
authors.lastname: Domínguez
authors.forename: Juan
authors.initials: J
authors.lastname: Zalvide
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics*; D002455:Cell Division; D003001:Cloning, Molecular; D051358:Cyclin-Dependent Kinase 4; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016161:Genes, Retinoblastoma; D016147:Genes, Tumor Suppressor; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D014176:Protein Biosynthesis; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000172:deficiency* / Q000235:genetics; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000235:genetics*
chemical_list: C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases