title: Biochemical characterization of p16INK4- and p18-containing complexes in human cell lines.
abstract: The regulation of the D-type cyclin-dependent kinase (CDK4 and CDK6) activity appears to be the key step in the progression of eukaryotic cells through the G1 cell cycle phase. One of the mechanisms involved in this process is the binding of some small proteic inhibitors, with a molecular mass ranging between 14 and 20 kDa, to these CDKs. We have evaluated the amount of two such inhibitors, namely p16(INK4) and p18, in normal and transformed cells, as well as the biochemical features of the macromolecular complexes containing these proteins. The results obtained indicated that (i) p18 gene expression, unlike p16(INK4) gene, is not regulated by pRb status, (ii) no evident relationship exists between the expression of p16(INK4) and p18 genes, (iii) significant amounts of the two proteins are not bound to CDKs but occur as free molecules, (iv) each inhibitor forms a complex with the CDK protein with a 1:1 stoichiometry, and (v) a competition exists between cyclin D and the inhibitor protein toward the CDK protein resulting in the absence of detectable cellular free kinase. Moreover, employing the human native partially purified p16(INK4)or the pure recombinant protein, we have been able to demonstrate in vitro the dissociation of CDK4-cyclin D1 complex and the formation of CDK4-p16(INK4) bimolecular complex. Our findings suggest that during the cell division cycle the members of the p16(INK4) protein family and cyclin Ds compete for binding to CDK4/CDK6 and that their quantitative ratio is essential for G1 --> S transition.
authors.affiliation: Institute of Biochemistry of Macromolecules, Medical School, Second University of Naples, Italy.
authors.forename: F D
authors.initials: FD
authors.lastname: Ragione
authors.forename: G L
authors.initials: GL
authors.lastname: Russo
authors.forename: A
authors.initials: A
authors.lastname: Oliva
authors.forename: C
authors.initials: C
authors.lastname: Mercurio
authors.forename: S
authors.initials: S
authors.lastname: Mastropietro
authors.forename: V D
authors.initials: VD
authors.lastname: Pietra
authors.forename: V
authors.initials: V
authors.lastname: Zappia
mesh_terms: D002352:Carrier Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002460:Cell Line; D002461:Cell Line, Transformed; D002850:Chromatography, Gel; D019938:Cyclin D1; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050763:Cyclin-Dependent Kinase Inhibitor p18; D018844:Cyclin-Dependent Kinases / Q000302:isolation & purification / Q000378:metabolism; D016213:Cyclins / Q000302:isolation & purification / Q000378:metabolism; D004791:Enzyme Inhibitors; D004926:Escherichia coli; D015870:Gene Expression; D016147:Genes, Tumor Suppressor; D006801:Humans; D015151:Immunoblotting; D007700:Kinetics; D008970:Molecular Weight; D015513:Oncogene Proteins / Q000302:isolation & purification / Q000378:metabolism; D011485:Protein Binding; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
chemical_list: C493971:CDKN2C protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050763:Cyclin-Dependent Kinase Inhibitor p18; D016213:Cyclins; D004791:Enzyme Inhibitors; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases