title: P27Kip1 serine 10 phosphorylation determines its metabolism and interaction with cyclin-dependent kinases.
abstract: p27Kip1 is a critical modulator of cell proliferation by controlling assembly, localization and activity of cyclin-dependent kinase (CDK). p27Kip1 also plays important roles in malignant transformation, modulating cell movement and interaction with the extracellular matrix. A critical p27Kip1 feature is the lack of a stable tertiary structure that enhances its "adaptability" to different interactors and explains the heterogeneity of its function. The absence of a well-defined folding underlines the importance of p27Kip1 post-translational modifications that might highly impact the protein functions. Here, we characterize the metabolism and CDK interaction of phosphoserine10-p27Kip1 (pS10- p27Kip1), the major phosphoisoform of p27Kip1. By an experimental strategy based on specific immunoprecipitation and bidimensional electrophoresis, we established that pS10-p27Kip1 is mainly bound to cyclin E/CDK2 rather than to cyclin A/CDK2. pS10- p27Kip1 is more stable than non-modified p27Kip1, since it is not (or scarcely) phosphorylated on T187, the post-translational modification required for p27Kip1 removal in the nucleus. pS10-p27Kip1 does not bind CDK1. The lack of this interaction might represent a mechanism for facilitating CDK1 activation and allowing mitosis completion. In conclusion, we suggest that nuclear p27Kip1 follows 2 almost independent pathways operating at different rates. One pathway involves threonine-187 and tyrosine phosphorylations and drives the protein toward its Skp2-dependent removal. The other involves serine-10 phosphorylation and results in the elongation of p27Kip1 half-life and specific CDK interactions. Thus, pS10-p27Kip1, due to its stability, might be thought as a major responsible for the p27Kip1-dependent arrest of cells in G1/G0 phase.
authors.affiliation: a Department of Biochemistry; Biophysics and General Pathology ; Second University of Naples ; Naples , Italy.
authors.forename: Debora
authors.initials: D
authors.lastname: Bencivenga
authors.forename: Annunziata
authors.initials: A
authors.lastname: Tramontano
authors.forename: Alessia
authors.initials: A
authors.lastname: Borgia
authors.forename: Aide
authors.initials: A
authors.lastname: Negri
authors.forename: Ilaria
authors.initials: I
authors.lastname: Caldarelli
authors.forename: Adriana
authors.initials: A
authors.lastname: Oliva
authors.forename: Silverio
authors.initials: S
authors.lastname: Perrotta
authors.forename: Fulvio
authors.initials: F
authors.lastname: Della Ragione
authors.forename: Adriana
authors.initials: A
authors.lastname: Borriello
mesh_terms: D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D011485:Protein Binding / Q000502:physiology; D012694:Serine / Q000378:metabolism*
chemical_list: C436291:CDKN1B protein, human; D050760:Cyclin-Dependent Kinase Inhibitor p27; D012694:Serine; D018844:Cyclin-Dependent Kinases
keywords: ATRA, all-trans retinoic acid; CDK, cyclin-dependent kinase; CKI, CDK inhibitor; IUP, intrinsically unstructured protein; cyclin-depedent kinases regulation; p27Kip1; p27Kip1 metabolism; p27Kip1 modifications; pS10-p27Kip1, phosphoserine 10 p27Kip1; pT187-p27Kip1, phosphothreonine p27Kip1