title: Phosphorylation of p16INK4A correlates with Cdk4 association.
abstract: Progression through the eukaryotic cell cycle is driven by the activity of cyclin-dependent kinases. The cyclin D-dependent kinase Cdk4 promotes progression through the G(1) phase of the cell cycle and is deregulated in many human tumors. The tumor suppressor protein p16(INK4A) (p16) forms a complex with Cdk4 and inhibits kinase activity. Here we report that p16 is phosphorylated, and the phosphorylated form of p16 is preferentially associated with Cdk4 in normal human fibroblasts. We mapped phosphorylation sites on exogenously overexpressed p16 to serines 7, 8, 140, and 152 and found that endogenous p16 associated with Cdk4 is phosphorylated at serine 152. All mapped phosphorylation sites lie outside of the conserved kinase-binding domain of p16 but in regions of the protein affected by mutations in familial and sporadic cancer. Our results suggest a novel regulation of p16 activity.
authors.affiliation: Cancer Research Institute, University of California, San Francisco, California 94143-0128, USA. jgump@cc.ucsf.edu
authors.forename: Jay
authors.initials: J
authors.lastname: Gump
authors.forename: David
authors.initials: D
authors.lastname: Stokoe
authors.forename: Frank
authors.initials: F
authors.lastname: McCormick
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002855:Chromatography, Thin Layer; D006224:Cricetinae; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins; D051381:Rats; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
chemical_list: D019941:Cyclin-Dependent Kinase Inhibitor p16; D011518:Proto-Oncogene Proteins; D012694:Serine; C495900:CDK4 protein, human; C495902:Cdk4 protein, mouse; C495903:Cdk4 protein, rat; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases