title: Substrate recognition and ubiquitination of SCFSkp2/Cks1 ubiquitin-protein isopeptide ligase.
abstract: p27, an important cell cycle regulator, blocks the G(1)/S transition in cells by binding and inhibiting Cdk2/cyclin A and Cdk2/cyclin E complexes (Cdk2/E). Ubiquitination and subsequent degradation play a critical role in regulating the levels of p27 during cell cycle progression. Here we provide evidence suggesting that both Cdk2/E and phosphorylation of Thr(187) on p27 are essential for the recognition of p27 by the SCF(Skp2/Cks1) complex, the ubiquitin-protein isopeptide ligase (E3). Cdk2/E provides a high affinity binding site, whereas the phosphorylated Thr(187) provides a low affinity binding site for the Skp2/Cks1 complex. Furthermore, binding of phosphorylated p27/Cdk2/E to the E3 complex showed positive cooperativity. Consistently, p27 is also ubiquitinated in a similarly cooperative manner. In the absence of p27, Cdk2/E and Cks1 increase Skp2 phosphorylation. This phosphorylation enhances Skp2 auto-ubiquitination, whereas p27 inhibits both phosphorylation and auto-ubiquitination of Skp2.
authors.affiliation: Department of Biochemistry and Biomarker Development, Signal Pharmaceuticals, LLC, San Diego, California 92121, USA. sxu@celgene.com
authors.forename: Shuichan
authors.initials: S
authors.lastname: Xu
authors.forename: Mahan
authors.initials: M
authors.lastname: Abbasian
authors.forename: Palka
authors.initials: P
authors.lastname: Patel
authors.forename: Kristen
authors.initials: K
authors.lastname: Jensen-Pergakes
authors.forename: Christian R
authors.initials: CR
authors.lastname: Lombardo
authors.forename: Brian E
authors.initials: BE
authors.lastname: Cathers
authors.forename: Weilin
authors.initials: W
authors.lastname: Xie
authors.forename: Frank
authors.initials: F
authors.lastname: Mercurio
authors.forename: Michele
authors.initials: M
authors.lastname: Pagano
authors.forename: David
authors.initials: D
authors.lastname: Giegel
authors.forename: Sarah
authors.initials: S
authors.lastname: Cox
mesh_terms: D000818:Animals; D042846:CDC2-CDC28 Kinases; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D002474:Cell-Free System / Q000737:chemistry / Q000378:metabolism; D019925:Cyclin A / Q000737:chemistry / Q000378:metabolism; D019927:Cyclin E / Q000737:chemistry / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000737:chemistry / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000737:chemistry / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000737:chemistry* / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology; D006801:Humans; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational / Q000502:physiology; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016196:S Phase / Q000502:physiology; D044786:S-Phase Kinase-Associated Proteins / Q000737:chemistry* / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry* / Q000378:metabolism
chemical_list: C093090:CKS1B protein, human; D002352:Carrier Proteins; D019925:Cyclin A; D019927:Cyclin E; D046912:Multiprotein Complexes; D011994:Recombinant Proteins; D044786:S-Phase Kinase-Associated Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D044767:Ubiquitin-Protein Ligases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases