Substrate Recognition and Ubiquitination of SCFSkp2/Cks1 Ubiquitin-Protein Isopeptide Ligase

• Published in: The Journal of biological chemistry 2007-05, Vol.282 (21), p.15462-15470
• Main Authors: Xu, Shuichan, Abbasian, Mahan, Patel, Palka, Jensen-Pergakes, Kristen, Lombardo, Christian R., Cathers, Brian E., Xie, Weilin, Mercurio, Frank, Pagano, Michele, Giegel, David, Cox, Sarah
• Format: Article
• Language: English
• Subjects: Animals; Carrier Proteins - chemistry; Carrier Proteins - metabolism; CDC2-CDC28 Kinases; Cell-Free System - chemistry; Cell-Free System - metabolism; Cyclin A - chemistry; Cyclin A - metabolism; Cyclin E - chemistry; Cyclin E - metabolism; Cyclin-Dependent Kinase 2 - chemistry; Cyclin-Dependent Kinase 2 - metabolism; Cyclin-Dependent Kinase Inhibitor p27 - chemistry; Cyclin-Dependent Kinase Inhibitor p27 - metabolism; Cyclin-Dependent Kinases - chemistry; Cyclin-Dependent Kinases - metabolism; G1 Phase - physiology; Humans; Multiprotein Complexes - chemistry; Multiprotein Complexes - metabolism; Phosphorylation; Protein Processing, Post-Translational - physiology; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; S Phase - physiology; S-Phase Kinase-Associated Proteins - chemistry; S-Phase Kinase-Associated Proteins - metabolism; Ubiquitin-Protein Ligases - chemistry; Ubiquitin-Protein Ligases - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M610758200

p27, an important cell cycle regulator, blocks the G1/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 Thr187 on p27 are essential for the recognition of p27 by the SCFSkp2/Cks1 complex, the ubiquitin-protein isopeptide ligase (E3). Cdk2/E provides a high affinity binding site, whereas the phosphorylated Thr187 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.