title: Control of the SCF(Skp2-Cks1) ubiquitin ligase by the APC/C(Cdh1) ubiquitin ligase.
abstract: Skp2 and its cofactor Cks1 are the substrate-targeting subunits of the SCF(Skp2-Cks1) (Skp1/Cul1/F-box protein) ubiquitin ligase complex that regulates entry into S phase by inducing the degradation of the cyclin-dependent kinase inhibitors p21 and p27 (ref. 1). Skp2 is an oncoprotein that often shows increased expression in human cancers; however, the mechanism that regulates its cellular abundance is not well understood. Here we show that both Skp2 and Cks1 proteins are unstable in G1 and that their degradation is mediated by the ubiquitin ligase APC/C(Cdh1) (anaphase-promoting complex/cyclosome and its activator Cdh1). Silencing of Cdh1 by RNA interference in G1 cells stabilizes Skp2 and Cks1, with a consequent increase in p21 and p27 proteolysis. Depletion of Cdh1 also increases the percentage of cells in S phase, whereas concomitant downregulation of Skp2 reverses this effect, showing that Skp2 is an essential target of APC/C(Cdh1). Expression of a stable Skp2 mutant that cannot bind APC/C(Cdh1) induces premature entry into S phase. Thus, the induction of Skp2 and Cks1 degradation in G1 represents a principal mechanism by which APC/C(Cdh1) prevents the unscheduled degradation of SCF(Skp2-Cks1) substrates and maintains the G1 state.
authors.affiliation: Department of Pathology, MSB 599, New York University School of Medicine, and New York University Cancer Institute, 550 First Avenue, New York, New York 10016, USA.
authors.forename: Tarig
authors.initials: T
authors.lastname: Bashir
authors.forename: N Valerio
authors.initials: NV
authors.lastname: Dorrello
authors.forename: Virginia
authors.initials: V
authors.lastname: Amador
authors.forename: Daniele
authors.initials: D
authors.lastname: Guardavaccaro
authors.forename: Michele
authors.initials: M
authors.lastname: Pagano
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D042846:CDC2-CDC28 Kinases / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D002455:Cell Division; D002460:Cell Line; D044842:Cullin Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D019925:Cyclin A / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D018844:Cyclin-Dependent Kinases; D006801:Humans; D051379:Mice; D009154:Mutation; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D034622:RNA Interference; D051381:Rats; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000235:genetics / Q000378:metabolism*
chemical_list: C093090:CKS1B protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C100318:Cullin 1; D044842:Cullin Proteins; D019925:Cyclin A; D019926:Cyclin B; D044786:S-Phase Kinase-Associated Proteins; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D044843:SKP Cullin F-Box Protein Ligases; D011494:Protein Kinases; D042846:CDC2-CDC28 Kinases; C474110:Cks1 protein, mouse; D018844:Cyclin-Dependent Kinases