title: Ubiquitylation of cyclin E requires the sequential function of SCF complexes containing distinct hCdc4 isoforms.
abstract: Cyclin E, an activator of cyclin-dependent kinase 2 (Cdk2), is targeted for proteasomal degradation by phosphorylation-dependent multiubiquitylation via the ubiquitin ligase SCF(hCdc4). SCF ubiquitin ligases are composed of a core of conserved subunits and one variable subunit (an F box protein) involved in substrate recognition. We show here that multiubiquitylation of cyclin E requires the sequential function of two distinct splice variant isoforms of the F box protein hCdc4 known as alpha and gamma. SCF(hCdc4alpha) binds a complex containing cyclin E, Cdk2, and the prolyl cis/trans isomerase Pin1 and promotes the activity of Pin1 without directly ubiquitylating cyclin E. However, due to the action of this SCF(hCdc4alpha)-Pin1 complex, cyclin E becomes an efficient ubiquitylation substrate of SCF(hCdc4gamma). Furthermore, in the context of Cdc4alpha and cyclin E, mutational data suggest that Pin1 isomerizes a noncanonical proline-proline bond, with the possibility that Cdc4alpha may serve as a cofactor for altering the specificity of Pin1.
authors.affiliation: Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Frank
authors.initials: F
authors.lastname: van Drogen
authors.forename: Olle
authors.initials: O
authors.lastname: Sangfelt
authors.forename: Aljona
authors.initials: A
authors.lastname: Malyukova
authors.forename: Ludmila
authors.initials: L
authors.lastname: Matskova
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Yeh
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Means
authors.forename: Steven I
authors.initials: SI
authors.lastname: Reed
mesh_terms: D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000145:classification* / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D019927:Cyclin E / Q000378:metabolism*; D044783:F-Box Proteins / Q000145:classification* / Q000235:genetics / Q000502:physiology*; D000073979:F-Box-WD Repeat-Containing Protein 7; D020868:Gene Silencing / Q000502:physiology; D006801:Humans; D007527:Isoenzymes / Q000145:classification* / Q000502:physiology; D008954:Models, Biological; D009154:Mutation; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D019696:Peptidylprolyl Isomerase / Q000502:physiology; D044843:SKP Cullin F-Box Protein Ligases / Q000502:physiology*; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000145:classification* / Q000235:genetics / Q000502:physiology*
chemical_list: D018797:Cell Cycle Proteins; D019927:Cyclin E; D044783:F-Box Proteins; D000073979:F-Box-WD Repeat-Containing Protein 7; C513273:FBXW7 protein, human; D007527:Isoenzymes; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D025801:Ubiquitin; D044843:SKP Cullin F-Box Protein Ligases; D044767:Ubiquitin-Protein Ligases; C000606846:PIN1 protein, human; D019696:Peptidylprolyl Isomerase