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Updated: Aug 7, 2026
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Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
Published on: May 3, 2018
Ubiquitylation of cyclin E requires the sequential function of SCF complexes containing distinct hCdc4 isoforms
Frank van Drogen1, Olle Sangfelt, Aljona Malyukova
1Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Molecular Cell
|July 5, 2006
Summary
The study reveals that two isoforms of the F box protein hCdc4, alpha and gamma, sequentially ubiquitylate cyclin E. This process involves the SCF(hCdc4alpha)-Pin1 complex priming cyclin E for SCF(hCdc4gamma) ubiquitylation and proteasomal degradation.
Area of Science:
- Cell Cycle Regulation
- Protein Degradation
- Ubiquitin Ligase Complexes
Background:
- Cyclin E activates cyclin-dependent kinase 2 (Cdk2), crucial for cell cycle progression.
- Proteasomal degradation targets proteins for destruction, regulating cellular processes.
- SCF ubiquitin ligases, including SCF(hCdc4), mediate substrate ubiquitylation via F box proteins for degradation.
Purpose of the Study:
- To elucidate the mechanism of cyclin E ubiquitylation and proteasomal degradation.
- To investigate the roles of distinct hCdc4 splice variants in cyclin E regulation.
- To understand the interplay between SCF(hCdc4) isoforms, Pin1, and cyclin E ubiquitylation.
Main Methods:
- Investigated the sequential function of hCdc4alpha and hCdc4gamma isoforms.
- Utilized biochemical assays to study SCF(hCdc4alpha)-Pin1 complex formation and activity.
- Employed mutational analysis to explore the role of Pin1 in isomerizing proline-proline bonds in cyclin E.
Main Results:
- Multiubiquitylation of cyclin E requires sequential action of SCF(hCdc4alpha) and SCF(hCdc4gamma).
- SCF(hCdc4alpha) binds cyclin E, Cdk2, and Pin1, promoting Pin1 activity without direct ubiquitylation.
- The SCF(hCdc4alpha)-Pin1 complex facilitates subsequent ubiquitylation of cyclin E by SCF(hCdc4gamma).
- Pin1 isomerizes a noncanonical proline-proline bond in cyclin E, potentially cofactor-assisted by Cdc4alpha.
Conclusions:
- The sequential action of hCdc4 isoforms and Pin1 is essential for cyclin E degradation.
- SCF(hCdc4alpha) acts upstream of SCF(hCdc4gamma) in a coordinated pathway for cyclin E ubiquitylation.
- Pin1 plays a critical role in modifying cyclin E for ubiquitylation, suggesting a novel regulatory mechanism.
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