Mechanisms controlling the temporal degradation of Nek2A and Kif18A by the APC/C-Cdc20 complex

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The Anaphase Promoting Complex/Cyclosome (APC/C) with its co-activator Cdc20 regulates protein degradation during mitosis.
• The Spindle Assembly Checkpoint (SAC) inhibits APC/C-Cdc20 activity in prometaphase, but some substrates are degraded.
• Nek2A degradation in prometaphase involves its C-terminal MR dipeptide, but the sufficiency of this motif is unknown.

Purpose of the Study:

• To identify novel substrates of the APC/C-Cdc20 complex.
• To investigate the degradation mechanisms of Nek2A and Kif18A during mitosis.
• To elucidate the role of specific motifs and dimerization in APC/C-mediated protein degradation.

Main Methods:

• Identification of Kif18A as a novel substrate for APC/C-Cdc20.
• Analysis of degradation timing for Nek2A and Kif18A during mitosis.
• Investigation of the role of C-terminal motifs (MR and LR) in substrate recognition and degradation.
• Examination of Nek2A dimerization and its requirement for APC/C binding and ubiquitination.

Main Results:

• Kif18A is a novel APC/C-Cdc20 substrate degraded via a C-terminal LR motif, but not until anaphase.
• Nek2A degradation requires dimerization via a leucine zipper and the MR motif for stable binding and ubiquitination by the APC/C.
• Nek2A and the mitotic checkpoint complex (MCC) share APC/C subunit binding requirements.
• Nek2A likely binds to apo-APC/C with high affinity and is degraded by Cdc20 pools that evade SAC inhibition.

Conclusions:

• Kif18A degradation timing suggests additional regulatory mechanisms beyond the MR motif for Nek2A.
• Dimerization is crucial for Nek2A's interaction with and ubiquitination by the APC/C.
• Nek2A's degradation pathway involves high-affinity binding to apo-APC/C and utilization of SAC-evading Cdc20, highlighting complex regulation of protein turnover in mitosis.