CDK1-PP2A-B55 interplay ensures cell cycle oscillation via Apc1-loop³⁰⁰.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Cell cycle progression depends on precise regulation of protein phosphorylation and dephosphorylation.
• The anaphase-promoting complex/cyclosome (APC/C) is a critical E3 ubiquitin ligase complex that controls cell cycle transitions.
• Identifying the key substrates and regulatory mechanisms governing APC/C activity is essential for understanding cell cycle control.

Purpose of the Study:

• To investigate the role of phospho-regulation in controlling the activity of the anaphase-promoting complex/cyclosome (APC/C).
• To identify the specific regulatory elements and enzymes involved in APC/C phospho-regulation during mitosis.
• To elucidate how APC/C regulation impacts key cell cycle events like Cyclin B degradation.

Main Methods:

• Utilized biochemical assays to study the phosphorylation status of APC/C components.
• Employed genetic manipulation, including kinase depletion and domain deletion, to assess functional consequences.
• Investigated protein-protein interactions using co-immunoprecipitation and analyzed protein degradation dynamics.

Main Results:

• The Apc1-loop300 domain (Apc1-300L) of the APC/C was identified as a critical substrate for CDK1 and PP2A-B55.
• Dephosphorylation of Apc1-300L by PP2A-B55, particularly upon premature activation, stalls APC/C activity and delays Cyclin B degradation.
• This delay can be rescued by inhibiting PP2A-B55 or mutating the Apc1-300L phosphorylation site, and it specifically impairs further Cdc20 recruitment to the APC/C.

Conclusions:

• The phospho-regulation of the Apc1-loop300 domain is a pivotal mechanism controlling APC/C activity and cell cycle progression.
• The interplay between CDK1 and PP2A-B55 on APC/C is a primary determinant of cell cycle oscillation.
• APC/C acts as a central substrate regulated by the CDK-phosphatase partnership, highlighting its role in cell cycle timing.