Phosphorylation and dephosphorylation regulate APC/C(Cdh1) substrate degradation

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The Anaphase Promoting Complex/Cyclosome (APC/C) is a crucial ubiquitin ligase regulating the cell cycle.
• APC/C activity is controlled by adaptor proteins, including Cdh1, which targets it for G1-specific activity.
• The precise kinetics and requirements for APC/C(Cdh1)-mediated substrate degradation remain largely uncharacterized.

Purpose of the Study:

• To investigate the consequences of constitutive APC/C(Cdh1) activation on cell cycle progression.
• To identify novel requirements for the degradation of APC/C(Cdh1) substrates.
• To explore the role of phosphorylation and dephosphorylation in APC/C(Cdh1) substrate targeting.

Main Methods:

• Overexpression of a constitutively active Cdh1 mutant (CDH1(m11)) that bypasses inhibitory phosphorylation.
• Analysis of mitotic exit in the absence of key regulatory pathways (FEAR and MEN).
• Assessment of DNA re-replication in the absence of specific kinases (Cdc7).

Main Results:

• Constitutive APC/C(Cdh1) activation induced mitotic exit independently of FEAR and MEN pathways.
• Overactive APC/C(Cdh1) promoted DNA re-replication even without Cdc7 activity.
• Substrate degradation by APC/C(Cdh1) exhibited differential requirements, with some substrates needing dephosphorylation (e.g., Pds1, Clb5) and others needing phosphorylation (e.g., Cdc5).

Conclusions:

• Constitutively active APC/C(Cdh1) can override normal cell cycle checkpoints, leading to premature mitotic exit and re-replication.
• APC/C(Cdh1) substrate degradation is a complex process influenced by the phosphorylation status of the substrates.
• This study uncovers new regulatory mechanisms governing APC/C(Cdh1) function and substrate turnover essential for cell cycle control.