Dynamic regulation of mitotic ubiquitin ligase APC/C by coordinated Plx1 kinase and PP2A phosphatase action on a flexible Apc1 loop.

The anaphase‐promoting complex/cyclosome (APC/C), a multi‐subunit ubiquitin ligase essential for cell cycle control, is regulated by reversible phosphorylation. APC/C phosphorylation by cyclin‐dependent kinase 1 (Cdk1) promotes Cdc20 co‐activator loading in mitosis to form active APC/C‐Cdc20. However, detailed phospho‐regulation of APC/C dynamics through other kinases and phosphatases is still poorly understood. Here, we show that an interplay between polo‐like kinase (Plx1) and PP2A‐B56 phosphatase on a flexible loop domain of the subunit Apc1 (Apc1‐loop500) controls APC/C activity and mitotic progression. Plx1 directly binds to the Apc1‐loop500 in a phosphorylation‐dependent manner and promotes the formation of APC/C‐Cdc20 via Apc3 phosphorylation. Upon phosphorylation of loop residue T532, PP2A‐B56 is recruited to the Apc1‐loop500 and differentially promotes dissociation of Plx1 and PP2A‐B56 through dephosphorylation of Plx1‐binding sites. Stable Plx1 binding, which prevents PP2A‐B56 recruitment, prematurely activates the APC/C and delays APC/C dephosphorylation during mitotic exit. Furthermore, the phosphorylation status of the Apc1‐loop500 is controlled by distant Apc3‐loop phosphorylation. Our study suggests that phosphorylation‐dependent feedback regulation through flexible loop domains within a macromolecular complex coordinates the activity and dynamics of the APC/C during the cell cycle. SYNOPSIS: The APC/C, a mitotic E3 ubiquitin ligase, is regulated by reversible phosphorylation. This study shows how dynamic APC/C regulation in mitosis is coordinated by Polo‐like kinase Plx1 and phosphatase PP2A‐B56 through a flexible loop domain on the Apc1 subunit. Plx1 directly binds to the Apc1‐loop500, and promotes the formation of an active APC/C‐Cdc20 complex.PP2A‐B56 is recruited to the Apc1‐loop500 and promotes dissociation of Plx1.Recruitment of Plx1 and PP2A‐B56 is determined by phosphorylation of CDK sites (T532, T539, S558) on the Apc1‐loop500.Phosphorylation status of the Apc1‐loop500 is controlled by phosphorylation of a flexible loop domain of Apc3.Crosstalk between remote flexible APC/C loop domains is important for fine‐tuning APC/C‐Cdc20 activity with CDK activity. [ABSTRACT FROM AUTHOR]