Molecular mechanisms of APC/C release from spindle assembly checkpoint inhibition by APC/C SUMOylation

Abstract

The anaphase-promoting complex/cyclosome (APC/C) is an E3 ubiquitin ligase that controls cell cycle transitions. Its regulation by the spindle assembly checkpoint (SAC) is coordinated with the attachment of sister chromatids to the mitotic spindle. APC/C SUMOylation on APC4 ensures timely anaphase onset and chromosome segregation. To understand the structural and functional consequences of APC/C SUMOylation, we reconstituted SUMOylated APC/C for electron cryo-microscopy and biochemical analyses. SUMOylation of the APC/C causes a substantial rearrangement of the WHB domain of APC/C's cullin subunit (APC2^WHB). Although APC/C^Cdc20 SUMOylation results in a modest impact on normal APC/C^Cdc20 activity, repositioning APC2^WHB reduces the affinity of APC/C^Cdc20 for the mitotic checkpoint complex (MCC), the effector of the SAC. This attenuates MCC-mediated suppression of APC/C^Cdc20 activity, allowing for more efficient ubiquitination of APC/C^Cdc20 substrates in the presence of the MCC. Thus, SUMOylation stimulates the reactivation of APC/C^Cdc20 when the SAC is silenced, contributing to timely anaphase onset.

Keywords: APC/C; MCC; SAC; SUMOylation; WHB domain; cell cycle; ubiquitination.