ANAPC15

ANAPC15 (APC15/Mnd2) is an integral subunit of the anaphase-promoting complex/cyclosome (APC/C) that is specifically required for spindle assembly checkpoint (SAC) silencing by promoting the ubiquitylation and degradation of the APC/C coactivator CDC20 within the mitotic checkpoint complex (MCC), thereby driving MCC disassembly and enabling timely mitotic exit. APC15 resides on the APC/C platform near the MCC binding site and its positioning depends on Apc1 WD40 domain-mediated conformational changes; it is dispensable for APC/C-mediated substrate ubiquitylation by CDC20 or CDH1 coactivators (PMID:23007861, PMID:27601667). APC15-dependent CDC20 ubiquitylation operates in parallel with the TRIP13-catalyzed pathway for MCC disassembly, and elimination of both pathways renders cells unable to exit mitosis even when checkpoint signaling is abrogated (PMID:30341343). This function is conserved from yeast to mammals, including a role in meiotic SAC inactivation during oocyte maturation (PMID:22940250, PMID:28366744, PMID:40153087).

1. 2011 High

   The first demonstration that APC15 is required for CDC20 turnover and MCC release from the APC/C resolved how the SAC-inhibited APC/C is reactivated upon checkpoint satisfaction.

   Evidence siRNA knockdown in human cells with live-cell imaging, immunoprecipitation, and ubiquitylation assays

   PMID:21926987

   Open questions at the time

   • Mechanism by which APC15 promotes CDC20 ubiquitylation was unknown
   • Structural position of APC15 on the APC/C was not resolved
   • Whether APC15 is required for APC/C activity toward other substrates was untested
2. 2012 High

   Reconstitution with purified components in both human and budding yeast systems established that APC15/Mnd2 specifically enables MCC-dependent CDC20 autoubiquitylation while being dispensable for substrate ubiquitylation by APC/C–CDC20 or APC/C–CDH1, defining APC15 as a selective regulator of coactivator fate rather than a general APC/C activity factor.

   Evidence Recombinant human APC/C reconstitution, purified budding yeast APC/C in vitro ubiquitylation, cryo-EM structural localization, genetic deletion in yeast

   PMID:22940250 PMID:23007861

   Open questions at the time

   • Atomic-resolution contacts between APC15 and MCC components were not defined
   • How APC15 discriminates MCC-bound CDC20 from free CDC20 was unclear
3. 2016 High

   Structural and genetic studies revealed that APC15 is part of the APC/C platform subcomplex and that its stable positioning depends on the Apc1 WD40 domain, linking APC/C conformational dynamics to APC15-mediated MCC disassembly; separately, APC15 and UBE2C were shown to cooperate functionally in SAC silencing.

   Evidence Apc1 crystal structure at 2.2 Å, cryo-EM of APC/C–Cdh1 with Apc1(WD40) deletion, CRISPR UBE2C KO combined with APC15 siRNA and live-cell mitotic timing

   PMID:27591192 PMID:27601667

   Open questions at the time

   • Whether APC15 conformational coupling is direct or mediated through other subunits was unresolved
   • Relative contributions of APC15 vs. UBE2C to SAC silencing kinetics were not quantified
4. 2017 High

   Fission yeast studies demonstrated that APC15 and the Mad3 C-terminal ABBA-KEN2-ABBA motif share a function in mediating MCC–APC/C binding and disassembly, and that APC/C can simultaneously accommodate two Cdc20 molecules whose ubiquitylation depends on APC15, clarifying the stoichiometry and epistatic logic of checkpoint disassembly.

   Evidence Genetic deletion and epistasis in fission yeast, dual-epitope-tag co-IP, in vitro reconstitution

   PMID:28366743 PMID:28366744

   Open questions at the time

   • Whether the dual-Cdc20 model applies to human APC/C was untested
   • Structural basis for APC15–Mad3 functional overlap was not resolved
5. 2018 High

   Establishing that APC15-dependent CDC20 degradation and TRIP13-catalyzed Mad2 removal constitute two parallel, redundant MCC disassembly pathways explained why loss of either alone permits mitotic exit, and demonstrated that interphase-produced MCC also requires active disassembly.

   Evidence Degron-tagging rapid depletion of TRIP13 combined with CRISPR APC15 knockout, live-cell mitotic exit assays

   PMID:30341343

   Open questions at the time

   • Relative pathway usage under physiological conditions and across cell types was not determined
   • Whether additional disassembly pathways exist beyond APC15 and TRIP13 was unresolved
6. 2025 Medium

   Extension of APC15 function to meiosis showed that APC15 dynamically localizes during mouse oocyte meiotic progression and is required for SAC inactivation at the metaphase I–anaphase I transition.

   Evidence Immunofluorescence/confocal microscopy and siRNA knockdown in mouse oocytes with kinetochore BUB3 readout

   PMID:40153087

   Open questions at the time

   • Single-lab observation not yet independently replicated
   • Molecular mechanism of APC15 in meiotic versus mitotic MCC disassembly not compared
   • Whether APC15 has meiosis II roles was not addressed

• The atomic-resolution mechanism by which APC15 selectively promotes CDC20 autoubiquitylation within the MCC-bound APC/C — including direct contact surfaces, conformational gating, and potential allosteric communication with the E2 binding site — remains structurally undefined.
• No high-resolution structure of APC15 in the context of the MCC–APC/C complex with substrate-level detail
• Potential post-translational regulation of APC15 activity is unexplored
• Whether APC15 has functions outside the SAC/MCC disassembly axis is unknown