Anaphase-Promoting Complex/Cyclosome (APC/C)

  • An E3 ubiquitin ligase assembles poly-ubiquitin chains on the substrate, thereby targeting them for degradation through the 26S proteasome.
  • Twelve core subunits and two cofactors (Cdc20 and Cdh1) have been identified in this complex.
  • Cdc20 and Cdh1 interact transiently with APC/C, thereby regulating its activity.
  • Activation of APC/C during early mitosis is regulated by Cdc20. However, Cdh1 regulates APC/C activation from late mitosis to G1-S transition.
  • Activation of APC/C during metaphase to anaphase transition: Binding of Cdc20 to APC/C activates APC/C. The binding of Cdc20 to APC/C is dependent on the ubiquitination status of cdc20. Unubiquinated Cdc20 forms a complex with Mad2-BubR1. APC/C ubiquitinate Cdc20 which is regulated by UBE2C/UbcH10 and p31Comet. Ubiquitinated Cdc20 is released from the Mad2-BubR1-Cdc20 complex and binds to ACP/C, thereby activating APC/C.
  • Inactivation of APC/C upon activation of Spindle Assembly Checkpoint: Deunubiquinating enzyme USP44 deubiquitinates the Cdc20, which ultimately results in the stabilization of Mad2-BubR1-Cdc20 complex.
  • A feedback regulation exists between APC/C and Cdk activation during cell cycle progression.

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