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The APC/C subunit Mnd2/Apc15 promotes Cdc20 autoubiquitination and spindle assembly checkpoint inactivation

Scott A Foster1, David O Morgan

  • 1Department of Physiology and Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA.

Molecular Cell
|September 4, 2012
PubMed

Insights

The spindle assembly checkpoint (SAC) relies on Cdc20 ubiquitination. Autoubiquitination by Cdc20, regulated by Mnd2, is crucial for both SAC establishment and inactivation during chromosome segregation.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Genetics

Background:

  • Chromosome segregation fidelity is maintained by the spindle assembly checkpoint (SAC).
  • The SAC delays anaphase onset by inhibiting Cdc20, the activator of the anaphase-promoting complex/cyclosome (APC/C), when kinetochores are unattached.
  • Key SAC components include Mad2, Mad3/BubR1, and Bub3, which interact with Cdc20.

Purpose of the Study:

  • To investigate the role of Cdc20 autoubiquitination in the spindle assembly checkpoint (SAC) in budding yeast.
  • To elucidate how Cdc20 ubiquitination impacts SAC establishment and inactivation.
  • To determine the contribution of the Mnd2/Apc15 subunit to SAC-dependent Cdc20 ubiquitination.

Main Methods:

  • Reconstitution experiments using purified proteins to analyze Cdc20 ubiquitination.
  • In vivo studies involving genetic manipulation (e.g., Mnd2 deletion) to assess SAC function.
  • Analysis of Cdc20 protein levels and SAC arrest/release dynamics.

Main Results:

  • A Mad2-Mad3/BubR1-Bub3 complex inhibits substrate ubiquitination by stimulating Cdc20 autoubiquitination.
  • SAC-dependent Cdc20 autoubiquitination requires the APC/C subunit Mnd2/Apc15.
  • Inhibition of Cdc20 ubiquitination leads to high Cdc20 levels, impairing SAC arrest establishment and delaying SAC inactivation.

Conclusions:

  • Cdc20 autoubiquitination, promoted by SAC components and Mnd2, is essential for proper SAC function.
  • Low Cdc20 levels, achieved through ubiquitination, are necessary for establishing a SAC arrest.
  • Cdc20 ubiquitination also plays a critical role in the inactivation of the SAC, facilitating timely anaphase progression.

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