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Requirement for proteolysis in spindle assembly checkpoint silencing

Roberta Visconti1, Luca Palazzo, Domenico Grieco

  • 1CEINGE Biotecnologie Avanzate, Naples, Italy.

Cell Cycle (Georgetown, Tex.)
|January 19, 2010
PubMed

Insights

Spindle assembly checkpoint (SAC) silencing requires proteolysis to resolve the Mad2-Cdc20 complex. This process involves okadaic acid-resistant phosphatases reversing key phosphorylations, ensuring accurate chromosome segregation.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Genetics

Background:

  • Anaphase initiation depends on the Anaphase Promoting Complex/Cyclosome (APC/C) and its coactivator Cdc20.
  • The spindle assembly checkpoint (SAC), involving proteins like Mad2 and BubR1, restrains APC/C(Cdc20) until spindle assembly to prevent chromosome segregation errors.

Purpose of the Study:

  • To investigate the mechanism of SAC silencing during mammalian cell division.
  • To elucidate how the Mad2-Cdc20 complex is resolved to allow for timely SAC inactivation and chromosome segregation.

Main Methods:

  • Analysis of Mad2-Cdc20 complex dynamics during prometaphase and metaphase in mammalian cells.
  • Investigation of the role of proteolysis in Mad2-Cdc20 complex dissociation.
  • Assessment of the effects of kinase inhibitors (CDK, Aurora) and phosphatase inhibitors (okadaic acid) on complex resolution.

Main Results:

  • The Mad2-Cdc20 complex peaks in prometaphase and its dissociation coincides with spindle assembly, requiring proteolysis.
  • Proteolysis is essential for resolving the Mad2-Cdc20 complex, not for metaphase spindle assembly.
  • Mad2-Cdc20 complex dissociation is reversed by CDK or Aurora kinase inhibition but is resistant to okadaic acid, suggesting phosphatase involvement.

Conclusions:

  • SAC silencing in mammalian cells necessitates proteolysis-dependent activation of specific phosphatases.
  • These phosphatases reverse phosphorylations that maintain the Mad2-Cdc20 complex, facilitating its disassembly.
  • This mechanism ensures accurate chromosome segregation by timely SAC inactivation.

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