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Ubiquitination by the anaphase-promoting complex drives spindle checkpoint inactivation


Eukaryotic cells rely on a surveillance mechanism known as the spindle checkpoint to ensure accurate chromosome segregation. The spindle checkpoint prevents sister chromatids from separating until all kinetochores achieve bipolar attachments to the mitotic spindle1,2,3. Checkpoint proteins tightly inhibit the anaphase-promoting complex (APC), a ubiquitin ligase required for chromosome segregation and progression to anaphase. Unattached kinetochores promote the binding of checkpoint proteins Mad2 and BubR1 to the APC-activator Cdc20, rendering it unable to activate APC. Once all kinetochores are properly attached, however, cells inactivate the checkpoint within minutes, allowing for the rapid and synchronous segregation of chromosomes4. How cells switch from strong APC inhibition before kinetochore attachment to rapid APC activation once attachment is complete remains a mystery. Here we show that checkpoint inactivation is an energy-consuming process involving APC-dependent multi-ubiquitination. Multi-ubiquitination by APC leads to the dissociation of Mad2 and BubR1 from Cdc20, a process that is reversed by a Cdc20-directed de-ubiquitinating enzyme5. The mutual regulation between checkpoint proteins and APC leaves the cell poised for rapid checkpoint inactivation and ensures that chromosome segregation promptly follows the completion of kinetochore attachment. In addition, our results suggest a mechanistic basis for how cancer cells can have a compromised spindle checkpoint without corresponding mutations in checkpoint genes6.

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Figure 1: UbcH10 activates CP-APC for substrate ubiquitination and degradation.
Figure 2: UbcH10 catalyses the dissociation of checkpoint components from APC.
Figure 3: Disassembly of checkpoint complexes requires APC-dependent multi-ubiquitination.
Figure 4: p31 comet lowers the threshold for UbcH10-mediated checkpoint inactivation.


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We are grateful to H. Yu, F. McKeon, R. King and P. Sorger for generous gifts of reagents, and to F. Stegmeier and S. Elledge for sharing results before publication. We thank members of the Kirschner laboratory, especially P. Jorgensen and M. Springer for helpful discussions. We thank P. Jorgensen, J. Son and J. Schaletzky for critical reading of the manuscript. S.K.R. acknowledges the support of the Medical Scientist Training Program. M.R. was supported by an EMBO long-term fellowship and by a fellowship of the Human Frontiers Science Organization. This work was supported by grants from the National Institutes of Health to M.W.K.

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Correspondence to M. W. Kirschner.

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Reddy, S., Rape, M., Margansky, W. et al. Ubiquitination by the anaphase-promoting complex drives spindle checkpoint inactivation. Nature 446, 921–925 (2007).

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