Abstract
During cell division, the spindle checkpoint ensures accurate chromosome segregation by monitoring the kinetochore–microtubule interaction and delaying the onset of anaphase until each pair of sister chromosomes is properly attached to microtubules. The spindle checkpoint is deactivated as chromosomes start moving toward the spindles in anaphase, but the mechanisms by which this deactivation and adaptation to prolonged mitotic arrest occur remain obscure. Our results strongly suggest that Cdc28-mediated phosphorylation of Bub1 at T566 plays an important role for the degradation of Bub1 in anaphase, and the phosphorylation is required for adaptation of the spindle checkpoint to prolonged mitotic arrest.
The spindle checkpoint protects cells from aneuploidy by monitoring the status of the kinetochore-microtubule attachment. Defects in this checkpoint pathway and in kinetochore-microtubule attachment can cause substantial aneuploidy in cells. The duration of the mitotic arrest induced by the spindle checkpoint is not indefinite: cells eventually exit from mitosis and re-enter interphase. Because continued activation of the spindle checkpoint is lethal, adaptation to the spindle checkpoint arrest is essential so that cells have a chance for survival as opposed to certain death. However, adaptation of the spindle checkpoint has a flip side—adapted cells could have an increased chance of aneuploidy due to premature mitotic exit. Thus, it is essential that this mechanism be regulated appropriately. Despite the importance of understanding the adaptation of the spindle checkpoint, little is known to date about this mechanism. We found that Cdc28-mediated phosphorylation of Bub1 at T566 plays an important role for adaptation of the spindle checkpoint, a finding providing the molecular insight on how adaptation to prolonged mitotic arrest induced by the spindle checkpoint occurs.
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