How the state of spindle microtubule capture at the kinetochore is translated into mitotic checkpoint signaling remains largely unknown. In this paper, we demonstrate that the kinetochore-associated mitotic kinase BubR1 phosphorylates itself in human cells and that this autophosphorylation is dependent on its binding partner, the kinetochore motor CENP-E. This CENP-E–dependent BubR1 autophosphorylation at unattached kinetochores is important for a full-strength mitotic checkpoint to prevent single chromosome loss. Replacing endogenous BubR1 with a nonphosphorylatable BubR1 mutant, as well as depletion of CENP-E, the BubR1 kinase activator, results in metaphase chromosome misalignment and a decrease of Aurora B–mediated Ndc80 phosphorylation at kinetochores. Furthermore, expressing a phosphomimetic BubR1 mutant substantially reduces the incidence of polar chromosomes in CENP-E–depleted cells. Thus, the state of CENP-E–dependent BubR1 autophosphorylation in response to spindle microtubule capture by CENP-E is important for kinetochore function in achieving accurate chromosome segregation.
- Submitted: 28 February 2012
- Accepted: 20 June 2012
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