BubR1 is a central component of the spindle assembly checkpoint (SAC) that inhibits progression into anaphase in response to improper kinetochore-microtubule interactions. In addition BubR1 also helps stabilize kinetochore-microtubule interactions by counteracting the Aurora B kinase but the mechanism behind this is not clear. Here we show that BubR1 directly binds to the B56 family of PP2A regulatory subunits through a conserved motif that is phosphorylated by Cdk1 and Plk1. Two highly conserved hydrophobic residues surrounding the S670 Cdk1 phosphorylation site are required for B56 binding and mutation of these residues prevents the establishment of a proper metaphase plate and delays cells in mitosis. Furthermore, we show that phosphorylation of S670 and S676 stimulates the binding of B56 to BubR1 and that BubR1 targets a pool of B56 to kinetochores. Our data suggests that BubR1 counteracts Aurora B kinase activity at improperly attached kinetochores by recruiting B56-PP2A phosphatase complexes.
Journal of Cell Science, 2013, Vol 126, p. 1086-1092