Direct binding between BubR1 and B56-PP2A phosphatase complexes regulate mitotic progression.

Mitotic progression is tightly regulated to ensure accurate chromosome segregation. The spindle assembly checkpoint (SAC) prevents anaphase onset until all chromosomes are properly attached to spindle microtubules. BubR1 is a key SAC component that also stabilizes kinetochore-microtubule interactions. Prior research has shown that BubR1 inhibits Aurora B kinase activity, but the underlying mechanism remains unclear. This gap motivated the investigation of BubR1's interaction with phosphatases. No prior work had resolved how BubR1 recruits phosphatases to counteract Aurora B. This uncertainty drove the current study to explore BubR1's binding partners. Researchers propose that phosphatases may regulate Aurora B activity at kinetochores. The SAC's role in cell division is well established, but its phosphatase interactions are less understood. This paper addresses the mechanism of BubR1's phosphatase recruitment during mitosis.

The study aimed to clarify how BubR1 regulates Aurora B activity during mitosis. The specific problem is the lack of understanding regarding BubR1's phosphatase recruitment. Researchers sought to determine if BubR1 interacts with B56-PP2A phosphatase complexes. The motivation stems from the known role of BubR1 in stabilizing kinetochore attachments. The authors propose that BubR1 recruits phosphatases to counteract Aurora B. This hypothesis is based on prior observations of BubR1's dual functions. The goal was to identify the molecular mechanism of BubR1-phosphatase interaction. This work could provide insight into mitotic regulation and SAC function.

The researchers used biochemical assays to test BubR1's interaction with B56 subunits. They employed site-directed mutagenesis to alter conserved residues in BubR1. Phosphorylation status was analyzed using kinase inhibitors and phospho-specific antibodies. Binding assays confirmed the direct interaction between BubR1 and B56. Fluorescence microscopy tracked B56 localization to kinetochores. Cell cycle progression was assessed using time-lapse imaging. Metaphase plate formation was evaluated in mutant cells. The study combined molecular biology and cell imaging techniques.

BubR1 directly binds to B56 subunits through a conserved motif. The binding motif is phosphorylated by Cdk1 and Plk1 kinases. Two hydrophobic residues around serine 670 are essential for B56 binding. Mutation of these residues disrupts metaphase plate formation. Cells with mutated residues delay in mitosis, suggesting functional importance. Phosphorylation of serines 670 and 676 enhances B56 binding to BubR1. BubR1 recruits B56 to kinetochores, as shown by fluorescence imaging. These findings suggest that BubR1 targets B56 to counteract Aurora B activity.

The authors propose that BubR1 recruits B56-PP2A phosphatase complexes to kinetochores. This recruitment may counteract Aurora B kinase activity at improperly attached kinetochores. The conserved motif in BubR1 is phosphorylated by Cdk1 and Plk1. These phosphorylations are necessary for B56 binding and mitotic progression. The two hydrophobic residues around serine 670 are critical for B56 interaction. Mutation of these residues disrupts metaphase plate formation and delays mitosis. The study suggests a mechanism by which BubR1 stabilizes kinetochore attachments. These findings provide new insights into the regulation of mitotic checkpoints.