Linking Kinetochore Attachment to Checkpoint Control: The Role of Aurora B in BubR1 Acetylation

We report here that Aurora B kinase is critical in BubR1 acetylation at K250, transducing kinetochore attachment status to spindle assembly checkpoint (SAC) activity. Aurora B phosphorylates BubR1 at serines 16 and 39 in an unattachment-dependent manner, which is a prerequisite for BubR1 acetylation at lysine 250 (K250). Utilizing a novel anti-AcK250 monoclonal antibody in structured illumination microscopy (SIM), we reveal that BubR1 acetylation is associated with kinetochore expansion, evidenced by crescent-shaped volume increase of ZW10 and Mad2 surrounding the kinetochore. Furthermore, K250-BubR1 acetylation enhances its interaction with CENP-E, a kinesin crucial for chromosome alignment through facilitating end-on attachment. Disrupting Aurora B-mediated phosphorylation of Ser16/39 impaired K250 acetylation, compromising both fibrous corona polymerization and mitotic checkpoint complex (MCC) maintenance. Conversely, introducing K250 acetylation mimetic form rescued MCC and fibrous corona in cells expressing phosphorylation-deficient S16A/S39A mutants. Our findings reveal Aurora B-BubR1 acetylation axis as a critical SAC signaling pathway, interlinking unattachment sensing with kinetochore expansion and SAC activity. We propose that this stepwise phosphorylation-acetylation on BubR1 constitutes a crucial part of SAC signaling code, transducing unattachment signal to fibrous corona polymerization and SAC activity. This phosphorylation-acetylation cascade in BubR1 offers potential therapeutic targets in treating cancers of chromosome instability.