No abstract

Deubiquitinase BRISC complex plays important role in the maintenance of spindle structure and function; however, the underlying mechanism remains largely undefined. Here we demonstrated that MERIT40, a core component of BRISC complex, directly interacts with the RXXPEG motif in the ARC-V domain of Tankyrase1(TNKS1). Mutation of the RXXPEG motif in the MERIT40 (R28A) disrupted its interaction with TNKS1. Consistent with these data, R28A mutant cells displayed multiple mitotic defects including aberrant spindle assembly and chromosome misalignment. These results support a critical role of RXXPEG motif of MERIT40 in BRISC-mediated regulation of TNKS1 function during spindle assembly.

Faithful chromosome segregation requires bi-oriented kinetochore-microtubule attachment on the metaphase spindle. Aurora B kinase, the catalytic core of the chromosome passage complex (CPC), plays a crucial role in this process. Aurora B activation has widely been investigated in the context of protein phosphorylation. Here, we report that Aurora B is ubiquitinated in mitosis through lysine-63 ubiquitin chains (K63-Ub), which is required for its activation. Mutation of Aurora B at its primary K63 ubiquitin site inhibits its activation, reduces its kinase activity, and disrupts the association of Aurora B with other components of CPC, leading to severe mitotic defects and cell apoptosis. Moreover, we identify that BRCC36 isopeptidase complex (BRISC) is the K63-specific deubiquitinating enzyme for Aurora B. BRISC deficiency augments the accumulation of Aurora B K63-Ubs, leading to Aurora B hyperactivation and erroneous chromosome–microtubule attachments. These findings define the role of K63-linked ubiquitination in regulating Aurora B activation and provide a potential site for Aurora B-targeting drug design.