A non-canonical role of the inner kinetochore in regulating sister-chromatid cohesion at centromeres.

The 16-subunit Constitutive Centromere-associated Network (CCAN)-based inner kinetochore is well-known for connecting centromeric chromatin to the spindle-binding outer kinetochore. Here, we report a non-canonical role for the inner kinetochore in directly regulating sister-chromatid cohesion at centromeres. We provide biochemical, X-ray crystal structure, and intracellular ectopic localization evidence that the inner kinetochore directly binds cohesin, a ring-shaped multi-subunit complex that holds sister chromatids together from S-phase until anaphase onset. This interaction is mediated by binding of the 5-subunit CENP-OPQUR sub-complex of CCAN to the Scc1-SA2 sub-complex of cohesin. Mutation in the CENP-U subunit of the CENP-OPQUR complex that abolishes its binding to the composite interface between Scc1 and SA2 weakens centromeric cohesion, leading to premature separation of sister chromatids during delayed metaphase. We further show that CENP-U competes with the cohesin release factor Wapl for binding the interface of Scc1-SA2, and that the cohesion-protecting role for CENP-U can be bypassed by depleting Wapl. Taken together, this study reveals an inner kinetochore-bound pool of cohesin, which strengthens centromeric sister-chromatid cohesion to resist metaphase spindle pulling forces. Synopsis: The inner kinetochore is well-known for connecting centromeric chromatin to the microtubule-binding outer kinetochore. This work reveals a non-canonical role for the inner kinetochore in binding cohesin complexes, and strengthening centromeric cohesion to resist metaphase spindle pulling forces. The CENP-OPQUR complex of the constitutive inner kinetochore interacts with the cohesin complex. Mutation of the CENP-U motif that interacts with the composite interface between the Scc1 and SA2 subunits of the cohesin complex weakens centromeric cohesion, leading to a defect in maintaining metaphase sister-chromatid cohesion. CENP-U competes with the cohesin release factor Wapl for binding to the Scc1-SA2 interface, thereby antagonizing Wapl-mediated cohesin removal from metaphase centromeres. CENP-U and Sgo1 additively contribute to the strength of centromeric cohesion. CENP-U competes with the release factor Wapl for Scc1-SA2 binding, providing a localized Sgo1-independent cohesin protection mechanism. [ABSTRACT FROM AUTHOR]