Coregulation of NDC80 Complex Subunits Determines the Fidelity of the Spindle-Assembly Checkpoint and Mitosis.

Unlabelled: NDC80 complex (NDC80C) is composed of four subunits (SPC24, SPC25, NDC80, and NUF2) and is vital for kinetochore-microtubule (KT-MT) attachment during mitosis. Paradoxically, NDC80C also functions in the activation of the spindle-assembly checkpoint (SAC). This raises an interesting question regarding how mitosis is regulated when NDC80C levels are compromised. Using a degron-mediated depletion system, we found that acute silencing of SPC24 triggered a transient mitotic arrest followed by mitotic slippage. SPC24-deficient cells were unable to sustain SAC activation despite the loss of KT-MT interaction. Intriguingly, our results revealed that other subunits of the NDC80C were co-downregulated with SPC24 at a posttranslational level. Silencing any individual subunit of NDC80C likewise reduced the expression of the entire complex. We found that the SPC24-SPC25 and NDC80-NUF2 subcomplexes could be individually stabilized using ectopically expressed subunits. The synergism of SPC24 downregulation with drugs that promote either mitotic arrest or mitotic slippage further underscored the dual roles of NDC80C in KT-MT interaction and SAC maintenance. The tight coordinated regulation of NDC80C subunits suggests that targeting individual subunits could disrupt mitotic progression and provide new avenues for therapeutic intervention.

Implications: These results highlight the tight coordinated regulation of NDC80C subunits and their potential as targets for antimitotic therapies.