Mapping Proximity Associations of Core Spindle Assembly Checkpoint Proteins

The spindle assembly
checkpoint (SAC) is critical for sensing defective
microtubule–kinetochore attachments and tension across the
kinetochore and functions to arrest cells in prometaphase to allow
time to repair any errors before proceeding into anaphase. Dysregulation
of the SAC leads to chromosome segregation errors that have been linked
to human diseases like cancer. Although much has been learned about
the composition of the SAC and the factors that regulate its activity,
the proximity associations of core SAC components have not been explored
in a systematic manner. Here, we have taken a BioID2-proximity-labeling
proteomic approach to define the proximity protein environment for
each of the five core SAC proteins BUB1, BUB3, BUBR1, MAD1L1, and
MAD2L1 in mitotic-enriched populations of cells where the SAC is active.
These five protein association maps were integrated to generate a
SAC proximity protein network that contains multiple layers of information
related to core SAC protein complexes, protein–protein interactions,
and proximity associations. Our analysis validated many known SAC
complexes and protein–protein interactions. Additionally, it
uncovered new protein associations, including the ELYS–MAD1L1
interaction that we have validated, which lend insight into the functioning
of core SAC proteins and highlight future areas of investigation to
better understand the SAC.