Coordination of late stages of cytokinesis by the inhibitor of apoptosis protein BRUCE

Cytokinesis involves the formation of a cleavage furrow, followed
by abscission, the cutting of the midbody channel, the final bridge
between dividing cells. Recently, the midbody ring became known as
central for abscission, but its regulation remains enigmatic. This
study identifies BRUCE, a 528 kDa multi-functional protein, which
processes ubiquitin-conjugating activity, as a major regulator of
abscission. During cytokinesis, BRUCE moves from the vesicular
system to the midbody ring and serves as a platform for the
membrane delivery machinery and mitotic regulators. Depletion of
BRUCE in cell cultures causes defective abscission and
cytokinesis-associated apoptosis, accompanied by a block of
vesicular targeting and defective formation of the midbody and the
midbody ring. Notably, ubiquitin relocalizes from midbody
microtubules to the midbody ring during cytokinesis, and depletion
of BRUCE disrupts this process. Therefore, BRUCE coordinates
multiple steps required for abscission, and ubiquitylation might
represent the crucial trigger.