Aurora B maintains spherical shape of mitotic cells via simultaneously stabilizing myosin II and vimentin.

Cells round up when they enter mitosis and maintain this rounded morphology until they pass the spindle assembly checkpoint during anaphase. However, the mechanisms that regulate and maintain this transient spherical state remain unclear. In this study, we demonstrate that both astral microtubules and Aurora B kinase are required to maintain cortex stability during prometaphase. Simultaneous inhibition of astral microtubules and Aurora B leads to severe and continuous deformation of mitotic cells, resulting in micronuclei containing chromosomes after the cells exit mitosis. Mechanistically, active Aurora B kinase reduces the activity of myosin light chain kinase through phosphorylation, which in turn decreases the motor activity of myosin II. Additionally, Aurora B kinase regulates the distribution of actin at the cortex by phosphorylating the intermediate filament protein vimentin. Blocking these phosphorylation events disrupts the para-cortex localization of vimentin around the cortex and leads to the dislocalization of actin at the cortex. These regulatory effects occur in highly mobile cells expressing vimentin. In summary, we show that during mitosis, Aurora B kinase coordinates the interactions between microtubules, actin, and intermediate filaments to stabilize the cortex of rounded mitotic cells, ensuring the successful completion of mitosis.