Cell cycle expression of FLJ25439, a cytokinesis-associated protein, is mediated by D-box recognition and APC/C-Cdc20 regulated degradation.

The midbody is a transient structure forming out of the central spindle at late telophase. Both the midbody and central spindle have important functions ensuring completion of cytokinesis and defects in this process may lead to genetic diseases, including cancer. Thus, understanding the mechanisms that control cytokinesis during mitosis can reveal the key components taking part in some of the processes that promote accurate cell division. Our previous study showed that overexpression of FLJ25439 causes cytokinesis defect with midbody arrest and induces tetraploids with prolonged cell growth/cell cycle progression (Pan et al., 2015). Here, we extend our investigation with regard to the expression profile/regulation and cellular localization/function of FLJ25439 during mitosis/cytokinesis. Using a monoclonal antibody 2A4 we found that FLJ25439 expression is cell cycle-dependent and subjected to APC/C complex regulation. Furthermore, it is a novel substrate for the APC/C-Cdc20 complex and its degradation is proteasome-dependent through D-box recognition during mitotic exit. Immunofluorescence microscopy showed it is distributed at the central spindle and midbody, two structures considered important for completion of cell division, in telophase and cytokinesis, respectively, during cell cycle progression. Depletion of FLJ25439 expression revealed defects in chromosome alignment/segregation and delayed mitosis/cytokinesis progression. We thus conclude that FLJ25439 is a hitherto undiscovered factor involved in cytokinesis regulation.