Apollon Promotes Early Mitotic Cyclin A Degradation Independent of the Spindle Assembly Checkpoint [Protein Synthesis and Degradation]

December 3rd, 2013 by Kikuchi, R., Ohata, H., Ohoka, N., Kawabata, A., Naito, M.

In the mammalian cell cycle, both cyclin A and cyclin B are required for the entry into mitosis, and their elimination is also essential to complete the process. During mitosis, cyclin A and cyclin B are ubiquitylated by the anaphase promoting complex/cyclosome (APC/C) and then subjected to proteasomal degradation. However, cyclin A, but not cyclin B, begins to be degraded in the prometaphase when APC/C is inactivated by the spindle assembly checkpoint (SAC). Here we show that Apollon (also known as BRUCE or BIRC6) plays a role in SAC-independent degradation of cyclin A in early mitosis. Apollon interacts with cyclin A that is not associated with cyclin-dependent kinases (CDKs). Apollon also interacts with APC/C, and facilitates cyclin A ubiquitylation. In Apollon-deficient cells, mitotic degradation of cyclin A is delayed, and total but not CDK-bound cyclin A level was increased. We propose Apollon to be a novel regulator of mitotic cyclin A degradation independent on SAC.