Figure 1.

Fine tuning between the mitotic protein kinases and protein phosphatases regulates mitotic progression. The relative activities of major mitotic protein kinases including Cdk1, AURKA, AURKB, and Plk1, indicated in blue spectrum, increase as the cells enter mitosis. This increase is accompanied by a relative decrease in the activities of major mitotic phosphatases including PP1, PP2A-B56 and PP2A-B55. While PP2A-B55 activity is completely inhibited by binding of its inhibitors ENSA and ARPP-19 at mitotic entry, PP2A-B56 is still active at localized complexes and regulates mitotic progression. Similarly, most of the PP1 activity is inhibited by Cdk1 dependent phosphorylation of its C-terminal Thr-320 residue at mitotic entry, but localized PP1 complexes remain active during mitosis. PP1 regains complete activity after the degradation of cyclin B and consequent decline of Cdk1 activity at metaphase-anaphase transition and controls the exit of cells from mitosis.