Regulation of Aurora B
Aurora B complexes with two other proteins, Survivin and INCENP. Each of the three components of the complex is required for the proper localization and function of the other two. INCENP stimulates Aurora B kinase activity. Survivin might do the same.
Localization of Aurora B to the centromere during prometaphase and metaphase requires phosphorylation of the mammalian kinetochore-specific histone-H3 variant centromere protein A (CENP-A). CENP-A associates with the centromere and is necessary for assembly of the kinetochore. Phosphorylation of CENP-A at serine 7 by Aurora A kinase recruits Aurora B to the centromere. Aurora B, itself, can also phosphorylate CENP-A at the same residue once it is recruited (see below).
Recently, topoisomerase II has been implicated in the regulation of Aurora B localization and enzymatic activity. This regulatory role may be directly associated with the role of topoisomerase II in disjoining sister chromatids prior to anaphase. In topoisomerase II-depleted cells, Aurora B and INCENP do not transfer to the central spindle in late mitosis. Instead, they remain tightly associated with the centromeres of non-disjoined sister chromatids. Also, cells deficient in topoisomerase II show significantly reduced Aurora B kinase activity. Inhibition of Aurora B due to loss of topoisomerase II seems to depend on BubR1 activity (see below).
Aurora B has been shown to bind to end-binding protein 1 (EB1), a protein that regulates microtubule dynamics. Indirect immunofluorescence showed that Aurora B and EB1 colocalize during anaphase on the central spindle and in the midbody during cytokinesis. Intriguingly, EB1 overexpression enhances Aurora B kinase activity, at least in part because EB1 blocks the dephosphorylation/inactivation of Aurora B by protein phosphatase 2A.
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