Component of the chromosomal passenger complex (CPC), a complex that acts as a key regulator of mitosis. The CPC complex has essential functions at the centromere in ensuring correct chromosome alignment and segregation and is required for chromatin-induced microtubule stabilization and spindle assembly. Acts as a scaffold regulating CPC localization and activity. The C-terminus associates with aurkb/aurora-B, the N-terminus associated with cdca8/borealin and/or cdca9/dasra-A tethers the CPC to the inner centromere, and the microtubule binding activity within the central SAH domain directs aurkb/aurora-B toward substrates near microtubules. Activates aurkb.