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. Major effector of the TTK kinase in the control of attachment-error-correction and chromosome alignment. May form homooligomers and homodimers. Component of the chromosomal passenger complex (CPC) composed of at least BIRC5/survivin, CDCA8/borealin, INCENP, AURKB or AURKC; in the complex forms a triple-helix bundle-based subcomplex with INCENP and BIRC5 (PubMed:17956729). Interacts with SENP3, UBE2I and RANBP2. Interacts (phosphorylated) with SGO1 and SGO2; the association is dependent on CDK1. Localizes on chromosome arms and inner centromeres from prophase through metaphase and then transferring to the spindle midzone and midbody from anaphase through cytokinesis. Colocalizes with SENP3 in the nucleolus in interphase cells. Cell-cycle regulated. Increases during G2/M phase and then reduces after exit from M phase. The C-terminal region (aa 207-280) represents the dimerization motif. Phosphorylated by TTK, essentially at Thr-88, Thr94, Thr-169 and Thr-230. Phosphorylation (probably by CDK1) promotes targeting of the CPC to centromeric DNA. Sumoylated by UBE2I and RANBP2. Desumoylated by SENP3 through the removal of SUMO2 and SUMO3. Cells lacking CDCA8 display a slight decrease in histone H3 'Ser-10' phosphorylation, suggesting that the CPC complex mediates phosphorylation of 'Ser-10' of histone H3. Belongs to the borealin family.