Essential component of the mitotic spindle required for normal chromosome segregation and progression into anaphase. Required for chromosome alignment; normal timing of sister chromatid segregation; and maintenance of spindle pole architecture. In complex with SKAP; promotes stable microtubule- kinetochore attachments. May contribute to the regulation of separase activity. May regulate AURKA localization to mitotic spindle; but not to centrosomes and CCNB1 localization to both mitotic spindle and centrosomes. In non-mitotic cells; upon stress induction; inhibits mammalian target of rapamycin complex 1 (mTORC1) association and recruits the mTORC1 component RPTOR to stress granules (SGs); thereby preventing mTORC1 hyperactivation- induced apoptosis. May enhance GSK3B-mediated phosphorylation of other substrates; such as MAPT/TAU. {ECO:0000269|PubMed:11724960; ECO:0000269|PubMed:12356910; ECO:0000269|PubMed:17664331; ECO:0000269|PubMed:18055457; ECO:0000269|PubMed:21402792; ECO:0000269|PubMed:23953116}.