Plays a role in mitotic exit and cytokinesis (PubMed:16198290, PubMed:17853893). Recruits PDCD6IP and TSG101 to midbody during cytokinesis. Required for successful completion of cytokinesis (PubMed:17853893). Not required for microtubule nucleation (PubMed:16198290). Plays a role in the development of the brain and kidney (PubMed:28264986). Homodimer (PubMed:16406728). Interacts (phosphorylated on Ser-425 and Ser-428) with PLK1 (PubMed:16198290). Interacts with AKAP9/CG-NAP; the interaction occurs in interphase and is lost upon mitotic entry (PubMed:16198290). Interacts with PCNT/Kendrin; the interaction occurs in interphase and is lost upon mitotic entry (PubMed:16198290). Directly interacts with PDCD6IP; this interaction is required for PDCD6IP targeting to the midbody; CEP55 binds PDCD6IP in a 2:1 stoichiometry; PDCD6IP competes with TSG101 for the same binding site (PubMed:17853893, PubMed:17556548, PubMed:18641129, PubMed:18948538). Interacts with TSG101; TSG101 competes with PDCD6IP for the same binding site; interaction is required for cytokinesis but not for viral budding (PubMed:17853893, PubMed:17556548, PubMed:18948538). Interacts with MVB12A, VPS37B, VPS37C and VPS28 (PubMed:17853893). Present at the centrosomes at interphase. A small portion is associated preferentially with the mother centriole, whereas the majority localizes to the pericentriolar material. During mitosis, loses affinity for the centrosome at the onset of prophase and diffuses throughout the cell. This dissociation from the centrosome is phosphorylation-dependent. May remain localized at the centrosome during mitosis in certain cell types. Appears at the cleavage furrow in late anaphase and in the midbody in cytokinesis. Expressed in embryonic brain (PubMed:28264986). Expressed in fetal brain ganglionic eminence, kidney tubules and multinucleate neurons in the temporal cortex (PubMed:28264986). Expressed in adult brain, cerebellum, kidney tubules, intestine and muscles (at protein level) (PubMed:28295209, PubMed:28264986). Widely expressed, mostly in proliferative tissues. Highly expressed in testis. Intermediate levels in adult and fetal thymus, as well as in various cancer cell lines. Low levels in different parts of the digestive tract, bone marrow, lymph nodes, placenta, fetal heart and fetal spleen. Hardly detected in brain. There is a hierachy of phosphorylation, where both Ser-425 and Ser-428 are phosphorylated at the onset of mitosis, prior to Ser-436. Phosphorylation at Ser-425 and Ser-428 is required for dissociation from the centrosome at the G2/M boundary. Phosphorylation at the 3 sites, Ser-425, Ser-428 and Ser-436, is required for protein function at the final stages of cell division to complete cytokinesis successfully. The disease is caused by variants affecting the gene represented in this entry. Truncated N-terminus.