ITGB3BP is a transcription coregulator that can have both coactivator and corepressor functions. Isoform 1, but not other isoforms, is involved in the coactivation of nuclear receptors for retinoid X (RXRs) and thyroid hormone (TRs) in a ligand-dependent fashion. ITGB3BP acts as a transcriptional corepressor via its interaction with the NFKB1 NF-kappa-B subunit, possibly by interfering with the transactivation domain of NFKB1. It induces apoptosis in breast cancer cells, but not in other cancer cells, via a caspase-2 mediated pathway that involves mitochondrial membrane permeabilization but does not require other caspases. ITGB3BP may also act as an inhibitor of cyclin A-associated kinase. ITGB3BP may be involved in incorporation of newly synthesized CENPA into centromeres via its interaction with the CENPA-NAC complex.