Antiapoptotic factor that may have a role in protein assembly. Negatively regulates ACIN1. By binding to ACIN1, it suppresses ACIN1 cleavage from CASP3 and ACIN1-mediated DNA fragmentation. Also known to efficiently suppress E2F1-induced apoptosis (By similarity). Monomer. Interacts with FGF2 and ACIN1 (By similarity). Mainly nuclear. Down-regulated in vascular smooth muscle cells (vSMCs) treated with benzo[a]pyrene (BaP). Acetylation at Lys-251 impairs antiapoptotic function. Belongs to the API5 family.