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. Its depletion enhances the cytotoxic action of the chemotherapeutic drugs. Monomer. Interacts with FGF2 and ACIN1. Mainly nuclear. Can also be cytoplasmic. Additional isoforms seem to exist. Expressed in all tissues tested, including heart, brain, placenta, lung, liver, skeletal muscle, kidney and pancreas. Highest levels in heart, pancreas and placenta. Highly expressed in several cancers. Preferentially expressed in squamous cell carcinoma versus adenocarcinoma in non-small cell lung cancer. Two regions, an N-terminal (aa 96-107) and a C-terminal (aa 274-311) are required for binding FGF2. Acetylation at Lys-251 impairs antiapoptotic function. Belongs to the API5 family. Extended N-terminus.