Apoptosis, also named programmed cell death, is a highly conserved physiological
mechanism. Apoptosis plays crucial roles in many life processes, such as tissue development, organ
formation, homeostasis maintenance, resistance against external aggression, and immune responses.
Apoptosis is regulated by many genes, among which Apoptosis Inhibitor-5 (API5) is an effective
inhibitor, though the structure of API5 is completely different from the other known Inhibitors
of Apoptosis Proteins (IAPs). Due to its high expression in many types of tumors, API5 has received
extensive attention, and may be an effective target for cancer treatment. In order to comprehensively
and systematically understand the biological roles of API5, we summarized the evolution
and structure of API5 and its roles in anti-apoptosis in this review.