B-cell leukemia/lymphoma 2 (Bcl-2) was one of the first oncogenic proteins discovered to inhibit apoptosis. The Bcl-2 family of proteins plays a crucial role in the regulation of cell death in many eukaryotic systems. Bcl-2 is a 26 kD protein associated with cell survival.

Bcl-2 is localized within the outer mitochondrial membrane, endoplasmic reticulum, and the nuclear envelope, where it exerts cell survival functions within many cell types. These functions include ion-conducting channel formation, integral protection from cytotoxic agents, inhibition of proteins that activate caspases responsible for disassembling cells, as well as the ability to modulate cell cycle initiation.