Emerging understanding of Bcl-2 biology: Implications for neoplastic progression and treatment

Bcl-2, the founding member of a family of apoptotic regulators, was initially identified as the protein product of a gene that is translocated and overexpressed in greater than 85% of follicular lymphomas (FLs). Thirty years later we now understand that anti-apoptotic Bcl-2 family members modulate the intrinsic apoptotic pathway by binding and neutralizing the mitochondrial permeabilizers Bax and Bak as well as a variety of pro-apoptotic proteins, including the cellular stress sensors Bim, Bid, Puma, Bad, Bmf and Noxa. Despite extensive investigation of all of these proteins, important questions remain. For example, how Bax and Bak breach the outer mitochondrial membrane remains poorly understood. Likewise, how the functions of anti-apoptotic Bcl-2 family members such as eponymous Bcl-2 are affected by phosphorylation or cancer-associated mutations has been incompletely defined. Finally, whether Bcl-2 family members can be successfully targeted for therapeutic advantage is only now being investigated in the clinic. Here we review recent advances in understanding Bcl-2 family biology and biochemistry that begin to address these questions.