BH3-only proteins in apoptosis and beyond: an overview

BH3-only Bcl-2 Family proteins are effectors of canonical mitochondrial Apoptosis. They discharge their pro-apoptotic functions through BH1-3 pro-apoptotic proteins such as Bax and Bak, while their activity is suppressed by BH1-4 anti-apoptotic Bcl-2 Family members. The precise mechanism by which BH3-only proteins mediate Apoptosis remains unresolved. The existing data are consistent with three mutually non-exclusive models (1) displacement of BH1-3 proteins from complexes with BH1-4 proteins; (2) direct interaction with and conformational activation of BH1-3 proteins; and (3) membrane insertion and membrane remodeling. The BH3-only proteins appear to play critical roles in restraining Cancer and inflammatory diseases such as rheumatoid arthritis. Molecules that mimic the effect of BH3-only proteins are being used in treatments against these diseases. The cell death activity of a subclass of BH3-only members (BNIP3 and BNIP3L) is linked to cardiomyocyte loss during heart failure. In addition to their established role in Apoptosis, several BH3-only members also regulate diverse cellular functions in cell-cycle regulation, DNA repair and metabolism. Several members are implicated in the induction of Autophagy and autophagic cell death, possibly through unleashing of the BH3-only autophagic effector Beclin 1 from complexes with Bcl-2/Bcl-xL. The Chapters included in the current Oncogene Review issues provide in-depth discussions on various aspects of major BH3-only proteins.