FIG. 2.

Extrinsic and intrinsic pathways of cell death. Initiation of the extrinsic apoptotic pathway through FasL results in activation of capase-8. Activated caspase-8 cleaves and activates executioner caspases-3 and - 7, resulting in cell death. Caspase-8 can also cleave and activate Bid, resulting in initiation of the intrinsic apoptotic pathway. Initiation of the intrinsic apoptotic pathway occurs when BH3-only proteins diminish the prosurvival function of antiapoptotic BCL-2 family members resulting in BAX/BAK-dependent mitochondrial outer-membrane permeabilization (MOMP). MOMP results in cytochrome c release, apoptosome formation, caspase-9 activation, and cell death.