Caspases are responsible for the deliberate disassembly of the cell into apoptotic bodies during apoptosis. Caspases are present as inactive pro-enzymes that are activated by proteolytic cleavage. Caspases 8, 9, 12 and 3 are situated at pivotal junctions in apoptosis pathways. Caspase 8 initiates disassembly in response to extracellular apoptosis-inducing ligands and is activated in a complex associated with the cytoplasmic death domain of many cell surface receptors for the ligands. Caspase 9 activates disassembly in response to agents or insults that trigger the release of cytochrome c from mitochondria and is activated when complexed with apoptotic protease activating factor 1 (APAF-1) and extra-mitochondrial cytochrome c. Caspase-12 appears to be activated by ER stress. All three caspase pathways lead to caspase-3 activation. Caspase 3 amplifies caspase 8, caspase 9, and caspase-12 initiation signals into full-fledged commitment to disassembly. Caspase 8 and caspase 9 activate caspase 3 by proteolytic cleavage and caspase 3 then cleaves vital cellular proteins or other caspases.

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