Cysteine aspartyl proteases related to the C. elegans CED-3 death protein comprise the caspase family. All are expressed as proenzymes which are activated by proteolysis. With respect to their roles in apoptosis, Caspases can be subdivided into initiator (Caspases 8, 9, 10) and effector (Caspases 3, 6, 7) caspases, depending on whether they are activated by receptor clustering (initiator) or by mitochondrial permeability transition (effector).
Effector caspases, most notably Caspase 3, cleave numerous substrates to effect the morphological changes associated with apoptosis. Among Caspase 3 substrates are DFF45/ICAD, which frees up the DNAse subunit of DFF to cause chromatin degradation, as well as gelsolin, PAK2, D4GDI, all of which are involved in cytoskeletal organization, nuclear lamins and PARP. The significance of PARP cleavage is not clear, but it is an excellent marker for caspase activation and the presumption of ongoing apoptosis.