Figure 1.

 The extrinsic or death receptor (DR) pathway. Pro‐apoptotic ligands, death signals, and Fas bind to Fas or TNFRs. The intracellular portion of the DR is known as the death domain (DD). Bunching of the receptor‐ligand complexes groups their DDs and a binding site for an adaptor protein is formed. This ligand‐receptor‐adaptor protein complex is called the death‐inducing signaling complex (DISC). It recruits and assembles initiator caspase‐8 that releases active caspase enzyme molecules into the cytosol. Here, they activate the effector caspases‐3 and ‐7, resulting in nuclear protein cleavage and the initiation of apoptosis. FasL, Fas ligand; TNFR tumor necrosis factor receptor; FADD, Fas‐associated death domain; TRADD, TNF‐associated death domain; c‐FLIP, FLICE‐like inhibitory protein; DISC, death‐inducing signaling complex.