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. Author manuscript; available in PMC: 2008 Jul 15.
Published in final edited form as: Arch Biochem Biophys. 2007 Feb 22;463(2):168–174. doi: 10.1016/j.abb.2007.01.033

Figure 2.

Figure 2

Role of XIAP in the extrinsic and intrinsic cell death signaling pathways. Two different pathways can initiate apoptosis. The death-receptor mediated (extrinsic) pathway involves the activation of caspase-8 following stimulation of the receptor by ligands such as Fas. The mitochondrial (intrinsic) pathway is initiated by a variety of stimuli including DNA damaging agents such as UV and chemotherapy resulting in the mitochondrial release of cytochrome c and subsequent activation of caspase-9. Both pathways converge to activate caspases- 3 and -7, effector caspases responsible for the death of the cell. XIAP regulates both pathways by its ability to directly bind and inhibit caspase-3, -7 and -9. The mitochondrial proteins, Smac and Omi, antagonize the caspase inhibitory properties of XIAP.