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Background
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Apoptosis plays a major role in normal organism development, tissue homeostasis, and removal of damaged cells. This process can be interrupted by a family of proteins termed inhibitors of apoptosis (IAP). Members of the IAP family contain one to three copies of an approximately 70 amino acid motif termed baculovirus IAP repeat (BIR). These BIRs promote protein-protein interactions with members of the TRAF family of signaling molecules as well as caspases such as caspase-3, -7, and -9, and inhibiting the apoptotic activity of these proteins. Neuronal apoptosis inhibitor protein (NAIP) was the first human inhibitor of apoptosis protein (IAP) identified and was discovered by its association with the neurodegenerative disorder spinal muscular atrophy. Other IAPs include the X-linked protein XIAP/ILP-1, the related cIAP protein which exists in two distinct isoforms, Livin (also known as KIAP as it is highly expressed in kidney), Survivin/TIAP, ILP-2, and Bruce, an extremely large IAP with ubiquitin-conjugating enzyme activity. Upregulation of these proteins inhibit the normal apoptotic process and thus may be involved in human diseases such as cancer.
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