Therapeutics
Smac/DIABLO (subsequently referred to as Smac) and others. The assembled multiprotein complex, the apoptosome, induces the activation of caspase- 9. Both pathways converge in a common pathway that ultimately leads to apoptosis by inducing the executioner caspases, caspase-3 and -7, which, when not blocked by XIAP, result in DNA frag- mentation and cell death5.
In addition to the controlled activation of cas- pases, apoptosis is also regulated by IAP inhibition of activated caspases. IAPs regulate the activity of initiator and executioner caspases and are defined by the baculovirus IAP repeat (BIR) domains of approximately 70 to 80 amino acid residues that chelate zinc ions and mediate protein-protein inter- actions. Of the eight mammalian IAPs that have been identified, four are involved in regulating apoptosis: cIAP1, cIAP2, XIAP and ML-IAP. With the exception of ML-IAP with only one BIR domain, each contains three BIR domains at their amino-terminus, BIR1, BIR2 and BIR3. All four IAPs contain a carboxy-terminal RING (really interesting new gene) zinc-finger domain which has
E3 ubiquitin ligase activity. XIAP is the only IAP that inhibits the executioner caspases, caspase-3 and -7 and the initiator caspase-96,1.
IAPs and NF-B pathways – cell survival mechanism
cIAP1and cIAP2 play an important role in regulat- ing TNF-mediated NF-B signal transduction via the canonical and non-canonical NF-B pathways. cIAPs interact with TNF receptor-associated fac- tor 2 (TRAF2) and activate the canonical pathway through ubiquitylation of receptor-interacting pro- tein (RIP) kinase (RIP1/RIPK1). The non-canonical pathway is inhibited by the cIAPs, TRAF2 and TRAF3 via ubiquitylation and degradation of NF- B-inducing kinase (NIK). The activated canonical pathway as well the inactivated non-canonical NF- B pathways influence the expression pattern of a variety of transcription factors that participate in immune responses, inflammation, cell growth, sur- vival and development1. The mammalian NF-B family includes five members that form various transcription regulating complexes. Importantly,
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10 Du, C, Fang, M, Li, Y, Li, L, Wang, X. Smac, a mitochondrial protein that promotes cytochrome c- dependent caspase activation by eliminating IAP inhibition. Cell. 2000 Jul 7;102(1):33-42. 11Verhagen, AM, Ekert, PG, Pakusch, M, Silke, J, Connolly, LM, Reid, GE, Moritz, RL, Simpson, RJ, Vaux, DL. Identification of DIABLO, a mammalian protein that promotes apoptosis by binding to and antagonizing IAP proteins. Cell. 2000 Jul 7;102(1):43-53. 12 Chai, J, Du, C, Wu, JW, Kyin, S, Wang, X, Shi, Y. Structural and biochemical basis of apoptotic activation by Smac/DIABLO. Nature. 2000 Aug 24;406(6798):855-62.
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HIGH ACHIEVE
THROUGHPUT ANALYSIS
© Agilent Technologies, Inc. 2011 Drug Discovery World Fall 2011 39
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