XIAP

There is also crosstalk between the two pathways above the mitochondria. The BH3-only protein BID is cleaved by caspase-8 and -10 which yields truncated BID (tBED), the active pro-apoptotic fragment of BID. Thereby, even in cells in which the direct apoptosis pathway which result from death receptor crosslinking is blocked, e.g. by high expression levels ofthex-linked IAP (XIAP), the activity of tBED on mitochondria can result in the activation of caspase-3 because the IAP-imposed block on full caspase-3 activation and caspase-9 activity at the apoptosome is released by Smac/ DIABLO. 

Eckelman BP, Salvesen G, Scott FL (2006) Human inhibitor of apoptosis proteins why XIAP is the black sheep of the family. EMBO Rep 7 988-994... 

Nikolovska-Coleska Z, Xu L, Hu Z, et al. Discovery of embelin as a cell-permeable, small-molecular weight inhibitor of XIAP through structure-based computational screening of a traditional herbal medicine three-dimensional structure database. J Med Chem 2004 47 2430-2440. 

Holcik, M., and Korneluk, R. G. (2000). Functional characterization of the X-linked inhibitor of apoptosis (XIAP) internal ribosome entry site element Role of La autoantigen in XIAP translation. Mol. Cell Biol. 20, 4648-4657. 

Antiapoptotic proteins. There are many different intracellular proteins that can prevent apoptosis by inhibiting specific steps in the cell death process. These include Bcl-2 family members such as Bcl-2 and Bcl-xL which can stabilize (mitochondrial, ER and plasma) membranes (Bcl-2 may also have intrinsic antioxidant activity). Other proteins, IAPs such as XIAP (X-linked) and NIAP (neuronal), which can directly inhibit caspases [31]. Additional examples of antiapoptotic proteins include protease inhibitors such as calpastatin, and protein chaperones such as GRP-78 and heat shock protein (HSP)-70. 

Fig. 4.4. Representative domains and interac- acting proteins are listed directly below the tions of members of RING finger families. In various domains. RING finger indicated by RF. (A-D) underlines indicate areas of interactions CARD domain not found in XIAP. with other proteins. In (E) representative inter-...

Suzuki, Y., et al., A serine protease, FItrA2, is released from the mitochondria and interacts with XIAP, inducing cell death. Mol Cell, 2001, 8(3), 613-21. 

MacFarlane, M., et al., Proteasome-mediated Degradation of Smac during Apoptosis XIAP Promotes Smac Ubiquitination in Vitro. J Biol Chem,... 

Supportive evidence comes from a study showing that intraventricular administration of z-VADfluoromethylketone (fmk), a pan-caspase inhibitor increases the lifespan of SODl transgenic mice by approximately 25% (Li et al, 2000). Furthermore, overexpression of XIAP, a mammalian inhibitor of caspases 3,7 and 9, in spinal motor neurons of mutant SODl mice attenuated disease progression without delaying onset, whilst expression of p35, a baculoviral caspase inhibitor that does not inhibit caspase-9, delayed onset without decreasing disease progression (Inoue et al, 2003). Moreover, caspase-9 was activated in spinal motor neurons of ALS patients. 

Tran J, Rak J, Sheehan C, et al. Marked induction of the IAP family antiapoptotic proteins surviving and XIAP by VEGF in vascular endothelial cells. Biochem Biophys Res Commun 1999 264(3) 781-788. 

Schimmer, A. D., Dalili, S., Riedl, S. J. (2006) Targeting XIAP for the treatment of malignancy. Cell Death Different 13, 179-188. 

This kind of interaction can be considered as the most challenging among our application examples because it is intrinsically characterized by the lowest degree of information [14]. We demonstrate the application of the GBPM procedure to a member of a family of proteins involved in the regulation of apoptosis, the X-linked inhibitor of apoptosis (XIAP). Its third baculovirus IAP repeat domain (BIR3) recognizes compounds 1-5 as shown in Fig. 7.2. 

Thus the GBPM approach was successfully applied to the XIAP application example, clearly indicating the most relevant features for the BIR3 domain interaction. Such information was derived starting from only one model and was able to recognize other XIAP BIR3 domain ligands. 

Huang, Y., Park, Y.C., Rich, R. L., Segal, D., Myszka, D.G., Wu, H. Stmctural basis of caspase inhibition by XIAP differential roles of the linker versus the BIR domain. Cell. 2001, 104, 781-790. 

There are just a few studies of the use of caspase inhibitors to prevent apoptosis. Most studies concentrate on the expression of proteins of the IAP family (XIAP being the most noticeable) and the viral components p35 and CrmA (Vives et al., 2003a). CrmA, encoded by the smallpox virus, is a pseudo-substrate for serine and cysteine proteases. It inhibits caspases 1, 8, and 10 in several cell types (Sauerwald et al., 2003). p35 is a wide-spectrum caspase inhibitor encoded by baculoviruses, and it also behaves as a pseudo-substrate, inhibiting caspases 1, 3, 6, 7, 8, and 10 (Zhou et al., 1998). XIAP is the most potent member of the IAP family. It is found in the mammalian genome and is responsible for the inhibition of caspases 3, 7, and 9 (Sauerwald et al., 2002). An increased protective effect is found in CHO and HEK-293 cells expressing a XIAP mutant resistant to degradation (XIAP-BIR123) when compared with the wild-type protein (Sauerwald et al., 2002). 

Bratton SB, Walker G, Srinivasula SM, Sun XM, Butterworth M, Alnemri ES, Cohen GM (2001), Recruitment, activation and retention of caspases-9 and -3 by Apaf-1 apoptosome and associated XIAP complexes, EMBO J. 20 998-1009. 

Sauerwald TM, Betenbaugh MJ, Oyler GA (2002), Inhibiting apoptosis in mammalian cell culture using the caspase inhibitor XIAP and deletion mutants, Biotechnol. Bioeng. 77 704-716. 

IAP Inhibitor of apoptosis proteins XIAP, APB, ILP, HILP, HIAP2,... 

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