Caspase-activation recruitment domain

Figure 18.3 The mammalian lAP family. The distinct domains are shown for each lAP. (BIR—baculovirus lAP repeat CARD-caspase activation recruitment domain RING—really interesting new gene zinc finger LRR—leucine rich repeat NOD-nucleotide-binding oligomerization domain).

So far ten catalytically active caspases have been reported in mouse (caspase-1, -2, -3, -6, -7, -8, -9, -11, -12,-14) and eleven in human (caspase-1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -14) (Fig. 1). Caspases are expressed as inactive proenzymes that contain an amino-terminal prodomain of variable length followed by two domains with conserved sequences a large subunit ( 20 kDa, p20) and a small carboxy-terminal subunit ( 10 kDa, plO). Caspases can be divided according to absence (-3, -6, -7, -14) or presence (-1, -2, -8, -9, -10, -11, -12) of an extended prodomain containing protein-protein interaction motifs belonging to the death domain (DD) superfamily, in particular the death effector domains (DED) and the caspase activation and recruitment domains (CARD). 

ALT, alanine aminotransferase ASC, apoptosis-associated speck-like protei containing a CARD AST, aspartate aminotransferase CARD, caspase activation and recruitment domains CD, Crohn s disease COP, CARD-only protein DD, death domain DED, death effector domains DIABLO, direct LAP-binding protein with low pi... 

Death domain (DD) superfamily consists of structurally related homotypic interaction motifs of approximately 90 amino acids. The motifs are organized in six antiparallel amphipathic a-helices, the so-called DD fold. The four members of the super family are the death domain (DD), the death effector domain (DED), the caspase activation and recruitment domain (CARD), and the Pyrin domain. All are important mediators for the assembly of caspase activating complexes. 

Recently Imai et al (1999) cloned a novel protein, FLASH, that contains a region with stmctural similarity to Apaf-1 and a duplicated domain similar to the DEDs of caspase-8. This region, designated DRD (DED-recruiting domain), would allow its interaction with caspase-8 and FADD and its recruitment to the DISC, where it is thought to participate in caspase-8 activation. 

Activation of the caspases requires the help of a number of cofactors that are also known as activators or adaptors. Different cofactors are involved depending on the trigger mechanism of caspase activation. A central function of the cofactors is to bring about aggregation and thus activation of the procaspases. This occurs by specific protein-protein interactions with the help of common structural motives. Examples of such motives are the death domains (DD), death effector domains (DED) and the caspase recruitment domains (CARD), which all have a similar structure of six a-heh-ces. 

Fig. 5. The execution phase of apoptosis. An apoptotic stimulus causes the release of cytochrome c from mitochondria. The first box contains the components required to activate caspase 9 card refers to the caspase-recruitment domain. Caspase 9 then activates caspase 3 (second box), which in turn activates caspase 6 (last box). The amino-acid sequences at the cleavage sites are shown. Caspases 3 and 6 also have a prodomain that is not present in the active protease in caspase 6 an additional cleavage removes a small portion of the middle of the protein. Various substrates of the caspases are shown, including the pathway by which caspase-activated deoxyribonuclease (CAD) is activated which in turn leads to DNA...

Extrinsic (death receptor) pathway of caspase activation during apoptosis involves the binding of death ligands to cell surface receptors (e.g., Fas/ CD95/Apo-l or TNF receptor), recruitment of adaptor molecules Fas-associated death domain (FADD) or TNF receptor-associated death domain (TRADD) to the cytosolic end of the receptor, and formation of the death-inducing signaling complex (DISC) at the plasma membrane. DISC recruits and activates the initiator caspases, caspase-8 or -10. 

Apoptosis PCR microarray is a relatively new methodology that uses real-time PCR to profile the expression of at least 112 key genes involved in apoptosis. The array includes the TNF ligands and their receptors members of the bcl-2, caspase, IAP, TRAF (TNF receptor associated factor), CARD (caspase activation and recruitment domain), death domain, death effector domain, and CIDE (cell death-inducing DFFA-like effector) families and genes involved in the p53 and ATM pathways. Also included in the evaluation are genes involved in anti-apoptosis. This assay allows for the evaluation of the expression of a focused panel of genes related to apoptosis. 

Caspase recruitment domain, mediates the formation of larger protein complexes via direct interactions between individual cards, involved in the regulation of caspase activation and apoptosis... 

Recruitment of the initiator procaspases into a multiprotein complex results from a regulated series of protein-protein interactions mediated by interaction modules . Four types of interaction modules are involved in the activation of initiator caspases and thus play important roles in the initiation of apoptosis (review Weber and Vin-cenz, 2001). These domains have been named the death domain (DD),, the death effector domain (DED), the caspase activation and recruitment domain (CARD), and the less characterized pyrin domain. The domains are found on several components of the apoptotic signaling pathways and mediate homotypic protein-protein interactions, i. e., a given module will interact only with a member of the same family and not with members of the other families. Since members of the same module are found on different proteins, these modules mediate the assembly of hetero-oligomeric protein complexes. As examples, DDs are found on death receptors and their cofactors, D EDs on cofactors and the initiator caspase-8, and CARDS on cofactors, caspase-2, and caspase-9. 

An alternative pathway involves the adaptor protein RAIDD (RIP-associated ICH/CED-3-homologous protein with a death domain), which is recruited by the Fas receptor via its C-terminal DD. At its N-terminus RAIDD contains a caspase recruitment domain (CARD) that is also present in procaspase-2. The adaptor protein TRADD (TNFR-associated death domain), most effectively bound following ligation of TNFR-1, functions as a platform that recruits several signalling molecules, such as TRAF-2 (the TNFR-associated factor-2), RIP (the receptor-interacting protein), both of which stimulate activation of NF-kB (the nuclear factor k B) and also FADD, which mediates activation of apoptosis (Ashkenazi and Dixit, 1998). TRAMP has been reported to bind TRADD, TRAF-2, FADD and caspase-8. TRAIL can bind either to a TRAIL-Rl trimer or to a TRAIL-R2 trimer, which recruit FADD and caspase-8 or caspase-10 (Schneider et al., 1997). 

Novel pathways include apoptotic protease-activating factor-1 (APAF-1) with an N-terminal caspase recruitment domain (CARD) recruiting caspase-9, or the RIP-like kinase CARDIAK specifically interacting with the CARD of caspase-1 (Thome et al., 1998). The overall structure of the... 

Fig. 1. Modulation of apoptosis by v-FLIP and v-Bcl-2. v-FLIPs specifically inhibit apoptosis mediated by death receptors. v-lCA specifically targets caspase-8 and inhibits its activation. v-Bcl-2 and vMIA inhibit those apoptotic pathways that are signaled through mitochondrial release of cytochrome c. FADD, Fas-associated death domain FLICE, FADD-like interleukin-converting enzyme CARD, cas-pase-recruiting domain PTPC. permeability transition pore complex FLIP, FLICE-inhibitory protein vie A, viral inhibitor of caspase 8-induced-apoptosis MIA. viral mitochondrial inhibitor of apoptosis Apcif-l, apoptotic protease-activating factor 1...

FasL binding induces the oligomerization of Fas via their death domains (DD) and the recruitment to the clustered receptors of the DD-containing adaptor molecule FADD. FADD contains an additional caspase recruitment domain, called death effector domain (DED), that binds to the DED of procaspase-8. Its activation initiates a cascade of proteolytic cleavages, involving downstream... 

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