The NOD: a Signaling Module That Regulates Apoptosis and Host Defense Against Pathogens

The NOD: a signaling module that regulates apoptosis and host defense against pathogens

Naohiro Inohara1 and Gabriel NunÄ ez*,1

1Department of Pathology and Comprehensive Cancer Center, The University of Michigan Medical School, Ann Arbor, Michigan, MI 48109, USA

Nods, a growing family of proteins containing a molecule that induces systemic acquired resistance nucleotide-binding oligomerization domain (NOD), are (SAR) (Feys and Parker, 2000). In higher multicellular involved in the regulation of programmed cell death organisms, appropriate development and tissue home- (PCD) and immune responses. Members of the family ostasis require highly regulated activation of PCD. include Apaf-1, Ced-4, Nod1, Nod2, and the cytosolic Whereas PCD induced during the defense against products of plant disease resistance genes. The NOD pathogens in both animal and plants is accompanied module is homologous to the ATP-binding cassette by the production of pro-in¯ammatory molecules, that (ABC) found in a large number of proteins with diverse associated with tissue development and homeostasis is biological function. The centrally located NOD promotes devoid of an in¯ammatory response (Jacobson et al., activation of eector molecules through self-association 1997; Feys and Parker, 2000). Despite these dierences, and induced proximity of binding partners. The C- both types of PCD are associated with the induction of terminal domain of Nods serves as a sensor for similar morphological features including membrane intracellular ligands, whereas the N-terminal domain blebbing, cytosolic fragmentation, nuclear condensa- mediates binding to dowstream eector molecules and tion and fragmentation as well as biochemical events activation of diverse signaling pathways. Thus, Nods such as degradation of genomic DNA, proteolysis and activate, through the NOD module, diverse signaling redistribution of membrane lipids (Kerr et al., 1972; pathways involved in the elimination of cells via PCD Wyllie, 1980). These changes associated with PCD, and the host defense against pathogens. Oncogene generally referred as apoptosis, are largely due to the (2001) 20, 6473 ± 6481. activation of caspases, a family of cysteine proteases (NuÂnÄ ez et al., 1998; Kumar, 1999). Mammalian cells Keywords: apoptosis; Apaf-1/Nod1/CED4 family; pro- have more than 14 caspases and synthesize them as grammed cell death; ATPase/GTPases; NOD domain enzymatically inactive forms. Once an apical caspase such as caspase-8 or caspase-9 is activated, the protease activates downstream (eector) caspases and non- caspase proteases causing massive proteolytic activity in the cytosol and the orderly demise of the cell Introduction (Kumar, 1999). Therefore, activation of apical caspases is a critical step in that it determines cell fate and as Programmed cell death (PCD) or apoptosis plays a such is strictly regulated by speci®c regulatory critical role not only during embryonic development molecules. and cellular homeostasis in the adult, but also in the clearance of invading pathogens by host tissues (Weinrauch and Zychlinsky, 1999). Multicellular Ced-4 and Apaf-1 contain a NOD domain that is critical organisms have several host defense systems to prevent for functional activity proliferation and propagation of invading pathogens. One of the most ancient types of immune reactions is Early genetic studies in the nematode Caenorhabditis the elimination of pathogen infected cells by PCD elegans revealed molecules which play critical roles in (Weinrauch and Zychlinsky, 1999). In addition, the induction, regulation and execution of PCD during infected host cells produce defensins and pro-in¯am- worm development. Ced-3 and Ced-4 are required for matory cytokines that play an important role in the the execution step of PCD, whereas Ced-9 protects clearance of the invading pathogen. In plants, patho- cells from PCD during normal development (Ellis and gens trigger a specialized form of PCD known as the Horvitz, 1986; Metzstein et al., 1998). Homology hypersensitive response (HR) and the production of analysis and functional assays demonstrated that defensins and salicylic acid, a phenolic signaling Ced-3 is a caspase, Ced-4 is the activator of Ced-3 and Ced-9 is a pro-survival member of the Bcl-2 family (Yuan and Horvitz, 1992; Yuan et al., 1993; *Correspondence: G NunÄ ez; E-mail: [email protected] Hengartner and Horvitz, 1994; Chinnaiyan et al., Proteins containing nucleotide-binding oligomerization domains N Inohara and G NunÄez 6474 1997a). Both Ced-3 and Ced-4 have N-terminal Ced-4 and Apaf-1 activate target caspases through caspase-recruitment domains (CARDs) that associate induced proximity with each other through homophilic interaction between their CARDs (Hofmann et al., 1997; Wu et The structural similarity between Ced-4 and Apaf-1 al., 1997a; Irmler et al., 1997; Seshagiri et al., 1998). re¯ects the fact that both molecules use a common Ced-4 has an additional module, the nucleotide-binding mechanism to activate their target caspases. The N- domain (NBD), which is essential for Ced-3 activation terminal CARD of each protein mediates interaction (Chinnaiyan et al., 1997b; Chaudhary et al., 1998). with that of the target caspase, whereas the NOD self- Biochemical approaches to identify cytosolic factors associates and oligomerizes (Figure 1a). Through their that activate human caspase-3, an eector caspase, NODs and CARDs, Apaf-1 and presumably Ced-4 revealed a cell death machinery in mammals similar form a large protein complex containing oligomerized to that identi®ed by genetic studies in C. elegans. Apaf-1/Ced-4 bound to caspase-9 or Ced-3, respec- Puri®cation of caspase-3 activators and functional tively, which allows proximity and enzymatic self- reconstitution assays revealed caspase-9 as a direct activation of the bound caspases (Yang et al., 1998; Hu activator of caspase-3 (Zou et al., 1997). Apaf-1 was et al., 1998a; Srinivasula et al., 1998; Salvesen and identi®ed as the activator of caspase-9, a step that Dixit, 1999). The mechanism by which these caspases requires dATP/ATP and cytochrome c, a ligand for are activated by Ced-4 and Apaf-1 appears to be Apaf-1 released from damaged mitochondria (Li et similar to that proposed for activation of caspase-8 in al., 1997). Sequence analysis revealed that Apaf-1 is the death-inducing receptor complex (DISC) (Muzio et structurally and functionally related to the nematode al., 1998; Salvesen and Dixit, 1999). Caspase-8 is Ced-4 (Zou et al., 1997). The N-terminal CARD of another mammalian apical caspase linked to death Apaf-1 is required for interaction with the CARD of receptor signaling pathways (Boldin et al., 1996; Muzio caspase-9 and is fused to a centrally located NBD et al., 1996). Caspase-8 binds to its upstream activator (Zou et al., 1997; Li et al., 1997). The NBD of Apaf- FADD (also called MORT1) through an homophilic 1 and Ced-4 is homologous to the ABC-ATP/GTPase interaction via their N-terminal CARD-related a helix- module that is present in a large number of proteins rich domains, namely the death eector domains with diverse biological function (Walker et al., 1982). (DEDs) (Boldin et al., 1995; Chinnaiyan et al., 1995; Both the ABC domain present in these ATP/GTPases Bertin et al., 1997). FADD also has a C-terminal death and the NBD of Apaf-1/Ced-4 contain conserved domain (DD) which binds to DD-containing receptors binding sites for nucleotide (P-loop or Walker's A or adapter molecules and mediates recruitment of box) and Mg2+ (Walker's B box) (Walker et al., caspase-8 to the membrane receptor complex triggered 1982; Seshagiri and Miller, 1997; Chinnaiyan et al., upon binding of the trimeric ligand (Boldin et al., 1995, 1997b; Chaudhary et al., 1998; Jaroszewski et al., 1996; Chinnaiyan et al., 1995; Muzio et al., 1996). 2000). In addition, the NBD of both Apaf-1 and Trimerization of death receptors (DRs) induces the CED-4 mediates protein homooligomerization, a proximity and activation of caspase-8 (Muzio et al., function that is critical for Apaf-1/Ced-4 activity 1998). A model for caspase-8 activation in the tumor (Chaudhary et al., 1998; Yang et al., 1998; Hu et al., necrosis factor receptor-1 (TNFR1) signaling pathway 1998a; Srinivasula et al., 1998). Therefore, we refer is shown in Figure 1b. Although the caspase-8/DISC here to the NBD present in Apaf-1 and homologues and caspase-9/Apaf-1 machineries have signi®cant as nucleotide-binding oligomerization domain (NOD) dierences, enzymatic activation of caspases in both and to structurally related NOD-containing proteins systems appear to require binding to their upstream such as Apaf-1 and Nod1 as Nods. Although the regulators and the induced proximity of apical caspases NOD mediates both nucleotide binding and oligo- though oligomerization (or trimerization) (Inohara et merization, studies with Apaf-1 and Ced-4 have not al., 2000). revealed dierent subdomains within the NOD that mediate these activities (Hu et al., 1998a; Yang et al., 1998). Regulation of Ced-4/Apaf-1 oligomerization and caspase Apaf-1 also has a C-terminal regulatory domain recruitment containing WD40 repeats (WDR), which is essential for the ability of Apaf-1 to respond to cytochrome c Because caspase activation plays a critical role in (Zou et al., 1997; Li et al., 1997; Hu et al., 1999). determining cell fate, oligomerization of caspase Analyses of mice lacking Apaf-1 and caspase-9 activators such as Apaf-1 and the subsequent recruit- revealed that Apaf-1 and caspase-9 play important ment of target caspases to their activators are highly roles in apoptosis during development of multiple regulated events. For example, activation of Ced-3 by tissues including brain, limb and eye, comparable to Ced-4 is regulated by Ced-9. The pro-survival Ced-9 that of Ced-4 in the nematode (Cecconi et al., 1998; binds Ced-4 and sequesters CED-4 from the cytosol to Yoshida et al., 1998). Furthermore, Apaf-1 and the mitochondria (Spector et al., 1997; Chinnaiyan et caspase-9 mediate p53-dependent cell death induced al., 1997a; Wu et al., 1997a; Seshagiri and Miller, by chemotherapeutic drugs, UV and g-irradiation 1997). Ced-9 can form a ternary complex with Ced-3 (Cecconi et al., 1998; Yoshida et al., 1998; Soengas et and Ced-4 (Chinnaiyan et al., 1997a; Wu et al., 1997b). al., 1999). Ced-9 binds the NOD of Ced-4 and inhibits NOD-

Oncogene Proteins containing nucleotide-binding oligomerization domains N Inohara and G NunÄez 6475

Figure 1 The Nods: structures of Ced4, Apaf-1, Nod1, Nod2 and related proteins. Schematic structures of Ced4, Apaf-1, Nod1, Nod2, CIITA, NAIP, Defcap, Nalp2, and Mater, are drawn. For abbreviations, AD, activation domain; BIR, baculovirus IAP repeat; CARD, caspase-recruitment domain; LRRs, leucine-rich repeats; NOD, nucleotide-binding oligomerization domain; Pyrin, pyrin domain; WDR, WD40 repeats region. The CARD (shown in parentheses) is present in the subtype of CIITA expressed in dendritic cells. An incomplete pyrin domain is present in the C-terminus of DefCap (shown in parentheses) mediated Ced-4 oligomerization, thereby preventing family members regulate Apaf-1 activity by controlling Ced-3 activation (Chaudhary et al., 1998; Yang et al., cytochrome c release from mitochondria (Yang et al., 1998). Genetic studies indicate that ced-4 function is 1997; Green and Reed, 1998; Desagher and Martinou, regulated by ced-9 and that of ced-9 is regulated by egl- 2000). The C-terminal WDR of Apaf-1 is required for 1, a gene that acts upstream of ced-9 during PCD in cytochrome c-dependent caspase-9 activation, whereas neurons (Trent et al., 1983; Conradt and Horvitz, the nematode Ced-4 lacks a corresponding WDR (Zou 1998). Egl-1, a member of the BH3-only proteins of the et al., 1997; Li et al., 1997; Hu et al., 1999). In addition Bcl-2 family, binds to Ced-9 and induces the release of to a role in the recognition of cytochome c, the WDR Ced-4 from the Ced-3/Ced-4 complex (Conradt and of Apaf-1 interacts with its NOD and inhibits the Horvitz, 1998; del Peso et al., 1998, 2000; Chen et al., ability of Apaf-1 to activate caspase-9 (Hu et al., 2000; Parrish et al., 2000). Because a gain-of-function 1998a; Adrain et al., 1999). Thus, the WDR of Apaf-1 mutant of Ced-9 still binds to Ced-4 in the presence of appears to be functionally equivalent to Ced-9 in that Egl-1, these results suggest that the interaction between both repress Apaf-1/Ced-4 activity through inhibition Ced-4 and Ced-9 (and presumably Ced-4 oligomeriza- of NOD-mediated oligomerization. Moreover, both the tion) plays a critical role in the regulation of Ced-4 WDR of Apaf-1 and Ced-9 link upstream death signals activity and PCD in the worm. Similar to Ced-9 in the to caspase activation. It is still unclear how non-speci®c C. elegans system, Bcl-2 family members regulate activation or aggregation of caspase activators such as apoptosis through Apaf-1 and caspase-9 in mammalian Apaf-1 is prevented. Ligand-independent apoptosis by cells (Green and Reed, 1998). However, the Ced-9 TNFR1 is regulated by BAG4 (also called SODD), a homologue Bcl-2 does not appear to interact directly member of the BAG family which facilitates the with Apaf-1, although initial studies demonstrated a function of Hsp70 and related unfoldases (Takayama weak interaction between Apaf-1 and certain members et al., 1999; Jiang et al., 1999). Activation of caspase-9 of the Bcl-2 family (Pan et al., 1998; Hu et al., 1998b; by Apaf-1 is also inhibited by Hsp70 and Hsp90 (Beere Inohara et al., 1998a; Song et al., 1999; Moriishi et al., et al., 2000, Saleh et al., 2000; Pandey et al., 2000). 1999; Newmeyer et al., 2000; Conus et al., 2000). Biochemical and genetic analyses suggest that Mac1, a Mounting evidence indicate that prosurvival Bcl-2 member of AAA family, of ATPases inhibits Ced-4

Oncogene Proteins containing nucleotide-binding oligomerization domains N Inohara and G NunÄez 6476 function (Wu et al., 1999). However, a physiological in plants (van der Biezen and Jones, 1998; Aravind et role for Hsp proteins and MAC-1 in controlling non- al., 1999; Koonin and Aravind, 2000). Plants have a speci®c activation of Apaf-1/Ced-4 and preventing large number of R genes to defend against a wide array signal-independent apoptosis remains to be determined. of pathogens and each R gene protects plant cells from speci®c pathogen(s) (Flor, 1971; Dixon et al., 2000; Feys and Parker, 2000). R gene products appear to Identi®cation of Apaf-1-like molecules: Nod1 and Nod2 recognize pathogen-derived components, called Aviru- lence factors (Avrs), though their leucine-rich repeats At the time that Apaf-1 was identi®ed, it was noted (LRRs) (Parniske et al., 1997; Dixon et al., 2000). that the NOD of Apaf-1 has signi®cant structural Genetic variation in LRR sequences of R proteins homology to a class of plant cytosolic disease determines the speci®city of R proteins for pathogens resistance (R) gene products, which mediate the HR (Parniske et al., 1997). A class of R proteins contains a transmembrane domain and extracellular LRRs and presumably recognize Avrs at the cell surface (Dixon et al., 2000). Another class of R proteins is cytosolic and contains a N-terminal a helix rich (formerly called leucine zipper-like) or Toll/interleukin-1 receptor (TIR) domain, a centrally located NOD and C-terminal LRRs (Dixon et al., 2000) (Figure 1). Thus, both Apaf-1 and cytosolic plant R gene products regulate PCD with their C-terminal domain mediating the response to speci®c ligands. Despite their structural and functional similarity, the molecular function of R proteins and the functional link between mammalian Apaf-1 and plant R proteins remains poorly under- stood. The recent identi®cation of Apaf-1-like molecules by bioinformatics has revealed multiple NOD- containing proteins and expanded our understanding of NOD function in the regulation of apoptosis and innate immunity (Figure 1). Initial homology searches identi®ed two related proteins, Nod1 (also called CARD4) and Nod2, which have one and two N- terminal CARDs, respectively, centrally located NODs, and C-terminal domains containing leucine-rich repeats (LRRs) (Bertin et al., 1999; Inohara et al., 1999; Ogura et al., 2001a). Overexpression of Nod1 and Nod2 in mammalian cells enhances caspase-9-induced cell death and, unexpectedly, induces NF-kB activation (Bertin et al., 1999; Inohara et al., 1999; Ogura et al., 2001a). Remarkably, both Nod proteins and plant R proteins have centrally located NODs and C-terminal LRRs, although R proteins have an a helix rich or TIR domain instead of a CARD on their N-termini (Dixon et al., 2000). The structural similarity between these Nods and plant R proteins led to studies that suggest that Nod1 and Nod2 act as cytosolic receptors for bacterial lipopolysaccharide (LPS), a well-characterized Figure 2 `Proximity-Activation' models of caspase and NF-kB product of Gram-negative bacteria (Inohara et al., activation. Apaf-1 and the TNFR1 complex induce the proximity 2001; Ogura et al., 2001a). Expression of Nod1 or of caspase-8 and caspase-9, respectively, whereas Nod1 and the Nod2 confers LPS responsiveness in human embryonic TNFR1 complex induce the proximity of IKK complexes through RICK and RIP, respectively. The TNFR1 complex contains kidney (HEK) cell lines which normally do not respond TRADD and recruitment of procaspase-8 to TNFR1 complex to LPS (Inohara et al., 2001; Ogura et al., 2001b). requires FADD. Nod1 functions as an intracellular receptor for Although Nod1 and Nod2 mutant proteins lacking LPS and trimeric TNFa induces trimerization of TNFR1 LRRs still activate NF-kB, they do not mediate LPS complexes, whereas cytochrome c mediates oligomerization of Apaf-1. For abbreviations, CARD, caspase-recruitment domain; responsiveness, suggesting that their LRRs are essential CC, coiled coil; DD, death domain; DED, death eector domain; for LPS-mediated NF-kB activation (Inohara et al., GBD, g subunit binding domain; HLH, helix ± loop ± helix; IGU, 2001). Importantly, a frameshift mutation resulting in a IKKg binding domain of upstream regulators; IPS, inhibitory truncated protein lacking part of the LRRs and single phosphorylation site; LBD, ligand binding domain; LRRs, nucleotide polymorphisms in the Nod2 gene are leucine-rich repeats; LZ, leucine zipper; NOD, nucleotide-binding oligomerization domain; TRADD-N, TRADD N terminal associated with susceptibility to Crohn's disease (Hugot domain; WDR, WD40 repeats region; ZF, zinc ®nger et al., 2001; Ogura et al., 2001b). The truncated Nod2

Oncogene Proteins containing nucleotide-binding oligomerization domains N Inohara and G NunÄez 6477 protein associated with disease susceptibility is de®cient derived from bacteria might be involved in the in inducing LPS-mediated NF-kB activation (Ogura et acquisition of the cellular machineries for PCD and al., 2001b). These observations suggest that Nod1 and defense against pathogens in multicellular organisms. Nod2 are mammalian functional homologues of plant R proteins and cytosolic counterparts of Toll-like receptors (Inohara et al., 2001). Nods: a family of NOD-containing proteins

Homology searches have revealed a growing family of Nod1 and Nod2 activate NF-kB through an induced structurally related proteins with centrally located proximity mechanism NODs (referred to here collectively as Nods and shown in Figure 1). CIITA is a signaling molecule Analysis of the molecular function of Nod1 and Apaf- that activates transcription of MHC class II (MHCII) 1 revealed a striking similarity between the mechanism genes. CIITA is homologous to Nod1 and Nod2 of caspase activation and that of NF-kB activation (Steimle et al., 1993; Inohara et al., 1999; Ogura et (Inohara et al., 2000). Whereas apoptosis mediated by al., 2001a) in that it has an N-terminal transcription membrane-associated DRs and Apaf-1 is dependent on activation domain, central NBD (GTPase) and C- activation of caspase-8 and caspase-9, respectively terminal LRRs (Steimle et al., 1993; Chin et al., 1997) (Salvesen and Dixit, 1999), NF-kB activation mediated (Figure 1). CIITA acts as a non-DNA binding by DRs and Nod1 is dependent on two related transcription factor in the nucleus, although it localizes molecules, RIP and RICK, respectively (Hsu et al., in both the nucleus and cytosol (Riley et al., 1995; 1996; Zhang et al., 2000; Bertin et al., 1999; Inohara et Zhou and Glimcher, 1995; Cressman et al., 1999; al., 1999). RIP and RICK (also called RIP2 and Harton et al., 1999). The N-terminal transactivation CARDIAK) are signaling molecules with highly domain is reported to bind several transcription homologous N-terminal kinase domains (Inohara et regulators including protein acetyltransferase family al., 1998b; McCarthy et al., 1998; Thome et al., 1998). members (Kretsovali et al., 1998; Fontes et al., 1999; RIP contains a C-terminal DD that mediates its Sisk et al., 2000; Spilianakis et al., 2000; Kanazawa et recruitment to DR signaling complexes such as those al., 2000). Similar to Nod1, the NOD of CIITA is formed by TNFR1 ligation (Stanger et al., 1995; Hsu essential for its activity and mediates MHCII gene et al., 1996), whereas RICK has a C-terminal CARD transcription and self-association (Chin et al., 1997; that mediates its recruitment to Nod1 and Nod2 Harton et al., 1999; Linho et al., 2001). Mutations in (Bertin et al., 1999; Inohara et al., 1999; Ogura et al., the NOD or LRRs render CIITA de®cient in MHCII 2001a) (Figure 3a). In addition, RIP and RICK gene transcriptional activity, resulting in lack of contain intermediate regions (IM) between the kinase MHCII protein expression and severe immunode®- domain and CARD/DD that binds to IKKg (also ciency in humans (Steimle et al., 1993; Bontron et al., called NEMO, FIP3, IKKAP1), the regulatory subunit 1997). These observations suggest that CIITA is an of I-kB kinase (IKK) complex (Yamaoka et al., 1998; Apaf-1- and Nod1-like molecule, although the ligand(s) Rothwarf et al., 1998; Li et al., 1999; Mercurio et al., that presumably binds to its LRRs has not been 1999; Ye et al., 2000; Inohara et al., 2000; Poyet et al., identi®ed. Moreover, CIITA produced from an alter- 2000). As trimerization of DR complex and oligomer- native ®rst exon in dendritic cells has an N-terminal ization of Apaf-1 cause the proximity of target CARD (Muhlethaler-Mottet et al., 1997; Nickerson et caspases and caspase activation, trimerization of the al., 2001). Dendritic cell-type CIITA exhibits approxi- DR complex and oligomerization of Nod1 induce the mately 100-fold more transcriptional activity than proximity of IKK complex through RIP and RICK, CARD-less CIITA (Nickerson et al., 2001). However, respectively (Figure 2) (Zhang et al., 2000; Inohara et the CARD of CIITA does not bind to that of RICK al., 2000; Poyet et al., 2000). Arti®cial oligomerization and CIITA does not induce NF-kB activation, whereas of RIP or RICK and IKK subunits, which stimulates Nod1 induces NF-kB activation but not MHCII gene the induced proximity, are sucient to activate NF-kB activation (Nickerson et al., 2001). CIITA, unlike (Inohara et al., 2000; Poyet et al., 2000). The similarity Nod1, is devoid of an intrinsic apoptosis function, between the mechanism involved in apical caspase although CIITA inhibits transcription of the FasL gene activation and that proposed for NF-kB activation (Gourley and Chang, 2001; Nickerson et al., 2001). may explain why the regulators of both signaling These observations suggest that, despite their structural pathways have common domains including CARDs, homology, CIITA and Nod1 regulate a dierent set of DDs and NODs (Figures 1 and 2). Furthermore, these genes and the CARD of CIITA might interact with an studies suggest that the apoptosis machinery resembles as yet unidenti®ed protein which enhances MHCII the machinery used by host cells to eliminate invading gene transcription (Nickerson et al., 2001). pathogens. It is interesting to note that Ced-4 and Neuronal apoptosis inhibitor protein (NAIP), which Apaf-1 are regulated by two mitochondrial proteins is located in the same chromosomal region as the Ced-9 and cytochrome c, respectively. Furthermore, spinal muscular atrophy (SMA) locus, also has a the symbiotic theory predicts that the mitochondrion is central NOD and C-terminal LRRs (Roy et al., 1995). an organelle derived from former Gram-negative Instead of a CARD, the N-terminus of NAIP is bacteria, suggesting that an ancestral mechanism composed of three N-terminal baculovirus-inhibitor-of-

Oncogene Proteins containing nucleotide-binding oligomerization domains N Inohara and G NunÄez 6478 apoptosis repeats (BIRs) (Roy et al., 1995). Mutations essential for binding and hydrolysis of Mg2+-ATP or associated with SMA were found initially in the NAIP -GTP and are predicted to share common nucleotide locus and in the gene for survival motoneuron (SMN), binding folds with ATP-binding cassettes (ABCs) of a gene located near NAIP. Recent analyses of mice members of the ABC ATPase/GTPase superfamily lacking SMN suggest that SMN is the most critical (Seshagiri and Miller, 1997; Chinnaiyan et al., 1997b; gene for SMA development (Schrank et al., 1997; Chaudhary et al., 1998; Jaroszewski et al., 2000). Hsieh-Li et al., 2000). Mouse NAIP is mainly Point mutations in the phosphate chain binding site expressed in macrophages, but not in brain, and is (also called P-loop or Walker's A box) of Apaf-1, encoded by multiple highly homologous genes, namely Ced-4, Nod1, Nod2 and CIITA resulted in loss-of- naip1 to naip7 in the same chromosomal region function (Seshagiri and Miller, 1997; Chinnaiyan et (Yaraghi et al., 1998; Diez et al., 2000). Overexpression al., 1997b; Chaudhary et al., 1998). Indeed, Apaf-1 of NAIP was reported to inhibit apoptosis of neuronal has been demonstrated to hydrolyze ATP (Zou et al., and non-neuronal cells (Liston et al., 1996) and mice 1999). These observations suggest that the NODs are lacking naip1 showed increased vulnerability to kainic active purine nucleotide triphosphatases and belong to acid-induced cell death (Holcik et al., 2000). However, the superfamily of ABC ATPase/GTPase domains. naip1 de®cient mice appeared normal and exhibited no The ABC-ATPase superfamily is the largest protein consistent histological or morphological abnormalities family known with over 1000 members which can be (Holcik et al., 2000). On the other hand, naip2 or naip5 grouped as belonging to several subfamilies based on appear to correspond to Lgn1, a locus which renders their biological function (Walker et al., 1982; macrophages permissive to replication by Legionella Gorbalenya and Koonin, 1990; Holland and Blight, pneumophila, a pathogenic Gram-negative bacteria 1999; Langer, 2000). This family is highly diverse and (Scharf et al., 1996; Diez et al., 2000; Growney and includes proteins which function in DNA repair, Dietrich, 2000). This suggests that NAIP may be active transport, signaling and protein degradation involved in the regulation of innate immunity, (Walker et al., 1982; Gorbalenya and Koonin, 1990; although the mechanism of tolerance to L. pneumophila Holland and Blight, 1999; Langer, 2000). In addition is still unknown. to the ABC, many ABC-containing proteins contain BLAST analysis also identi®ed several Nod1-like one or more domains that serve to couple and proteins which are poorly characterized (Figure 1). coordinate several biochemical activities within one Mater, the oocyte-speci®c maternal protein has an N- molecule. For example, RecA is composed of ABC- terminal uncharacterized domain, central NOD and C- ATPase and DNA-binding domains and binding of terminal LRRs (Tong and Nelson, 1999; Tong et al., ATP to RecA is involved in the induction of an 2000a). Although the molecular function of Mater allosteric conformational change that mediates high remains unknown, the null Mater mutation is lethal at anity binding to DNA (Silver and Fersht, 1982). the two-cell embryo stage, suggesting that Mater plays Similarly, small G proteins such as Ras undergo an essential role on cell viability at early stages of conformational changes from active GTP-bound embryogenesis (Tong et al., 2000b). Defcap (also called forms, capable of binding to eector molecules, to Card7, Nac and Nalp1) is a multi-domain protein inactive GDP-bound forms (Sprang, 1997). Biochem- containing a N-terminal pyrin domain, a central NOD, ical studies suggest that dATP/ATP binding, but not LRRs, incomplete pyrin domain and C-terminal dATP/ATP hydrolysis, to Apaf-1 is required for CARD (Bertin and DiStefano, 2000; Hlaing et al., oligomerization of Apaf-1 and binding to caspase-9 2001; Chu et al., 2001; Martinon et al., 2001). It was (Jiang and Wang, 2000). It is unknown how reported that overexpression of Defcap induces or cytochrome c causes a conformational change in promotes cell death and that Defcap binds to caspase- Apaf-1 or how dATP/ATP hydrolysis is utilized. 2, caspase-9 (Hlaing et al., 2001), Apaf-1 (Chu et al., Apaf-1 and related proteins might use ATP hydrolysis 2001) and Asc1 (Martinon et al., 2001). A critical role to verify the identity of their physiological partners for Defcap in Apaf-1 function has been suggested and/or ligands. Alternatively, conformational transi- based on studies with antisense oligonucleotides (Chu tion of NODs may trigger ATP hydrolysis. For et al., 2001). However, the physiological function of example, conformational transition between ADP Defcap is unclear, particularly when there is no and ATP binding forms of small G proteins is evidence that mice have a Defcap orthologue (Inohara facilitated by GTP exchanging or releasing factors and NunÄ ez, unpublished). The pyrin domain of Defcap (Sprang, 1997). It is unclear if the function of Apaf-1 (Nalp1) was demonstrated to be an a helix-rich and related proteins is facilitated by nucleotide homophilic protein/protein interaction domain, as their exchanging or releasing factors, although puri®ed related CARD, DED and DD (Martinon et al., 2001). Apaf-1 has been demonstrated to hydrolyze ATP (Zou et al., 1999). The Drosophila Apaf-1 orthologue lacks the asparatic acid residue which supports an Comparison between Apaf-1-related proteins and other interaction with Mg2+ at the conserved position in the ABC-containing proteins Walker's B box (Rodriguez et al., 1999; Kanuka et al., 1999; Zhou et al., 1999), suggesting that Drosophila All NODs in mammalian and plant Apaf-1/Nod1-like Apaf-1 cannot hydrolyze ATP/GTP or that residues proteins have residues at catalytic sites which are required for substrate binding are dierent from those

Oncogene Proteins containing nucleotide-binding oligomerization domains N Inohara and G NunÄez 6479 found in related proteins. Because cell death is an Conclusion irreversible act, reversible conformational transition between ADP and ATP binding forms of Apaf-1 may Recent studies have identi®ed a family of Apaf-1- not be required for the regulation of apoptosis. related proteins that are referred to here collectively as Caspase-9 is active when bound to Apaf-1 but largely Nods. These Nod proteins contain centrally located inactive in processed free form (Rodriguez and NOD modules that are homologous to the ABC- Lazebnik, 1999), suggesting that the amount of ATPase domain found in a large number of proteins caspase-9/Apaf-1 complex, but not the enzymatic with diverse function. Apaf-1 and Ced-4, the ®rst turnover of Apaf-1, is critical for progression to NOD-containing proteins to be identi®ed, play a apoptosis. critical role in the regulation of PCD by promoting CIITA has been proposed to act as a bridging the activation of their target caspases through NOD protein between several transcription factors to form oligomerization. The NOD of Apaf-1 and Ced-4 is an active transcriptional machinery on the MHC critical for functional activity and is subjected to tight class II promoter (Zhu et al., 2000). Similarly, Apaf-1 regulation. In addition to Apaf-1 and Ced-4, a growing seems to promote recruitment of caspase-3 to family of Nods has recently emerged. Some of these caspase-9 through the WDR in addition to enzymatic Nod proteins, including Nod1 and Nod2, appear to be activation of caspase-9 (Hu et al., 1999). Such functional and structural homologues of plant R `scaold' activity has also been observed in other proteins, a large family of proteins involved in plant ABC-ATPase containing proteins. For example, resistance to bacteria, fungi and viruses. Future studies recruitment of MutH to mutL requires the mutS/ using mutant mice de®cient in Nods should clarify the DNA complex in the DNA repair system (Harfe and physiological role of these NOD-containing proteins in Jinks-Robertson, 2000). Furthermore, there are nu- vivo. merous ABC containing subunits which are required for the formation of functional multipeptide complexes including the FoF1 ATPase (Futai, 1997). These observations suggest that Apaf-1 and related Acknowledgments proteins may have scaold-like activity as a second The authors thank P Lucas for critical review of the function in addition of being activators of eector manuscript. This work was supported by grant R01 enzymes during apoptosis. CA64556-01 from the NIH.

References

Adrain C, Slee EA, Harte MT and Martin SJ. (1999). J. Biol. Chaudhary D, O'Rourke K, Chinnaiyan AM and Dixit VM. Chem., 274, 20855 ± 20860. (1998). J. Biol. Chem., 273, 17708 ± 17712. Aravind L, Dixit VM and Koonin EV. (1999). Trends Chen F, Hersh BM, Conradt B, Zhou Z, Riemer D, Biochem. Sci., 24, 47 ± 53. Gruenbaum Y and Horvitz HR. (2000). Science, 287, Beere HM, Wolf BB, Cain K, Mosser DD, Mahboubi A, 1485 ± 1489. Kuwana T, Tailor P, Morimoto RI, Cohen GM and Green Chin K-C, Li GX and Ting JP. (1997). Proc. Natl. Acad. Sci. DR. (2000). Nat. Cell Biol., 2, 469 ± 475. USA, 94, 2501 ± 2506. Bertin J, Armstrong RC, Ottilie S, Martin DA, Wang Y, Chinnaiyan AM, O'Rourke K, Tewari M and Dixit VM. Banks S, Wang GH, Senkevich TG, Alnemri ES, Moss B, (1995). Cell, 81, 505 ± 512. Lenardo MJ, Tomaselli KJ and Cohen JI. (1997). Proc. Chinnaiyan AM, O'Rourke K, Lane BR and Dixit VM. Natl. Acad. Sci. USA, 94, 1172 ± 1176. (1997a). Science, 275, 1122 ± 1126. Bertin J, Nir WJ, Fischer CM, Tayber OV, Errada PR, Grant Chinnaiyan AM, Chaudhary D, O'Rourke K, Koonin EV JR, Keilty JJ, Gosselin ML, Robison KE, Wong GH, and Dixit VM. (1997b). Nature, 388, 728 ± 729. Glucksmann MA and DiStefano PS. (1999). J. Biol. Conradt B and Horvitz HR. (1998). Cell, 93, 519 ± 529. Chem., 274, 12955 ± 12958. Conus S, Rosse T and Borner C. (2000). Cell Death Dier., 7, Bertin J and DiStefano PS. (2000). Cell Death Dier., 7, 947 ± 954. 1273 ± 1274. Chu ZL, Pio F, Xie Z, Welsh K, Krajewska M, Krajewski S, van der Biezen EA and Jones JD. (1998). Curr. Biol., 8, Godzik A and Reed JC. (2001). J. Biol. Chem., 276, 9239 ± R226 ± R227. 9245. Boldin MP, Varfolomeev EE, Pancer Z, Mett IL, Camonis delPesoL,GonzalezVMandNuÂnÄ ez G. (1998). J. Biol. JH and Wallach D. (1995). J. Biol. Chem., 270, 7795 ± Chem., 273, 33495 ± 33500. 7798. delPesoL,GonzalezVM,InoharaN,EllisREandNuÂnÄ ez G. Boldin MP, Goncharov TM, Goltsev YV and Wallach D. (2000). J. Biol. Chem., 275, 27205 ± 27211. (1996). Cell, 85, 803 ± 815. Diez E, Yaraghi Z, MacKenzie A and Gros P. (2000). J. Bontron S, Steimle V, Ucla C, Eibl MM and Mach B. (1997). Immunol., 164, 1470 ± 1477. Hum. Genet., 99, 541 ± 546. Dixon MS, Golstein C, Thomas CM, van Der Biezen EA and Cecconi F, Alvarez-Bolado G, Meyer BI, Roth KA and Jones JD. (2000). Proc. Natl. Acad. Sci. USA, 97, 8807 ± Gruss P. (1998). Cell, 94, 727 ± 737. 8814. Cressman DE, Chin KC, Taxman DJ and Ting JP. (1999). Desagher S and Martinou JC. (2000). Trends Cell. Biol., 10, Immunity, 10, 163 ± 171. 369 ± 377.

Oncogene Proteins containing nucleotide-binding oligomerization domains N Inohara and G NunÄez 6480 Ellis HM and Horvitz HR. (1986). Cell, 44, 817 ± 829. Jiang Y, Woronicz JD, Liu W and Goeddel DV. (1999). Feys BJ and Parker JE. (2000). Trends Genet., 16, 449 ± 455. Science, 283, 543 ± 546. Flor HH. (1971). Annu. Rev. Phytopathol., 9, 275 ± 296. Kanazawa S, Okamoto T and Peterlin BM. (2000). Fontes JD, Kanazawa S, Jean D and Peterlin BM. (1999). Immunity, 12, 61 ± 70. Mol. Cell. Biol., 19, 941 ± 947. Kanuka H, Sawamoto K, Inohara N, Matsuno K, Okano H Futai M. (1977). Biochem. Biophys. Res. Commun., 79, and Miura M. (1999). Mol. Cell, 4, 757 ± 769. 1231 ± 1237. Koonin EV and Aravind L. (2000). Trends Biochem. Sci., 25, Green DR and Reed JC. (1998). Science, 281, 1309 ± 1312. 223 ± 224. Growney JD and Dietrich WF. (2000). Genome Res., 10, Kretsovali A, Agalioti T, Spilianakis C, Tzortzakaki E, 1158 ± 1171. Merika M and Papamatheakis J. (1998). Mol. Cell. Biol., Gorbalenya AE and Koonin EV. (1990). J. Mol. Biol., 213, 18, 6777 ± 6783. 583 ± 591. Kumar S. (1999). Cell Death Dier., 6, 1060 ± 1066. Gourley TS and Chang CH. (2001). J. Immunol., 166, 2917 ± Kerr JF, Wyllie AH and Currie AR. (1972). Br.J.Cancer,26, 2921. 239 ± 257. Harfe BD and Jinks-Robertson S. (2000). Annu. Rev. Genet., Langer T. (2000). Trends Biochem. Sci., 25, 247 ± 251. 34, 359 ± 399. Li P, Nijhawan D, Budihardjo I, Srinivasula SM, Ahmad M, Harton JA, Cressman DE, Chin KC, Der CJ and Ting JP. Alnemri ES and Wang X. (1997). Cell, 91, 479 ± 489. (1999). Science, 285, 1402 ± 1405. Li Y, Kang J, Friedman J, Tarassishin L, Ye J, Kovalenko A, Hofmann K, Bucher P and Tschopp J. (1997). Trends Wallach D and Horwitz MS. (1999). Proc. Natl. Acad. Sci. Biochem. Sci., 22, 155 ± 156. USA, 96, 1042 ± 1047. Hengartner MO and Horvitz HR. (1994). Cell, 76, 665 ± 676. Linho MW, Harton JA, Cressman DE, Martin BK and Hlaing T, Guo RF, Dilley KA, Loussia JM, Morrish TA, Shi Ting JP. (2001). Mol. Cell. Biol., 21, 3001 ± 3011. MM, Vincenz C and Ward PA. (2001). J. Biol. Chem., 276, Liston P, Roy N, Tamai K, Lefebvre C, Baird S, Cherton- 9230 ± 9238. Horvat G, Farahani R, McLean M, Ikeda JE, MacKenzie Holcik M, Thompson CS, Yaraghi Z, Lefebvre CA, A and Korneluk RG. (1996). Nature, 379, 349 ± 353. MacKenzie AE and Korneluk RG. (2000). Proc. Natl. Mercurio F, Murray BW, Shevchenko A, Bennett BL, Acad. Sci. USA, 97, 2286 ± 2290. Young DB, Li JW, Pascual G, Motiwala A, Zhu H, Mann Holland IB and Blight MA. (1999). J. Mol. Biol., 293, 381 ± M and Manning AM. (1999). Mol. Cell. Biol., 19, 1526 ± 399. 1538. Hsieh-LiHM,ChangJG,JongYJ,WuMH,WangNM,Tsai Martinon F, Hofmanndouble dagger K and Tschopp J. CH and Li H. (2000). Nat. Genet., 24, 66 ± 70. (2001). Curr. Biol., 11, R118 ± R120. Hsu H, Huang J, Shu HB, Baichwal V and Goeddel DV. McCarthyJV,NiJandDixitVM.(1998).J. Biol. Chem., (1996). Immunity, 4, 387 ± 396. 273, 16968 ± 16975. Hu Y, Ding L, Spencer DM and NuÂnÄ ez G. (1998a). J. Biol. Metzstein MM, Stan®eld GM and Horvitz HR. (1998). Chem., 273, 33489 ± 33494. Trends Genet., 14, 410 ± 416. Hu Y, Benedict MA, Wu D, Inohara N and NuÂnÄ ez G. Moriishi K, Huang DC, Cory S and Adams JM. (1999). Proc. (1998b). Proc. Natl. Acad. Sci. USA, 95, 4386 ± 4391. Natl. Acad. Sci. USA, 96, 9683 ± 9688. Hu Y, Benedict MA, Ding L and NuÂnÄ ez G. (1999). EMBO J., Muhlethaler-Mottet A, Otten LA, Steimle V and Mach B. 18, 3586 ± 3595. (1997). EMBO J., 16, 2851 ± 2860. Hugot JP, Chamaillard M, Zouali H, Lesage S, Cezard JP, Muzio M, Chinnaiyan AM, Kischkel FC, O'Rourke K, BelaicheJ,AlmerS,TyskC,MontagueS,GassullM, Shevchenko A, Ni J, Scadi C, Bretz JD, Zhang M, Gentz Binder V, Finkel Y, Cortot A, Modigliani R, Laurent- R, Mann M, Krammer PH, Peter ME and Dixit VM. Puig P, Gower-Rousseau C, Macry J, Colombel JF, (1996). Cell, 85, 817 ± 827. Sahbatou M and Thomas G. (2001). Nature, 411, 599 ± MuzioM,StockwellBR,StennickeHR,SalvesenGSand 603. Dixit VM. (1998). J. Biol. Chem., 273, 2926 ± 2930. Inohara N, Gourley TS, Carrio R, Muniz M, Merino J, Newmeyer DD, Bossy-Wetzel E, Kluck RM, Wolf BB, Beere Garcia I, Koseki T, Hu Y, Chen S and NuÂnÄ ez G. (1998a). HM and Green DR. (2000). Cell. Death Dier., 7, 402 ± J. Biol. Chem., 273, 32479 ± 32486. 407. Inohara N, del Peso L, Koseki T, Chen S and NuÂnÄ ez G. Nickerson K, Sisk TJ, Inohara N, Yee CSK, Kennell J, Cho (1998b). J. Biol. Chem., 273, 12296 ± 12300. M-C, Yannie PJ, NuÂnÄ ez G and Chang CH. (2001). J. Biol. InoharaN,KosekiT,delPesoL,HuY,YeeC,ChenS, Chem., 276, 19089 ± 19093. Carrio R, Merino J, Liu D, Ni J and NuÂnÄ ez G. (1999). J. NuÂnÄ ez G, Benedict MA, Hu Y and Inohara N. (1998). Biol. Chem., 274, 14560 ± 14567. Oncogene, 17, 3237 ± 3245. Inohara N, Koseki T, Lin J, del Peso L, Lucas PC, Chen FF, Ogura Y, Inohara N, Benito A, Chen FF, Yamaoka S and Ogura Y and NuÂnÄ ez G. (2000). J. Biol. Chem., 275, NuÂnÄ ez G. (2001a). J. Biol. Chem., 276, 4812 ± 4818. 27823 ± 27831. Ogura Y, Bonen DK, Inohara N, Nicolae DL, Chen FF, Inohara N, Ogura Y, Chen FF, Muto A and NuÂnÄ ez G. Ramos R, Britton H, Moran T, Karaliuskas R, Duerr RH, (2001). J. Biol. Chem., 276, 2551 ± 2554. Achkar JP, Brant SR, Bayless TM, Kirschner BS, Irmler M, Hofmann K, Vaux D and Tschopp J. (1997). FEBS Hanauer SB, NuÂnÄ ez G and Cho JH. (2001b). Nature, Lett., 406, 189 ± 190. 411, 603 ± 606. Jacobson MD, Weil M and Ra MC. (1997). Cell, 88, 347 ± Pan G, O'Rourke K and Dixit VM. (1998). J. Biol. Chem., 354. 273, 5841 ± 5845. Jaroszewski L, Rychlewski L, Reed JC and Godzik A. Pandey P, Saleh A, Nakazawa A, Kumar S, Srinivasula SM, (2000). Proteins, 39, 197 ± 203. Kumar V, Weichselbaum R, Nalin C, Alnemri ES, Kufe D Jiang X and Wang X. (2000). J. Biol. Chem., 275, 31199 ± and Kharbanda S. (2000). EMBO J., 19, 4310 ± 4322. 31203.

Oncogene Proteins containing nucleotide-binding oligomerization domains N Inohara and G NunÄez 6481 Parniske M, Hammond-Kosack KE, Golstein C, Thomas Tong ZB and Nelson LM. (1999). Endocrinology, 140, 3720 ± CM,JonesDA,HarrisonK,WulBBandJonesJD. 3726. (1997). Cell, 91, 821 ± 832. Tong ZB, Nelson LM and Dean J. (2000a). Mamm. Genome, Parrish J, Metters H, Chen L and Xue D. (2000). Proc. Natl. 11, 281 ± 287. Acad. Sci. USA, 97, 11916 ± 11921. TongZB,GoldL,PfeiferKE,DorwardH,LeeE,Bondy Poyet JL, Srinivasula SM, Lin JH, Fernandes-Alnemri T, CA, Dean J and Nelson LM. (2000b). Nat. Genet., 26, Yamaoka S, Tsichlis PN and Alnemri ES. (2000). J. Biol. 267 ± 268. Chem., 275, 37966 ± 37977. Trent C, Tsung N and Horvitz HR. (1983). Genetics, 104, Riley JL, Westerheide SD, Price JA, Brown JA and Boss JM. 619 ± 647. (1995). Immunity, 2, 533 ± 543. Walker JE, Saraste M, Runswick MJ and Gay NJ. (1982). RodriguezA,OliverH,ZouH,ChenP,WangXandAbrams EMBO J., 1, 945 ± 951. JM. (1999). Nat. Cell Biol., 1, 272 ± 279. Weinrauch Y and Zychlinsky A. (1999). Annu. Rev. Rodriguez J and Lazebnik Y. (1999). Genes Dev., 13, 3179 ± Microbiol., 53, 155 ± 187. 3184. WuD,ChenPJ,ChenS,HuY,NuÂnÄ ez G and Ellis RE. Rothwarf DM, Zandi E, Natoli G and Karin M. (1998). (1999). Development, 126, 2021 ± 2031. Nature, 17, 297 ± 300. Wu D, Wallen HD, Inohara N and NuÂnÄ ez G. (1997a). J. Biol. Roy N, Mahadevan MS, McLean M, Shutler G, Yaraghi Z, Chem., 272, 21449 ± 21454. Farahani R, Baird S, Besner-Johnston A, Lefebvre C and Wu D, Wallen HD and NuÂnÄ ez G. (1997b). Science, 275, Kang X. (1995). Cell, 80, 167 ± 178. 1126 ± 1129. Saleh A, Srinivasula SM, Balkir L, Robbins PD and Alnemri Wyllie AH. (1980). Nature, 284, 555 ± 556. ES. (2000). Nat. Cell Biol., 2, 476 ± 483. Yang J, Liu X, Bhalla K, Kim CN, Ibrado AM, Cai J, Peng Salvesen GS and Dixit VM. (1999). Proc. Natl. Acad. Sci. TI, Jones DP and Wang X. (1997). Science, 275, 1129 ± USA, 96, 10964 ± 10967. 1132. Schrank B, Gotz R, Gunnersen JM, Ure JM, Toyka KV, Yang X, Chang HY and Baltimore D. (1998). Science, 281, Smith AG and Sendtner M. (1997). Proc. Natl. Acad. Sci. 1355 ± 1357. USA, 94, 9920 ± 9925. YamaokaS,CourtoisG,BessiaC,WhitesideST,WeilR, Scharf JM, Damron D, Frisella A, Bruno S, Beggs AH, Agou F, Kirk HE, Kay RJ and Israel A. (1998). Cell, 93, Kunkel LM and Dietrich WF. (1996). Genomics, 38, 405 ± 1231 ± 1240. 417. Yaraghi Z, Korneluk RG and MacKenzie A. (1998). Seshagiri S and Miller LK. (1997). Curr. Biol., 7, 455 ± 460. Genomics, 51, 107 ± 113. Silver MS and Fersht AR. (1982). Biochemistry, 21, 6066 ± Ye J, Xie X, Tarassishin L and Horwitz MS. (2000). J. Biol. 6072. Chem., 275, 9882 ± 9889. Sisk TJ, Gourley T, Roys S and Chang CH. (2000). J. Yoshida H, Kong YY, Yoshida R, Elia AJ, Hakem A, Immunol., 165, 2511 ± 2517. Hakem R, Penninger JM and Mak TW. (1998). Cell, 94, Soengas MS, Alarcon RM, Yoshida H, Giaccia AJ, Hakem 739 ± 750. R, Mak TW and Lowe SW. (1999). Science, 284, 156 ± 159. Yuan J and Horvitz HR. (1992). Development, 116, 309 ± 320. Song Q, Kuang Y, Dixit VM and Vincenz C. (1999). EMBO Yuan JY, Shaham S, Ledoux S, Ellis MH and Horvitz RH. J., 18, 167 ± 178. (1993). Cell, 75, 641 ± 652. Sprang SR. (1997). Curr. Opin. Struct. Biol., 7, 849 ± 856. Zhang SQ, Kovalenko A, Cantarella G and Wallach D. Spector MS, Desnoyers S, Hoeppner DJ and Hengartner (2000). Immunity, 12, 301 ± 311. MO. (1997). Nature, 385, 653 ± 656. Zhou H and Glimcher LH. (1995). Immunity, 2, 545 ± 553. Spilianakis C, Papamatheakis J and Kretsovali A. (2000). Zhou L, Song Z, Tittel J and Steller H. (1999). Mol. Cell, 4, Mol. Cell. Biol., 20, 8489 ± 8498. 745 ± 755. Srinivasula SM, Ahmad M, Fernandes-Alnemri T and Zhu XS, Linho MW, Li G, Chin KC, Maity SN and Ting Alnemri ES. (1998). Mol. Cell, 1, 949 ± 957. JP. (2000). Mol. Cell. Biol., 20, 6051 ± 6061. Stanger BZ, Leder P, Lee TH, Kim E and Seed B. (1995). Zou H, Henzel WJ, Liu X, Lutschg A and Wang X. (1997). Cell, 81, 513 ± 523. Cell, 90, 405 ± 413. Steimle V, Otten LA, Zuerey M and Mach B. (1993). Cell, Zou H, Li Y, Liu X and Wang X. (1999). J. Biol. Chem., 274, 75, 135 ± 146. 11549 ± 11556. Takayama S, Xie Z and Reed JC. (1999). J. Biol. Chem., 274, 781 ± 786. Thome M, Hofmann K, Burns K, Martinon F, Bodmer JL, Mattmann C and Tschopp J. (1998). Curr. Biol., 8, 885 ± 888.

Oncogene