Tumor Necrosis Factor Receptor-Associated Factors (Trafs)

Tumor necrosis factor receptor-associated factors (TRAFs)

John R Bradley*,1 and Jordan S Pober2

1Department of Medicine, University of Cambridge School of Clinical Medicine, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK; 2Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut, USA

Tumor necrosis factor receptor-associated factors hTNFR2. Despite the co-immunoprecipitation studies, (TRAFS) were initially discovered as adaptor proteins only a very weak interaction between TRAF1 and the that couple the tumor necrosis factor receptor family to cytoplasmic domains of hTNFR2 or mTNFR2 could signaling pathways. More recently they have also been be detected using the two-hybrid system. This seeming shown to be signal transducers of Toll/interleukin-1 contradiction was reconciled by the observations that a family members. Six members of the TRAF family have strong heteromeric interaction occurred between been identi®ed. All TRAF proteins share a C-terminal TRAF1 and TRAF2, and that TRAF1 and TRAF2 homology region termed the TRAF domain that is could form homo- and heterotypic dimers. Conse- capable of binding to the cytoplasmic domain of quently, TRAF1 and TRAF2 can associate with the receptors, and to other TRAF proteins. In addition, cytoplasmic domain of TNFR2 as a heterodimeric TRAFs 2 ± 6 have RING and zinc ®nger motifs that are complex in which only TRAF2 contacts the receptor important for signaling downstream events. TRAF directly. proteins are thought to be important regulators of cell The two proteins were found to share 53% death and cellular responses to stress, and TRAF2, homology in their C-terminal domains, providing TRAF5 and TRAF6 have been demonstrated to mediate evidence of a novel structural domain of about 150 activation of NF-kB and JNK. TRAF proteins are amino acids that was designated the TRAF domain. expressed in normal and diseased tissue in a regulated TRAF domains can be subdivided into TRAF-N and fashion, suggesting that they play an important role in TRAF-C subdomains, corresponding to the amino- physiological and pathological processes. Oncogene and carboxy-terminal proteins of the common TRAF (2001) 20, 6482 ± 6491. sequence. At their less conserved N-terminal regions TRAF1 and TRAF2 were found to be free of proline Keywords: tumor necrosis factor (TNF); TRAF; inter- and glycine residues which destabilize alpha-helices, leukin-1; receptor; signaling exhibiting a distribution of polar and non polar amino acids which could favor formation of coiled-coil alpha- helices. At its N-terminus TRAF2 contains a RING Tumor necrosis factor receptor-associated factors ®nger sequence motif, and ®ve zinc ®nger motifs. (TRAFs) are a family of adaptor proteins that share RING ®ngers have a characteristic pattern of cysteines a common structural domain at their C-terminus. This and histidines that are capable of forming zinc ®nger conserved region allows TRAFs to interact with cell structures, which are thought to mediate DNA binding surface receptors or other signaling molecules. and protein ± protein interactions. RING ®ngers also Although initially identi®ed through their interaction can serve at ubiquitin ligases, targeting proteins for with tumor necrosis factor receptor-2 (TNFR2), degradation by the proteosome (Lorick et al., 1999). TRAFs are able to serve as adaptor proteins for a TRAF1 contains zinc ®ngers but lacks the RING wide variety of receptors that are involved in regulating ®nger domain found in TRAF2. cell death and survival and cellular responses to stress. Rothe and colleagues proposed that TRAF1 and TRAF1 was identi®ed as a novel 45 kd protein that TRAF2 were members of a novel family of signal could be co-immunoprecipitated with human TNF transducers that could interact with TNFR2, and receptor 2 (TNFR2) transfected into the murine perhaps other members of the TNF receptor super- interleukin-2-dependent cytotoxic T cell line CT6, and family. This hypothesis proved well founded. To date also from CT6 cell lysates by a GST fusion protein six members of the TRAF family which share the containing the region of human TNFR2 required for conserved C-terminal domain have been identi®ed. signal transduction (Rothe et al., 1994). At the same TRAF3 was identi®ed using the yeast two hybrid time TRAF2 was identi®ed as a novel 56 kd protein by system as a CD40 binding protein (Hu et al., 1994), using the yeast two-hybrid system to detect proteins also termed CAP-1 (CD40 associated protein-1) (Sato that interact directly with the cytoplasmic domain of et al., 1995) and CRAF1 (Cheng et al., 1995), and as a protein that interacts with the Epstein-Barr virus transforming protein LMP1 (Mosialos et al., 1995). *Correspondence: JR Bradley; TRAF4 was identi®ed by dierential screening of a E-mail: [email protected] cDNA library of breast cancer-derived metastatic Tumor necrosis factor receptor-associated factors JR Bradley and JS Pober 6483 lymph nodes. It was originally termed CART1, because Table 1 TNF receptor family members it contained a conserved C-rich domain associated with Receptor Other names Death domain Ligand RING and TRAF (CART) domains (ReÂ gnier et al., TNFR1 CD120a, p55 + TNF, LT 1995). TRAF5 was identi®ed as a lymphotoxin-b TNFR2 CD120b, p75 ± TNF, LT receptor interacting protein by polymerase chain LTbR±LT reaction ampli®cation using degenerate oligonucleotide Fas CD95, APO-1 + FasL primers corresponding to conserved amino acids in the DR3 WSL-1, TRAMP, LARD, APO-3 + APO-3L TRAF domain of TRAF1, TRAF2, and TRAF3 DR4 TRAILR1 + TRAIL DR5 TRAILR2, KILLER, + TRAIL (Nakano et al., 1996), and independently as a CD40 TRICK2 binding protein using the yeast two hybrid system DR6 + (Ishida et al., 1996). TRAF 6 was separately identi®ed DcR1 TRAILR3, TRID ± TRAIL as a signal transducer involved in the activation of NF- DcR2 TRAILR4, TRUND ± TRAIL DcR3 ± FasL kB by CD40 (Ishida et al., 1996) and interleukin 1 CD27 ± CD27L (Cao et al., 1996), using the yeast two hybrid system CD30 ± CD30L and screening of an EST expression library respec- CD40 ± CD40L tively. Like TRAF2, TRAFs 3 ± 6 have an N-terminal OX40 CD134 ± OX40L RING ®nger as well as zinc ®nger motifs. NGFR P75 + NGF AITR GITR ± AITRL Before considering the structure and potential HVEM HveA, ATAR, TR2, ± LIGHT functions of each of these TRAF proteins further, we LIGHTR will ®rst describe the two main receptor families with 4-1BB CD137 ± CD137L which they have been shown to interact. RANK TRANCE-R ± RANKL TACO ± APRIL BCMA ± APRIL, BLYS TNF receptor family OPG TR1 ± RANKL TROY ± Tumor necrosis factor (also known as TNF-a), and EDAR + EDA XEDAR EDA-A2R ± EDA TNF-b (also known as lymphotoxin) are structurally related molecules that modulate a wide spectrum of responses, including the activation of many genes involved in in¯ammatory and immuno-regulatory especially Jun N-terminal kinase (JNK) activation, responses, cell proliferation, anti-viral responses, and cell death, their cytoplasmic domains are devoid of growth inhibition and cell killing. TNF and lympho- intrinsic enzymatic activity, and generally lack recog- toxin compete for binding to two cell surface receptors, nizable common motifs. The exception occurs in a TNFR1 (CD120a, 55 kd) and TNF-R2 (CD120b, subgroup, which contain a protein motif of approxi- 75 kd). TNFR1 and TNFR2 both contain a 6-cysteine mately 80 amino acids called a `death domain', which consensus motif repeated four times in their extra- is able to bind other death domain containing proteins. cellular regions, but have shown no similarity in their Death domains were originally identi®ed as regions in cytoplasmic regions. Since the identi®cation of these the cytoplasmic tails of TNFR1 and the death inducing two distinct TNF receptors a growing number of TNF receptor Fas/Apo1 (CD95), which were required for receptor family members have been identi®ed through the induction of apoptosis. Four death domain homologies in their extracellular domains, which containing adaptor proteins couple TNFR1 and Fas contain cysteine residues arranged in a repetitive to signaling pathways. FADD (Fas-associated death pattern (Table 1). These cysteine rich domains form domain protein, also known as MORT1 or mediator of tertiary structures that are responsible for ligand receptor-induced cytotoxicity 1) (Chinnaiyan et al., binding, and most of the identi®ed ligands are 1995; Boldin et al., 1995), TRADD (TNF receptor- structurally homologous to TNF. X-ray crystallogra- associated death domain protein) (Hsu et al., 1995), phy has shown that lymphotoxin binds as a trimer to RIP (receptor interacting protein) (Stanger et al., trimeric TNFR1 (Banner et al., 1993), and it has been 1995), and RAIDD (receptor-interacting protein predicted that most ligands bind to TNF receptor (RIP)-associated ICH-1/CED-3-homologous protein family members as trimeric receptor-ligand complexes. with a death domain)/CRADD (caspase and RIP A number of viral proteins containing cysteine-rich adaptor with death domain) (Duan and Dixit, 1997; repeats have also been identi®ed. These viral TNF Ahmad et al., 1997) all contain death domains and receptor homologues are thought to suppress the host bind through homo- and hetero-typic interactions to immune response by sequestering TNF (McFadden et the receptors and to each other. Induction of apoptosis al., 1997). The entry of herpes simplex virus-1 into cells by these adaptor proteins involves caspases, a family of is mediated by a member of the TNF receptor family ICE-related (interleukin-1 b-converting enzyme) aspar- (Montgomery et al., 1996). tyl-directed cysteine proteases that exist in cells as Although members of the TNF receptor superfamily inactive precursors that become activated by cleavage signal a wide range of overlapping cellular responses, at an internal caspase substrate site, so that caspases including dierentiation, proliferation, NF-kB activa- are typically activated as a result of cleavage by tion, stress-activated protein kinase (SAP kinase), themselves or other caspases. Caspases have been

Oncogene Tumor necrosis factor receptor-associated factors JR Bradley and JS Pober 6484 found to be activated following direct association with polarity in Drosophila, but is also important for death domain proteins. Caspase-8 (FLICE) and defense against fungal infection in the adult ¯y caspase-10 (FLICE2) bind through N-terminal death (Lemaitre et al., 1996). The homologous cytosolic eector domains (DED) to an N-terminal DED in Toll/interleukin-1 receptor (TIR) domain has de®ned a FADD (Muzio et al., 1996) and caspase-2 binds Toll/interleukin-1 receptor (TIR) family of mamma- through an N-terminal motif termed CARD (caspase lian, insect, plant and viral proteins. Family members recruitment domain) to a CARD in RAIDD (Chou et include the IL-18 receptor (Torigoe et al., 1997), the al., 1998). Th2 cell regulator T1/ST2 (Coyle et al., 1999), and a TRADD has not been shown to interact directly number of human Toll-like receptors (TLRs). TLR-4 with caspases, and yet was identi®ed as a novel 34 kDa is required for responsiveness to LPS (Hirschfeld et protein that speci®cally interacts with an intracellular al., 2000). A dominant negative mutant of TRAF6 domain of TNFR1 known to be essential for mediating inhibits NF-kB activation through hToll, and it is programmed cell death (Hsu et al., 1995). Further- likely that TRAF6 acts as a signal transducer for more, these studies showed that TRADD leads to both other members of the Toll/IL-1R family (Muzio et al., apoptosis and activation of NF-kB, and that the C- 1998). terminal 118 amino acids of TRADD are sucient to Each member of the TRAF family was identi®ed trigger both of these activities and likewise sucient through its interaction with one or more members of for interaction with the death domain of TNFR1. This the TNF receptor family or IRAK signaling molecules. capacity for TRADD to initiate two divergent The interactions and functions of individual TRAF signaling cascades was explained by the observation proteins have often been considered predominantly in that TRADD can directly interact with FADD, leading relation to the ®rst receptor with which it was found to to induction of apoptosis, and also with TRAF2 interact. However, it is clear that TRAF proteins form leading to activation of NF-kB and JNK (Hsu et al., a complex network in which each TRAF is able to 1996). Thus, two mechanisms for TRAF proteins to interact with, and in¯uence the function of, many interact with members of the TNF receptor super- signaling molecules, either directly or through interac- family were de®ned. TRAF2 can interact directly with tion between dierent TRAF family members. With the cytoplasmic tail of receptors such as TNFR-2 that this background, we will now consider each of the do not contain death domains, and indirectly with TRAF proteins in more detail. death domain containing receptors through association with their death domain adaptor proteins. TRAF1

Toll/IL-1 receptor family The absence of an N-terminal ring ®nger, and the fact that its zinc ®ngers are not arranged in CART (C-rich Interleukin-1 (IL-1) signals its pro-in¯ammatory associated with RING and TRAF) domains make eects through the type-1 IL-1 receptor (IL-1R1). TRAF1 unique amongst the TRAF family. In addition The signaling pathways involve recruitment to the TRAF1 is inducible and shows a restricted tissue cytoplasmic tail of the receptor of the death domain distribution. TRAF1 has been shown to interact containing adaptor protein MyD88. The recruitment indirectly with TNFR2, and directly with several of the receptor associated kinases, IRAK (IL-1 TNFR family members, including CD30 (Lee et al., receptor-associated kinase) (Cao et al., 1996) and/or 1996; Gedrich et al., 1996), 41-BB (Arch and IRAK-2 (Muzio et al., 1997) is then required for Thompson, 1998), herpes virus entry mediator (Mar- activation of NF-kB and SAP kinases. TRAF6 was sters et al., 1997), RANK (receptor activator of NF- identi®ed as a TRAF family member that could kB, also known as TNF-related activation-induced activate NF-kB when overexpressed in human em- cytokine receptor, TRANCE-R) (Wong et al., 1998; bryonic kidney 293 cells, and a dominant negative Galibert et al., 1998), CD40 (Pullen et al., 1999), AITR mutant of TRAF6 was found to inhibit NF-kB (activation-inducible TNFR family member) (Kwon et activation signaled by IL-1, but not TNF (Cao et al., 1999), the Epstein-Barr virus transforming protein al., 1996). TRAF6 participates in IL-1 signaling by LMP-1 (Latent membrane protein-1) (Kaye et al., associating with IRAK and IRAK-2, coupling the 1996) and BCMA (B cell maturation protein) (Hatzo- receptor complex to downstream kinases (Muzio et glou et al., 2000). In addition TRAF1 has been shown al., 1998). Although TRAF6 can associate with IRAK to associate with a number of cytoplasmic proteins and IRAK can associate with the IL-1R complex, the including TANK/I-TRAF (TRAF-associated NF-kap- IRAK-TRAF6 complex has not been shown to paB activator/TRAF interacting protein) (Cheng and associate with the IL-1 receptor, suggesting that Baltimore, 1996; Rothe et al., 1996), TRIP (TRAF- IRAK may dissociate from the receptor before interacting protein) (Lee et al., 1997), A20 (Song et al., binding to TRAF6 (Ling and Goeddel, 2000). 1996), RIP (Hsu et al., 1996), RIP2/CARDIAK IL-1R-1 has a cytoplasmic domain of approximately (CARD-containing interleukin (IL)-1 beta converting 200 amino acids with sequence similarity to the enzyme (ICE) associated kinase) (Thome et al., 1998), Drosophila Toll receptor. Toll was ®rst described as and the caspase 8 binding protein FLIP (FLICE a protein important in establishing dorso-ventral inhibitory protein) (Chaudhary et al., 1999). Although

Oncogene Tumor necrosis factor receptor-associated factors JR Bradley and JS Pober 6485 most of these molecules have been implicated in NF- signaling functions (Takeuchi et al., 1996). The two kB activation, as well as JNK activation and apoptosis, distinct TRAF-N and TRAF-C subdomains of the the role of TRAF1 in these processes is not fully TRAF domain appear to independently mediate self- understood. association and interaction with TRAF1. Interaction TRAF1 has little or no eect on ligand independent with TNFR2 and TRADD requires sequences at the NF-kB or JNK when overexpressed (Schwenzer et al., C terminus of the TRAF-C domain, whereas interac- 1999; Leo et al., 1999), but appears to regulate tion with RIP occurs via sequences at the N-terminus transcriptional activation induced by other mediators. of the TRAF-C domain. The N-terminal RING Overexpression of full-length TRAF1 has been re- ®nger, and two adjacent zinc ®ngers are required for ported to suppress activation of NF-kB by TNF, IL-1, NF-kB activation. Crystallographic studies of the TRAF2 and TRAF6 in human embryonic kidney cells TRAF domain (Park et al., 1999) have shown that (Carpentier and Beyaert, 1999). In HELA cells full- the TRAF-N domain contains a coiled-coil domain length TRAF1 potentiates TNF or IL-1 induced NF- that forms a single alpha-helix. The TRAF-C domain kB activation, and prolongs TNF induced JNK forms a novel eight-stranded anti-parallel beta-sand- activation, whereas overexpression of an N-terminal wich. The TRAF domain self associates into a trimer deletion mutant of TRAF1 interferes with TNF in the shape of a mushroom, with the TRAF-C induced activation of NF-kB and JNK (Schwenzer et domain as the cap, and the coiled-coil domain as the al., 1999). TRAF1 may act as a co-stimulator of NF- stalk. The amino acid residues contributing to kB by CD30 and LMP-1 (ReÂ gnier et al., 1995; trimerization of the TRAF domain of TRAF2 are Devergne et al., 1996; Duckett et al., 1997). To date, conserved among the TRAF-family members. In there have been no reports of mice with natural or crystal structure a receptor peptide from TNFR2 targeted disruption of the TRAF1 gene. binds to a shallow surface depression on the side of An explanation for these apparently divergent roles the mushroom-shaped trimer. The peptide contacts of TRAF1 may in part be provided by the only one TRAF domain, with no contact to the other observation that TRAF1, but not other members of two molecules of the trimer. An SXXE motif, where the TRAF family, is a substrate for caspases that are X may be one of many amino acids, in the TNFR2 activated by TNF family death receptors (Leo et al., peptide interacts with three residues in TRAF2 (R393, 2001; Jang et al., 2001). TRAF1 is cleaved at a Y395 and S467) that are conserved in TRAFs 1, 2, 3 160LVED163 motif to yield two fragments of approxi- and 5. In TRAF6 only R393 is conserved, whereas in mately 28 and 22 kd. The larger C-terminal TRAF TRAF4, which has not yet been shown to interact domain containing fragment can bind TRAF2, with any receptors, none of these residues are sequestering it from the TNFR1 complex (Jang et conserved. Other linear sequences mediate interaction al., 2001). Overexpression of this C-terminal TRAF1 between TRAFs and other receptors. For example, a fragment is capable of suppressing NF-kB induction PXQX(T/S) TRAF binding site has been identi®ed in by TNFR1 and TRAF2, and enhancing the apoptotic CD27 (Akiba et al., 1998); CD30 (Gedrich et al., signal induced through this receptor, consistent with 1996; Aizawa et al., 1997; Boucher et al., 1997), CD40 the observation that inhibition of TNFR1 mediated (Lee et al., 1999), and LMP-1 (Brodeur et al., 1997; NF-kB activation can enhance the apoptotic signal Sandberg et al., 1997). transduced through this receptor (Beg and Baltimore, Although signaling by TRAF molecules involves the 1996; Wang et al., 1996; Van Antwerp et al., 1996; N-terminal RING and zinc ®nger motifs, the structural Liu et al., 1996). In contrast, the N-terminal fragment, basis for downstream events of TRAF2-mediated or a non-cleavable TRAF1 protein in which Asp163 signal transduction are largely unknown. The TRAF was mutated to alanine, had no signi®cant eect on domain of TRAF2 binds receptor peptide without TNFR1 or TRAF2 mediated NF-kB activation. Thus signi®cant conformational change, although full-length cellular responses to signaling through TNF family TRAF proteins may behave in a dierent manner. death receptors may depend on the relative amounts However the downstream events of TRAF2 mediated of full-length versus caspase cleaved TRAF1. Inter- signal transduction, particularly with reference to estingly, TRAF1 is upregulated by ligands of the TNF activation of the NF-kB and activating protein-1 family, and its promoter contains several functionally (AP-1) families of transcription factors, have been important NF-kB binding sites (Schwenzer et al., extensively characterized. 1999). Role of TRAF2 in NF-kB activation NF-kB is comprised of dimers of c-Rel, RelA, RelB, TRAF2 p50, or p52 that are endogenously complexed to members of the IkB family of inhibitor proteins, which Structural studies of TRAF2 sequester NF-kB silently in the cytoplasm. Signals that TRAF2 has been the most extensively studied TRAF, lead to the degradation of IkB permit nuclear both in terms of structure and function. Mutational translocation of NF-kB, where it activates transcrip- analysis of TRAF2 has shown that distinct domains tion of many genes with NF-kB binding sites. At least are involved in interaction with other proteins and two dierent kinases, NF-kB-inducing kinase (NIK)

Oncogene Tumor necrosis factor receptor-associated factors JR Bradley and JS Pober 6486 and mitogen activated protein kinase/extracellular Role of TRAF2 in regulation of AP-1 signal-regulated kinase (ERK) kinase-1 (MEKK1) can phosphorylate IkB kinases (IKKs), which in turn AP-1 is a member of the basic region leucine zipper phosphorylate IkB. Although intimal biochemical family of transcriptional activators and is usually experiments suggested that TRAF2 mediates NF-kB formed from a homo- or heterodimer of Jun, Fos, activation through interaction with NF-kB-inducing and activating transcription factor (ATF) family kinase (NIK), mice with targeted disruptions of the members (Karin et al., 1997). TNF activates two NIK gene are de®cient in NF-kB activation in response subfamilies of the mitogen-activated protein kinase to signals from the LT-b receptor (Luftig et al., 2001), (MAPK) family of serine/threonine kinases that a TRAF3 or TRAF5 pathway, yet retain TNFR1 together are largely responsible for the regulation of signals involving TRAF2. Nevertheless, the TRAF2 AP-1. These are the Jun NH2-terminal kinases (JNKs), interaction with NIK may still be a useful model for also known as stress activated protein kinase 1 understanding interactions with other kinases. A WKI (SAPK1) and the p38 kinases (also known as SAPK2). motif within the TRAF domain of TRAF2, that is Activation of these kinases involves a protein kinase conserved among TRAF family members, is required cascade in which JNK or p38 are activated by a for NIK binding and NF-kB induction. NIK itself MAPK kinase (MAPKK), also known as SAPK/ERK contains a TRAF binding domain, and is able to kinase (SEK) or MEK (MAPK/ERK kinase), which is interact with TRAF2 (and also TRAF1, 3, 5, and 6; itself phosphorylated by a MAPKK kinase Song et al., 1997). The TRAF binding domain contains (MAPKKK, also known as MEKK), which can be within it an IKK interacting domain. A mutation activated by phosphorylation by germinal center kinase within the IKK binding domain that interferes with (GCK, a MAPKKK kinase) and germinal center IKKa binding but not binding of TRAF1, 2, 3 or 6 to kinase-related kinase (GCKK). TRAF2 can interact NIK and blocks NF-kB activation has been described with the SAPK activators MEKK1 (Baud et al., 1999), (Luftig et al., 2001). apoptosis signal-regulating kinase-1, also known as Three new TRAF-domain containing human pro- Ask1, a MAPKKK (Nishitoh et al., 1998; Hoe¯ich et teins termed TEFs (TRAF domain-encompassing al., 1999), germinal center kinase (Yuasa et al., 1998) factors) have recently been identi®ed using bioinfor- and the germinal center kinase-related kinase (Shi and matics approaches. One of these proteins, USP7 Kehrl, 1997; Shi et al., 1999). Ligand induced (TEF1), is a ubiquitin-speci®c protease, in which the oligomerization of chimeric TRAF2 proteins in which TRAF domain is located in the N-terminal part of the the amino-terminal is fused to an FK506 binding molecule, rather than the C-terminal localization seen immunophilin is sucient to induce MEKK1 binding in classical TRAF family members. Recruitment of and JNK activation (Baud et al., 1999). USP7 to TRAFs might be expected to interfere with TRAF2 is thus able to regulate two distinct kinase NF-kB activation by preventing I-kB degradation cascades which lead to activation of NF-kB and JNK. resulting from polyubiquination. In support of this Evidence that TRAF2 mediated NF-kB activation can USP7 inhibits NF-kB induction caused by transient be disengaged from JNK activation is provided by over-expression of TRAF2 and/or TRAF6 (Zapata et studies using the rotavirus caspid protein V4 and its al., 2001). However, expression of a TRAF domain- cleavage product VP8*, which contains the conserved containing region of USP7 in the absence of its TRAF interacting sequence PXQXT, and can selec- ubiquitin-protease domain is more inhibitory than tively direct transcription through NF-kB via a full-length USP7. TRAF2-NIK signaling pathway whilst inhibiting Several other molecules that in¯uence TRAF2 transcriptional responses through AP-1 (LaMonica et mediated NF-kB activation have been described. TRIP al., 2001). (TRAF-interacting protein) inhibits TRAF2 mediated NF-kB activation (Lee et al., 1997), whereas I-TRAF/ Genetic manipulation of TRAF2 TANK has been described as both an inhibitor (Rothe et al., 1996) and a co-inducer of TRAF2 mediated Further clari®cation of the distinct roles of TRAF2 in NFkB activation (Cheng and Baltimore, 1996). NF-kB and JNK activation is provided by experiments Receptor interacting protein-2 (RIP2) was identi®ed using dominant negative TRAF2 molecules and as a novel NF-kB-activating and cell death inducing TRAF2 null mice. In vitro studies have shown that kinase that can be recruited to the TNFR1 and CD40 expression of a dominant negative TRAF2 mutant receptor signaling complexes. RIP2 interacts directly lacking the amino-terminal RING ®nger domain with TRAF1, TRAF5, and TRAF6, but not with (TRAF2DN) prevents TNF-induced, but not IL-1- TRAF2, TRAF3 or TRAF4 (McCarthy et al., 1998). induced, IkBa degradation and NF-kB activation, and Although RIP2 and TRAF2 do not directly interact, a also TNF induced JNK activation (Rothe et al., 1995; dominant negative TRAF2 can inhibit RIP2-induced Jobin et al., 1999). However, mice expressing this NF-kB activity, suggesting that TRAF2 may interact dominant negative TRAF2 transgene show normal with RIP2 through TRAF1. The zinc ®nger protein TNF-mediated NF-kB activation, but severely im- A20 can also act as an inhibitor of NF-kB activation paired JNK activation (Lee et al., 1997). Fibroblasts through interaction with TRAF1/TRAF2 (Song et al., from TRAF2 null mice show complete disruption of 1996). TNF-mediated JNK activation, but only quantitative

Oncogene Tumor necrosis factor receptor-associated factors JR Bradley and JS Pober 6487 abnormalities in TNF-induced NF-kB activation (Yeh CD40 in a ligand dependent manner, but is not et al., 1997). Thus, TRAF2 appears to be essential for required for CD40 induction of antibody secretion. JNK activation, but its role in NF-kB activation TRAF2 appears to play a positive role in B cell appears to be dispensable. RIP null mice have a more dierentiation, but this activity is apparent even when severe defect in TNF-mediated activation of NF-kB, its binding site on CD40 is disrupted. and TRAF2 may act on the NF-kB pathway through Further evidence that TRAF3 is not required for its interactions with RIP. CD40 signaling in B cells is provided by experiments TRAF2 null and TRAF2DN mice also provide using TRAF3 null mice. Mice de®cient in TRAF3 evidence for a role of TRAF2 in apoptotic signaling are depleted in all lineages of peripheral leucocytes, pathways. Sensitivity to TNF induced cell death is and die shortly after birth (Xu et al., 1996). increased in thymocytes and embryonic ®broblasts However, B cells from TRAF37/7 upregulate CD23 from TRAF2DN and TRAF2 null mice, suggesting and proliferate normally in response to CD40 ligand that TRAF2 has an anti-apoptotic function distinct stimulation, and fetal liver cells from TRAF3 from that mediated by NF-kB. TRAF2 binds a de®cient mice can reconstitute the immune system number of proteins that inhibit apoptosis, including of irradiated wild type mice, although isotype c-IAPs. c-IAP1 and c-IAP2 are mammalian proteins switching in response to T-dependent antigens is that are closely related to the inhibitor of apoptosis defective. Thus TRAF3 is not required for CD40 protein (IAP) family originally identi®ed in baculo- signaling, but appears to be important in T cell- viruses. Both c-IAPs are recruited to TNFR2 through dependent immune responses. interaction with a TRAF1-TRAF2 heterocomplex These eects of TRAF3 may be mediated through (Rothe et al., 1995). other TNF receptor family members. TRAF3 was In addition to these functional studies using mutated independently identi®ed as a protein that interacts TRAF2 proteins, nature has provided its own with the Epstein-Barr virus latent membrane protein, dominant negative TRAF2 protein in the form of LMP1, and has since been shown to interact with TRAF2A, a splice variant of TRAF2. TRAF2A several TNF receptor family members. Epstein-Barr mRNA encodes an additional seven amino acid virus causes proliferation of infected B lymphocytes residues within the amino terminal RING ®nger through the expression of nuclear proteins and the domain of TRAF2 (Brink and Lodish, 1998). TRA- integral membrane protein, LMP1, which is a F2A is unable to stimulate NF-kB activity when constitutively active TNF receptor. The C-terminal overexpressed in 293 cells and acts as a dominant cytoplasmic domain contains a site that binds inhibitor of TNFR2 mediated NF-kB activation. TRAF3, and also TRAFs 1, 2 and 5, and mediates Furthermore TRAF2A has a short half life of both EBV induced B cell proliferation and NF-kB approximately 100 min, but is stabilized by TRAF1 activation (Izumi et al., 1999). TRAF3 is also (and TRAF2), providing a further mechanism by recruited in a ligand dependent manner to the which TRAF1 may act as a negative regulator of lymphotoxin-b receptor (LTbR) and can have an NF-kB activation. inhibitory eect on NF-kB activation through LTbR. It is also involved in the induction of cell death by LT-b (VanArsdale et al., 1997), and a dominant TRAF3 negative mutant of TRAF3 inhibits cell death signaling by lymphotoxin-b, but not TNF (Force et TRAF3 was ®rst described as a molecule that binds to al., 1997). the cytoplasmic tail of CD40. CD40 is expressed on many cell types, including B cells, dendritic cells, macrophages and monocytes, endothelial cells, smooth TRAF4 muscle cells and ®broblasts. CD40 is a receptor for CD40 ligand (CD 154), which is transiently expressed TRAF4 (originally designated CART1 because it on activated CD4+ T cells. Signaling through CD40 contained a C-rich domain associated with RING in B cells induces rescue from apoptosis, proliferation, and TRAF) was identi®ed by dierential screening of a dierentiation, Ig production, class switching and cDNA library of breast cancer-derived metastatic expression of co-stimulatory molecules. The interac- lymph nodes (ReÂ gnier et al., 1995). TRAF4 localizes tion of TRAF3 with CD40 is ligand dependent predominantly to the nucleus, and has not been shown (KuhneÂ et al., 1997), but binding of TRAF3 to to regulate signaling through cell surface receptors. In CD40 in B cells is not necessary for the induction of vitro binding assays have demonstrated that TRAF4 antibody secretion (Hostager and Bishop, 1999). interacts weakly with LTbR, and weakly with the p75 Rather, overexpression of TRAF3 inhibits CD40 nerve growth factor receptor, but not with TNFR1, mediated antibody secretion, and this eect was TNFR2, Fas or CD40 (Krajewska et al., 1998). dependent on an intact TRAF binding site on TRAF4 is highly expressed during embryogenesis in CD40. A dominant negative N-terminal truncated the mouse, most noticeably in the central and TRAF3 is also inhibitory, suggesting that the physical peripheral nervous system (Masson et al., 1998). In association of TRAF3 with CD40 mediates its the adult mouse it is expressed in the hippocampus and negative regulatory function. TRAF2 also binds to olfactory bulb but not other normal tissues.

Oncogene Tumor necrosis factor receptor-associated factors JR Bradley and JS Pober 6488 TRAF5 Mutant CD40 molecules that eliminate interaction with TRAF 1, 2 and 3 or with TRAF6 have helped TRAF5 was identi®ed as a protein that could interact to de®ne the role of TRAF6 in CD40 mediated with LTbR (Nakano et al., 1996) and CD40 (Ishida et signaling (Pullen et al., 1999). Mutations that eliminate al., 1996), and has subsequently been implicated in NF- TRAF6 binding but allow binding of TRAF1, 2 and 3 kB activation by CD27 (Akiba et al., 1998) and CD30 to CD40 diminish CD40 dependent NF-kB, JNK and (Aizawa et al., 1997). NF-kB is activated by over- p38 activation, whereas mutations that prevent binding expression of full-length TRAF5 but not a truncated of all TRAFs abolish JNK and p38 activation, but form lacking the zinc binding region (Nakano et al., permit diminished NF-kB activation. 1996). The same truncated TRAF5 mutant also The abnormal phenotype of TRAF6 null mice partially inhibits NF-kB activation mediated by over- relates predominantly to defective bone formation. expression of LTbR, suggesting that TRAF5 is Severe osteopetrosis with defects in bone remodeling involved in LTbR signal transduction. Interaction of and tooth eruption caused by impaired osteoclast TRAF5 with CD40 is indirect, involving hetero- formation are found in TRAF6 de®cient mice which oligomerization with TRAF3 (Leo et al., 1999). An become runted, and die at an early age (Naito et al., N-terminal deletion mutant of TRAF5 lacking the 1999; Lomaga et al., 1999). Studies using cells derived RING ®nger suppresses CD40 mediated CD23 expres- from these mutant mice con®rm the role of TRAF6 in sion (Ishida et al., 1996). Further evidence for a role of IL-1 and CD40 mediated signaling. IL-1 induced TRAF5 in CD40 signaling is provided by studies using activation of NF-kB and JNK in embryonic ®broblasts cells from TRAF5 null mice. TRAF5 null mice are and IL-1 induced thymocyte proliferation are defective. born healthy with no obvious defects (Nakano et al., In addition CD40 mediated NF-kB activation and 1999). Cells from these mutant mice display normal proliferation in splenic B cells is signi®cantly reduced. NFkB and JNK activation through CD27 or CD40, Studies using embryonic ®broblasts from TRAF6 but CD27 or CD40 mediated lymphocyte activation knockout mice have also de®ned a role for TRAF6 in was substantially impaired. IL17 signal transduction. IL17 fails to activate NF-kB and JNK in TRAF6 de®cient cells, abolishing IL17 induced IL6 and intracellular adhesion molecule 1 TRAF6 expression (Schwandner et al., 2000). This defect can be overcome by restoration of TRAF6 to the cells by TRAF6 was initially identi®ed as a signal transducer transient transfection. for IL-1 (Cao et al., 1996). Overexpression of TRAF6 activates NFkB, and a dominant negative mutant of TRAF6 inhibits NF-kB activation by IL-1 but not Subcellular localization of TRAF proteins TNF. TRAF 6 also activates JNK and p38 when overexpressed (Song et al., 1997), and as with TRAF2 TRAF proteins acts as intracellular adaptors that are oligomerization of TRAF6 has been shown to be recruited to dierent receptors, and the molecular basis important for JNK activation (Baud et al., 1999). IL-1 for the functional interactions between dierent induces recruitment of IRAK to activated receptors. TRAFs and receptors have been characterized. The IRAK becomes highly phosphorylated and then forms mechanism through which TRAF proteins move to a complex with TRAF6 that is not associated with the dierent subcellular localizations is less clear, although receptor. After IL-1 stimulation TRAF6 can also exist there is evidence that TRAF proteins associate with in a separate complex with T6BP (TRAF6 binding dierent intracellular proteins that may facilitate their protein). IRAK is not present in TRAF6-T6BP recruitment to cell surface receptor complexes. In complexes, but is required for their formation (Ling addition, targeting of TRAF proteins to the nucleus and Goeddel, 2000). T6BP does not seem to play a may provide a mechanism for directly regulating direct role in NF-kB or JNK activation. transcriptional activity. TRAF6 can activate IKK through interaction with a With the exception of TRAF4, TRAF proteins are separate hetero-dimeric protein complex composed of cytosolic proteins, although overexpressed TRAF2, the ubiquitin conjugating enzyme Ubc13 and the Ubc- TRAF5 and TRAF6 predominantly localize to mem- like protein Uev1A. Ubiquitination of proteins involves brane containing cell fractions (Dadgostar and Cheng, an enzyme cascade composed of a ubiquitin activating 2000). TRAF4 predominantly localizes to the nucleus, enzyme, a ubiquitin conjugating enzyme, and a but overexpressed TRAF4 can be found in the cytosol ubiquitin protein ligase. The RING ®nger domain of of transfected cells (Krajewska et al., 1998). TRAF6 can function as a ubiquitin ligase, which, Endogenous TRAF2 is a cytosolic protein (Rothe et together with the Ubc13/Uev1A complex mediates al., 1994), that is recruited to membrane associated polyubiquitination of an as yet unidenti®ed protein receptors. TRAF2 interacts through its RING domain that is involved in IKK activation (Deng et al., 2000). with the actin-binding protein ®lamin (Leonardi et al., TRAF6 also interacts with CD40, using a dierent 2000). Overexpression of ®lamin inhibits TRAF2- site than TRAFs 1, 2 and 3. TRAF6 binds within the induced activation of NF-kB and JNK, and NF-kB sequence 231QEPQEINF that has been mapped to a activation induced by TNF, IL-1, Toll receptors and membrane proximal region (Pullen et al., 1998). TRAF6, possibly by sequestering TRAF2 (and

Oncogene Tumor necrosis factor receptor-associated factors JR Bradley and JS Pober 6489 TRAF6) away from signaling complexes. In endothelial TRAF2A is ubiquitously expressed, but its expression cells TRAF2 constitutively associates with the mem- relative to TRAF2 varies from very low in brain, lung brane organizing protein caveolin-1, and is recruited as and heart, to almost equivalent levels in spleen (Brink part of a TRAF2-caveolin complex to TNF receptors and Lodish, 1998). High levels of TRAF5 are observed (Feng et al., 2001). A fragment containing the RING in both spleen and lung. TRAF4 was identi®ed and zinc ®ngers, can be targeted to the nucleus of through its selective expression in breast carcinoma, endothelial cells, where it may directly regulate but can be detected in normal human adult thymic transcriptional regulatory activity (Min et al., 1998). epithelial cells and lymph node dendritic cells, and the TRAF3 is linked to the microtubule network by basal cell layer of most epithelia in the body MIP-T3 (Ling and Goeddel, 2000). MIP-T3 is a novel (Krajewska et al., 1998). protein that binds to tubulin in vitro, and to Taxol- The pattern of TRAF expression is altered in stabilized microtubules in cells. MIP-T3 recruits lymphoid malignancies, with certain cancer types TRAF3 to microtubules when both proteins are displaying particular patterns of TRAF expression overexpressed. CD40 ligand stimulation induces dis- (Zapata et al., 2000). For example, upregulation of sociation of TRAF3 from endogenous TRAF3-MIP- TRAF1 has consistently been reported in lymphoid T3 complexes, and recruitment of TRAF3 to the CD40 malignancies (Zapata et al., 2000; Durkop et al., 1999; receptor complex. Thus MIP-T3 may sequester TRAF3 Izban et al., 2000), with increased expression of to the cytoskeletal network, providing a mechanism TRAF1 in Epstein-Barr virus-transformed lymphoid through which it may be directed to dierent cellular cells and Reed-Sternberg cells in Hodgkin's disease. compartments. Enforced membrane localization of TRAF proteins thus physically and functionally TRAF3 through the addition of a myristolation signal connect cell surface receptors to signaling pathways is sucient to convert it to a potent activator of JNK involved in regulation of diverse cellular responses, (Dadgostar and Cheng, 2000). which include activation, dierentiation and survival. Considerable progress has been made towards understanding the molecular basis of their physical and Tissue expression of TRAF proteins functional interactions. The regulated expression of these proteins in normal and diseased tissues suggests Although considerable information has accumulated that they play an important role in physiological and concerning the molecular structure and function of pathological processes. TRAF proteins, less is known about their expression and role in vivo. In mice TRAF1 is selectively expressed in spleen, lung and testis, whereas TRAF2, TRAF3, TRAF5 and TRAF6 are ubiquitously expressed (Rothe Acknowledgments et al., 1995; Nakano et al., 1996; Ishida et al., 1996). JR Bradley is supported by the National Kidney Research The highest levels of TRAF2 are found in spleen. Fund (UK).

References

Ahmad M, Srinivasula SM, Wang L, Talanian RV, Litwack Cao Z, Xiong J, Takeuchi M, Kurama T and Goeddel DV. G, Fernandes-Alnemri T and Alnemri ES. (1997). Nature, (1996). Nature, 383, 443 ± 446. 385, 86 ± 89. Carpentier I and Beyaert R. (1999). FEBS Lett., 460, 246 ± Aizawa S, Nakano H, Ishida T, Horie R, Nagai M, Ito K, 250. Yagita H, Okumura K, Inoue J and Watanabe T. (1997). Chaudhary PM, Jasmin A, Eby MT and Hood L. (1999). J. Biol. Chem., 272, 2042 ± 2045. Oncogene, 18, 5738 ± 5746. Akiba H, Nakano H, Nishinaka S, Shindo M, Kobata T, Cheng G and Baltimore D. (1996). Genes Dev., 10, 963 ± 973. Atsuta M, Morimoto C, Ware CF, Malinin NL, Wallach ChengG,ClearyAM,YeZ-S,HongDI,LedermanSand D, Yagita H and Okumura K. (1998). J. Biol. Chem., 273, Baltimore D. (1995). Science, 267, 1494 ± 1498. 13353 ± 13358. Chinnaiyan AM, O'Rourke K, Tewari M and Dixit VM. Arch RH and Thompson CB. (1998). Mol. Cell. Biol., 18, (1995). Cell, 81, 505 ± 512. 558 ± 565. Chou JJ, Matsuo H, Dvan H and Wagner G. (1998). Cell, 94, Banner DW, D'Arcy A, Janes W, Gentz R, Schoenfeld HJ, 171 ± 180. Broger C, Loetscher H and Lesslauer W. (1993). Cell, 73, CoyleAJ,LloydC,TianJ,NguyenT,ErikksonC,WangL, 431 ± 445. Ottoson P, Persson P, Delaney T, Lehar S, Lin S, Poisson Baud V, Liu Z-G, Bennett B, Suzuki N, Xia Y and Karin M. L, Meisel C, Kamradt T, Bjerke T, Levinson D and (1999). Genes Dev., 13, 1297 ± 1308. Gutierrez-Ramos JC. (1999). J. Exp. Med., 190, 895 ± 902. Beg AA and Baltimore D. (1996). Science, 274, 782 ± 784. Dadgostar H and Cheng G. (2000). J. Biol. Chem., 28, 2539 ± Boucher L-M, MarengeÁ re LEM, Y, Thukral S and Mak TW. 2544. (1997). Biochem. Biophys. Res. Comm., 233, 592 ± 600. Deng L, Wang C, Spencer E, Yang L, Broun A, You J, Brink R and Lodish HF. (1998). J. Biol. Chem., 273, 4129 ± Slaughter C, Pickart C and Chen ZJ. (2000). Cell, 103, 4134. 351 ± 361. Brodeur SR, Cheng G, Baltimore D and Thorley-Lawson DA. (1997). J. Biol. Chem., 272, 19777 ± 19784.

Oncogene Tumor necrosis factor receptor-associated factors JR Bradley and JS Pober 6490 Devergne O, Hatzivassiliou E, Izumi KM, Kaye KM, Lee HH, Dempsey PW, Parks TP, Zhu X, Baltimore D and Kleijnen MF, Kie E and Mosialos G. (1996). Mol. Cell. Cheng G. (1999). Proc. Natl. Acad. Sci. USA, 96, 1421 ± Biol., 16, 7098 ± 7108. 1426. Duan H and Dixit VM. (1997). Nature, 385, 86 ± 89. Lee SY, Lee SY and Choi Y. (1997). J. Exp. Med., 185, Duckett CS, Gedrich RW, Gil®llan MC and Thompson CB. 1275 ± 1285. (1997). Mol. Cell. Biol., 17, 1535 ± 1542. LeeSY,LeeSY,KandalaG,LiouM-L,LiouH-CandChoi Durkop H, Foss HD, Demel G, Klotzbach H, Hahn C and Y. (1996). Proc. Natl. Acad. Sci. USA, 93, 9699 ± 9703. Stein H. (1999). Blood, 93, 617 ± 623. Lee SY, Reichlin A, Santana A, Sokol KA, Nussenzweig MC Feng X, Gaeta ML, Madge LA, Yang JH, Bradley JR and and Choi Y. (1997). Immunity, 7, 703 ± 713. Pober JS. (2001). J. Biol. Chem., 276, 8341 ± 8349. Lemaitre B, Nicolas E, Michaut L, Reichhart JM and Force WR, Cheung TC and Ware CF. (1997). J. Biol. Chem., Homann JA. (1996). Cell, 86, 973 ± 983. 272, 30835 ± 30840. Torigoe K, Ushio S, Okura T, Kobayashi S, Taniai M, Galibert L, Tometsko ME, Anderson DM, Cosman D and Kunikata T, Murakami T, Sanou O, Kojima H, Fujii M, Dougall WC. (1998). J. Biol. Chem., 273, 34120 ± 34127. Ohta T, Ikeda M, Ikegami H and Kurimoto M. (1997). J. Gedrich RW, Gil®llan MC, Duckett CS, Van Dongen JL and Biol. Chem., 272, 25737 ± 25742. Thompson CB. (1996). J. Biol. Chem., 271, 12852 ± 12858. Leo E, Deveraux QL, Buchholtz C, Welsh K, Matsuzawa S-i, Hatzoglou A, Roussel J, Bourgeade MF, Rogier E, Madry C, Stennicke HR, Salvesen GS and Reed JC. (2001). J. Biol. Inoue J, Devergne O and Tsapis A. (2000). J. Immunol., Chem., 276, 8087 ± 8093. 165, 1322 ± 1330. Leo E, Welsh K, Matsuzawa S, Zapata JM, Kitada S, Hirschfeld M, Ma Y, Weis JH, Vogel SN and Weis JJ. (2000). Mitchell RS, Ely KR and Reed JC. (1999). J. Biol. Chem., J. Immunol., 165, 618 ± 622. 274, 22414 ± 22422. Hoe¯ichKP,YehWC,YaoZ,MakTWandWoodgettJR. Leonardi A, Ellinger-Ziegelbauer H, Franzoso G, Brown K (1999). Oncogene, 18, 5814 ± 5820. and Siebenlist U. (2000). J. Biol. Chem., 27, 271 ± 278. Hostager BS and Bishop GA. (1999). J. Immunol., 162, Ling L and Goeddel DV. (2000). J. Biol. Chem., 275, 23852 ± 6307 ± 6311. 23860. Hsu H, Shu H-B, Pan M-G and Goeddel DV. (1996). Cell, Ling L and Goeddel DV. (2000). Proc. Natl. Acad. Sci. USA, 84, 299 ± 308. 97, 9567 ± 9572. Hsu H, Xiong J and Goeddel DV. (1995). Cell, 81, 495 ± 504. Liu Z-g, Hsu H, Goeddel DV and Karin M. (1996). Cell, 87, HuHM,O'RourkeK,BogusiMSandDixitVM.(1994).J. 565 ± 576. Biol. Chem., 269, 30069 ± 30072. Lomaga MA, Yeh W-C, Sarosi I, Duncan GS, Furlonger C, Ishida T, Tojo T, Aoki T, Kobayashi N, Ohishi T, Watanabe Ho A, Morony S, Capparelli C, Van G, Kaufman S, van T, Yamamoto T and Inoue J-I. (1996). Proc. Natl. Acad. der Heiden A, Itie A, Wakeham A, Khoo W, Sasaki T, Sci. USA, 93, 9437 ± 9442. Cao Z, Penninger JM, Paige CJ, Lacey DL, Dunstan CR, Ishida T, Mizushima S, Azuma S, Kobayashi N, Tojo S, Boyle WJ, Goeddel DV and Mak TW. (1999). Genes Dev., Kobayashi N, Tojo T, Suzuki K, Aizawa S, Watanabe T, 13, 1015 ± 1024. Mosialos G, Kie E, Yamamoto T and Inoue J-I. (1996). Lorick KL, Jensen JP, Fang S, Ong AM, Hatakeyama S and J. Biol. Chem., 271, 28745 ± 28748. Weissman AM. (1999). Proc. Natl. Acad. Sci. USA, 96, Izban KF, Ergin M, Martinez RL and Alkan S. (2000). Mod. 11364 ± 11369. Pathol., 13, 1324 ± 1331. Luftig MA, Cahir-McFarland E, Mosialos G and Kie ED. Izumi KM, McFarland EC, Riley EA, Rizzo D, Chen Y and (2001). J. Biol. Chem., 276, 14602 ± 14606. Kie E. (1999). J. Virol., 73, 9908 ± 9916. Marsters SA, Ayres TM, Skubatch M, Gray CL, Rothe M Jang HD, Chung YM, Baik JH, Choi YG, Park IS, Jung YK and Ashkenazi A. (1997). J. Biol. Chem., 272, 14029 ± and Lee SY. (2001). Biochem. Biophys. Res. Commun., 14032. 281, 499 ± 505. Masson R, ReÂ gnier CH, Chenard M-P, Wendling C, Mattei Jobin C, Holt L, Bradham CA, Streetz K, Brenner DA and M-G, Tomasetto C and Rio M-C. (1998). Mech. Dev., 71, Sartor RB. (1999). J. Immunol., 162, 4447 ± 4454. 187 ± 191. Karin M, Liu Zg and Zandi E. (1997). Curr. Opin. Cell. Biol., McCarthyJV,NiJandDixitVM.(1998).J. Biol. Chem., 9, 240 ± 246. 273, 16968 ± 16975. Nishitoh H, Saitoh M, Mochida Y, Takeda K, Nakano H, McFadden G, Schreiber M and Sedger L. (1997). J. Rothe M, Miyazono K and Ichijo H. (1998). Mol. Cell, 2, Neuroimmunol., 72, 119 ± 126. 389 ± 395. Min W, Bradley JR, Galbraith JJ, Jones SJ, Ledgerwood EC Kaye KM, Devergne O, Harada JN, Izumi KM, Zalaman- and Pober JS. (1998). J. Immunol., 161, 319 ± 324. chili R, Kie E and Mosialos G. (1996). Proc. Natl. Acad. Montgomery RI, Warner MS, Lum BJ and Spear PG. (1996). Sci. USA, 93, 11085 ± 11090. Cell, 87, 427 ± 436. Krajewska M, Krajewski S, Zapata JM, Van Arsdale T, Boldin MP, Varfolomeev EE, Pancer Z, Mett IL, Camonis Gascoyne RD, Berern K, McFadden D, Shabaik A, Hugh JH and Wallach D. (1995). J. Biol. Chem., 270, 7795 ± J, Reynolds A, Clevenger CV and Reed JC. (1998). Am. J. 7798. Pathol., 152, 1549 ± 1561. Mosialos G, Birkenbach M, Yalamanchili R, VanArsdale T, KuhneÂ MR, Robbins M, Hambor JE, Mackey MF, Kosaka Ware C and Kie E. (1995). Cell, 80, 389 ± 399. Y, Nishimura T, Gigley JP, Noelle RJ and Calderhead Muzio M, Chinnaiyan AM, Kischkel FC, O'Rourke K, DM. (1997). J. Exp. Med., 186, 337 ± 342. Shevchenko A, Ni J, Scadi C, Bretz JD, Zhang M, Gentz KwonB,YuKY,NiJ,YuGL,JangIK,KimYJ,XingL, R, Mann M, Krammer PH, Peter ME and Dixit VM. Liu D, Wang SX and Kwon BS. (1999). J. Biol. Chem., (1996). Cell, 85, 817 ± 827. 274, 6056 ± 6061. Muzio M, Natoli G, Saccani S, Levrero M and Mantovani A. LaMonica R, Kocer SS, Nazarova J, Dowling W, Geimonen (1998). J. Exp. Med., 187, 2097 ± 2101. E, Shaw RD and Mackow ER. (2001). J. Biol. Chem., 276, Muzio M, Ni J, Feng P and Dixit VM. (1997). Science, 278, 19889 ± 19896. 1612 ± 1615.

Oncogene Tumor necrosis factor receptor-associated factors JR Bradley and JS Pober 6491 Naito A, Azuma S, Tanaka S, Miyazaki T, Takaki S, Shi CS, Leonardi A, Kyriakis J, Siebenlist U and Kehrl JH. Takatsu K, Nakao K, Nakamura K, Katsuki M, (1999). J. Immunol., 163, 3279 ± 3285. Yamamoto T and Inoue J. (1999). Genes Cells, 4, 353 ± Song HY, ReÂ gnier CH, Kirschning CJ, Goeddel DV and 362. Rothe M. (1997). Proc. Natl. Acad. Sci. USA, 94, 9792 ± Nakano H, Oshima H, Chung W, Williams-Abbott L, Ware 9796. CF, Yagita H and Okumura K. (1996). J. Biol. Chem., 271, Song HY, Rothe M and Goeddel DV. (1996). Proc. Natl. 14661 ± 14664. Acad.Sci.USA,93, 6721 ± 6725. Nakano H, Sakon S, Koseki H, Takemori T, Tada K, Stanger BZ, Leder P, Lee T-H, Kim E and Seed B. (1995). Matsumoto M, Munechika E, Sakai T, Shirasawa T, Cell, 81, 513 ± 523. AkibaH,KobataT,SanteeSM,WareCF,RennertPD, Takeuchi M, Rothe M and Goeddel DV. (1996). J. Biol. Taniguchi M, Yagita H and Okumura K. (1999). Proc. Chem., 271, 19935 ± 19942. Natl. Acad. Sci. USA, 96, 9803 ± 9808. Thome M, Hofmann K, Burns K, Martinon F, Bodmer JL, Park YC, Burkitt V, Villa AR, Tong L and Wu H. (1999). Mattmann C and Tschopp J. (1998). Curr. Biol., 8, 885 ± Nature, 398, 533 ± 538. 888. Pullen SS, Dang TT, Crute JJ and Kehry MR. (1999). J. Biol. VanAntwerpDJ,MartinSJ,KafriT,GreenDRandVerma Chem., 274, 14246 ± 14254. IM. (1996). Science, 274, 787 ± 789. Pullen SS, Miller HG, Everdeen DS, Dang TT, Crute JJ and VanArsdale TL, VanArsdale SL, Force WR, Walter BN, Kehry MR. (1998). Biochemistry, 37, 11836 ± 11845. Mosialos G, Kie E, Reed JC and Ware CF. (1997). Proc. ReÂ gnier CH, Song HY, Gao X, Goeddel DV, Cao Z and Natl. Acad. Sci. USA, 94, 2460 ± 2465. Rothe M. (1997). Cell, 90, 373 ± 383. Wang C-Y, Mayo MW and Baldwin AS. (1996). Science, ReÂ gnier CH, Tomasetto C, Moog-Lutz C, Chenard MP, 274, 784 ± 787. Wendling C, Basset P and Rio MC. (1995). J. Biol. Chem., Wong BR, Josien R, Lee SY, Vologodskaia M, Steinman 270, 25715 ± 25721. RM and Choi Y. (1998). J. Biol. Chem., 273, 28355 ± Rothe M, Pan M-G, Henzel WJ, Ayres TM and Goeddel 28359. DV. (1995). Cell, 83, 1243 ± 1252. Xu Y, Cheng G and Baltimore D. (1996). Immunity, 5, 407 ± Rothe M, Wong SC, Henzel WJ and Goeddel DV. (1994). 415. Cell, 78, 681 ± 692. Yeh W-C, Shahinian A, Speiser D, Kraunus J, Billia F, Rothe M, Xiong J, Shu H-B, Williamson K, Goddard A and Wakeham A, de la Pompa JL, Ferrick D, Hum B, Iscove Goeddel DV. (1996). Proc. Natl. Acad. Sci. USA, 93, N, Ohashi P, Rothe M, Goeddel DV and Mak TW. (1997). 8241 ± 8246. Immunity, 7, 715 ± 725. Sandberg M, Hammerschmidt W and Sugden B. (1997). J. Yuasa T, Ohno S, Kehrl JH and Kyriakis JM. (1998). J. Biol. Virol., 71, 4649 ± 4656. Chem., 273, 22681 ± 22692. Sato T, Irie S and Reed JC. (1995). FEBS Lett., 358, 113 ± ZapataJM,KrajewskaM,KrajewskiS,KitadaS,WelshK, 118. Monks A, McCloskey N, Gordon J, Kipps TJ, Gascoyne Schwandner R, Yamaguchi K and Cao Z. (2000). J. Exp. RD, Shabaik A and Reed JC. (2000). J. Immunol., 165, Med., 19, 1233 ± 1240. 5084 ± 5096. Schwenzer R, Siemienski K, Liptay S, Schubert G, Peters N, Zapata JM, Pawlowski K, Haas E, Ware CF, Godzik A and Scheurich P, Schmid RM and Wajant H. (1999). J. Biol. Reed JC. (2001). J. Biol. Chem., 276, 24242 ± 24252. Chem., 274, 19368 ± 19374. Shi CS and Kehrl JH. (1997). J. Biol. Chem., 272, 32102 ± 32107.

Oncogene