TRAF2-binding BIR1 domain of c-IAP2/MALT1 fusion protein is essential for activation of NF-κB

Abstract

Marginal zone mucosa-associated lymphoid tissue (MALT) B-cell lymphoma is the most common extranodal non-Hodgkin lymphoma. The t(11;18)(q21;q21) translocation occurs frequently in MALT lymphomas and creates a chimeric NF-jB-activating protein containing the baculoviral IAP repeat (BIR) domains of c-IAP2 (inhibitor of apoptosis protein 2) fused with portions of the MALT1 protein. The BIR1 domain of c-IAP2 interacts directly with TRAF2 (TNFa-receptor-associated factor-2), but its role in NF-jB activation is still unclear. Here, we investigated the role of TRAF2 in c-IAP2/MALT1-induced NF-jB activation. We show the BIR1 domain of c-IAP2 is essential for NF-jB activation, whereas BIR2 and BIR3 domains are not. Studies of c-IAP2/MALT1 BIR1 mutant (E47A/R48A) that fails to activate NF-jB showed loss of TRAF2 binding, but retention of TRAF6 binding, suggesting that interaction of c-IAP2/MALT1 with TRAF6 is insufficient for NF-jB induction. In addition, a dominant-negative TRAF2 mutant or downregulation of TRAF2 achieved by small interfering RNA inhibited NF-jB activation by c-IAP2/MALT1 showing that TRAF2 is indispensable. Comparisons of the bioactivity of intact c-IAP2/MALT1 oncoprotein and BIR1 E47A/R48A c-IAP2/MALT1 mutant that cannot bind TRAF2 in a lymphoid cell line provided evidence that TRAF2 interaction is critical for c-IAP2/MALT1-mediated increases in the NF-jB activity, increased expression of endogenous NF-jB target genes (c-FLIP, TRAF1), and resistance to apoptosis.

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“…In mucosa-associated lymphoid tissue (MALT) lymphoma, the fusion of the BIR domain of cIAP2 with the MALT1 is prevalent, and is associated with constitutive activation of canonical NF-kB signaling [41, 42]. Inactivating mutations of cIAP proteins leads to constitutive activation of the non-canonical NF-kB pathway in multiple myeloma [43, 44].…”

Oncogenic Activation of NF- B

“…This activity may require TRAF6 (Noels et al 2007) and/or the ability of the fusion protein to bind an E2 ubiquitin conjugating enzyme containing Ubc13 (Zhou et al 2005). TRAF2 binding to the BIR domains could also contribute to IKKg ubiquitination, but this has not been explicitly shown (Garrison et al 2009;Lucas et al 2007;Samuel et al 2006). c-IAP2 also contains a ubiquitin binding domain (UBD) that is retained in most of the c-IAP1-MALT1 fusion proteins from MALT lymphomas (Gyrd-Hansen et al 2008) (Fig.…”

“…The carboxy-terminal BIR1 domain appears to mediate two functions required for NF-kB activation. First, this domain binds TRAF2, which contributes to NF-kB activation by the c-IAP2-MALT1 fusion protein by an unknown mechanism (Garrison et al 2009;Lucas et al 2007;Samuel et al 2006). Second, the BIR1 domain mediates oligomerization of the c-IAP2-MALT1 fusion protein by interacting heterotypically with the carboxy-terminal region from MALT1 (Lucas et al 2007;Zhou et al 2005).…”

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“…The exact mechanisms of API2-MALT1 triggered oncogenic NF-kB activation are not fully understood, but clearly API2 scaffolding function and MALT1 proteolytic activity contribute to this process. The baculovirus IAP repeat domains of API2 bind to RIP1 and TRAF2, whereas TRAF6 is recruited to the MALT1 moiety [28][29][30][31]. Destruction of the interaction sites abrogates NF-kB activation proving that an involvement of these regulators for API2-MALT1 triggered canonical NF-kB signaling is essential (Figure 2A).…”