The caspase recruitment domain (CARD)-containing proteins CARMA1-3 share high degree of sequence, structure and functional homology. Whereas CARMA1 and CARMA3 have been identified as crucial components of signal transduction pathways that lead to activation of NF-κB transcription factor, little is known about the function of CARMA2. Here we report the identification of two splice variants of CARMA2. One transcript, named CARMA2short (CARMA2sh), is predicted to encode for a CARMA2 polypeptide containing the CARD, coiled coil, and a PDZ domains, but lacking the SH3 and the GuK domains. The second variant, CARMA2cardless (CARMA2cl), encodes for a polypeptide lacking the CARD domain and containing only a portion of the coiled coil domain and a linker region. Expression analysis confirmed the presence of the CARMA2 alternatively spliced transcripts in both human cell lines and tissues. Fluorescence microscopy data show that both splice variants localize in the cytosol. Biochemical experiments indicate that CARMA2sh interacts with TRAF2 and activates NF-κB in a TRAF2-dependent manner. Finally, CARMA2sh variant protects cells from apoptosis induced by different stimuli. Taken together, these results demonstrate that multiple transcripts encoding several CARMA2 isoforms exist in vivo and regulate NF-κB activation and apoptosis. J. Cell. Physiol. 226: 3121–3131, 2011. © 2011 Wiley Periodicals, Inc.

Tumor necrosis factor receptor-associated factor (TRAF) proteins are cytoplasmic regulatory molecules that function as signal transducers for receptors involved in both innate and adaptive humoral immune responses. In this study, we show that TRAF7, the unique noncanonical member of the TRAF family, physically associates with IB kinase/NF-B essential modulator (NEMO) and with the RelA/p65 (p65) member of the NF-B transcription factor family. TRAF7 promotes Lys-29-linked polyubiquitination of NEMO and p65 that results in lysosomal degradation of both proteins and altered activation. TRAF7 also influences p65 nuclear distribution. Microarray expression data are consistent with an inhibitory role for TRAF7 on NF-B and a positive control of AP-1 transcription factor. Finally, functional data indicate that TRAF7 promotes cell death. Thus, this study identifies TRAF7 as a NEMO-and p65-interacting molecule and brings important information on the ubiquitination events that control NF-B transcriptional activity.Tumor necrosis factor receptor-associated factors (TRAFs) 2 have been defined by their ability to couple TNF receptor family proteins to signaling pathways that transduce the cellular effects mediated by TNF family ligands (1, 2). Functionally, TRAF proteins act both as cytoplasmic regulatory molecules and as signal transducers for receptors involved in innate and adaptive humoral immune responses. There are seven known mammalian TRAF proteins (TRAF1-7), of which TRAF1-3 and -5-7 have been shown to interact directly or indirectly with members of the TNF receptor superfamily (1, 2). The domain organization of TRAF proteins is made of a modular structure characteristic of adaptor proteins whose function is to link structurally dissimilar factors. TRAF proteins present a conserved C-terminal coiled-coil domain, the TRAF domain, which is involved in both homo-and heterodimerization (1, 2). Except for TRAF1, TRAFs also contain a conserved RING finger domain and several adjacent zinc finger domains at their N termini (1, 2). The RING finger domains of TRAF2, -6, and -7 have been shown to promote ubiquitination events, which are required for activation of their downstream pathways (3-6).TRAF7 is the most recently identified member of the family, based on its high homology to the RING and zinc finger domains of TRAF proteins (3, 7). However, TRAF7 lacks the conserved C-terminal domain found in TRAF1-6, and instead it has several WD40 repeats in its C-terminal domain (3, 7). The function of TRAF7 is still not completely elucidated. TRAF7 specifically interacts with MEKK3 and potentiates MEKK3-mediated signaling (3, 7). TRAF7 also binds to c-Myb and stimulates its sumoylation, thereby inhibiting its trans-activation activity (8). Finally, it has been shown that TRAF7 is involved in the signal transduction pathway that links Toll-like receptor 2 stimulation to activation of NF-B transcription factor (9). In fact, among the TRAF family of proteins, TRAF2, -5, and -6 are activators of the canonical NF-B pathway, which involves...

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