Differential Requirements for Tumor Necrosis Factor Receptor-associated Factor Family Proteins in CD40-mediated Induction of NF-κB and Jun N-terminal Kinase Activation

Abstract

CD40 is a member of the tumor necrosis factor receptor family that mediates a number of important signaling events in B-lymphocytes and some other types of cells through interaction of its cytoplasmic (ct) domain with tumor necrosis factor receptor-associated factor (TRAF) proteins. Alanine substitution and truncation mutants of the human CD40ct domain were generated, revealing residues critical for binding TRAF2, TRAF3, or both of these proteins. In contrast to TRAF2 and TRAF3, direct binding of TRAF1, TRAF4, TRAF5, or TRAF6 to CD40 was not detected. However, TRAF5 could be recruited to wild-type CD40 in a TRAF3-dependent manner but not to a CD40 mutant (Q263A) that selectively fails to bind TRAF3. CD40 mutants with impaired binding to TRAF2, TRAF3, or both of these proteins completely retained the ability to activate NF-B and Jun N-terminal kinase (JNK), implying that CD40 can stimulate TRAF2-and TRAF3-independent pathways for NF-B and JNK activation. A carboxyl-truncation mutant of CD40 lacking the last 32 amino acids required for TRAF2 and TRAF3 binding, CD40(⌬32), mediated NF-B induction through a mechanism that was suppressible by co-expression of TRAF6(⌬N), a dominant-negative version of TRAF6, but not by TRAF2(⌬N), implying that while TRAF6 does not directly bind CD40, it can participate in CD40 signaling. In contrast, TRAF6(⌬N) did not impair JNK activation by CD40(⌬32). Taken together, these findings reveal redundancy in the involvement of TRAF family proteins in CD40-mediated NF-B induction and suggest that the membrane-proximal region of CD40 may stimulate the JNK pathway through a TRAF-independent mechanism.

TRAF interactions with raft‐like buoyant complexes, better than TRAF rates of degradation, differentiate signaling by CD40 and EBV latent membrane protein 1

“…A series of recent publications suggest that TRAF2 has a key role in CD40 activation of the JNK and NF-KB pathways, whereas it seems to have only a marginal role in the activation of the same pathways by LMP1. 7,44,45,46 This would suggest that TRAF2 association with buoyant complexes is linked in some way with its contribution to JNK and NF-KB cascades. On the other hand, a binding of TRAF2 to LMP1 in vivo is well documented in several types of cell contexts.…”

“…3, lower panel). This mutation, which affects the distal TRAF-binding motif (PVQET -aa 250-254) of CD40, is known to suppress TRAF2-binding (7). On the other hand, it has no significant impact on the association of CD40 itself with the rafts of Hela cells (data not shown).…”

“…2,7 A maximum of JNK-activity is often reached within minutes and is rapidly followed by a sharp decrease even under sustained stimulation of CD40. In the murine model investigated by Brown et al, 18 this negative feed-back has been ascribed to the CD40-induced decrease of TRAF2 concentration.…”

“…3,4 LMP1 and CD40 share a series of common signaling mediators including TRAF2, TRAF3, TRAF5 and TRAF6. [5][6][7][8] A large number of signaling pathways can be activated by both membrane proteins including the NF-kB, JNK/AP1, p38/MAPK and PI3-Kinase pathways. 2,8,9,10 Numerous reports have emphasized the fact that LMP1 can mimic a constitutively active CD40-like receptor, although it does not have extracellular ligand.…”

CD40 on Adult Human Airway Epithelial Cells: Expression and Proinflammatory Effects

“…In particular, since CD40 signaling leads to the activation of Janus kinase 3 (JAK3)-and TNFR-associated factor 2 (TRAF2)-dependent pathways (15,16), we demonstrated the interplay of CD40 with these two signaling molecules. This model may account for the wide range of effects observed and for the identification of a potential therapeutic target in allergic diseases.…”