Cellular responses to murine CD40 in a mouse B cell line may be TRAF dependent or independent

Abstract

Engagement of CD40 by its ligand induces IKK and mitogen‐activated protein kinase (MAPK) phosphorylation and transcriptional activation, leading to activation and differentiation of B cells. These events are most likely transduced by adaptor molecules that are recruited to the CD40 cytoplasmic domain, called TNF receptor‐associated factors (TRAF). We have engineered a chimeric CD40 molecule using the human extracellular sequence and the murine cytoplasmic domain to assess the contribution that specific TRAF binding domains provide to the cytoplasmic signaling functions of CD40. Thedata presented here show that the shared binding site for TRAF2 and TRAF3 accounts for receptor internalization, and the majority of signaling through CD40, but is redundant with the TRAF6 binding site for activation of p38 and NFκB signaling pathways. Disruption of the TRAF2/3 binding site results in a delayed and diminished kinase pathway induction, but complete preclusion of all signals requires the disruption of more than the two known TRAF binding sites. The specific TRAF dependency of CD40‐induced growth arrest, TNF‐α production, and phosphorylation of signaling molecules are shown, while p38 MAPK activation and cell surface antigen modulation suggest TRAF independent CD40 signaling in B cells.

Distinct contributions of different CD40 TRAF binding sites to CD154‐induced dendritic cell maturation and IL‐12 secretion

“…The same differences were observed up to 60 min after stimulation (data not shown). Thus, the impact of each TRAF binding site mutation on biochemical signaling by CD40 in BMDC did not simply reflect a delay in the kinetics of activation, as previously reported to occur after CD40 engagement in a murine B cell line [37].…”

“…Disruption of both TRAF binding sites ( ¿ T2/3/6 hCD40) resulted in further loss of receptor activity, suggesting that both domains make significant contributions to CD40 signaling leading to BMDC maturation. The decreased receptor activity in the double as compared to each single mutant supports biochemical evidence that the two TRAF binding sites function in an independent rather than a fully cooperative manner [31,37]. Based on these findings, subsequent experiments utilizing the CD154-transfected cell line were performed in the presence of neutralizing anti-CD154 antibody.…”

A CD40 Kozak sequence polymorphism and susceptibility to antibody-mediated autoimmune conditions: the role of CD40 tissue-specific expression

“…Even though the signaling pathways of activation of CD40 in thyrocytes have not yet been examined, these can be postulated based on data from studies of activation of necrosis factor kappa B (NFkB) by transforming growth factor-beta (TGF-b) in Graves' thyrocytes, 49 as well as of CD40 signaling in other cell types. [50][51][52][53][54][55][56][57][58][59] According to our intrinsic hypothesis, CD40 ligand more readily activates CD40, overexpressed on the surface of thyrocytes in individuals harboring the CC genotype. Once activated, CD40 receptors multimerize, recruiting TNF-receptor associated factors (TRAFs) to their cytoplasmic tails.…”

“…Downstream of the initial receptor ligation, TRAFs recruit and activate kinases such as inhibitor of k-B (IkB) kinase (IKK), leading to activation of NFkB pathway. NFkB is able to turn on transcription of a number of genes including cytokines, chemokines and adhesion molecules, which could augment thyroidal inflammation [50][51][52][53][54][55][56][57][58][59] (Figure 4b). Moreover, activation of the CD40 pathway has been shown to activate anti-apoptotic pathways in several non-lympho- The intrinsic thyroidal CD40 model.…”

The TRAF3-binding site of human molluscipox virus FLIP molecule MC159 is critical for its capacity to inhibit Fas-induced apoptosis

“…51 Binding of TRAF2 and -3 to CD40 has indeed been shown to be required for ligand-induced downmodulation of this receptor, possibly by TRAF2-dependent recruitment to lipid rafts and subsequent TRAF3-dependent receptor internalization. 52 Binding to TRAF2 and TRAF3 has been reported not only for MC159 but also for the long form of cellular FLIP, c-FLIP L , under conditions of overexpression, 53,54 and increased recruitment of TRAF2 to the Fas DISC was observed in Jurkat and Raji cells upon stable transfection with cFLIP L . 53 While this suggests that both MC159 and cFLIP L interfere with the function of TRAF2, it is unclear whether c-FLIP L also recruits endogenous TRAF3 to the DISC and if so, whether this has a similar or rather an opposing impact on TRAF2 and TRAF3 function.…”