Identifying the MAGUK Protein Carma-1 as a Central Regulator of Humoral Immune Responses and Atopy by Genome-Wide Mouse Mutagenesis

Abstract

In a genome-wide ENU mouse mutagenesis screen a recessive mouse mutation, unmodulated, was isolated with profound defects in humoral immune responses, selective deficits in B cell activation by antigen receptors and T cell costimulation by CD28, and gradual development of atopic dermatitis with hyper-IgE. Mutant B cells are specifically defective in forming connections between antigen receptors and two key signaling pathways for immunogenic responses, NF-kappaB and JNK, but signal normally to calcium, NFAT, and ERK. The mutation alters a conserved leucine in the coiled-coil domain of CARMA-1/CARD11, a member of the MAGUK protein family implicated in organizing multimolecular signaling complexes. These results define Carma-1 as a key regulator of the plasticity in antigen receptor signaling that underpins opposing mechanisms of immunity and tolerance.

Potential role of CARMA1 in CD40‐induced splenic B cell proliferation and marginal zone B cell maturation

“…PMA + Ionomycin-induced proliferation also showed complete defect in CARMA1 KO B cells (Fig. 1B), consistent with previously published data [20,23,24]. Importantly, stimulation of B cells with LPS showed no significant difference between WT and CARMA1 KO B cells, suggesting that signaling through TLR4 (receptor for LPS) does not depend on CARMA1 (Fig.…”

“…Surprisingly, CD40-induced proliferation has been shown to be defective in CARMA1-deficient B cells, while underlying molecular mechanisms are not understood [20,23,24]. To confirm these observations in our experimental system, negatively selected splenic B cells from WT and CARMA1 KO mice were stimulated with anti-CD40 antibodies and proliferation was measured by [ 3 H]thymidine incorporation.…”

“…CARMA1-deficient B cells are defective in activation and proliferation upon BCR stimulation and in humoral immune responses [23,24]. PKC-h in T cells and PKC-b in B cells have been shown to phosphorylate CARMA1 upon antigen receptor stimulation, leading to the activation of NF-jB [25,26].…”

“…PKC-h in T cells and PKC-b in B cells have been shown to phosphorylate CARMA1 upon antigen receptor stimulation, leading to the activation of NF-jB [25,26]. Surprisingly, CARMA1-deficient splenic B cells are defective in CD40-induced proliferation [20,23,24]. However, mechanisms responsible for the defective proliferation upon CD40 stimulation in CARMA1defi-cient B cells remain to be investigated.…”

Uncovering the uncharacterized and unexpected: Unbiased phenotype‐driven screens in the mouse

“…The Goodnow lab's first screen identified 11 mutant lines with defective T-cell formation and all 11 lines have molecularly identified the responsible gene variant (Nelms and Goodnow, 2001;Jun et al, 2003;Papathanasiou and Goodnow, 2005). Several of these have revealed unsuspected players.…”