Contrasting requirements for DAP12 in receptor-mediated mast cell activation (86.4)

Abstract

Abstract By inducing FcϵRI aggregation, antigen/IgE promotes mast cell cytokine production; a response markedly enhanced by specific TLR agonists. Critical to the ability of FcϵRI to activate mast cells is the recruitment of the tyrosine kinase Syk via the FcϵRIγ chains. Recent reports in other cell types have indicated that TLR’s may alternatively signal via the adaptor molecule DAP12 which also has the ability to bind Syk following tyrosine phosphorylation. We therefore examined whether DAP12 similarly regulates TLR-mediated responses in mast cells. DAP12 was confirmed to be expressed in both human and mouse mast cells (BMMCs) and, following its phosphorylation by pervanadate treatment, DAP12 recruited Syk. Although the TLR agonists LPS, Pam3Cys, and MALP2 induced cytokine production and synergistically enhanced this response mediated by FcϵRI, they failed to increase basal DAP12 phosphorylation. Furthermore, no up-regulation or down-regulation of TLR-mediated responses, nor FcϵRI-mediated responses, was observed in DAP12-/- BMMCs. In contrast, DAP12 phosphorylation and Syk recruitment were observed in mast cells following concanavalin A (Con A)-induced aggregation of mannose-glycosylated receptors, and these responses, together with ConA-induced degranulation, were substantially reduced in the DAP12-/- BMMCs. These data show that in mast cells DAP12 does not regulate TLR- or FcϵRI-mediated responses, but is required for responses elicited by mannose-glycosylated receptors.