The adapter molecule Gab2 regulates FcεRI-mediated signal transduction in mast cells

The recently cloned scaffolding molecule Gab2 can assemble multiple molecules involved in signaling pathways. Bone marrow-derived mast cells isolated from Gab2(-/-) mice have defective signaling probably due to the lack of the activation of phosphatidylinositol-3 kinase (P13-kinase). In this study, we investigated the role of Gab2 using the rat basophilic leukemia 2H3 cell line mast cells. FcepsilonRI aggregation induced the tyrosine phosphorylation of Gab2 and translocation of a significant fraction of it from the cytosol to the plasma membrane. As in other cells, Gab2 was found to associate with several signaling molecules including Src homology 2-containing protein tyrosine phosphatase 2, Grb2, Lyn, and phospholipase Cgamma (PLCgamma). The association of Gab2 with Lyn and PLCgamma were enhanced after receptor aggregation. Overexpression of Gab2 in rat basophilic leukemia 2H3 cell line cells inhibited the FcepsilonRI-induced tyrosine phosphorylation of the subunits of the receptor, and the phosphorylation and/or activation of Syk and mitogen-activated protein kinase. Downstream events such as calcium mobilization, degranulation, and induction of TNF-alpha and IL-6 gene transcripts were decreased in Gab2 overexpressing cells, although Akt phosphorylation as a measure of P13-kinase activation was unaffected. These results suggest that in addition to the positive effects mediated by P13-kinase that are apparent in Gab2(-/-) mast cells, Gab2 by interacting with Lyn and PLCgamma may have negative regulatory effects on FcepsilonRI-induced mast cell signaling and functions.