[Identification of proteins interacting with adaptor protein Bam32].
ABSTRACT To study the role of adaptor protein Bam32 in B cell antigen receptor (BCR) signaling cascades.
Using full length Bam32 as bait, yeast two-hybrid technique was used to screen the protein that could interact with Bam32. The interaction was further confirmed by co-transfection of 293T cells and coimmunoprecipitation.
Protein tyrosine kinase Lyn was one of the strong positive clones identified by the yeast two-hybrid screening. This interaction was further confirmed in 293T cells by co-transfection and coimmunoprecipitation. By using specific anti-phosphotyrosine antibody, it was found that Bam32 could be phosphorylated by Lyn.
The interaction of Bam32 with Lyn leads to Bam32 phosphorylation, which might play an important role in activating downstream signaling molecules.
- [Show abstract] [Hide abstract]
ABSTRACT: Mast cell activation triggered by IgE binding to its high affinity receptor FcɛRI is highly dependent on signaling via phosphoinositde 3-kinases (PI3K). The phosphoinositide phosphatase SHIP controls mast cell activation by regulating accumulation of D3 phosphoinositide second messengers generated by PI3K. The PH domain adaptor protein Bam32/DAPP1 binds specifically to the D3 phosphoinositides PI(3,4,5)P3 and PI(3,4)P2 (the substrate and product of SHIP respectively). In B cells, Bam32 is phosphorylated by Src family kinases including Lyn, and is required for antigen receptor-induced activation; however the function of Bam32 in mast cells is unknown. Here we report that Bam32 is expressed in mast cells, is recruited to the plasma membrane upon stimulation and functions in FcɛRI signaling. Examination of bone marrow-derived mast cells (BMMC) isolated from Bam32-deficient mice revealed enhanced FcɛRI-induced degranulation and IL-6 production, indicating that Bam32 may function to restrain signaling via FcɛRI. These enhanced degranulation responses were PI3K-dependent, as indicated by blockade with PI3K inhibitors wortmannin or IC87114. While Bam32-deficient BMMC showed reduced FcɛRI-induced activation of mitogen-activated protein kinases ERK and JNK, FcɛRI-induced calcium flux and phosphorylation of PLCγ1 and Akt were increased. Bam32-deficient BMMC showed significantly reduced phosphorylation of Lyn and SHIP, indicating reduced activity of inhibitory signaling pathways. Together our results identify Bam32 as a novel regulator of mast cell activation, potentially functioning in membrane-proximal integration of positive and negative signaling pathways.Molecular Immunology 10/2010; 48(1-3):89-97. · 3.00 Impact Factor