Structural requirements of SLP-76 in signaling via the highaffinity immunoglobulin E receptor (Fc�RI) in mast cells

cells (BMMC) fail to degranulate and release interleukin-6 (IL-6) following FcRI ligation. To define the role of SLP-76 domains and motifs in FcRI signaling, SLP-76/ BMMC were retrovirally transduced with SLP-76 and SLP-76 mutants. The SLP-76 N-terminal and Gads binding domains, but not the SH2 domain, were critical for FcRI-mediated degranulation and IL-6 secretion, whereas all three domains are essential for T-cell proliferation following T-cell receptor (TCR) ligation. Unexpectedly, the three tyrosine residues in SLP-76 critical for TCR signaling, Y112, Y128, and Y145, were not essential for IL-6 secretion, but were required for degranulation and mitogen-activated protein kinase activation. Furthermore, a Y112/128F SLP-76 mutant, but not a Y145F mutant, strongly reconstituted mast cell degranulation, suggesting a critical role for Y145 in FcRI-mediated exocytosis. These results point to important differences in the function of SLP-76 between T cells and mast cells. The high-affinity receptor for immunoglobulin E (IgE) (FcεRI) is a multimolecular complex of the IgE-binding subunit, two signal-transducing subunits, and a subunit that promotes assembly of the receptor and amplifies signal trans-duction (3, 32). Both and chains contain immunorecepto