SLP-76-CBL-GRB2-SHC INTERACTIONS IN FC-GAMMA-RI SIGNALING

SLP-76 and Cbl are complex adapter proteins that have the capacity to hind to smaller adapter proteins, such as Grb2, which subsequently bin ds the nucleotide exchange protein Sos in the transmission of intracel lular signals. SLP-76, Cbl, Shc, and Grb2 have been implicated in immu noreceptor tyrosine-based activation motif (ITAM) signaling, leading t o activation of Has. However, their mechanism of action has not been d etermined. To date, there have been no reports of SLP-76 involvement i n Fc gamma RI-receptor signaling and no data exist for an interaction between Cbl, Shc, and SLP-76 in vivo. We provide evidence that SLP-76, Cbl, and Shc are tyrosine phosphorylated on Fc gamma RI-receptor stim ulation and are associated with the adapter protein Grb2 in gamma-inte rferon-differentiated U937 cells (U937IF). The interactions between SL P-76 and Cbl and SLP-76 and Grb2 are present in resting U937IF cells. However, the interaction between SLP-76 and Grb2 becomes augmented two fold on Fc gamma RI-receptor aggregation. Our results provide the firs t evidence for a phosphorylation-dependent interaction between SLP-76 and Shc, induced at least 10-fold on Fc gamma RI receptor stimulation. Our data indicate that a significant portion of a multimolecular comp lex containing Cbl, SLP-76, Shc, and Grb2 is distinct from a trimotecu lar complex containing the pas guanine nucleotide exchanger Sos, Shc, and Grb2. Fc gamma RI-induced tyrosine phosphorylation of SLP-76, Cbl, Shc, and the highly induced SLP-76-Shc interaction provide the first evidence that SLP-76 and Cbl are involved in Fc gamma RI signaling and suggest a functional significance for these interactions in Fc gamma RI signal relay in the control of pas in myeloid cells. (C) 1998 by Th e American Society of Hematology.