Differential interaction of Shc-SH2 domain with FcγRIII (CD16)-associated ζ and γ chains

FcγRIII (CD16) is a hetero-oligomeric receptor composed of a ligand-binding α subunit associated with homo- or heterodimers of the TcRζ or of the FceRI γ chain. We have previously demonstrated that CD16 ligation promotes formation of complexes between tyrosine phosphorylated Shc or p36 (lnk) adaptor proteins, and Grb-2, leading to activation of ras signalling pathway in human NK cells. Here we report that CD16 engagement induces rapid Shc association with tyrosine-phosphorylated receptor complex in human NK cells. In vitro binding studies demonstrate that this interaction is mediated by Shc-SH2 domain and immunodepletion experiments indicate that ζ but not γ chain has the capability to mediate this association. Jurkat cell clones expressing CD16-ζ or -γ homodimers have been used to gain more information about the mechanism of Shc/CD16 association. Our data show that, while engagement of both receptors induces tyrosine phosphorylation of Shc and Grb-2 recruitment, Shc-SH2 association is evident only with CD16-ζ but not with CD16-γ-Overall, our data demonstrate that the adaptor protein Shc can be recruited to the activated CD16 complex by interaction with tyrosine-phosphorylated ζ chain in a SH2-dependent manner. These results also provide further support to the notion that ζ and γ chains might couple to different biochemical pathways. The functional consequences of the differential association of ζ vs. γ chain in regard to the activation of the ras/MAPK cascade are under investigation.