Differential Activation of the Tyrosine Kinases ZAP-70 and Syk After FcgRI Stimulation

Engagement of the high-affinity IgG Fc receptor (FcgRI) actiSyk nor MAP kinase activation was affected by the presence of ZAP-70. Although transduced ZAP-70 had in vitro kinase vates a signal transduction pathway involving tyrosine phosphorylation of associated kinases. We compared the activity and associated with FceRIg after receptor aggregation, it was not tyrosine phosphorylated. In contrast, both activation of the related protein tyrosine kinases (PTKs), Syk and ZAP-70, in FcgRI-mediated signaling. Cross-linking of ZAP-70 and Syk were phosphorylated in a T-cell line in which their respective levels of expression were similar to those the FcgRI multimeric receptor in monocytic cells results in tyrosine phosphorylation of the FceRIg subunit and associadetected in U937/ZAP-70 cells. Therefore, these results suggest that requirements for Syk and ZAP-70 phosphorylation tion of Syk with this complex. We stably introduced ZAP-70 via a retroviral vector into two monocytic cell lines, U937 are distinct in a monocytic cell context. q 1997 by The American Society of Hematology. and THP-1, which normally do not express ZAP-70. Neither