PROTEIN-TYROSINE-PHOSPHATASE INHIBITORS IN FC-GAMMA-RI-INDUCED MYELOID OXIDANT SIGNALING

Fc-receptor stimulation in myeloid cells results in increased oxygen c onsumption, termed the respiratory burst, which is coupled to a rapid and transient increase in tyrosine phosphorylation of cellular protein s. In a previous paper in this journal we showed that the protein tyro sine phosphatase (PTPase) inhibi tors sodium orthovanadate and phenyla rsine oxide (PAO) block the Fc gamma RI-induced respiratory burst in i nterferon-gamma-differentiated U937 cells (U937IF) while augmenting th e Fc gamma RI-induced tyrosine phosphorylation of cellular proteins. H erein we examine the effects of PTPase inhibitors on specific molecule s involved in Fc gamma RI signaling. We show that orthovanadate and PA O augmented the Fc gamma RI-induced tyrosine phosphorylation of the ad aptor protein CBL. CBL interactions with other phosphoproteins, among them SHC and CRKL, were also augmented in response to pretreatment wit h the PTPase inhibitors. SHC was tyrosine phosphorylated in response t o Fc gamma RI stimulation of U937IF cells and bound to the SH2 domain of GRB2 in a stimulation-dependent manner. In fusion protein pull-down experiments the interaction of SHC with the SH2 domain of GRB2 was in creased in PTPase inhibitor pretreated U937IF cells in response to Fc gamma RI stimulation. Our data support the hypothesis that a tyrosine dephosphorylation event is required for effective transmission of the Fc gamma RI signal to result in activation of the myeloid respiratory burst response. (C) 1997 Academic Press.