TYROSINE PHOSPHORYLATION OF PHOSPHOLIPASE C-GAMMA-2 IS INVOLVED LN THE ACTIVATION OF PHOSPHOINOSITIDE HYDROLYSIS BY FC-RECEPTORS IN HUMAN NEUTROPHILS

The stimulation of phosphoinositide hydrolysis by a number of agonists (phosphoinositide response) is a ubiquitous transmembrane signalling process for the regulation of several cell functions. Two mechanisms o f activation have been identified that involve different phospholipase s C: one regulated by G-proteins and another regulated by receptors ha ving an intrinsic tyrosine kinase domain or that stimulate intracellul ar tyrosine kinase activity. This last mechanism is activated in sever al immunological cells, including lymphocytes, mastocytes, NK cells an d monocytes, in response to agonists that bind antigen receptors, and receptors for IgE and IgG. In the present study, we have investigated the role of tyrosine phosphorylation in the stimulation of phosphoinos itide hydrolysis mediated by Fc gamma Rs in human neutrophils. The res ults demonstrated that: 1) the activation of Fc gamma Rs with insolubl e immune complexes (ITC) induced a tyrosine phosphorylation of several proteins that was dose-dependently inhibited by the tyrosine kinase i nhibitor, genistein; 2) the activation of Fc gamma Rs caused a stimula tion of phosphoinositide hydrolysis measured as [H-3]inositol phosphat es formation; 3) genistein depressed the activation of phosphoinositid e hydrolysis; 4) among the several proteins that became tyrosine phosp horylated upon Fc gamma Rs activation by IIC, one 145 kDa protein was identified as PLC-gamma 2, using a specific antiserum. The phosphoryla tion of PLC-gamma 2 was completely inhibited by genistein. These resul ts demonstrate that the phosphoinositide response to activation of Fc gamma Rs involves the tyrosine phosphorylation of PLC-gamma 2. (C) 199 4 Academic Press, Inc.