Tyrosine phosphorylation-dependent activation of phosphatidylinositide 3-kinase occurs upstream of Ca^(2+)-signalling induced by Fcy receptor cross-linking in human neutrophils
The effect of wortmannin on IgG-receptor (FcyR)-mediated
stimulation of human neutrophils was investigated. The Ca^(2+)
influx induced by clustering of both Fcy receptors was inhibited
by wortmannin, as was the release of Ca^(2+) from intracellular
stores. Wortmannin also inhibited, with the same efficacy, the
accumulation of Ins(1,4,5)P3 observed after FcyR stimulation,
but did not affect the increase in Ins(1,4,5)P3 induced by the
chemotactic peptide, formyl-methionine-leucine-phenylalanine.
Because wortmannin is, in the concentrations used here, an
inhibitor of PtdIns 3-kinase, these results suggested a role for
PtdIns 3-kinase upstream of Ca^(2+) signalling, induced by FcyR
cross-linking. Support for this notion was obtained by investigating
the effect of another inhibitor of PtdIns 3-kinase, LY
294002, and by studying the kinetics of PtdIns 3-kinase activation.
We found translocation of PtdIns 3-kinase to the plasma
membrane and increased PtdIns 3-kinase activity in the membrane
as soon as 5 s after FccR cross-linking, even before the
onset of the Ca^(2+) response. Moreover, the translocation of
PtdIns 3-kinase to the plasma membrane was inhibited by cocross-
linking of either FcyRIIa and FcyRIIIb with the tyrosine
phosphatase, CD45, indicating a requirement for protein tyrosine
phosphorylation in the recruitment of PtdIns 3-kinase to the
plasma membrane. Taken together, our results suggest a role for
PtdIns 3-kinase in early signal transduction events after FcyR
cross-linking in human neutrophils