Interferon-gamma elicits a G-protein-dependent Ca2+ signal in human neutrophils after depletion of intracellular Ca2+ stores

Interferon-gamma (IFN-gamma) has multiple effects on Ca2+ signalling in pol ymorphonuclear neutrophils (PMNs), including evoked cytosolic Ca2+ transien ts, increased capacitative calcium influx and increased sequestration of Ca 2+ in intracellular stores. The present study was conducted to elucidate th e mechanism behind the Ca2+ transients. As observed before, the IFN-gamma-e voked Ca2+ signals were apparent when extracellular Ca2+ was removed. A new finding was that the proportion of responding cells and the extent of calc ium release increased with increasing time in EGTA buffer. A, assessed by N -formyl-methionyl-leucyl-phenylalanine (fMLP) stimulated Ca2+ release, the intracellular stores were depleted during this incubation period, and the e xtent of depletion correlated well with the appearance of IFN-gamma-induced Ca2+ signals. This store dependence of the IFN-gamma-induced Ca2+ signals was confirmed by the appearance of IFN-gamma-evoked Ca2+ signals in the pre sence of extracellular Ca2+ after store depletion by thapsigargin. The appearance of IFN-gamma-mediated Ca2+-signals in the presence of EGTA i ndicates that IFN-gamma stimulates Ca2+ release from intracellular stores. This was confirmed by the inability of the calcium transportation blocker L a3+ to abolish the IFN-gamma response and the total abrogation of the respo nse by the phospholipase C inhibitor U73122. Although these latter results imply a role for inositol 1,4,5-trisphosphate(IP3) in IFN-gamma signalling, comparison of IFN-gamma-evoked responses with fMLP responses revealed clea r differences that suggest different signal-transduction pathways. However, responses to fMLP and IFN-gamma were both depressed by pertussis toxin, an d the IFN-gamma responses were, in addition, inhibited by the tyrosine kina se inhibitor genistein. Further evidence of the involve ment of tyrosine ki nase was a slight stimulatory effect of the protein tyrosine phosphatase in hibitor sodium orthovanadate. The PI-3K activity was of minor importance. I n conclusion, we present evidence of a novel signal-transduction mechanism for IFN-gamma in PMNs, dependent on tyrosine kinase activity, a pertussis t oxin-sensitive G protein and phospholipase C activity. CELL SIGNAL. 11;2:10 1-110, 1999. (C) 1998 Elsevier Science Inc.