Effects of pertussis and cholera toxin on the interferon-gamma stimulated immunocytochemical staining of ICAM-1 and inositol phosphate formation in a human renal carcinoma cell line

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 polymorphonuclear neutrophils (PMNs), including evoked cytosolic Ca2+ transients, increased capacitative calcium influx and increased sequestration of Ca2+ in intracellular stores. The present study was conducted to elucidate the mechanism behind the Ca2+ transients. As observed before, the IFN-gamma-evoked Ca2+ signals were apparent when extracellular Ca2+ was removed. A new finding was that the proportion of responding cells and the extent of calcium release increased with increasing time in EGTA buffer. As assessed by N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated Ca2+ release, the intracellular stores were depleted during this incubation period, and the extent 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 presence of extracellular Ca2+ after store depletion by thapsigargin. The appearance of IFN-gamma-mediated Ca2+-signals in the presence of EGTA indicates that IFN-gamma stimulates Ca2+ release from intracellular stores. This was confirmed by the inability of the calcium transportation blocker La3+ to abolish the IFN-gamma response and the total abrogation of the response 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 clear differences that suggest different signal-transduction pathways. However, responses to fMLP and IFN-gamma were both depressed by pertussis toxin, and the IFN-gamma responses were, in addition, inhibited by the tyrosine kinase inhibitor genistein. Further evidence of the involvement of tyrosine kinase was a slight stimulatory effect of the protein tyrosine phosphatase inhibitor sodium orthovanadate. The PI-3K activity was of minor importance. In conclusion, we present evidence of a novel signal-transduction mechanism for IFN-gamma in PMNs, dependent on tyrosine kinase activity, a pertussis toxin-sensitive G protein and phospholipase C activity.

Interferon-gamma increases inositol phosphate formation and cellular calcium ion concentration independent of ICAM-1 antigen enhancement in renal tubular cells

In the present study, we investigated the effect of interferon-gamma (IFN-gamma) on cellular inositol phosphate formation and cellular calcium ion concentration [Ca2+]i in human renal proximal tubular (HRPT) cells. We also examined the possible role of the inositol phosphate-Ca2+ signalling pathway during IFN-gamma-induced intercellular adhesion molecule-1 (ICAM-1) antigen expression. IFN-gamma caused an increase in the formation of inositol 1-monophosphate (Ins 1-P), inositol 1,4-bisphosphate (Ins 1,4-P2), inositol 1,4,5-trisphosphate (Ins 1,4,5-P3) and inositol 1,3,4,5-tetrakisphosphate (Ins 1,3,4,5-P4). A rapid time-dependent rise in [Ca2+]i was observed upon IFN-gamma stimulation, with maximal levels reached after 1 min. A lower rise in [Ca2+]i was observed when cells were stimulated in Ca2+-free medium. This correlated with the generation of Ins 1,4,5-P3 by IFN-gamma, a well-known secondary messenger capable of releasing Ca2+ from intracellular stores. The induction of ICAM-1 antigen expression was enhanced by IFN-gamma, 4-bromocalcium ionophore A23187 (Bromo-A23187), and their combinations. However, the calcium antagonist diltiazem and calcium chelator EGTA had no effect on IFN-gamma antigen induction. In conclusion, our data suggest that IFN-gamma stimulation of HRPT cells results in the cleavage of phosphatidylinositol bisphosphate by phospholipase C, generating inositol phosphates, of which Ins 1,4,5-P3 probably releases Ca2+ from intracellular stores. A further increase in [Ca2+]i upon IFN-gamma stimulation results from influx of extracellular Ca2+. IFN-gamma signal transduction in HRPT cells may not be limited to the inositol phosphate-Ca2+ pathway since IFN-gamma-induced ICAM-1 antigen expression was unaffected by calcium antagonist/chelator.