title: Fibronectin promotes calcium signaling by interferon-gamma in human neutrophils via G-protein and sphingosine kinase-dependent mechanisms.
abstract: A common intracellular signal activating polymorphonuclear leukocytes (PMN) in inflammation is a change in cytosolic calcium concentration. Previously, we have shown that interferon-gamma (IFN-gamma) induces transient calcium signals in PMN, but only after intracellular calcium store depletion. Using a digital imaging system, we show that adhesion of PMN is critical for IFN-gamma-induced calcium signals, and with PMN attached to the optimal coating, the calcium signals are evoked even in presence of extracellular calcium, that is, non-depleted calcium stores. Adhesion to fibronectin, pure or extracted from plasma by gelatin, improved the IFN-gamma responses compared with serum, plasma, or vitronectin coats. In accordance with previous observations, IFN-gamma-induced calcium signals in fibronectin adherent cells were totally abolished by the G-protein inhibitor pertussis toxin and were also inhibited by the sphingosine kinase inhibitors dimethylsphingosine (DMS) and N-acetylsphingosine (N-Ac-Sp). PMN contact with fibronectin alone, measured in cells sedimenting onto a fibronectin-coated surface or by addition of fibronectin to glass-adherent cells, evoked transient calcium signals. However, PMN in suspension did not respond to the addition of fibronectin or arginine-glycine-aspartate (RGD). The fibronectin-induced calcium signals were also clearly depressed by pertussis toxin and by the sphingosine kinase inhibitors DMS, dihydrosphingosine (DHS), and N-Ac-Sp. When the product of sphingosine kinase activity, sphingosine 1-phosphate (S1-P), was added to the cells, similar calcium signals were induced, which were dependent on a pertussis toxin-sensitive G-protein activity. Finally, addition of S1-P to the cells prior to stimulation with IFN-gamma partly mimicked the priming effect of fibronectin. In conclusion, fibronectin contact evokes by itself a calcium signal in PMN and further promotes calcium signaling by IFN-gamma. We suggest that fibronectin might activate sphingosine kinase, and that the sphingosine 1-phosphate thereby generated induces a calcium signal via a G-protein-dependent mechanism. Apparently, sphingosine kinase activity is also involved in IFN-gamma induced calcium signals.
authors.affiliation: Department of Pharmacology, School of Pharmacy, University of Oslo, Norway. vigdisaa@farmasi.uio.no
authors.forename: V
authors.initials: V
authors.lastname: Aas
authors.forename: S
authors.initials: S
authors.lastname: Algerøy
authors.forename: K L
authors.initials: KL
authors.lastname: Sand
authors.forename: J G
authors.initials: JG
authors.lastname: Iversen
mesh_terms: D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D020013:Calcium Signaling; D002448:Cell Adhesion; D003600:Cytosol / Q000378:metabolism; D005353:Fibronectins / Q000494:pharmacology*; D005780:Gelatin / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D008246:Lysophospholipids / Q000502:physiology; D009504:Neutrophils / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D015398:Signal Transduction; D013110:Sphingosine / Q000031:analogs & derivatives / Q000502:physiology; D000099157:Sphingosine Kinase
chemical_list: D002118:Calcium; D005353:Fibronectins; D005780:Gelatin; D020962:Heterotrimeric GTP-Binding Proteins; D007371:Interferon-gamma; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor); D013110:Sphingosine; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate