Protein kinase C promotes restoration of calcium homeostasis to platelet activating factor-stimulated human neutrophils by inhibition of phospholipase C

Background: The role of protein kinase C (PKC) in regulating the activity of phospholipase C (PLC) in neutrophils activated with the chemoattractant, platelet-activating factor (PAF, 20 and 200 nM), was probed in the current study using the selective PKC inhibitors, GF10903X (0.5 - 1 M) and staurosporine (400 nM). Methods: Alterations in cytosolic Ca2+, Ca2+ influx, inositol triphosphate (IP3), and leukotriene B4production were measured using spectrofluorimetric, radiometric and competitive binding radioreceptor and immunoassay procedures, respectively. Results: Activation of the cells with PAF was accompanied by an abrupt increase in cytosolic Ca 2+ followed by a gradual decline towards basal levels. Pretreatment of neutrophils with the PKC inhibitors significantly increased IP 3production with associated enhanced Ca2+ release from storage vesicles, prolongation of the peak cytosolic Ca2+ transients, delayed clearance and exaggerated reuptake of the cation, and markedly increased synthesis of LTB4. The alterations in Ca2+ fluxes observed with the PKC inhibitors were significantly attenuated by U73122, a PLC inhibitor, as well as by cyclic AMP-mediated upregulation of the Ca 2+-resequestering endomembrane ATPase. Taken together, these observations are compatible with a mechanism whereby PKC negatively modulates the activity of PLC, with consequent suppression of IP3production and down-regulation of Ca2+ mediated pro-inflammatory responses of PAF-activated neutrophils. Conclusion: Although generally considered to initiate and/or amplify intracellular signalling cascades which activate and sustain the pro-inflammatory activities of neutrophils and other cell types, the findings of the current study have identified a potentially important physiological, anti-inflammatory function for PKC, at least in neutrophils. © 2009 Tintinger et al; licensee BioMed Central Ltd.