title: iPLA2, a novel determinant in Ca2+- and phosphorylation-dependent S100A8/A9 regulated NOX2 activity.
abstract: The neutrophil NADPH oxidase (NOX2) is a key enzyme responsible for host defense against invading pathogens, via the production of reactive oxygen species. Dysfunction of NOX2 can contribute to inflammatory processes, which could lead to the development of diseases such as atherosclerosis. In this paper, we characterize a pathway leading to NOX2 activation in which iPLA(2)-regulated p38 MAPK activity is a key regulator of S100A8/A9 translocation via S100A9 phosphorylation. Studies in cell-free or recombinant systems involved two Ca2+-binding proteins of the S100 family, namely S100A8 and S100A9, in NOX2 activation dependent on intracellular Ca2+ concentration ([Ca2+](i)) elevation. Using differentiated HL-60 cells as a model of neutrophils, we provide evidence that [Ca2+](i)-regulated S100A8/A9 translocation is mediated by an increase in [Ca2+](i) through intracellular Ca2+ store depletion. Moreover, we confirm that p38 MAPK induces S100A9 phosphorylation, a mandatory precondition for S100 translocation. Based on a pharmacological approach and an siRNA strategy, we identify iPLA(2) as a new molecular player aiding S100 translocation and NOX2 activity. Inhibition of p38 MAPK activity and S100A9 phosphorylation by bromoenol lactone, a selective inhibitor of iPLA(2), indicated that p38 MAPK-mediated S100A9 phosphorylation is dependent on iPLA(2). In conclusion, we have characterized a pathway leading to NOX2 activation in which iPLA(2)-regulated p38 MAPK activity is a key regulator of S100A8/A9 translocation via S100A9 phosphorylation.
authors.affiliation: Life Sciences Research Unit, University of Luxembourg, 162A Avenue de la Faïencerie, L-1511 Luxembourg.
authors.forename: Véronique
authors.initials: V
authors.lastname: Schenten
authors.forename: Sabrina
authors.initials: S
authors.lastname: Bréchard
authors.forename: Sébastien
authors.initials: S
authors.lastname: Plançon
authors.forename: Chantal
authors.initials: C
authors.lastname: Melchior
authors.forename: Jean-Pol
authors.initials: JP
authors.lastname: Frippiat
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Tschirhart
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D040501:Calgranulin A / Q000235:genetics / Q000378:metabolism*; D040502:Calgranulin B / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D054522:Group VI Phospholipases A2 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D016877:Oxidants / Q000378:metabolism; D010766:Phosphorylation; D034622:RNA Interference; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D040501:Calgranulin A; D040502:Calgranulin B; D008562:Membrane Glycoproteins; D016877:Oxidants; D006861:Hydrogen Peroxide; C056558:CYBB protein, human; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; D048051:p38 Mitogen-Activated Protein Kinases; D054522:Group VI Phospholipases A2; C516475:PLA2G6 protein, human; D002118:Calcium