title: The molecular basis for adhesion-mediated suppression of reactive oxygen species generation by human neutrophils.
abstract: Human neutrophil adherence to ECMs induces an initial inhibition of stimulated reactive oxygen species (ROS) formation, followed by an enhanced phase of oxidant production. The initial integrin-mediated suppression of ROS constitutes a mechanism to prevent inappropriate tissue damage as leukocytes migrate to inflammatory sites. The Rac2 guanosine 5'-triphosphatase (GTPase) is a critical regulatory component of the phagocyte NADPH oxidase. We show that activation of Rac2 is inhibited in adherent neutrophils, correlating with inhibition of ROS formation. Conversely, NADPH oxidase components p47 and p67 assemble normally, suggesting a specific action of adhesion on the Rac2 molecular switch. Reconstitution with activated Rac2 restored rapid NADPH oxidase activation kinetics to adherent neutrophils, establishing that inhibition was due to defective Rac2 activity. We provide evidence that integrins inhibit Rac2 activation via a membrane-associated guanine nucleotide exchange factor, likely to be Vav1. Activation of Vav1, but not its upstream activator, Syk, is suppressed by cell adhesion. Vav1 activity is inhibited due to dephosphorylation of the regulatory Tyr174 via enhanced tyrosine phosphatase activity in adherent cells. These studies identify an integrin-mediated pathway in which Vav1 is as a strong candidate for the critical regulatory point in suppression of Rac2 activation and ROS generation during inflammatory responses.
authors.affiliation: Department of Immunology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
authors.forename: Tieming
authors.initials: T
authors.lastname: Zhao
authors.forename: Valerie
authors.initials: V
authors.lastname: Benard
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Bohl
authors.forename: Gary M
authors.initials: GM
authors.lastname: Bokoch
mesh_terms: D002448:Cell Adhesion; D018797:Cell Cycle Proteins; D004789:Enzyme Activation; D006801:Humans; D019255:NADPH Oxidases / Q000378:metabolism; D009504:Neutrophils / Q000502:physiology*; D010750:Phosphoproteins / Q000378:metabolism; D021381:Protein Transport; D017027:Protein Tyrosine Phosphatases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D051567:Proto-Oncogene Proteins c-vav; D017382:Reactive Oxygen Species / Q000378:metabolism*; D020744:rac GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D000097766:RAC2 GTP-Binding Protein
chemical_list: D018797:Cell Cycle Proteins; D019255:NADPH Oxidases; D010750:Phosphoproteins; D017027:Protein Tyrosine Phosphatases; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D017382:Reactive Oxygen Species; D020744:rac GTP-Binding Proteins; D000097766:RAC2 GTP-Binding Protein; C496618:VAV1 protein, human; C079789:neutrophil cytosol factor 67K; C060505:neutrophil cytosolic factor 1