title: Disturbed granulocyte macrophage-colony stimulating factor priming of phosphatidylinositol 3,4,5-trisphosphate accumulation and Rac activation in fMLP-stimulated neutrophils from patients with myelodysplasia.
abstract: The production of reactive oxygen species (ROS) by human neutrophils is imperative for their bactericidal activity. Proinflammatory agents such as granulocyte macrophage-colony stimulating factor (GM-CSF) can prime ROS production in response to chemoattractants such as N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP). In neutrophils from patients suffering from Myelodysplastic syndromes (MDS), a clonal, hematological disorder characterized by recurrent bacterial infections, this GM-CSF priming is severely impaired. In this study, we set out to further delineate the defects in neutrophils from MDS patients. We examined the effect of GM-CSF priming on fMLP-triggered activation of Rac, a small GTPase implicated in neutrophil ROS production. In contrast to healthy neutrophils, activation of Rac in response to fMLP was not enhanced by GM-CSF pretreatment in MDS neutrophils. Furthermore, activation of Rac was attenuated by pretreatment of neutrophils with the phosphatidylinositol 3-kinase (PI-3K) inhibitor LY294002. Unlike healthy neutrophils, fMLP-induced accumulation of the PI-3K lipid product PI(3,4,5)trisphosphate was not increased by GM-CSF pretreatment in MDS neutrophils. The disturbed Rac and PI-3K activation observed in MDS neutrophils did not appear to reflect a general GM-CSF or fMLP receptor-signaling defect, as fMLP-triggered Ras activation could be primed by GM-CSF in MDS and healthy neutrophils. Moreover, fMLP-induced activation of the GTPase Ral was also normal in neutrophils from MDS patients. Taken together, our data suggest that in neutrophils from MDS patients, a defect in priming of the PI-3K-Rac signaling pathway, located at the level of PI-3K, results in a decreased GM-CSF priming of ROS production.
authors.affiliation: Department of Hematology Research, University Hospital Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
authors.forename: Gwenny M
authors.initials: GM
authors.lastname: Fuhler
authors.forename: Karen A
authors.initials: KA
authors.lastname: Cadwallader
authors.forename: Gerlinde J
authors.initials: GJ
authors.lastname: Knol
authors.forename: Edwin R
authors.initials: ER
authors.lastname: Chilvers
authors.forename: A Lyndsay
authors.initials: AL
authors.lastname: Drayer
authors.forename: Edo
authors.initials: E
authors.lastname: Vellenga
mesh_terms: D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D006801:Humans; D009190:Myelodysplastic Syndromes; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D018375:Neutrophil Activation / Q000187:drug effects / Q000502:physiology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D020725:ral GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D018631:ras Proteins / Q000187:drug effects / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D018129:Phosphatidylinositol Phosphates; D017382:Reactive Oxygen Species; C060974:phosphatidylinositol 3,4,5-triphosphate; D009240:N-Formylmethionine Leucyl-Phenylalanine; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D019869:Phosphatidylinositol 3-Kinases; D020744:rac GTP-Binding Proteins; D020725:ral GTP-Binding Proteins; D018631:ras Proteins