Decreased phosphorylation of protein kinase B and extracellular signal-regulated kinase in neutrophils from patients with myelodysplasia.
Neutrophils from patients with myelodysplastic syndrome (MDS) show a disturbed differentiation pattern and are generally dysfunctional. To study these defects in more detail, we investigated reactive-oxygen species (ROS) production and F-actin polymerization in neutrophils from MDS patients and healthy controls and the involvement of N-formyl-L-methionyl-L-lucyl-L-phenylaline (fMLP) and granulocyte macrophage-colony-stimulating factor (GM-CSF)-stimulated signal transduction pathways. Following fMLP stimulation, similar levels of respiratory burst, F-actin polymerization, and activation of the small GTPase Rac2 were demonstrated in MDS and normal neutrophils. However, GM-CSF and G-CSF priming of ROS production were significantly decreased in MDS patients. We subsequently investigated the signal transduction pathways involved in ROS generation and demonstrated that fMLP-stimulated ROS production was inhibited by the phosphatidylinositol 3 kinase (PI3K) inhibitor LY294002, but not by the MAPK/ERK kinase (MEK) inhibitor U0126. In contrast, ROS production induced by fMLP stimulation of GM-CSF-primed cells was inhibited by LY294002 and U0126. This coincides with enhanced protein kinase B (PKB/Akt) phosphorylation that was PI3K dependent and enhanced extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) phosphorylation that was PI3K independent. We demonstrated higher protein levels of the PI3K subunit p110 in neutrophils from MDS patients and found that though the fMLP-induced phosphorylation of PKB/Akt and ERK1/2 could also be enhanced by pretreatment with GM-CSF in these patients, the degree and kinetics of PKB/Akt and ERK1/2 phosphorylation were significantly disturbed. These defects were observed despite a normal GM-CSF-induced signal transducer and activator of transcription 5 (STAT5) phosphorylation. Our results indicate that the reduced priming of neutrophil ROS production in MDS patients might be caused by a disturbed convergence of the fMLP and GM-CSF signaling routes.
Fuhler
Gwenny M
GM
Division of Hematology, Department of Medicine, University Hospital Groningen, The Netherlands.
Drayer
A Lyndsay
AL
Vellenga
Edo
E
D000199:Actins / Q000378:metabolism; D016022:Case-Control Studies; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009190:Myelodysplastic Syndromes / Q000097:blood* / Q000201:enzymology / Q000378:metabolism; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000096:biosynthesis; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D021122:Protein Subunits / Q000096:biosynthesis; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction
D000199:Actins; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009240:N-Formylmethionine Leucyl-Phenylalanine; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D021122:Protein Subunits; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017382:Reactive Oxygen Species; C494918:AKT1 protein, human