Decreased phosphorylation of protein kinase B and extracellular signal-regulated kinase in neutrophils from patients with myelodysplasia

Abstract

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 reactiveoxygen 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. (Blood.

Stem Cell Factor Synergistically Enhances Thrombopoietin‐Induced STAT5 Signaling in Megakaryocyte Progenitors through JAK2 and Src Kinase

“…Regulation of the cellular response is strongly dependent on the sequence of events in which growth factors or additional factors are presented to the cell. This has especially been demonstrated for granulocytes, in which priming by GM-CSF results in a more pronounced effect [46]. Similarly, prostaglandins might affect the Epo response in erythroid progenitors [47].…”

Platelet Factor 4 (CXC Chemokine Ligand 4) Differentially Regulates Respiratory Burst, Survival, and Cytokine Expression of Human Monocytes by Using Distinct Signaling Pathways

“…In the latter cells, stimulation with the chemotactic peptide fMLP caused a rapid activation of p38 MAPK, Erk, and PI3K. Interestingly, inhibition of p38 MAPK and PI3K, but not Erk, resulted in a drastic reduction of ROS formation and neutrophil chemotaxis (42)(43)(44)(45)(46)(47). Noteworthy, PF4 activates in human neutrophils neither PI3K nor p38 MAPK and is indeed unable to induce ROS release or chemotaxis in these cells (19,21,48).…”

Reduced activation of protein kinase B, Rac, and F-actin polymerization contributes to an impairment of stromal cell–derived factor-1–induced migration of CD34+ cells from patients with myelodysplasia

“…1 For instance, bactericidal functions in granulocytes from MDS patients are impaired, and migration of these cells toward the chemoattractant interleukin-8 (IL-8) is severely decreased. [2][3][4][5] Recent evidence suggests that the association and interaction of hematopoietic progenitor cells (HPCs) with their bone marrow microenvironment is imperative for their proliferation, differentiation, and function. [6][7][8] One of the major factors involved in retention and adhesion of HPCs to the bone marrow is the chemokine SDF-1.…”