Phosphoinositide 3-kinase and Akt occupy central roles in inflammatory responses of Toll-like receptor 2-stimulated neutrophils.
Neutrophils are critical initiators and effectors of the innate immune system and express Toll-like receptor 2 (TLR2) and TLR4. Although signaling through pathways involving phosphoinositide 3-kinase (PI3-K) and the downstream kinase Akt (protein kinase B) plays a central role in modulating neutrophil chemotaxis and superoxide generation in response to engagement of G protein-coupled receptors, the importance of these kinases in affecting inflammatory responses of neutrophils stimulated through TLR2 has not been examined. In these experiments, we found activation of Akt in neutrophils stimulated with the TLR2-specific ligands peptidoglycan and the lipopeptide tri-palmitoyl-S-glyceryl-Cys-Ser-(Lys)(4) that occurred earlier and was of greater magnitude than that present after exposure to the TLR4 agonist LPS. The release of the proinflammatory mediators TNF-alpha and macrophage inflammatory protein-2 was inhibited in a dose-dependent manner by PI3-K blockade. The IC(50) for inhibition of peptidoglycan-stimulated Akt activation and macrophage inflammatory protein-2 release correlated closely, indicating linkage of these two events. PI3-K blockade did not inhibit nuclear translocation of NF-kappa B, but did prevent Ser(536) phosphorylation of the p65 subunit of NF-kappa B, an event required for maximal transcriptional activity of NF-kappa B. Inhibition of PI3-K also prevented activation of p38 mitogen-activated protein kinase and extracellular receptor-activated kinase 1/2 in TLR2-stimulated neutrophils. These results demonstrate that the PI3-K-Akt axis occupies a central role in TLR2-induced activation of neutrophils.
Strassheim
Derek
D
Division of Pulmonary Science and Critical Care Medicine, Department of Medicine, University of Colorado Health Sciences Center, Denver, CO 80262, USA. derek.strassheim@uchsc.edu
Asehnoune
Karim
K
Park
Jong-Sung
JS
Kim
Jae-Yeol
JY
He
Qianbin
Q
Richter
Donald
D
Kuhn
Katherine
K
Mitra
Sanchayita
S
Abraham
Edward
E
D000818:Animals; D002478:Cells, Cultured; D054426:Chemokine CXCL2; D018925:Chemokines / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D004789:Enzyme Activation; D007249:Inflammation / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D008297:Male; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D018375:Neutrophil Activation / Q000276:immunology; D009504:Neutrophils / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases
D054426:Chemokine CXCL2; D018925:Chemokines; D016207:Cytokines; D008562:Membrane Glycoproteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D016328:NF-kappa B; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011956:Receptors, Cell Surface; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases; C404915:Cxcl2 protein, mouse