Lipopolysaccharide-binding protein- and CD14-dependent activation of mitogen-activated protein kinase p38 by lipopolysaccharide in human neutrophils is associated with priming of respiratory burst.
Neutrophil (PMN) functions can be primed for greatly increased oxidative radical release by exposure to certain agents such as lipopolysaccharide (LPS). Although a variety of signaling pathways involving both tyrosine kinases and mitogen-activated protein (MAP) kinases may be operative, the mechanisms of PMN priming are still not understood. We found that PMN priming was not achieved by treatment of cells with a very low concentration (5 ng/ml) of LPS unless additional "helper" factors were present in plasma (5%). Under these conditions, LPS induced tyrosine phosphorylation of a 38-kDa protein, which was coincident with the MAP kinase p38 action in this situation. LPS-mediated activation of p38 in human PMNs was dependent on the presence of LPS binding protein from plasma and CD14 on the surfaces of the cells. Phosphorylation of p38 was highly correlated with LPS priming of a formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PMN respiratory burst. Treatment of PMN with the p38-specific inhibitor SB203580 significantly attenuated the respiratory burst in cells primed by LPS and stimulated by fMLP. These results suggest that the LPS signaling pathway leading to p38 activation may be an important mechanism in regulation of PMN priming. The mediator(s) linking CD14 to p38 involves proteins that are functionally sensitive to genistein but insensitive to tyrphostin AG126 and to Src- and Syk-family kinase, protein kinase C, and phosphatidylinositol 3-kinase inhibitors. Elucidating this pathway will provide insight into possible regulation of PMN priming by LPS.
Department of Pediatrics, Dalhousie University and IWK Health Centre, Halifax, Nova Scotia, Canada.
Sen Rong
SR
Yan
Walla
W
Al-Hertani
David
D
Byers
Robert
R
Bortolussi
D000209:Acute-Phase Proteins; D002352:Carrier Proteins / Q000276:immunology*; D002478:Cells, Cultured; D004789:Enzyme Activation; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000276:immunology*; D008070:Lipopolysaccharides / Q000276:immunology* / Q000494:pharmacology; D008562:Membrane Glycoproteins; D020928:Mitogen-Activated Protein Kinases / Q000276:immunology*; D009504:Neutrophils / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000276:immunology; D011518:Proto-Oncogene Proteins / Q000276:immunology; D051572:Proto-Oncogene Proteins c-hck; D016897:Respiratory Burst / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology*; D014443:Tyrosine / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases; D019061:src-Family Kinases / Q000276:immunology; D000099231:Lipopolysaccharide-Binding Protein
D000209:Acute-Phase Proteins; D002352:Carrier Proteins; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D020928:Mitogen-Activated Protein Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051572:Proto-Oncogene Proteins c-hck; D014443:Tyrosine; D048051:p38 Mitogen-Activated Protein Kinases; D019061:src-Family Kinases; D000099231:Lipopolysaccharide-Binding Protein; C496631:HCK protein, human; C060902:lyn protein-tyrosine kinase