title: Primary granule release from human neutrophils is potentiated by soluble fibrinogen through a mechanism depending on multiple intracellular signaling pathways.
abstract: N-Formyl-methionyl-leucyl-phenylalanine (fMLP) is a potent activator of neutrophil degranulation. The intracellular signaling mechanisms involved in the potentiating effect of fibrinogen on fMLP-induced primary granule release from human neutrophils were investigated. Fibrinogen caused a significant leftward shift of the concentration-response curve of fMLP-induced elastase release. An antibody against Mac-1 (CD11b/CD18) prevented the potentiating effect of fibrinogen, suggesting that soluble fibrinogen potentiates fMLP-induced degranulating effect by a mechanism mediated by the integrin Mac-1. Fibrinogen enhanced fMLP-induced tyrosine phosphorylation in human neutrophils and markedly enhanced the phosphorylation of mitogen-activated protein kinases (MAPK) caused by fMLP. However, U0126, an inhibitor of p44/42 MAPK activation, or SB-203580, an inhibitor of p38 MAPK, did not alter the effect of fibrinogen on fMLP-induced elastase release. Wortmannin, a phosphatidylinositol 3-kinase (PI3K) kinase inhibitor, and genistein, a nonspecific tyrosine kinase inhibitor, strongly inhibited fMLP-induced elastase release both in the presence and in the absence of fibrinogen. An Akt/PKB inhibitor failed to alter the potentiating effect of fibrinogen, suggesting that the effect of fibrinogen is mediated by Akt-independent pathways. Go6976, an inhibitor of classical PKC isoforms, caused a significant inhibition of fMLP-induced elastase release in the presence or absence of fibrinogen, while nonselective inhibitors of PKC, Ro 31-8220, GF-109203X, and staurosporine, caused potentiation of fMLP-induced elastase release. We conclude that fibrinogen potentiation of primary granule release induced by fMLP is mediated by the integrin CD11b/CD18 through pathways dependent on PI3K and tyrosine kinases, but other regulatory mechanisms may be also involved.
authors.affiliation: Department of Physiology, Temple University Medical School, Philadelphia, Pennsylvania 19140, USA.
authors.forename: Florin
authors.initials: F
authors.lastname: Tuluc
authors.forename: Analia
authors.initials: A
authors.lastname: Garcia
authors.forename: Ovidiu
authors.initials: O
authors.lastname: Bredetean
authors.forename: John
authors.initials: J
authors.lastname: Meshki
authors.forename: Satya P
authors.initials: SP
authors.lastname: Kunapuli
mesh_terms: D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005340:Fibrinogen / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D016177:Macrophage-1 Antigen / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D010196:Pancreatic Elastase / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D016177:Macrophage-1 Antigen; D014443:Tyrosine; D009240:N-Formylmethionine Leucyl-Phenylalanine; D005340:Fibrinogen; D020928:Mitogen-Activated Protein Kinases; D010196:Pancreatic Elastase; D002118:Calcium