title: Tumor necrosis factor-alpha-mediated signal transduction in human neutrophils: involvement of sphingomyelin metabolites in the priming effect of TNF-alpha on the fMLP-stimulated superoxide production.
abstract: We investigated the mechanism underlying the priming effect of TNF-alpha on fMLP-stimulated superoxide production in human neutrophils. TNF-alpha enhanced fMLP-stimulated superoxide production in a concentration-dependent manner. TNF-alpha also induced sphingomyelin (SM) hydrolysis and increased the formation of its metabolite, sphingosine-1-phosphate (SP-1-P). The treatment of neutrophils with sphingomyelinase also resulted in a similar priming effect. C2 ceramide produced a concentration-dependent inhibition of fMLP-stimulated superoxide production within the concentration range of 1-30 microM. Sphingosine had a dual effect on fMLP-stimulated superoxide generation, exhibiting a priming effect at lower concentrations (0.2-1 microM), but an inhibitory effect at higher concentrations (1-30 microM). SP-1-P (1-30 microM), showed a concentration-dependent enhancement of fMLP stimulated superoxide production. Furthermore, after treating neutrophils with DL-threo-dihydro-sphingosine, a competitive inhibitor of sphingosine kinase, TNF-alpha produced a similar dual effect as observed with sphingosine. These results strongly suggest that SM hydrolysis plays a key role in the intracellular signal transduction mediating the TNF-alpha-mediated priming effect.
authors.affiliation: Department of Pharmacology, Gifu University School of Medicine, Japan. mniwa@cc.gifu-u.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Niwa
authors.forename: O
authors.initials: O
authors.lastname: Kozawa
authors.forename: H
authors.initials: H
authors.lastname: Matsuno
authors.forename: Y
authors.initials: Y
authors.lastname: Kanamori
authors.forename: A
authors.initials: A
authors.lastname: Hara
authors.forename: T
authors.initials: T
authors.lastname: Uematsu
mesh_terms: D006801:Humans; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D009504:Neutrophils / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000187:drug effects*; D013108:Sphingomyelin Phosphodiesterase / Q000494:pharmacology; D013109:Sphingomyelins / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D000099157:Sphingosine Kinase
chemical_list: D009240:N-Formylmethionine Leucyl-Phenylalanine; D017853:Phosphotransferases (Alcohol Group Acceptor); D013108:Sphingomyelin Phosphodiesterase; D013109:Sphingomyelins; D013110:Sphingosine; D013481:Superoxides; D014409:Tumor Necrosis Factor-alpha; D000099157:Sphingosine Kinase; C005682:safingol