title: Peptidoglycan induces cyclooxygenase-2 expression in macrophages by activating the neutral sphingomyelinase-ceramide pathway.
abstract: The sphingomyelin signal transduction pathway is known to play a role in mediating the action of various cytokines. Herein, we examined the role of neutral sphingomyelinase (nSMase)/ceramide in peptidoglycan (PGN)-induced NF-kappaB activation and cyclooxygenase-2 (COX-2) expression in macrophages. PGN-induced COX-2 expression was attenuated by an nSMase inhibitor (3-O-methyl-sphingomyeline, 3-OMS) and ceramidase, but not by an acidic SMase inhibitor (imipramine). C2-ceramide, bacterial SMase (which mimics cellular SMase activity), and a ceramidase inhibitor (N-oleoyl-ethanolamine) individually had no effect on COX-2 expression; however, they markedly enhanced PGN-induced COX-2 expression. PGN activated nSMase, but not acidic SMase, resulting in increased ceramide generation. PGN-induced nSMase activation and ceramide formation were inhibited by 3-OMS, but not by imipramine. PGN-induced COX-2 expression was inhibited by a p38 MAPK inhibitor (SB 203580) and dominant negative mutants of MAPK kinase (MKK) 3, MKK6, and p38 MAPKalpha. 3-OMS selectively inhibited PGN-induced p38 MAPK and MKK3/6 activation, but not JNK or ERK1/2. C2-ceramide, bacterial SMase, and N-oleoyl-ethanolamine all induced p38 MAPK or MKK3/6 activation. The PGN-mediated increases in kappaB-luciferase activity were also inhibited by 3-OMS and the p38 MAPKalphaDN, but not by imipramine. Furthermore, C2-ceramide caused an increase in kappaB-luciferase activity. Our data demonstrate for the first time that PGN activates the nSMase/ceramide pathway to induce MKK3/6/p38 MAPK activation, which in turn initiates NF-kappaB activation and ultimately induces COX-2 expression in macrophages. The nSMase/ceramide pathway is required but might not be sufficient for COX-2 expression induced by PGN.
authors.affiliation: School of Respiratory Therapy, College of Medicine, Taipei Medical University, Taipei 110, Taiwan.
authors.forename: Bing-Chang
authors.initials: BC
authors.lastname: Chen
authors.forename: Huey-Mei
authors.initials: HM
authors.lastname: Chang
authors.forename: Ming-Jen
authors.initials: MJ
authors.lastname: Hsu
authors.forename: Chwen-Ming
authors.initials: CM
authors.lastname: Shih
authors.forename: Yi-Hua
authors.initials: YH
authors.lastname: Chiu
authors.forename: Wen-Ta
authors.initials: WT
authors.lastname: Chiu
authors.forename: Chien-Huang
authors.initials: CH
authors.lastname: Lin
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002518:Ceramides / Q000378:metabolism*; D051546:Cyclooxygenase 2 / Q000096:biosynthesis*; D004789:Enzyme Activation / Q000187:drug effects; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D048371:MAP Kinase Kinase 3 / Q000378:metabolism; D048669:MAP Kinase Kinase 6 / Q000378:metabolism; D017737:Macrophages, Peritoneal / Q000187:drug effects* / Q000201:enzymology*; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D010457:Peptidoglycan / Q000494:pharmacology*; D013108:Sphingomyelin Phosphodiesterase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D002518:Ceramides; D004791:Enzyme Inhibitors; D016328:NF-kappa B; D010457:Peptidoglycan; C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; C482531:Map2k3 protein, mouse; C482567:Map2k6 protein, mouse; D013108:Sphingomyelin Phosphodiesterase