Abstract
Macrophages produce large amounts of nitric oxide (NO) in response to proinflammatory cytokines and lipopolysaccharide (LPS) by expressing inducible isoform of NO synthase (iNOS). We examined the role of extracellular signal-regulated kinase p42/44MAPK (Erk1/2) in signal transduction pathways leading to induction of NO synthesis in response to LPS in J774 mouse macrophages and T-84 human colon epithelial cells. LPS activated Erk1/2 and induced iNOS and subsequent NO production. Erk1/2 activation was inhibited by PD 98059, a specific inhibitor of mitogen-activated protein kinase kinase (Mek) that is an upstream activator of Erk1/2. At corresponding concentrations PD 98059 reduced LPS-induced NO formation by 40 to 50% by inhibiting iNOS expression in J774 and T-84 cells. Inhibition of iNOS expression was not mediated by nuclear factor-κB because PD 98059 had no effect on nuclear factor-κB activity in J774 macrophages. In addition, PD 98059 reduced LPS-induced l-arginine transport into the cells as measured in J774 macrophages, whereas the availability of tetrahydrobiopterin was not a limiting factor in NO production after PD 98059. Our results indicate that Erk1/2 activation mediates up-regulation but is not essential for LPS-induced iNOS expression.
Footnotes
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Send reprint requests to: Eeva Moilanen, University of Tampere, Medical School, Department of Pharmacology, FIN-33014, Tampere, Finland.
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↵1 This work was supported by Medical Research Fund of Tampere University Hospital, The Academy of Finland, and The Finnish Anti-Tuberculosis Association Foundation.
- Abbreviations:
- NO
- nitric oxide
- NOS
- NO synthase
- iNOS
- inducible NOS
- LPS
- lipopolysaccharide
- PKC
- protein kinase C
- Erk1/2
- extracellular signal-regulated kinase p42/p44
- MAPK
- mitogen-activated protein kinase
- Mek-1
- mitogen-activated protein kinase kinase-1
- PD 98059
- 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one
- PDTC
- pyrrolidinedithiocarbamate
- l-NMMA
- N-monomethyl-l-arginine
- PMSF
- phenylmethylsulfonyl fluoride
- TBS/T
- Tris-buffered saline/Tween
- DTT
- dithiothreitol
- NF-κB
- nuclear factor-κB
- BH4
- tetrahydrobiopterin
- AHR
- aryl hydrocarbon receptor
- C/EBPβ
- CCAAT/enhancer binding protein β, NF-IL-6
- Received February 8, 2000.
- Accepted May 31, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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