Nitric oxide reduces early growth response-1 gene expression in rat lung macrophages treated with interferon-gamma and lipopolysaccharide.
Since early growth response-1 (Egr-1) is required for macrophage differentiation and nitric oxide (NO) is immunosuppressive, we hypothesized that NO would reduce Egr-1 expression in rat lung macrophages. The inflammatory stimuli interferon-gamma and lipopolysaccharide induced an early, transient increase in Egr-1 mRNA (> 5-fold at 2 h) and a sustained, high level of inducible NO synthase mRNA (> 100-fold from 4 to 24 h). The NO metabolites nitrite and nitrate rose > 10-fold in medium from stimulated versus unstimulated cells over 24 h. Concomitant with elevated nitrogen oxides, Egr-1 mRNA levels declined to 80% below unstimulated cells at 24 h. This decline was blocked by an inhibitor of NO production, NG-monomethyl-L-arginine. Further, the NO donor S-nitroso-N-acetylpenicillamine inhibited Egr-1 expression in a dose-dependent manner, producing complete inhibition at 0.5 mM. The effect of S-nitroso-N-acetylpenicillamine was not due to reduced macrophage viability. We conclude that Egr-1 induction precedes inducible NO synthase induction in stimulated rat macrophages and that subsequent NO production reduces macrophage expression of Egr-1. We propose that this mechanism is used to regulate macrophage differentiation in human immunodeficiency virus infection and other inflammatory states.
Henderson
S A
SA
Department of Physiological Science, UCLA 90024.
Lee
P H
PH
Aeberhard
E E
EE
Adams
J W
JW
Ignarro
L J
LJ
Murphy
W J
WJ
Sherman
M P
MP
D000594:Amino Acid Oxidoreductases / Q000096:biosynthesis; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D004347:Drug Interactions; D051766:Early Growth Response Protein 1; D005786:Gene Expression Regulation; D017874:Immediate-Early Proteins; D007249:Inflammation / Q000209:etiology; D007371:Interferon-gamma / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide / Q000494:pharmacology*; D019001:Nitric Oxide Synthase; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D013997:Time Factors; D014157:Transcription Factors / Q000096:biosynthesis*
D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486110:Egr1 protein, rat; D017874:Immediate-Early Proteins; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D014157:Transcription Factors; D009569:Nitric Oxide; D007371:Interferon-gamma; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases