Elk-3 is a transcriptional repressor of nitric-oxide synthase 2.
The inducible isoform of nitric-oxide synthase (NOS2), a key enzyme catalyzing the dramatic increase in nitric oxide by lipopolysaccharide (LPS), plays an important role in the pathophysiology of endotoxemia and sepsis. Recent evidence suggests that Ets transcription factors may contribute to NOS2 induction by inflammatory stimuli. In this study, we investigated the role of Ets transcription factors in the regulation of NOS2 by LPS and transforming growth factor (TGF)-beta 1. Transient transfection assays in macrophages showed that Ets-2 produced an increase in NOS2 promoter activity, whereas the induction by Ets-1 was modest and NERF2 had no effect. Elk-3 (Net/Erp/Sap-2a) markedly repressed NOS2 promoter activity in a dose-dependent fashion, and overexpression of Elk-3 blunted the induction of endogenous NOS2 message. Mutation of the Net inhibitory domain of Elk-3, but not the C-terminal-binding protein interaction domain, partially alleviated this repressive effect. We also found that deletion of the Ets domain of Elk-3 completely abolished its repressive effect on the NOS2 promoter. LPS administration to macrophages led to a dose-dependent decrease in endogenous Elk-3 mRNA levels, and this decrease in Elk-3 preceded the induction of NOS2 mRNA. In a mouse model of endotoxemia, the expression of Elk-3 in kidney, lung, and heart was significantly down-regulated after systemic administration of LPS, and this down-regulation also preceded NOS2 induction. Moreover, TGF-beta 1 significantly increased endogenous Elk-3 mRNA levels that had been down-regulated by LPS in macrophages. This increase in Elk-3 correlated with a TGF-beta 1-induced down-regulation of NOS2. Taken together, our data suggest that Elk-3 is a strong repressor of NOS2 promoter activity and mRNA levels and that endogenous expression of Elk-3 inversely correlates with NOS2. Thus, Elk-3 may serve as an important mediator of NOS2 gene expression.
Chen
Yen-Hsu
YH
Pulmonary and Critical Care Division, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA.
Layne
Matthew D
MD
Chung
Su Wol
SW
Ejima
Kuniaki
K
Baron
Rebecca M
RM
Yet
Shaw-Fang
SF
Perrella
Mark A
MA
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D004247:DNA / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D050783:Proto-Oncogene Proteins c-ets; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D053773:Transforming Growth Factor beta1
C086924:Elk3 protein, mouse; D008070:Lipopolysaccharides; D015513:Oncogene Proteins; D050783:Proto-Oncogene Proteins c-ets; D012333:RNA, Messenger; D012097:Repressor Proteins; C508961:Tgfb1 protein, mouse; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D004247:DNA; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse