Uncoupling protein 2 plays an important role in nitric oxide production of lipopolysaccharide-stimulated macrophages.
The expression of uncoupling protein 2 (UCP2) was reduced in macrophages after stimulation with lipopolysaccharide (LPS). The physiological consequence and the regulatory mechanisms of the UCP2 down-regulation by LPS were investigated in a macrophage cell line, RAW264 cells. UCP2 overexpression in RAW264 cells transfected with eukaryotic expression vector containing ucp2 cDNA markedly reduced the production of intracellular reactive oxygen species. Furthermore, in the UCP2 transfectant, nitric oxide (NO) synthesis, inducible NO synthase (NOS II) protein, NOS II mRNA, and NOS II promoter activity were definitely decreased after LPS stimulation compared with those in parental RAW264 or RAW264 cells transfected with the vector alone. Reporter assays suggested that an enhancer element was located in the region of intron 2 of the UCP2 gene and that the UCP2 expression was down-regulated not by the 7.3-kb promoter region but by the 5' region of the UCP2 gene containing two introns. Deletion of intron 2 resulted in the low transcriptional activities and abolishment of the LPS-associated negative regulation. In addition, the mRNA expression of transfected UCP2 was suppressed in RAW264 cells transfected with expression vector containing UCP2 genomic DNA, but was markedly increased in cells transfected with the vector containing UCP2 intronless cDNA. These findings suggest that the LPS-stimulated signals suppress UCP2 expression by interrupting the function of intronic enhancer, leading to an up-regulation of intracellular reactive oxygen species, which activate the signal transduction cascade of NOS II expression, probably to ensure rapid and sufficient cellular responses to a microbial attack.
Kizaki
Takako
T
Department of Molecular Predictive Medicine and Sport Science, Kyorin University, School of Medicine, Mitaka 181-8611, Japan. kizaki@kyorin-u.ac.jp
Suzuki
Kenji
K
Hitomi
Yoshiaki
Y
Taniguchi
Naoyuki
N
Saitoh
Daizoh
D
Watanabe
Kenji
K
Onoé
Kazunori
K
Day
Noorbibi K
NK
Good
Robert A
RA
Ohno
Hideki
H
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D018076:DNA, Complementary / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects; D007438:Introns; D007473:Ion Channels; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism*; D026901:Membrane Transport Proteins; D051379:Mice; D024101:Mitochondrial Proteins; D016297:Mutagenesis, Site-Directed; D009569:Nitric Oxide / Q000096:biosynthesis*; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D011401:Promoter Regions, Genetic; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D000071246:Uncoupling Protein 2
D018076:DNA, Complementary; D007473:Ion Channels; D008070:Lipopolysaccharides; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D012333:RNA, Messenger; C000604390:Ucp2 protein, mouse; D000071246:Uncoupling Protein 2; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse