Obesity and immune system -with enphasis on macrophages-

解偶联蛋白2(UCP-2)通过降低线粒体膜电位来限制ROS的产生。尽管活性氧参与了内毒素刺激后巨噬细胞诱导型一氧化氮合酶(NOSII)基因表达的细胞信号转导，但UCP-2在调节对内毒素的反应中的作用尚不清楚。巨噬细胞经内毒素刺激后，UCP2的表达减少。本文研究了脂多糖下调巨噬细胞系RAW264细胞UCP-2表达的生理效应及其调控机制。含UCP-2真核表达载体的RAW264细胞中UCP-2的过表达显著减少了ROS的产生，而且与…相比，UCP-2的NO合成、NOSII蛋白、NOSIImRNA和NOSII启动子的活性明显降低在单独转染载体的亲本RAW264或RAW264细胞中表达更多。报道分析表明，在UCP-2基因的第二内含子区域有一个增强子元件，UCP-2的表达不是被7.3 kb的启动子区域下调，而是被含有两个内含子的UCP-2基因的5‘端区域下调。第二内含子的缺失导致转录活性降低，并取消了与内毒素相关的负调控。此外，携带UCP-2基因组DNA的表达载体可抑制RAW264细胞中UCP-2基因的表达，而携带UCP-2内含子基因的表达载体可显著增强RAW264细胞中UCP-2基因的表达。这些发现表明，内毒素刺激的信号通过干扰内含子增强子的功能来抑制UCP-2的表达，导致细胞内ROS的上调，从而激活了NOS II表达的信号转导级联反应，可能是为了确保细胞对微生物攻击的快速和足够的反应。较少

It has been proposed that uncoupling protein 2 (UCP-2) limits production of reactive oxygen species (ROS) by decreasing the mitochondrial membrane potential. Although reactive oxygen species are involved in cellular signaling for inducible nitric oxide synthase (NOS II) gene expression following lipopolysaccharide (LPS) stimulation in macrophages, the role of UCP-2 in the regulation of the response to LPS has not been elucidated. The expression of UCP2 was reduced in macrophages following stimulation with LPS. The physiological consequence and the regulatory mechanisms of the UCP-2 down-regulation by LPS were investigated in a macrophage cell line, RAW264 cells. UCP-2 overexpression in RAW264 cells transfected with eukaryotic expression vector containing ucp-2 cDNA markedly reduced the production of ROS, Furthermore, in the UCP-2 transfectant, NO synthesis, NOS II protein, NOS II mRNA, and NOS II promoter activity were definitely decreased following LPS stimulation compared with those … More in parental RAW264 or RAW264 cells transfected with the vector alone. Reporter assays suggested that an enhancer element was located in the region of the second intron of UCP-2 gene and that the UCP-2 expression was down-regulated not by the 7.3 kb promoter region but by the 5'-region of UCP-2 gene containing two introns. Deletion of the second intron resulted in the low transcriptional activities and abolishment of the LPS-associated negative regulation. In addition, the mRNA expression of transfected UCP-2 was suppressed in RAW264 cells transfected with expression vector containing UCP-2 genomic DNA, but was markedly increased in cells transfected with the vector containing UCP-2 intronless cDNA. These findings suggest that the LPS stimulated signals suppress UCP-2 expression by interrupting the function of intronic enhancer, leading to an up-regulation of intracellular ROS which activate the signal transduction cascade of NOS II expression, probably to ensure rapid and sufficient cellular responses to a microbial attack. Less