ABSTRACT
The human genome contains 25 genes coding for selenocysteine-containing proteins (selenoproteins). These proteins are involved in a variety of functions, most notably redox homeostasis. Selenoprotein enzymes with known functions are designated according to these functions: TXNRD1, TXNRD2, and TXNRD3 (thioredoxin reductases), GPX1, GPX2, GPX3, GPX4, and GPX6 (glutathione peroxidases), DIO1, DIO2, and DIO3 (iodothyronine deiodinases), MSRB1 (methionine sulfoxide reductase B1), and SEPHS2 (selenophosphate synthetase 2). Selenoproteins without known functions have traditionally been denoted by SEL or SEP symbols. However, these symbols are sometimes ambiguous and conflict with the approved nomenclature for several other genes. Therefore, there is a need to implement a rational and coherent nomenclature system for selenoprotein-encoding genes. Our solution is to use the root symbol SELENO followed by a letter. This nomenclature applies to SELENOF (selenoprotein F, the 15-kDa selenoprotein, SEP15), SELENOH (selenoprotein H, SELH, C11orf31), SELENOI (selenoprotein I, SELI, EPT1), SELENOK (selenoprotein K, SELK), SELENOM (selenoprotein M, SELM), SELENON (selenoprotein N, SEPN1, SELN), SELENOO (selenoprotein O, SELO), SELENOP (selenoprotein P, SeP, SEPP1, SELP), SELENOS (selenoprotein S, SELS, SEPS1, VIMP), SELENOT (selenoprotein T, SELT), SELENOV (selenoprotein V, SELV), and SELENOW (selenoprotein W, SELW, SEPW1). This system, approved by the HUGO Gene Nomenclature Committee, also resolves conflicting, missing, and ambiguous designations for selenoprotein genes and is applicable to selenoproteins across vertebrates.
Subject(s)
Selenoproteins/classification , Selenoproteins/genetics , Humans , Terminology as TopicABSTRACT
BACKGROUND: Cardiomyopathy is common to areas with low selenium (Se) intake and in patients receiving total parenteral nutrition. Although controversial, a few studies have suggested a protective role for Se in coronary heart disease on the basis of modulation of high-density lipoproteins (HDL). AIMS OF THE STUDY: In this study, the role of Se as a positive regulator of expression of a key HDL, apolipoprotein A-I (apoA-I), has been evaluated in human hepatoblastoma (HepG2) cell culture model. We further examined if the transcription of apoA-I, driven by the nuclear hormone receptor, peroxisome-proliferator activated receptor, PPARalpha, was trans-repressed by the presence of the oxidative stress-responsive transcription factor, NF-kappaB. METHODS: Modulation of expression of apoA-I and activation of nuclear NF-kappaB subunit p65 and PPARalpha by Se status were evaluated by Western blot and luciferase-based assays. Interaction of p65 with PPARalpha was evaluated by immunoprecipitation. RESULTS: HepG2 cultured in media with Se (100 nM) demonstrated an increase in the expression of apoA-I when compared to Se-deficient cells. A similar trend was also seen in mice that were supplemented with 0.4 ppm of Se as sodium selenite. Treatment of Se-supplemented cells with bacterial lipopolysaccharide (LPS) showed induction of apoA-I. Supplementation of hepatocytes with Se decreased the nuclear levels of p65, which prevented its interaction with PPARalpha to modulate apoA-I transcription. CONCLUSION: Our results suggest that supplementation of hepatocytes with Se mitigates oxidative stress-dependent repression of apoA-I expression by suppressing the NF-kappaB pathway, which allows PPARalpha to effectively drive the expression of apoA-I.
Subject(s)
Apolipoprotein A-I/metabolism , Lipoproteins, HDL/blood , NF-kappa B/metabolism , Selenium/pharmacology , Animals , Apolipoprotein A-I/antagonists & inhibitors , Cell Line, Tumor , Gene Expression Regulation/drug effects , Humans , Mice , Mice, Inbred C57BL , NF-kappa B/antagonists & inhibitors , PPAR alpha/metabolism , Selenium/deficiency , Transcription Factor RelAABSTRACT
Selenium (Se) is an important element required for the optimal functioning of the immune system. Particularly in macrophages, which play a pivotal role in immune regulation, Se acts as a major antioxidant in the form of selenoproteins to mitigate the cytotoxic effects of reactive oxygen species. Here we describe the role of Se as an anti-inflammatory agent and its effect on the macrophage signal transduction pathways elicited by bacterial endotoxin, LPS. Our studies demonstrate that supplementation of Se to macrophages (Se-deficient) leads to a significant decrease in the LPS-induced expression of two important pro-inflammatory genes, cyclooxygenase-2 (COX-2) and tumor necrosis factor-alpha (TNF-alpha) via the inhibition of MAP kinase pathways. Furthermore, Se-deficiency in mice exacerbated the LPS-mediated infiltration of macrophages into the lungs suggesting that Se status is a crucial host factor that regulates inflammation. In summary, our results indicate that Se plays an important role as an anti-inflammatory agent by tightly regulating the expression of pro-inflammatory genes in immune cells.
