Transcriptional up-regulation of disk abalone selenium dependent glutathione peroxidase by H(2)O(2) oxidative stress and Vibrio alginolyticus bacterial infection.
ABSTRACT Selenium dependent glutathione peroxidase (Se-GPx) belongs to the family of selenoprotein, which acts mainly as an antioxidant in the cellular defence system. We have identified Se-GPx full length cDNA from disk abalone (Haliotis discus discus) designated as AbSe-GPx. It has a characteristic codon at (223)TGA(225) that corresponds to selenocysteine (Sec) amino acid as U(75). The full length cDNA consists of 675 bp, an open reading frame encoding 225 amino acids. Sequence characterization revealed that AbSe-GPx contains a characteristic GPx signature motif 2 ((97)LGFPCNQF(104)), an active site motif ((183)WNFEKF(188)) and essential residues for the enzymatic function. Additionally, the eukaryotic selenocysteine insertion sequence (SECIS) is conserved in the 3' UTR. The AbSe-GPx amino acid sequence exhibited the highest level of identity (46%) with insect (Ixodes scapularis) GPx, and shares 41% with bivalve (Unio tumidus) Se-GPx. The RT-PCR analysis revealed that AbSe-GPx mRNA was expressed constitutively in gill, mantle, gonad, abductor muscle, digestive tract, and hemocytes in a tissue specific manner. AbSe-GPx mRNA expression was significantly up-regulated in gill and digestive tract tissues after H(2)O(2) injection and Vibrio alginolyticus infection. However, AbSe-GPx expression was not up-regulated after Aroclor 1,254 injection. These results indicate that AbSe-GPx mRNA is expressed at a basal level in abalone tissues, which can be up-regulated transcriptionally by H(2)O(2) oxidative stress and Vibrio alginolyticus infection. Therefore, AbSe-GPx may be involved in a protective role against H(2)O(2) oxidative stress and immune defence against bacterial infection.
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ABSTRACT: Expression of selenocysteine (Sec)-containing proteins requires the presence of a cis-acting mRNA structure, called selenocysteine insertion sequence (SECIS) element. In bacteria, this structure is located in the coding region immediately downstream of the Sec-encoding UGA codon, whereas in eukaryotes a completely different SECIS element has evolved in the 3'-untranslated region. Here, we report that SECIS elements in the coding regions of selenoprotein mRNAs support Sec insertion in higher eukaryotes. Comprehensive computational analysis of all available viral genomes revealed a SECIS element within the ORF of a naturally occurring selenoprotein homolog of glutathione peroxidase 4 in fowlpox virus. The fowlpox SECIS element supported Sec insertion when expressed in mammalian cells as part of the coding region of viral or mammalian selenoproteins. In addition, readthrough at UGA was observed when the viral SECIS element was located upstream of the Sec codon. We also demonstrate successful de novo design of a functional SECIS element in the coding region of a mammalian selenoprotein. Our data provide evidence that the location of the SECIS element in the untranslated region is not a functional necessity but rather is an evolutionary adaptation to enable a more efficient synthesis of selenoproteins.Nucleic Acids Research 02/2007; 35(2):414-23. · 8.28 Impact Factor
- Nucleic Acids Research 01/1991; 18(23):7144. · 8.28 Impact Factor
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ABSTRACT: Eukaryotic cells have to constantly cope with highly reactive oxygen-derived free radicals. Their defense against these free radicals is achieved by natural antioxidant molecules but also by antioxidant enzymes. In this paper, we review some of the data comparing the efficiency of three different antioxidant enzymes: Cu/Zn-superoxide dismutase (Cu/Zn-SOD), catalase, and selenium-glutathione peroxidase. We perform our comparison on one experimental model (human fibroblasts) where the activities of these three antioxidant enzymes have been modulated inside the cells, and the repercussion of these changes was investigated in different conditions. We also focus our attention on the protecting role of selenium-glutathione peroxidase, because this enzyme is very rarely studied due to the difficulties linked to its biochemical properties. These studies evidenced that all three antioxidant enzymes give protection for the cells. They show a high efficiency for selenium-glutathione peroxidase and emphasize the fact that each enzyme has a specific as well as an irreplaceable function. They are all necessary for the survival of the cell even in normal conditions. In addition, these three enzymes act in a cooperative or synergistic way to ensure a global cell protection. However, optimal protection is achieved only when an appropriate balance between the activities of these enzymes is maintained. Interpretation of the deleterious effects of free radicals has to be analyzed not only as a function of the amount of free radicals produced but also relative to the efficiency and to the activities of these enzymatic and chemical antioxidant systems. The threshold of protection can indeed vary dramatically as a function of the level of activity of these enzymes.Free Radical Biology and Medicine 10/1994; · 5.27 Impact Factor