Effects of Se-depletion on glutathione peroxidase and selenoprotein W gene expression in the colon.

Selenium (Se)-containing proteins have important roles in protecting cells from oxidative damage. This work investigated the effects of Se-depletion on the expression of the genes encoding selenoproteins in colonic mucosa from rats fed diets of different Se content and in human intestinal Caco-2 cells grown in Se-adequate or Se-depleted culture medium. Se-depletion produced statistically significant (P<0.05) falls in glutathione peroxidase (GPX) 1 mRNA (60-83%) and selenoprotein W mRNA (73%) levels, a small but significant fall in GPX4 mRNA (17-25%) but no significant change in GPX2. The data show that SelW expression in the colon is highly sensitive to Se-depletion.

A novel single nucleotide polymorphism in the 3' untranslated region of human glutathione peroxidase 4 influences lipoxygenase metabolism.

Selenium (Se) is an essential micronutrient for human health. The biological roles of the essential micronutrient Se are attributed to its presence in a range of 20-30 selenoproteins including the cytosolic and phospholipid hydroperoxide glutathione peroxidases (GPX1 and GPX4). It has been suggested that GPX4 may play a role in regulation of leukotriene biosynthesis and thus inflammation. In eukaryotes Se is incorporated into selenoproteins as the amino acid selenocysteine in a process requiring a stem-loop within the 3' untranslated region (3'UTR) of the mRNA. In this study the region of the GPX4 gene corresponding to the 3'UTR was scanned for mutations in a group of 66 volunteers. The data show a T/C variant at position 718. The distribution of this SNP in our population was 34% CC, 25% TT and 41% TC; i.e., it is in Hardy-Weinberg equilibrium. Individuals of different genotypes exhibited significant differences in the levels of lymphocyte 5-lipoxygenase total products, with C718 showing increased levels of those products compared to T718 and T/C718 (36% and 44% increases, respectively). The data suggest that the SNP718 that we have identified has functional effects and support the hypothesis that GPX4 plays a regulatory role in leukotriene biosynthesis.

Intracellular trafficking of micronutrients: from gene regulation to nutrient requirements.

The intracellular distribution of micronutrients, as well as their uptake, is important for cell function. In some cases the distribution of micronutrients or their related proteins is determined by gene expression mechanisms. The 3' untranslated region (3'UTR) of metallothionein-1 mRNA determines localisation of the mRNA, and in turn intracellular trafficking of the protein product. Using transfected cells we have evidence for the trafficking of metallothionein-1 into the nucleus and for its involvement in protection from oxidative stress and DNA damage. When nutritional supply of Se is limited, selenoprotein expression is altered, but not all selenoproteins are affected equally; the available Se is prioritised for synthesis of particular selenoproteins. The prioritisation involves differences in mRNA translation and stability due to 3'UTR sequences. Potentially, genetic variation in these regulatory mechanisms may affect nutrient requirements. Genetic polymorphisms in the 3'UTR from two selenoprotein genes have been observed; one polymorphism affects selenoprotein synthesis. These examples illustrate how molecular approaches can contribute at several levels to an increased understanding of nutrient metabolism and requirements. First, they provide the tools to investigate regulatory features in genes and their products. Second, understanding these processes can provide model systems to investigate nutrient metabolism at the cellular level. Third, once key features have been identified, the availability of human genome sequence information and single nucleotide polymorphism databases present possibilities to define the extent of genetic variation in genes of nutritional relevance. Ultimately, the functionality of any variations can be defined and subgroups of the population with subtly different nutrient requirements identified.