Selenoprotein K (Sel K) is a selenium-containing protein for which no function has been identified. We found that Sel K is an endoplasmic reticulum (ER) transmembrane protein expressed at relatively high levels in immune cells and is regulated by dietary selenium. Sel K−/− mice were generated and found to be similar to WT controls regarding growth and fertility. Immune system development was not affected by Sel K deletion, but specific immune cell defects were found in Sel K−/− mice. Receptor-mediated Ca2+ flux was decreased in T cells, neutrophils, and macrophages from Sel K−/− mice compare to controls. Ca2+-dependent functions including T cell proliferation, T cell and neutrophil migration, and Fcγ-receptor-mediated oxidative burst in macrophages were decreased in cells from Sel K−/− mice compared to controls. West Nile virus (WNV) infections were performed and Sel K−/− mice exhibited decreased viral clearance in the periphery and increased viral titers in brain. Furthermore, WNV-infected Sel K−/− mice demonstrated significantly lower survival (2/23; 8.7%) compared to WT controls (10/26; 38.5%). These results establish Sel K as an ER-membrane protein important for promoting effective Ca2+ flux during immune cell activation and provide insight into molecular mechanisms by which dietary selenium enhances immune responses.

The immune-enhancing effects of selenium (Se) supplementation make it a promising complementary and alternative medicine modality for boosting immunity, although mechanisms by which Se influences immunity are unclear. Mice fed low (0.08 mg/kg), medium (0.25 mg/kg), or high (1.0 mg/kg) Se diets for 8 wk were challenged with peptide/adjuvant. Antigen-specific CD4(+) T cell responses were increased in the high Se group compared with the low and medium Se groups. T cell receptor signaling in ex vivo CD4(+) T cells increased with increasing dietary Se, with all 3 groups differing from one another in terms of calcium mobilization, oxidative burst, translocation of nuclear factor of activated T cells, and proliferation. The high Se diet increased expression of interleukin (IL)-2 and the high affinity chain of the IL-2 receptor compared with the low and medium Se diets. The high Se diet skewed the T helper (Th)1/Th2 balance toward a Th1 phenotype, leading to higher interferon-gamma and CD40 ligand levels compared with the low and medium Se diets. Prior to CD4(+) T cell activation, levels of reactive oxygen species did not differ among the groups, but the low Se diet decreased free thiols compared with the medium and high Se diets. Addition of exogenous free thiols eliminated differences in CD4(+) T cell activation among the dietary groups. Overall, these data suggest that dietary Se levels modulate free thiol levels and specific signaling events during CD4(+) T cell activation, which influence their proliferation and differentiation.

Selenoprotein P (Sel P) is a selenium-rich glycoprotein believed to play a key role in selenium (Se) transport throughout the body. Development of a Sel P knockout mouse model has supported this notion and initial studies have indicated that selenium supply to various tissues is differentially affected by genetic deletion of Sel P. Se in the form of the amino acid, selenocysteine, is incorporated into selenoproteins at UGA codons. Thus, Se availability affects not only selenoprotein levels, but also the turnover of selenoprotein mRNAs via the nonsense-mediated decay pathway. We investigated how genetic deletion of Sel P in mice affected levels of the mRNAs encoding all known members of the murine selenoprotein family, as well as three non-selenoprotein factors involved in their synthesis, selenophosphate synthetase 1 (SPS1), SECIS-binding protein 2 (SBP2) and SECp43. Our findings present a comprehensive description of selenoprotein mRNA expression in the following murine tissues: brain, heart, intestine, kidney, liver, lung, spleen and testes. We also describe how abundance of selenoproteins and selenoprotein-synthesis factors are affected by genetic deletion of Sel P in some of these tissues, providing insight into how the presence of this selenoprotein influences selenoprotein mRNA levels, and thus, the selenoproteome.

Selenium (Se) is an essential trace element used for biosynthesis of selenoproteins and is acquired either through diet or cellular recycling mechanisms. Selenocysteine lyase (Scly) is the enzyme that supplies Se for selenoprotein biosynthesis via decomposition of the amino acid selenocysteine (Sec). Knockout (KO) of Scly in a mouse affected hepatic glucose and lipid homeostasis. Mice lacking Scly and raised on an Se-adequate diet exhibit hyperinsulinemia, hyperleptinemia, glucose intolerance, and hepatic steatosis, with increased hepatic oxidative stress, but maintain selenoprotein levels and circulating Se status. Insulin challenge of Scly KO mice results in attenuated Akt phosphorylation but does not decrease phosphorylation levels of AMP kinase alpha (AMPK␣). Upon dietary Se restriction, Scly KO animals develop several characteristics of metabolic syndrome, such as obesity, fatty liver, and hypercholesterolemia, with aggravated hyperleptinemia, hyperinsulinemia, and glucose intolerance. Hepatic glutathione peroxidase 1 (GPx1) and selenoprotein S (SelS) production and circulating selenoprotein P (Sepp1) levels are significantly diminished. Scly disruption increases the levels of insulin-signaling inhibitor PTP1B. Our results suggest a dependence of glucose and lipid homeostasis on Scly activity. These findings connect Se and energy metabolism and demonstrate for the first time a unique physiological role of Scly in an animal model. S elenium (Se) is an essential trace element acquired through the diet that has been implicated in brain (53), immune, and thyroid function (49), in fertility (2), and in cancer prevention (43). Dietary Se is found in inorganic or organic forms. Se is mostly utilized for biosynthesis of the unique amino acid selenocysteine (Sec), which is cotranslationally incorporated into selenoproteins (36), functioning primarily in redox reactions. The Sec incorporation mechanism involves de novo synthesis of Sec via selenophosphate (SeϳP), which is synthesized by selenophosphate synthetases (SPS) (60). SeϳP is enzymatically attached to the O-phosphoseryl-tRNA, which is then converted to the specific selenocysteyl-tRNA [Ser]Sec used in the selenoprotein translation (54,61). Se is thought to enter the SeϳP pool for Sec biosynthesis either from diet or via recycling after selenoprotein degradation and release of Sec.Selenocysteine lyase (Scly) is responsible for cellular Sec decomposition to mobilize Se for utilization in selenoprotein synthesis (10, 41). Scly was first isolated and characterized from pig liver (18) and subsequently shown to break down Sec into alanine and selenide (41). Scly has been the target of several in vitro studies: it was reported to interact with SPS (58), and its crystal structure revealed the mechanism for the enzyme reaction specificity toward Se (10, 46). In vivo, Scly was recently shown to be involved in selenoprotein biosynthesis in HeLa cells (30). However, the physiological role of Scly in cellular Se metabolism and in vertebrate whole-body Se homeostasis remain...

Background: Selenoprotein M (SelM) is highly expressed in the brain and postulated to have neuroprotective properties. Results: SelM expression is present in high levels in hypothalamic nuclei involved in energy metabolism, and SelM KO mice exhibit increased adiposity without apparent cognitive deficits. Conclusion: SelM protects against obesity. Significance: Increased understanding of the genes that protect against obesity may yield improved treatments and prevention strategies.