Selenoprotein H Is a Redox-sensing High Mobility Group Family DNA-binding Protein That Up-regulates Genes Involved in Glutathione Synthesis and Phase II Detoxification

Abstract

Selenoprotein H is a recently identified member of the selenoprotein family whose function is not fully known. Previous studies from our laboratory and others showed that Drosophila melanogaster selenoprotein H is essential for viability and antioxidant defense. In this study we investigated the function of human selenoprotein H in murine hippocampal HT22 cells engineered to stably overexpress the protein. After treatment of cells with L-buthionine-(S,R)-sulfoximine to deplete glutathione, selenoprotein H-overexpressing cells exhibited higher levels of total glutathione, total antioxidant capacities, and glutathione peroxidase enzymatic activity than did vector control cells. Overexpression of selenoprotein H also up-regulated the mRNA levels of endogenous selenoprotein H, glutamylcysteine synthetase heavy and light chains, and glutathione S-transferases Alpha 2, Alpha 4, and Omega 1. The amino acid sequence of selenoprotein H contains four putative nuclear localization sequences and an AT-hook motif, a small DNA-binding domain first identified in high mobility group proteins. Chromatin immunoprecipitation using a green fluorescent protein-selenoprotein H fusion revealed binding to sequences containing heat shock and/or stress response elements. Thus, selenoprotein H is a redox-responsive DNA-binding protein of the AT-hook family and functions in regulating expression levels of genes involved in de novo glutathione synthesis and phase II detoxification in response to redox status.Selenium has long been known for its antioxidant properties, and accumulated evidence indicates that many of the beneficial effects of this trace element in our diet are attributable to selenoenzymes. The functions of selenoenzymes include protecting cell membranes, proteins, and nucleic acids from cumulative oxidative damage and maintaining cellular redox balance. Selenium is highly retained in neuronal tissue during selenium deficiency (1), and the functions of selenoproteins in the brain are highlighted by the development of neurological defects in mice that underwent targeted disruption of selenoprotein P, a selenium transport protein whose functions may also include antioxidant defense and heavy metal chelation (2, 3). To date, 25 selenoprotein genes have been identified in the human genome (4), but the functions of many of them are yet to be fully defined. Selenoprotein H (SelH) 3 was initially identified in the Drosophila melanogaster genome and subsequently in the human and mouse genomes, where expression is high in the brain. In previous studies we and others showed that D. melanogaster SelH is required for viability, and overexpression of the protein increased antioxidant capacity in Drosophila embryo-derived Schneider S2 cells when exposed to homocysteic acid-induced GSH depletion (5, 6).Two recent studies have begun to investigate the functions of human SelH. We reported that overexpression of human SelH protects against UV-induced cell death via a decrease in superoxide levels (7). A study employing bioinformatic analysis a...

Selenoprotein H Suppresses Cellular Senescence through Genome Maintenance and Redox Regulation

“…SelH-deficient cells display persistent DNA damage, increased oxidative stress and Nrf2 activation, and decreased GSH level. Previous reports suggest dual roles of human SelH as an oxidoreductase and a transactivator on genes involved in GSH synthesis and phase II detoxification (24,27). Although these results are based on overexpressed SelH in immortalized mouse cells incapable of developing replicative senescence, they offer insightful clues to explain the new role of SelH demonstrated herein.…”

“…The expression of glutamylcysteine synthetase, a key enzyme for de novo GSH biosynthesis, is increased in murine hippocampal HT22 cells overexpressing human SelH (27). Here we showed that the level of intracellular GSH was significantly lower (p Ͻ 0.05) in SelH shRNA than in scrambled shRNA HeLa cells before and after exposure with H 2 O 2 for 24 h (Fig.…”

Selenium biochemistry and its role for human health

“…108 It is moderately expressed in various mouse tissues, whereas elevated expression levels were found in brain during early development, but also in the thyroid, lung, stomach, and liver human tumors. 109 These data suggest a possible role of SelH in cellular proliferation during development or cancer growth.…”

“…SelH is also involved in up-regulating the levels of GSH, the activity of GPx and the total antioxidant capacity in response to the redox state, with protective effects against superoxide and cell damage induced by ultraviolet B (UVB) irradiation. 108,110 A recent study has shown that SelH may exert its protective function through the activation of mitochondrial biogenesis signalling pathway by increasing the level of the nuclear encoded regulators PGC-1a, NRF1 and Tfam. 111 …”

Selenium and asthma: a complex relationship

“…There are, in fact, five human GPX selenoenzymes: GPX1-4 and 6. In addition to the GPX enzymes, other selenoproteins to which antioxidant or redox properties have been attributed include thioredoxin reductase-1, -2 and -3 as well as selenoproteins H, P, R and W (12)(13)(14)(15). A total of 25 selenoproteins have been identified in humans, 24 of which exist as selenoproteins in rodents (16).…”