ABSTRACT
Selenium has been implicated in cancer prevention in numerous animal models and some human studies, as previously reviewed (Davis et al., 2012). As discussed in Chapter 3, selenium is incorporated into proteins in the form of selenocysteine, which is typically present in the active centers of selenium-containing proteins, termed selenoproteins. At least three of these selenoproteins are known to play dual roles in the cancer process, including both cancer prevention and promotion. This chapter describes one such protein, designated the 15-kDa Selenoprotein (SEP15). In 1998, SEP15 was purified from human T-cells, sequenced, and molecularly characterized (Gladyshev et al., 1998). In subsequent studies, the highest levels of Sep15 expression were reported to occur in human, rat, and mouse tissues from liver, kidney, testes, thyroid, and prostate (Hu et al., 2001). Sep15 orthologs have been described in many animals, including mice, cows, dogs, chickens (Liu et al., 2014), zebra fish (Thisse et al., 2003), the Western clawed frog, the nematode Caenorhabditis elegans, fruit fly (Ferguson et al., 2006), and others. The endoplasmic reticulum-residing fish SEP15-like protein (Fep15) likely evolved by gene duplication and is homologous to mammalian SEP15, but its function is not known (Labunskyy et al., 2014). A selenoprotein of similar molecular weight, Selenoprotein M (SelM), is also found in many species and is thought to be a distant SEP15 homolog; however, its function and implications to human health remain to be elucidated, too (Ferguson et al., 2006).
