SELENOPROTEINS ARE EXPRESSED IN FETAL HUMAN OSTEOBLAST-LIKE CELLS

Selenoproteins are involved in mechanisms of cell differentiation and defense. We investigated the expression of glutathione peroxidases, as well as other selenoproteins, in fetal human osteoblasts (hFOB-cells) . Using 75-selenium metabolic labelling of viable hFOB-cells, we ident ified several selenoproteins in cell lysates of about 45-80 kDa and in the migration range of 14 kDa to 24 kDa. Cells expressed low mRNA lev els of both cellular glutathione peroxidase and plasma glutathione per oxidase mRNA as analysed by Southern analysis of RT-PCR products. Basa l cellular glutathione peroxidase enzyme activity in hFOB-cells (19.7 nmol NADPH oxidised per min and mu g protein) was further increased 2. 5-fold by the addition of 100 nM sodium selenite to the culture medium for 3 days. Furthermore, expression of selenoprotein P mRNA was demon strated by RT-PCR, hFOB-cells did not show activities of the selenopro teins type I or type II 5'-deiodinase. In summary, we identified cellu lar glutathione peroxidase, plasma glutathione peroxidase and selenopr otein P among of a panel of several 75-selenium labelled proteins in h uman fetal osteoblasts. The expression of selenoproteins like glutathi one peroxidases in hFOB-cells represents a new system of osteoblast an tioxidative defense that may be relevant for the protection against hy drogen peroxide produced by osteoclasts during bone remodelling. (C) 1 998 Academic Press.