CHARACTERIZATION OF ANTIOXIDANT PROPERTIES OF NATURAL KILLER-ENHANCING FACTOR-B AND INDUCTION OF ITS EXPRESSION BY HYDROGEN-PEROXIDE

Natural killer-enhancing factor B (NKEF-B) belongs to a highly conserv ed family of recently discovered antioxidants. The role of NKEF-B as a n antioxidant was demonstrated by its protection of transfected cells to oxidative damage by hydrogen peroxide. To further characterize the antioxidant properties of NKEF-B, we compared the sensitivity of a hum an endothelial cell line ECV304 and its transfectant, B/1 that hyperex presses NKEF-B, to various oxidants. In addition, we investigated the changes in the expression of NKEF-B mRNA upon oxidative stress. We fou nd that B/1 was significantly more resistant than the control cells to the oxidative stresses caused by t-butyl hydroperoxide (t-BHP) and me thyl mercury (MeHg). In contrast, there was no difference in the sensi tivity of B/1 and the control cells to sulfhydryl reactive agents, die thyl maleate and diamide. B/1 was also as sensitive as the control cel ls to buthionine sulfoximine. The expression of NKEF-B mRNA was induce d when the parental cell line ECV304 was treated with 2 mM HP. The ind uction reached a maximum level around 2 hr and decreased to the basal level around 4 hr. NKEF-A mRNA was not induced by HP. These results de monstrate antioxidant activities of NKEF-B toward prooxidants such as alkyl hydroperoxide and MeHg. Together with its antioxidant activity, the induction of NKEF-B by HP indicates that NKEF-B is an important ox idative stress protein providing protection against a variety of xenob iotic toxic agents. (C) 1997 Academic Press.