ENDOGENOUS NATURAL-KILLER ENHANCING FACTOR-B INCREASES CELLULAR-RESISTANCE TO OXIDATIVE STRESSES

Natural killer-enhancing factor (NKEF) was identified and cloned on th e basis of its ability to increase NK cytotoxicity. Two genes, NKEF-A and -B, encode NKEF proteins and sequence analysis presented suggests that each belongs to a highly conserved family of antioxidants. To exa mine the antioxidant potential of NKEF, we transfected the coding regi on of NKEF-B cDNA into the human endothelial cell line ECV304. The sta ble transfectant, B/1, was found to overexpress NKEF-B gene transcript and protein. We subjected B/1 to oxidative stress by either culturing them with glucose oxidase (GO), which continuously generates hydrogen peroxide, or by direct addition of hydrogen peroxide. We found that B /1 cells were more resistant than control cell lines. Resistance to hy drogen peroxide was originally thought to be mediated mainly by catala se and the glutathione cycle. Therefore,we used inhibitors to block th e two pathways and found that B/1 cells were more resistant to oxidati ve stress than control cells when we used inhibitors to preblock eithe r pathway. We also examined the cellular inflammatory responses to oxi dized low-density lipoprotein (LDL) and bacterial lipopolysaccharide ( LPS) by measuring monocyte adhesion to endothelial cells in vitro and found that B/1 cells were resistant to such responses. Lastly, we foun d that B/1 cells were more resistant to a novel chemotherapeutic agent CT-2584, which appears to kill tumor cells by stimulating production of reactive oxygen intermediates in mitochondria. These results demons trate that the NKEF-B is an antioxidant that protects cells from oxida tive stress, chemotherapy agents, and inflammation-induced monocyte ad hesion. Furthermore, its expression may mediate cellular responses to proinflammatory molecules. Copyright (C) 1996 Elsevier Science Inc.