Fas ligand induction in human NK cells is regulated by redox through a calcineurin-nuclear factors of activated T cell-dependent pathway

Fas ligand (FasL) on cytotoxic lymphocytes is important for mediating apopt osis of activated lymphocytes and other target cells. We have reported that NK cell functions, such as proliferation, cell death, and killing activity , are subject to regulation by cellular redox status. Here, we report that expression of Fast protein and mRNA in activated NK cells is also regulated by redox, Ligation of CD16 on IL-2-preactivated NK cells resulted in reduc tion of intracellular peroxide level as well as induction of Fast expressio n. This CD16-induced Fast expression was suppressed by oxidative stress, in cluding thiol deprivation or treatment with hydrogen peroxide (H2O2), Addit ion of thiol-reducing compounds, such as L-cystine, 2-ME, or N-acetyl cyste ine, restored FasL expression. These data suggest that CD16 stimulation req uires cellular reducing status for Fast induction in NK cells. Because Fast gene activation following CD16 cross-linking is regulated by the NF of act ivated T cells (NFAT), we examined the effect of oxidative stresses on NFAT activation, Electrophoretic mobility shift assays revealed that both thiol insufficiency and H2O2 treatment suppressed DNA-binding activity of NFAT a nd that addition of thiol-reducing compounds reversed or even enhanced it. Furthermore, these oxidative stresses inhibited activity of calcineurin, a serine/threonine phosphatase that regulates NFAT activation. These results suggest that suppression of calcineurin and NFAT activation is a mechanism by which oxidative stress inhibits Fast induction in activated NK cells and further support the hypothesis that thiol-reducing compounds might be requ ired for maintenance of optimal NK functions under physiologic oxidative co nditions.