K. Furuke et al., Fas ligand induction in human NK cells is regulated by redox through a calcineurin-nuclear factors of activated T cell-dependent pathway, J IMMUNOL, 162(4), 1999, pp. 1988-1993
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.