During beneficial inflammation, potentially tissue-damaging granulocytes un
dergo apoptosis before being cleared by phagocytes in a non-phlogistic mann
er. Here we show that the rate of constitutive apoptosis in human neutrophi
ls and eosinophils is greatly accelerated in both a rapid and concentration
-dependent manner by the fungal metabolite gliotoxin, but not by its inacti
ve analog methylthiogliotoxin, This induction of apoptosis was abolished by
the caspase inhibitor zVAD-fmk, correlated with the inhibition of nuclear
factor-kappa B (NF-kappa B), and was mimicked by a cell permeable inhibitor
y peptide of NF-kappa B, SN-50; other NF-kappa B inhibitors, curcumin and p
yrrolidine dithiocarbamate; and the proteasome inhibitor, MG-132, Gliotoxin
also augmented dramatically the early (2-6 h) pro-apoptotic effects of tum
or necrosis factor-alpha (TNF-alpha) in neutrophils and unmasked the abilit
y of TNF-alpha to induce eosinophil apoptosis, In neutrophils, TNF-alpha ca
used a gliotoxin-inhibitable activation of an inducible form of NF-kappa B,
a response that may underlie the ability of TNF-alpha to delay apoptosis a
t later times (12-24 h) and limit its early killing effect. Furthermore, cy
cloheximide displayed a similar capacity to enhance TNF-alpha induced neutr
ophil apoptosis even at time points when cycloheximide alone had no pro-apo
ptotic effect, suggesting that NF-kappa B may regulate the production of pr
otein(s) which protect neutrophils from the cytotoxic effects of TNF-alpha,
These data shed light on the biochemical and molecular mechanisms regulati
ng human granulocyte apoptosis and, in particular, indicate that the transc
ription factor NF-kappa B plays a crucial role in regulating the physiologi
cal cell death pathway in granulocytes.