Although
zinc is a well-known inhibitor of apoptosis, it may contribute to oxidative stress-induced
necrosis. We noted that N,N,N',N'- tetrakis(2-pyridylmethyl)ethylenediamine (
TPEN; >10 microM), a
zinc chelator, quenched fluorescence of the
zinc-specific fluorophore
Zinquin and resulted in an increase in spontaneous apoptosis in cultured sheep pulmonary artery endothelial cells (SPAECs). Addition of exogenous
zinc (in the presence of
pyrithione, a
zinc ionophore) to the medium of SPAECs caused an increase in
Zinquin fluorescence and was associated with a concentration-dependent increase in necrotic cell death. Exposure of SPAECs to
TPEN (10 microM) resulted in enhanced apoptosis after
lipopolysaccharide or complete inhibition of
t-butyl hydroperoxide (tBH)-induced
necrosis. We further investigated the role of two
zinc-dependent
enzymes,
poly(ADP-ribose) polymerase (PARP) and
protein kinase (PK) C, in tBH toxicity. tBH toxicity was only affected by the
PARP inhibitors 4-amino-1,8-naphthalimide or
3-aminobenzamide over a narrow range, whereas the PKC inhibitors
bisindolylmaleimide and
staurosporine significantly reduced tBH toxicity. tBH caused translocation of PKC to the plasma membrane of SPAECs that was partially inhibited by
TPEN. Thus pulmonary endothelial cell
zinc inhibits spontaneous and
lipopolysaccharide-dependent apoptosis but contributes to tBH-induced
necrosis, in part, via a PKC-dependent pathway.