The Protective Mechanism of Zinc in Fungal Metabolte Gliotoxin - induced Apoptosis

ABSTRACT

Gliotoxin, a fungal metabolite, is one of the epipolythiodioxopiperazine classes and has a variety of effects including imrnunomodulatory and apoptotic agents. This study is designed to evaluate the effect of zinc on gliotoxin-induced death of HL-60 cells. Here, we demonstrated that treatment of gliotoxin decreased cell viability in a dose and time-dependent manner. Gliotoxin-induced cell death was confirtned as apoptosis characterized by chromatin marginafion, fragmentation and ladder-pattern digestion of genomic DNA. Gliotoxin increased the proteolytic activities of caspase 3, 6, 8, and 9. Caspase-3 activation was further confirmed by the degradation of procaspase-3 and PARP in gliotoxin-treated HL-60 cells. Zinc compounds including ZnC12 and ZnSO4 markedly inhibited gliotoxin-induced apoptosis in HL-60 cells (from 30% to 90%). Consistent with anti- apoptotic effects, zinc also suppressed the enzymatic activities of caspase-3 and -9 proteases. In addition, cleavage of both PARP and procaspase 3 in gliotoxin-treated HL-60 cells was inhibited by the addition of zinc compounds. We further demonstrated that expression of Fas ligand by gliotoxin was suppressed by zinc compounds. These data suggest that zinc may prevent gliotoxin- induced apoptosis via inhibition of Fas ligand expression as well as suppression of caspase family cysteine proteases-3 and -9 in HL-60 cells.