Role of zinc ions in ricin-induced apoptosis in U937 cells.
We found that treatment of U937 cells with ZnCl(2) resulted in marked inhibition of ricin-induced DNA fragmentation and nuclear morphological change. Zn(2+) also completely inhibited the activation of caspase-3-, caspase-6-, and caspase-9-like proteases in ricin-treated cells, while no significant effect of Zn(2+) on these protease activities was observed when added directly to the lysate of ricin-treated cells, suggesting that Zn(2+) blocks the process of the activation of these caspases rather than the direct inhibition of the already activated enzymes. Fluorescence microscopic observation with Zn(2+) specific fluorescent probe dansylaminoethyl-cyclen suggested that there was a substantial increase in probe-detectable Zn(2+) in ricin-treated cells. Since the differences in the total Zn(2+) contents between ricin-treated and -untreated cells as measured with an atomic absorption spectrophotometer were too small to explain the increase in probe fluorescence in ricin-treated cells, it was suggested that release of Zn(2+) from intracellular stores or metalloproteins may occur rather than enhanced uptake from the medium. The Zn(2+) probe fluorescence change was observed prior to the depletion of intracellular glutathione. Carbobenzoxy-Asp-1-yl-[(2,6-dichlorobenzoyl)oxy]methane (Z-Asp-CH(2)-DCB), a caspase family protease inhibitor, prevented ricin-induced increase in Zn(2+) probe fluorescence. These results suggest that redistribution of intracellular Zn(2+) occurs during ricin-induced apoptosis as early apoptotic event, and exogenously added Zn(2+) may prevent such intracellular Zn(2+) redistribution resulting in the inhibition of apoptosis.
Tamura
Tadashi
T
Division of Biochemistry, Faculty of Fisheries, Nagasaki University, Bunkyo-machi 1-14, Nagasaki 852-8521, Japan.
Sadakata
Noriko
N
Oda
Tatsuya
T
Muramatsu
Tsuyoshi
T
D017209:Apoptosis / Q000187:drug effects*; D001252:Astringents / Q000627:therapeutic use*; D020169:Caspases / Q000187:drug effects / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D006801:Humans; D012276:Ricin / Q000037:antagonists & inhibitors* / Q000633:toxicity; D020298:U937 Cells; D019287:Zinc Sulfate / Q000627:therapeutic use*
D001252:Astringents; D019287:Zinc Sulfate; D012276:Ricin; D020169:Caspases