Zinc-mediated regulation of caspases activity: dose-dependent inhibition or activation of caspase-3 in the human Burkitt lymphoma B cells (Ramos)

Divalent cations, including Zinc and Manganese ions, are important modulato rs of cell activation. We investigated the ability of these two divalent ca tions to modulate apoptosis in human Burkitt lymphoma B cells line (Ramos), We found that Zinc (from 10 to 50 muM) inhibited Manganese-induced caspase -3 activation and apoptosis of Ramos cells. Higher concentration of Zinc (5 0 to 100 muM) did not prevent Manganese-mediated apoptosis but rather incre ased cell death among Ramos cells. This Zinc-mediated cell death was associ ated with apoptotic features such as cell shrinkage, the presence of phosph atidylserine residues on the outer leaflet of the cells, chromatin condensa tion, DNA fragmentation and decrease of mitochondrial transmembrane potenti al. Zinc-mediated apoptosis was associated with caspase-9 and caspased acti vation as revealed by the appearance of active p35 fragment of caspase-9 an d p19 and p17 of caspase-9 as well as in vivo cleavage of PARP and of a cel l-permeable fluorogenic caspase-3 substrate (Phiphilux-G(1)D(2)) Both Zinc- mediated apoptosis and caspase-3 activation were prevented by the cell-perm eable, broad-spectrum inhibitor of caspases (zVAD-fmk) or overexpression of bcl-2, In addition, we show that Zinc-induced loss of transmembrane mitoch ondrial potential is a caspase-independent event, since it is not modified by the presence of zVAD-fmk, which is inhibited by overexpression of bcl-2, These results indicate that depending on its concentration, Zinc can exert opposite effects an caspase-3 activation and apoptosis in human B lymphoma cells: concentrations below 50 muM inhibit caspase-3 activation and apopto sis whereas higher concentrations of Zinc activate a death pathway associat ed with apoptotic-like features and caspase-3 activation.