Nitric-oxide-induced apoptosis in human leukemic lines requires mitochondrial lipid degradation and cytochrome C...

We have previously shown that nitric oxide (NO) stimulates apoptosis in different human neoplastic lymphoid cell lines through activation of caspases not only via CD95/CD95L interaction, but also independently of such death receptors. Here we investigated mitochondria-dependent mechanisms of NO-induced apoptosis in Jurkat leukemic cells. NO donor glycerol trinitrate (at the concentration, which induces apoptotic cell death) caused (1) a significant decrease in the concentration of cardiolipin, a major mitochondrial lipid; (2) a downregulation in respiratory chain complex activities; (3) a release of the mitochondrial protein cytochrome c into the cytosol; and (4) an activation of caspase-9 and caspase-3. These changes were accompanied by an increase in the number of cells with low mitochondrial transmembrane potential and with a high level of reactive oxygen species production. Higher resistance of the CD95-resistant Jurkat subclone (APO-R) cells to NO-mediated apoptosis correlated with the absence of cytochrome c release and with less alterations in other mitochondrial parameters. An inhibitor of lipid peroxidation, trolox, significantly suppressed NO-mediated apoptosis in APO-S Jurkat cells, whereas bongkrekic acid (BA), which blocks mitochondrial permeability transition, provided only a moderate antiapoptotic effect. Transfection of Jurkat cells with bcl-2 led to a complete block of apoptosis due to the prevention of changes in mitochondrial functions. We suggest that the mitochondrial damage (in particular, cardiolipin degradation and cytochrome c release) induced by NO in human leukemia cells plays a crucial role in the subsequent activation of caspase and apoptosis.