BCL-2 PROTECTS ISOLATED PLASMA AND MITOCHONDRIAL-MEMBRANES AGAINST LIPID-PEROXIDATION INDUCED BY HYDROGEN-PEROXIDE AND AMYLOID BETA-PEPTIDE

The bcl-2 protooncogene product possesses antiapoptotic properties in neuronal and nonneuronal cells. Recent data suggest that Bcl-2's poten cy as a survival factor hinges on its ability to suppress oxidative st ress, but neither the subcellular site(s) nor the mechanism of its act ion is known. In this report electron paramagnetic resonance (EPR) spe ctroscopy analyses were used to investigate the local effects of Bcl-2 on membrane lipid peroxidation. Using hydrogen peroxide (H2O2) and am yloid beta-peptide (A beta) as lipoperoxidation initiators, we determi ned the loss of ERR-detectable paramagnetism of nitroxyl stearate (NS) spin labels 5-NS and 12-NS. In intact cell preparations and postnucle ar membrane fractions, A beta and H2O2 induced significant loss of 5-N S and 12-NS signal amplitude in control PC12 cells, but not PC12 cells expressing Bcl-2. Cells were subjected to differential subcellular fr actionation, yielding preparations of plasma membrane and mitochondria . In preparations derived from Bcl-2-expressing cells, both fractions contained Bcl-2 protein. 5-NS and 12-NS signals were significantly dec reased following A beta and H2O2 exposure in control PC12 mitochondria l membranes, and Bcl-2 largely prevented these effects. Plasma membran e preparations containing Bcl-2 were also resistant to radical-induced loss of spin label. Collectively, our data suggest that Bcl-2 is loca lized to mitochondrial and plasma membranes where it can act locally t o suppress oxidative damage induced by A beta and H2O2, further highli ghting the important role of lipid peroxidation in apoptosis.