Role of glutathione S-transferases in protection against lipid peroxidation - Overexpression of hgsta2-2 in k562 cells protects against hydrogen peroxide-induced apoptosis and inhibits JNK and caspase 3 activation

The physiological significance of the selenium-independent glutathione pero xidase (GPx) activity of glutathione S-transferases (GSTs), associated with the major Alpha class isoenzymes hGSTA1-1 and hGSTA2-2, is not known. In t he present studies we demonstrate that these isoenzymes show high GPx activ ity toward phospholipid hydroperoxides (PL-OOH) and they can catalyze GSH-d ependent reduction of PL-OOH in situ in biological membranes. A major porti on of GPx activity of human liver and testis toward phosphatidylcholine hyd roperoxide (PC-OOH) is contributed by the Alpha class GSTs. Overexpression of hGSTA2-2 in K562 cells attenuates lipid peroxidation under normal condit ions as well as during the oxidative stress and confers about 1.5-fold resi stance to these cells from H2O2 cytotoxicity. Treatment with 30 muM H2O2 fo r 48 h or 40 muM PC-OOH for 8 h causes apoptosis in control cells, whereas hGSTA2-2-overexpressing cells are protected from apoptosis under these cond itions. In control cells, H2O2 treatment causes an early (within 2 h), robu st, and persistent (at least 24 h) activation of JNK, whereas in hGSTA2-2-o verexpressing cells, only a slight activation of JNK activity is observed a t 6 h which declines to basal levels within 24 h. Caspase 3-mediated poly(A DP-ribose) polymerase cleavage is also inhibited in cells overexpressing hG STA2-2. hGSTA2 transfection does not affect the function of antioxidant enz ymes including C:Px activity toward H2O2 suggesting that the Alpha class GS Ts play an important role in regulation of the intracellular concentrations of the lipid peroxidation products that may be involved in the signaling m echanisms of apoptosis.