In order to explore the role of lipid peroxidation (LPO) products in the initial phase of stress mediated signaling, we studied the effect of mild, transient, oxidative or heat stress on parameters which regulate the cellular concentration of 4-hydroxynonenal (4-HNE). When K562 cells were exposed to mild heat shock (42 0C, 30 min) or oxidative stress (50 µM H2O2, 20 min) and allowed to recover for 2 h, there was a several fold induction of hGST5.8, which catalyzes formation of glutathione-4-HNE conjugate (GS-HNE), and RLIP76 which mediates the transport of GS-HNE from cells (S. Awasthi et al. Biochemistry 39, 9327-9334, 2001). Enhanced LPO was observed in stressed cells but the major antioxidant enzymes and HSP70 remained unaffected. The stressed cells showed higher GS-HNE conjugating activity and increased efflux of GS-HNE. Stress pre-conditioned cells with induced hGST5.8 and RLIP76 acquired resistance to 4-HNE and H2O2 mediated apoptosis by suppressing a sustained activation of c-Jun N-terminal kinase and caspase 3. The protective effect of stress pre-conditioning against apoptosis was abrogated by coating the cells with anti-RLIP76 IgG which inhibited the efflux of GS-HNE from cells, indicating that the cells acquired resistance to apoptosis by metabolizing and excluding 4-HNE at a higher rate. Induction of hGST5.8 and RLIP76 by mild, transient stress and the resulting resistance of stress pre-conditioned cells to apoptosis appears to be a general phenomenon since it was not limited to K562 cells but was also evident in lung cancer cells, H-69, H-226, human leukemia cells, HL-60, and human retinal pigmented epithelial cells. These results strongly suggest a role of LPO products, particularly 4-HNE, in the initial phase of stress mediated signaling, and are consistent with our recent studies (Yang, Y., et al. J. Biol. Chem. 276:19220-19230, 2001) demonstrating an important role of glutathione S-transferases in protection against oxidative stress.