Cells preconditioned with mild, transient UVA irradiation acquire resistance to oxidative stress and UVA-induced apoptosis - Role of 4-hydroxynonenal in UVA-mediated signaling for apoptosis

Because 4-hydroxynonenal (4-HNE) has been suggested to be involved in oxidative stress-mediated apoptosis (Cheng, J.Z., Sharma, R., Yang, Y., Singhal, S. S., Sharma, A., Saini, M. K., Singh, S. V., Zimniak, P., Awasthi, S., and Awasthi, Y. C. ( 2001) J. Biol. Chem. 276, 41213 - 41223) and UVA irradiation also causes lipid peroxidation, we have examined the role of 4-HNE in UVA-mediated apoptosis. K562 cells irradiated with UVA (3.0 milliwatts/cm(2)) for 5, 15, and 30 min showed a time dependent increase in 4-HNE levels. As judged by the activation of caspases, apoptosis was observed only in cells irradiated for 30 min. Within 2 h of recovery in normal medium, 4-HNE levels in 5 and 15 min UVA, irradiated cells returned to the basal or even lower levels but in cells irradiated for 30 min, 4-HNE levels remained consistently higher. The cells irradiated with UVA for 5 min and allowed to recover for 2 h in normal medium (UVA-preconditioned cells) showed a remarkable induction of hGST5.8, which catalyzes conjugation of 4-HNE to glutathione (GSH), and RLIP76 (Ral BP-1), which mediates the transport of the conjugate, GS-HNE. In cells irradiated with UVA for 30 min the induction of RLIP76 or hGST5.8 was not observed. The preconditioned cells transported GS-HNE into the medium at a rate about 2-fold higher than the controls and the transport was inhibited (65%) by coating the cells with anti-RLIP76 IgG. Upon treatment with xanthine/ xanthine oxidase (XA/XO), 4-HNE, or prolonged UVA exposure, the control cells showed a sustained activation of c-Jun N-terminal kinase (JNK) and apoptosis. However, in the UVA-preconditioned cells, apoptosis was not observed, and JNK activation was inhibited. This resistance of preconditioned cells to XA/ XO-, 4-HNE-, or UVA-induced apoptosis could be abrogated when these cells were coated with anti-RLIP76 IgG to block the efflux of GS-HNE. These studies strongly suggest a role of 4-HNE in UVA-mediated apoptosis.