Oxidative preconditioning and apoptosis in L-cells - Roles of protein kinase B and mitogen-activated protein kinases

Oxidative stress can cause significant cell death by apoptosis, We performed studies in L-cells to explore whether prior exposure to oxidative stress ("oxidative preconditioning") can protect the cell against the apoptotic consequences of subsequent oxidative insults and to establish the mediators in the preconditioning signaling cascade. Cells were preconditioned with three 5-min exposures to H2O2, followed by 10-h recovery and subsequent exposure to 600 muM H2O2 for 10 h. A Single 10-h exposure to H2O2 induced substantial apoptotic cell death (similar to 90%), as determined by enzyme-linked immunosorbent assay, TUNEL (terminal deoxyribonucleotide transferase-mediated dUTP nick end labeling), and Annexin V methods, but apoptosis was largely prevented in preconditioned cells. The degree of cytoprotection depended on the strength of preconditioning or H(2)O2 concentration (20 similar to 600 muM), Transient increases in mitogen-activated protein kinase (MAPK), p38, and JNK/SAPK activities and sustained protein kinase B (Akt) activation, accompanied by drastically reduced caspase 3 activity, were seen after preconditioning, The expression levels of these kinases were unaltered. Inhibitors of p38 (SB203580) and phosphoinositide 5-kinase (PI3K, LY294002) pathways abolished the protection provided by preconditioning, We conclude that oxidative preconditioning protects cells against apoptosis and that this effect involves MAPK and PI3K/Akt pathways. This system may be important in regulating apoptotic cell death in development and disease states.