Activation of p38MAPK by repetitive low-grade oxidative stress leads to pro-survival effects

V79 lung fibroblasts were subjected to repetitive oxidative stress in culture through exposures to 30 microM H2O2 for 4 weeks. Within the first week of treatment p38MAPK became dually phosphorylated and became increasingly phosphorylated during the 4-week stress period. Akt also became phosphorylated on Ser473 and Thr308 after the second week of treatment and remained phosphorylated throughout the study. NFkappaB p65 and IkappaB kinase (IKK) became phosphorylated and NFkappaB transcriptional activity became augmented during repetitive stress. Treatment of the cells concurrently with SB203580, a specific p38MAPK inhibitor, robustly blocked activation of NFkappaB transcriptional activity, phosphorylation of p65, and IKK but only partially blocked Akt phosphorylation. Similar simultaneous treatment with PI-3 kinase inhibitor LY294002 prominently blocked Akt phosphorylation. Pre-exposure to short interfering RNA (si RNA ) to p38MAPK resulted in a complete blockage of the NFkappaB p65 and IKK phosphorylations as well as the anti-apoptotic influence induced by a single low dose of H2O2 but produced a partial obstruction of Akt phosphorylation. Repetitively stressed cells were found to be significantly resistant to apoptosis-inducing agents such as ultraviolet radiation (UVR) and mM H2O2. Concurrent treatment with SB203580 almost completely restored the normal apoptotic response such as DNA fragmentation after UVR and mM H2O2. LY294002, a PI-3 kinase inhibitor and SN-50, an inhibitor of NFkappaB, produced partial restorations of the apoptotic response. We conclude that activation of p38MAPK by repetitive oxidative stress is the key event which through its command over down-stream survival elements such as Akt and NFkappaB controls the anti-apoptotic environment of the repetitively H2O2-stressed cells.