Autophagy inhibits reactive oxygen species-mediated apoptosis via activating p38-nuclear factor-kappa B survival pathways in oridonin-treated murine fibrosarcoma L929 cells

Autophagy and apoptosis have been known to be interconnected positively or negatively; however, the molecular mechanisms mediating these two cellular processes are not fully understood. In the present study, we demonstrated that the exposure of L929 cells to oridonin led to intracellular reactive oxygen species generation, followed by lipid peroxidation, as well as decreases in superoxide dismutase and glutathione activities. The reactive oxygen species scavenger N-acetyl-cysteine resulted in the complete inhibition of oridonin-induced apoptosis and mitochondrial membrane potential collapse. We showed that reactive oxygen species triggered apoptosis by Bax translocation, cytochrome c release and extracellular signal-regulated kinase activation. Further data confirmed that oridonin also induced L929 cell autophagy, as demonstrated by extensive autophagic vacuolization and the punctuate distribution of monodansylcadaverine staining and GFP-LC3, as well as the LC3-II/LC3-I proportion and Beclin 1 activation. Subsequently, we found that inhibition of autophagy by 3-methyladenine or small interfering RNA against LC3 and Beclin 1 promoted oridonin-induced cell apoptosis. The effects of p38 and nuclear factor-kappa B in oridonin-induced apoptosis and autophagy were further examined. Interruption of p38 and nuclear factor-kappa B activation by specific inhibitors or small interfering RNAs promoted apoptosis and reactive oxygen species generation, but decreased autophagy. Moreover, we showed that inhibition of autophagy reduced oridonin-induced activation of p38. Additionally, nuclear factor-kappa B activation was inhibited by blocking the p38 pathway. Consequently, these findings indicate that oridonin-induced L929 cell apoptosis is regulated by reactive oxygen species-mediated signaling pathways, and that oridonin-induced autophagy may block apoptosis by up-regulating p38 and nuclear factor-kappa B activation.