ROS-dependent activation of autophagy is a critical mechanism for the induction of anti-glioma effect of sanguinarine

Abstract

Malignant gliomas are notoriously resistant to therapies that induce apoptosis, but are less resistant to therapies that induce autophagy. Therefore, drugs targeting autophagy are promising candidates in the treatment of malignant gliomas. In this study, we investigated the anti-glioma potential of sanguinarine (SNG) in vitro, and further examined the molecular mechanisms of SNG-induced cell death. In human malignant glioma cells SNG activated autophagic cell death pathway characterized by increased acidic vesicular organelles formation, GFP-LC3 punctate formation, LC3-II conversion, and expression of autophagy related proteins, such as Atg5 and Beclin-1. The autophagy inhibitor bafilomycin A1 or knockdown of Atg5 markedly inhibited the SNG-induced autophagic cell death. Apart from inducing autophagic cell death, SNG has also been shown to induce apoptotic cell death in these cell lines. Importantly, the study also identified the crucial role of reactive oxygen species (ROS)-dependent activation of the extracellular signal-regulated kinase1/2 (ERK1/2) in the facilitation of SNG-induced autophagic cell death. Antioxidants, such as glutathione and N-acetyl cysteine, significantly abrogated ROS production, ERK1/2 activation, and in turn, prevented SNG-induced autophagic cell death. Moreover, scavengers of H2O2 (sodium pyruvate and catalase) significantly attenuated the activity of SNG. Down-regulation of ERK1/2 activity, by using selective ERK1/2 inhibitor (U0126) or siERK1/2, led to an inhibition of SNG-induced autophagic cell death. Furthermore, tumor cells transfected with constitutively active ERK2-MEK1-LA fusion protein accentuated SNG-induced autophagic cell death. Overall, our findings unveil a novel anti-tumor mechanism of action of SNG in human malignant glioma cells, opening up the possibility of using SNG based pro-autophagic drugs for the treatment of malignant glioma.