Cobalt chloride treatment induces autophagic apoptosis in human glioma cells via a p53-dependent pathway

Malignant glioma is the most aggressive brain tumor. Hypoxic condition has been explored for killing cancer stem cells or drug-resistant tumor cells. This study investigated the effects of hypoxia on autophagic death and the possible mechanisms. Exposure of human malignant glioma U87-MG cells to cobalt chloride (CoCl2) increased cellular hypoxia-inducible factor-1α levels and concurrently decreased cell viability concentration-and time-dependently. In parallel, treatment with CoCl2 suppressed proliferation of human U87-MG cells. Autophagic cells and levels of LC3-II were concentration-and time-dependently induced in human U87-MG cells after exposure to CoCl₂. However, pretreatment with 3-mehyladenine (3-MA) and chloroquine, inhibitors of cell autophagy, caused significant alleviations in CoCl₂-induced cell autophagy. In contrast, exposure to rapamycin, an inducer of cell autophagy, synergistically induced hypoxiainduced autophagy of U87-MG cells. Administration of human U87-MG cells with CoCl₂ triggered caspase-3 activation and cell apoptosis. Interestingly, pretreatment with 3-MA and chloroquine remarkably suppressed CoCl2-induced caspase-3 activation and cell apoptosis. Application of p53 small interference (si)RNA into human U87-MG cells downregulated levels of this protein and simultaneously lowered hypoxiaand 3-MA-induced alterations in cell autophagy, apoptosis, and death. The hypoxia-induced autophagy and apoptosis of DBTRG-05MG cells were significantly lowered by 3-MA pretreatment and p53 knockdown. Therefore, the present study shows that CoCl₂ treatment can induce autophagy of human glioma cells and subsequent autophagic apoptosis via a p53-dependent pathway. Hypoxia-induced autophagic apoptosis may be applied as a therapeutic strategy for treatment of glioma patients.