Autophagic Degradation of Caspase-8 Protects U87MG Cells Against H2O2-induced Oxidative Stress

Oxidative stress induces apoptosis in many cellular systems including glioblastoma cells, with caspase-8activation was regarded as a major contribution to H2O2-induced cell death. This study focused on the roleof the autophagic protein p62 in H2O2-induced apoptosis in U87MG cells. Oxidative stress was applied withH2O2, and cell apoptosis and viability were measured with use of caspase inhibitors or autophagic mediators orsiRNA p62, GFP-p62 and GFP-p62-UBA (del) transfection. We found that H2O2 -induced U87MG cell death wascorrelated with caspase-8. To understand the role of p62 in MG132-induced cell death, the levels of p62/SQSTM1or autophagy in U87MG cells were modulated with biochemical or genetic methods. The results showed that theover-expression of wild type p62/SQSTM1 significantly reduced H2O2 induced cell death, but knockdown of p62aggravated the process. In addition, inhibition of autophagy promoted p62 and active caspase-8 increasing H2O2-induced apoptosis while induction of autophagy manifested the opposite effect. We further demonstrated thatthe function of p62/SQSTM1 required its C-terminus UBA domain to attenuate H2O2 cytotoxity by inhibitionof caspase-8 activity. Our results indicated that p62/SQSTM1 was a potential contributor to mediate caspase-8activation by autophagy in oxidative stress process.