Over Expression of BCL2 and Low Expression of Caspase 8 Related to TRAIL Resistance in Brain Cancer Stem Cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been investigated as an effective agentto treat various cancers. Cancer stem cells are resistant to TRAIL treatment, but the mechanism of TRAILresistance remains unknown. In this study, brain cancer stem cells were isolated by CD133 magnetic sorting, andthe number of CD133 positive cells detected by flow cytometry. The self-renewing capacity of brain cancer stemcells was examined by a neurosphere formation assay, and the percentage of cell death after TRAIL treatment wasexamined by an MTS assay. Expression of DR5, FADD, caspase 8 and BCL2 proteins was detected by westernblot. The amount of CD133 positive cells was enriched to 71% after CD133 magnetic sorting. Brain cancer stemcell neurosphere formation was significantly increased after TRAIL treatment. TRAIL treatment also reducedthe amount of viable cells and this decrease was inhibited by a caspase 8 inhibitor or by the pan-caspase inhibitorz-VAD (P<0.05). Brain cancer stem cells expressed lower levels caspase 8 protein and higher levels of BCL2protein when compared with CD133 negative cells (P<0.05). Our data suggest that TRAIL resistance is relatedto overexpression of BCL2 and low expression of caspase 8 which limit activation of caspase 8 in brain cancerstem cells.