CASP8 and cancer: To test the hypothesis that the caspase-8/Bid pathway is also a central mediator of ER stress-induced cell death in human cancer cells, we treated HeLa control cells and HeLa Bid kd cells with apoptosis-inducing concentrations of three ER stressors, each having a different mechanism of action (Tunicamycin, Thapsigargin, and Brefeldin A).