Endoplasmic reticulum stress inducers, but not imatinib, sensitize Philadelphia chromosome-positive leukemia cells to TRAIL-mediated apoptosis.

Philadelphia-chromosome (Ph1)-positive leukemia cells frequently express death receptors DR4/DR5 for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and show high TRAIL-sensitivity. It has been reported that imatinib damaged cardiomyocytes by triggering endoplasmic reticulum (ER) stress and that ER stress inducers intensified TRAIL-sensitivity of some cancer cells by upregulating DR4/DR5 expression. In fact, ER stress inducers enhanced TRAIL-sensitivity of Ph1-positive leukemia cells by upregulating DR4/DR5 expression. In contrast, imatinib did not induce ER stress responses and unexpectedly downregulated DR4/DR5 expression, indicating that sensitization of Ph1-positive leukemia cells to TRAIL-mediated cellular immunity by imatinib through upregulation of DR4/DR5 expression is unlikely.