OBJECTIVE-The unfolded protein response (UPR) is a conserved cellular response designed to alleviate damage and promote survival of cells experiencing stress; however, prolonged UPR activation can result in apoptotic cell death. The UPR, activated by cytokine-induced nitric oxide (NO) production, has been proposed to mediate ␤-cell death in response to cytokines. In this study, the role of UPR activation in cytokine-induced ␤-cell death was examined. RESEARCH DESIGN AND METHODS-The effects of cytokine treatment of rat and human islets and RINm5F cells on UPR activation, NO production, and cell viability were examined using molecular and biochemical methodologies.RESULTS-UPR activation correlates with ␤-cell death in interleukin (IL)-1-treated rat islets. NO mediates both cytokineinduced UPR activation and ␤-cell death as NO synthase inhibitors attenuate each of these IL-1-stimulated events. Importantly, cytokines and tunicamycin, a classical UPR activator, induce ␤-cell death by different mechanisms. Cell death in response to the classical UPR activator is associated with a 2.5-fold increase in caspase-3 activity, while IL-1 fails to stimulate caspase-3 activity. In addition, cell death is enhanced by ϳ35% in tunicamycintreated cells expressing an S51A eIF2␣ mutant that cannot be phosphorylated or in cells lacking PERK (protein kinase regulated by RNA/endoplasmic reticulum-like kinase). In contrast, neither the absence of PERK nor the expression of the S51A eIF2␣ mutant affects the levels of cytokine-induced death.CONCLUSIONS-While cytokine-induced ␤-cell death temporally correlates with UPR activation, the lack of caspase activity and the ability of NO to attenuate caspase activity suggest that prolonged UPR activation does not mediate cytokine-induced ␤-cell death. Diabetes 57:124-132, 2008