The role of nitric oxide and the unfolded protein response in cytokine-induced beta-cell death
Program in Gene Function and Expression; Program in Molecular Medicine
Medical Subject Headings
Alternative Splicing; Animals; Caspase 3; Cell Culture Techniques; Cell Death; Cell Line, Tumor; Cell Survival; Cytokines; DNA-Binding Proteins; Gene Expression Profiling; Green Fluorescent Proteins; Humans; Insulin-Secreting Cells; Insulinoma; Male; Nitric Oxide; Nitrites; Nuclear Proteins; Pancreatic Neoplasms; *Protein Denaturation; RNA, Messenger; Rats; Rats, Sprague-Dawley; Transcription Factors; Transfection
Genetics and Genomics
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 beta-cell death in response to cytokines. In this study, the role of UPR activation in cytokine-induced beta-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 beta-cell death in interleukin (IL)-1-treated rat islets. NO mediates both cytokine-induced UPR activation and beta-cell death as NO synthase inhibitors attenuate each of these IL-1-stimulated events. Importantly, cytokines and tunicamycin, a classical UPR activator, induce beta-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 approximately 35% in tunicamycin-treated cells expressing an S51A eIF2 alpha 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 alpha mutant affects the levels of cytokine-induced death.
CONCLUSIONS: While cytokine-induced beta-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 beta-cell death.
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Citation: Diabetes. 2008 Jan;57(1):124-32. Epub 2007 Oct 10. Link to article on publisher's site