The role of nitric oxide and the unfolded protein response in cytokine-induced beta-cell death.
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.


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.
Chambers
Kari T
KT
Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Saint Louis, Missouri, USA.
Unverferth
Julie A
JA
Weber
Sarah M
SM
Wek
Ronald C
RC
Urano
Fumihiko
F
Corbett
John A
JA
D017398:Alternative Splicing; D000818:Animals; D053148:Caspase 3 / Q000378:metabolism; D018929:Cell Culture Techniques; D016923:Cell Death / Q000187:drug effects* / Q000502:physiology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D016207:Cytokines / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000235:genetics; D020869:Gene Expression Profiling; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007340:Insulinoma; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D009573:Nitrites / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics; D010190:Pancreatic Neoplasms; D011489:Protein Denaturation; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D014162:Transfection
D016207:Cytokines; D004268:DNA-Binding Proteins; D009573:Nitrites; D009687:Nuclear Proteins; D012333:RNA, Messenger; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D009569:Nitric Oxide; D053148:Caspase 3