Fromthe ‡ EdwardA.DoisyDepartmentofBiochemistryandMolecularBiology,St.LouisUniversitySchoolofMedicine,St.Louis, Missouri63104,the § ComprehensiveDiabetesCenter,DepartmentofMedicine,DivisionofEndocrinology,Diabetes,and Metabolism,UniversityofAlabamaatBirmingham,Birmingham,Alabama35294,andtheDepartmentofBiochemistry,Medical

For many cell types, including pancreatic -cells, nitric oxide is a mediator of cell death; paradoxically, nitric oxide can also activate pathways that promote the repair of cellular damage. In this report, a role for FoxO1-dependent transcriptional activation and its regulation by SIRT1 in determining the cellular response to nitric oxide is provided. In response to nitric oxide, FoxO1 translocates from the cytoplasm to the nucleus and stimulates the expression of the DNA repair gene GADD45, resulting in FoxO1-dependent DNA repair. FoxO1-dependent gene expression appears to be regulated by the NAD-dependent deacetylase SIRT1. In response to SIRT1 inhibitors, the FoxO1-dependent protective actions of nitric oxide (GADD45 expression and DNA repair) are attenuated, and FoxO1 activates a proapoptotic program that includes PUMA (p53-up-regulated mediator of apoptosis) mRNA accumulation and caspase-3 cleavage. These findings support primary roles for FoxO1 and SIRT1 in regulating the cellular responses of -cells to nitric oxide. Nitric oxide plays a central role in regulating the response(s) of pancreatic -cells to cytokine treatment. Cytokines such as IL-1 (rat) and a combination of IL-1 IFN(mouse and human) stimulate the expression of the inducible isoform of nitric-oxide synthase (NOS) and the production of micromolar levels of nitric oxide by -cells (1– 4). Nitric oxide attenuates insulin secretion by inhibiting the oxidation of glucose to CO2 and the activity of mitochondrial iron-sulfur center containing enzymes such as aconitase and complexes of the electron transport system (5, 6). The result is a 4-fold reduction in cellular ATP concentration (2, 7) that leads to the inhibition of glucose-induced insulin secretion due to the inability to generate sufficient levels of ATP to close the ATPsensitive K channels, an event required for -cell depolariza