Cytokine induction of Fas gene expression in insulin-producing cells requires the transcription factors NF-κB and C/EBP

Fas-mediated cell death may play a role in the autoimmune destruction of pancreatic beta -cells in type 1 diabetes. beta -Cells do not express Fas under physiological conditions, but Fas mRNA and protein are induced in cytokine-exposed mouse and human islets, rendering the beta -cells susceptible to Fas ligand-induced apoptosis. The aim of the present study was to investigate the molecular regulation of Fas by cytokines in rat beta -cells and in insulin-producing RINm5F cells. Fas mRNA expression was increased 15-fold in fluorescence-activated cell sorting-purified rat beta -cells exposed to interleukin (IL)-l beta, whereas gamma -interferon had no effect. Transfection experiments of rat Fas promoter-luciferase reporter constructs into purified rat beta -cells and RINm5F insulinoma cells identified an IL-1 beta -responsive region between nucleotides -223 and -54. Inactivation of two adjacent NF-kappaB and C/EBP sites in this region abolished IL-1 beta -induced Fas promoter activity in RINm5F cells. Binding of NF-kappaB and C/EBP factors to their respective sites was confirmed by gel shift assays. In cotransfection experiments, NF-kappaB p65 transactivated the Fas promoter. NF-kappaB p50 and C/EBP beta overexpression had no effect by themselves on the Fas promoter activity, but when cotransfected with p65, each factor inhibited transactivation by p65. These results suggest a critical role for NF-kappaB and C/EBP factors in cytokine-regulation of Fas expression in insulin-producing cells.