Cytokine Induction of Fas Gene Expression in Insulin-Producing Cells Requires the Transcription Factors NF-κB and C/EBP

Abstract

Fas-mediated cell death may play a role in the autoimmune destruction of pancreatic β-cells in type 1 diabetes. β-Cells do not express Fas under physiological conditions, but Fas mRNA and protein are induced in cytokine-exposed mouse and human islets, rendering the β-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 β-cells and in insulin-producing RINm5F cells. Fas mRNA expression was increased 15-fold in fluorescence-activated cell sorting–purified rat β-cells exposed to interleukin (IL)-1β, whereas γ-interferon had no effect. Transfection experiments of rat Fas promoter-luciferase reporter constructs into purified rat β-cells and RINm5F insulinoma cells identified an IL-1β–responsive region between nucleotides −223 and −54. Inactivation of two adjacent NF-κB and C/EBP sites in this region abolished IL-1β–induced Fas promoter activity in RINm5F cells. Binding of NF-κB and C/EBP factors to their respective sites was confirmed by gel shift assays. In cotransfection experiments, NF-κB p65 transactivated the Fas promoter. NF-κB p50 and C/EBPβ 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-κB and C/EBP factors in cytokine-regulation of Fas expression in insulin-producing cells.