Induction of nuclear factor-κB and its downstream genes by TNF-α and IL-1β has a pro-apoptotic role in pancreatic beta cells

Aims/hypothesis IL-1 beta and TNF-alpha contribute to pancreatic beta cell death in type 1 diabetes. Both cytokines activate the transcription factor nuclear factor-kappa B (NF-kappa B), but recent observations suggest that NF-kappa B blockade prevents IL-1 beta + IFN-gamma- but not TNF-alpha + IFN-gamma-induced beta cell apoptosis. The aim of the present study was to compare the effects of IL-1 beta and TNF-alpha on cell death and the pattern of NF-kappa B activation and global gene expression in beta cells. Methods Cell viability was measured after exposure to IL-1 beta or to TNF-alpha alone or in combination with IFN-gamma, and blockade of NF-kappa B activation or protein synthesis. INS-1E cells exposed to IL-1 beta or TNF-alpha in time course experiments were used for I kappa B kinase (IKK) activation assay, detection of p65 NF-kappa B by immunocytochemistry, real-time RT-PCR and microarray analysis. Results Blocking NF-kappa B activation protected beta cells against IL-1 beta + IFN gamma- or TNF alpha + IFN gamma-induced apoptosis. Blocking de novo protein synthesis did not increase TNF-alpha- or IL-1 beta-induced beta cell death, in line with the observations that cytokines induced the expression of the anti-apoptotic genes A20, Iap-2 and Xiap to a similar extent. Microarray analysis of INS-1E cells treated with IL-1 beta or TNF-alpha showed similar patterns of gene expression. IL-1 beta, however, induced a higher rate of expression of NF-kappa B target genes putatively involved in beta cell dysfunction and death and a stronger activation of the IKK complex, leading to an earlier translocation of NF-kappa B to the nucleus. Conclusions/interpretation NF-kappa B activation in beta cells has a pro-apoptotic role following exposure not only to IL-1 beta but also to TNF-alpha. The more marked beta cell death induced by IL-1 beta is explained at least in part by higher intensity NF-kappa B activation, leading to increased transcription of key target genes.