Synergistic activation of NF-kappa B and inducible isoform of nitric oxidesynthase induction by interferon-gamma and tumor necrosis factor-alpha in INS-1 cells

Interferon-gamma (IFN-gamma) is known to exert deleterious effects on pancr eatic beta-cells and is implicated in the development of type 1 (autoimmune ) diabetes mellitus. In this study, we investigated signaling mechanisms me diating the effects of IFN-gamma in pancreatic beta-cells using a different iated rat insulin-secreting cell line, INS-1, with special reference to the activation of transcription factors STAT (signal transducers and activator s of transcription)1 and NF-kappa B. Exposure of INS-1 cells to 100 IU/ml I FN-gamma for 24 h resulted in significant inhibition of nutrient-induced in sulin secretion associated with impaired metabolism. In combination with tu mor necrosis factor-alpha (TNF-alpha) (50 ng/ml), IFN-gamma elicited severe cytotoxicity and induced the expression of the inducible isoform of nitric oxide synthase (iNOS) mRNA. IFN-gamma promoted tyrosine phosphorylation an d DNA-binding of STAT1 through Janus kinase (JAK)1 activation without appar ent phosphorylation of JAK2. TNF-alpha did not affect STAT1 activation, but stimulated DNA-binding and transcriptional activity of NF-kappa B, both of which were further increased by IFN-gamma. These effects of IFN-gamma and TNF-alpha seem physiologically relevant, because either inhibition of STAT1 by the tyrosine kinase inhibitor herbimycin A or that of NF-kappa B by sul fasalazine resulted in the reduction of iNOS mRNA expression. In conclusion . IFN-gamma activates STAT1 and potentiates TNF-alpha-induced NF-kappa B ac tivation in INS-1 cells, thereby inducing iNOS and cell destruction. J. Cel l. Physiol. 184:46-57, 2000. (C) 2000 Wiley-Liss, Inc.