Interleukin-1 beta-induced nitric oxide synthase expression by rat pancreatic beta-cells: evidence for the involvement of nuclear factor kappa B in the signaling mechanism.

Recent evidence indicates that overproduction of nitric oxide mediates cytokine-induced inhibition of insulin secretion by pancreatic islets. The current studies were designed to characterize signaling events involving the transcriptional factor NFkappaB in interleukin-1 (IL-1)-induced expression of inducible nitric oxide synthase (iNOS) by primary and transformed rat pancreatic beta-cells. Due to limitations of cell numbers of purified primary beta-cells, biochemical and molecular studies were performed primarily using the insulinoma cell line, RINm5F. Inhibitors of NFkappaB, diethyldithiocarbamate, pyrrolidine dithiocarbamate, and N-acetyl cysteine prevent IL-1-induced iNOS expression at the level of messenger RNA, protein, and nitrite generation. IL-1 induces a time-dependent translocation of NFkappaB from cytosol to nucleus, with maximal translocation observed approximately 15-30 min after IL-1 treatment, as determined by electrophoretic mobility shift assays. The specificity of the band containing the NF kappa B DNA-protein complex was shown by competition with a 150-fold excess of nonradiolabeled NF kappa B oligonucleotide. Supershift assays using immunoglobulins G against NF kappa b subunits p50 an p65 indicate that the protein complex contains a heterodimer of p50 and p65. IL-1-induced translocation of NF kappa B was blocked by 100 microns 100 microM diethyldithiocarbamate or 100 microM pyrrolidine dithiocarbamate, further establishing a critical role for NF kappa B in the induction of iNOS by IL-1 in rat pancreatic beta-cells. Activation of tyrosine kinase appears to precede NF kappa B activation, as the tyrosine kinase inhibitor genistein (100 microM) blocks IL-1-induced translocation of NF kappa B. An understanding of the signal transduction pathway of cytokine-induced nitric oxide generation by beta-cells will provide strategies of intervention to further evaluate the role of nitric oxide in mediating beta-cell dysfunction.