MODULATION OF INDUCIBLE NITRIC-OXIDE SYNTHASE IN RINM5F CELLS

The rat insulinoma beta-cell line RINm5F, which shares some homology w ith pancreatic islets, was used to study nitric oxide synthase inducti on. Nitric oxide is involved during beta-cell destruction and possibly in propagation of insulin-dependent diabetes mellitus. The cytokine i nterleukin-1 (IL-1) turned out to be the ultimate inducer, whereas tum our necrosis factor-alpha (TNF) and unexpectedly the phorbol ester TPA (12-O-tetradecanoylphorbol-13-acetate; 10 nM) synergistically promote d nitrite accumulation. Besides employing TPA directly, the synergisti c effect of TNF could be traced back to protein kinase C activation si nce protein kinase C inhibitors (IC50 value for staurosporine: 4 nM) p otently suppressed nitrite production in the case of IL-1/TNF administ ration. Further experiments using anti-TNF antibodies aimed to an auto crine loop following IL-1 addition to RINm5F cells, possibly involved in nitrite generation. Moreover, the nitric oxide synthase inductive I L-1 signal was antagonized by lipophilic cAMP analogues. Our results f or nitrite accumulation in RINm5F cells point to activating protein ki nase C and inhibitory protein kinase A signalling pathways.