Inhibition of NF-kappa B by I kappa B prevents cytokine-induced NO production and promotes enterocyte apoptosis in vitro

Nuclear factor-kappaB (NF-kappaB) plays a key role in gut inflammation. NF- kappaB up-regulates proinflammatory genes encoding cytokines, adhesion mole cules, and inducible nitric oxide synthase (iNOS). However, NF-kappaB has a lso been shown to up-regulate protective or anti-apoptotic factors. We util ized an adenoviral vector carrying a super-repressor form of the inhibitor of NF-kappaB, I kappaB, to examine the effects of NF-kappaB inhibition on c ytokine-induced nitric oxide production and apoptosis in rat small intestin al epithelial cells (IEC-6). Chemical inhibitors of NF-kappaB, including py rrolidine dithiocarbamate (PDTC), tosyl-lysine-chloromethylketone (TLCK), g enistein, and N-acetyl-leu-leu-norleucinal (n-LLnL) were also utilized. Tre atment of AdI kappaB-transfected cells with cytomix [1000 U/mL IFN-gamma, 1 nM IL-1 beta, and 10 ng/mL tumor necrosis factor alpha (TNF alpha)] or TNF alpha -containing cytokine combinations resulted in inhibition of cytokine -induced nitrite production and a marked increase in apoptosis compared to control cells. Apoptosis occurred independently of nitric oxide (NO) produc tion since exogenous sources of NO did not inhibit apoptosis. Inducible NOS and cIAP were dawn-regulated in AdI kappaB-transfected cells treated with cytomix. TLCK and LLnL treatment also induced apoptosis in cytomix-treated cells, while PDTC and genistein did not. Thus, although NF-kappaB up-regula tes various pro-inflammatory genes, it may also have protective or anti-apo ptotic effects in enterocytes. NF-kappaB appears necessary for upregulating cIAP in IEC-6 cells upon cytokine exposure.