INHIBITION OF NF-κB BY IκB PREVENTS CYTOKINE-INDUCED NO PRODUCTION AND PROMOTES ENTEROCYTE APOPTOSIS IN VITRO

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Abstract
Nuclear factor-κB (NF-κB) plays a key role in gut inflammation. NF-κB up-regulates proinflammatory genes encoding cytokines, adhesion molecules, and inducible nitric oxide synthase (iNOS). However, NF-κB has also been shown to up-regulate protective or anti-apoptotic factors. We utilized an adenoviral vector carrying a super-repressor form of the inhibitor of NF-κB, IκB, to examine the effects of NF-κB inhibition on cytokine-induced nitric oxide production and apoptosis in rat small intestinal epithelial cells (IEC-6). Chemical inhibitors of NF-κB, including pyrrolidine dithiocarbamate (PDTC), tosyl-lysine-chloromethylketone (TLCK), genistein, and N-acetyl-leu-leu-norleucinal (n-LLnL) were also utilized. Treatment of AdlκB-transfected cells with cytomix [1000 U/mL IFN-γ, 1 nM IL-1β, and 10 ng/mL tumor necrosis factor alpha (TNFα)] or TNFα-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) production since exogenous sources of NO did not inhibit apoptosis. Inducible NOS and cIAP were down-regulated in AdlκB-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-κB up-regulates various pro-inflammatory genes, it may also have protective or anti-apoptotic effects in enterocytes. NF-κB appears necessary for upregulating cIAP in IEC-6 cells upon cytokine exposure.

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