Complement component C3 production in IL-1beta-stimulated human intestinal epithelial cells is blocked by NF-kappaB inhibitors and by transfection with ser 32/36 mutant IkappaBalpha.

BACKGROUND: Recent studies suggest that interleukin-1beta (IL-1beta) stimulates the production of the acute phase protein complement component C3 in human intestinal epithelial cells. The transcription factor NF-kappaB activates different genes involved in the response to cytokines. It is not known if IL-1beta-induced C3 production in the enterocyte is regulated by NF-kappaB. MATERIALS AND METHODS: Cultured Caco-2 cells, a human intestinal epithelial cell line, were treated with one of the NF-kappaB inhibitors, tosyl-lys-chloromethylketone (TLCK), genistein, or pyrrolidine dithiocarbamate (PDTC), or with N-acetyl-leu-leu-norleucinal (LLnL), a proteasome inhibitor known to block the degradation of Ikappabeta, the cytosolic inhibitor of NF-kappaB. Following this treatment, the Caco-2 cells were stimulated with IL-1beta, and C3 levels in the culture medium were measured after 24 h by ELISA. C3 mRNA levels were determined after 4 h by Northern blot analysis. In other experiments, Caco-2 cells were transfected with a mutant IkappaBalpha in which serines 32 and 36 were substituted by alanine. This mutation prevents IkBalpha phosphorylation and subsequent NF-kappaB nuclear translocation. After transfection, the cells were stimulated with IL-1beta, and C3 levels in the culture medium were measured after 24 h. Cytosolic IkappaBalpha was determined by Western blot analysis. RESULTS: TLCK, genistein, and LLnL each inhibited IL-1beta-induced C3 production in a dose-dependent fashion. These responses were associated with decreased C3 mRNA levels. In contrast, PDTC did not influence C3 production or C3 mRNA in the Caco-2 cells. Transfection of the Caco-2 cells with the Ser 32/36 mutant IkBalpha resulted in maintained IkappaBalpha levels and decreased IL-beta-induced C3 production. CONCLUSIONS: IL-1beta-stimulated C3 production in the enterocyte may be regulated by NF-kappaB.

Transcriptional regulation of human inducible nitric oxide synthase gene in an intestinal epithelial cell line.

The inducible form of nitric oxide synthase (iNOS) is expressed during inflammation of the intestine and may contribute to tissue injury. We have examined iNOS transcriptional regulation in DLD-1 cells, a human intestinal epithelial line that produces large amounts of nitric oxide and iNOS mRNA in response to a combination of the proinflammatory cytokines interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN-gamma). Levels of iNOS mRNA are extremely low in unstimulated DLD-1 cells but increase dramatically after cytokine treatment. Nuclear run-on analyses demonstrated that transcriptional activation, which accounts for a portion of this increase, is dependent on both IL-1 beta and IFN-gamma and requires de novo protein synthesis. Transfection of DLD-1 cells with reporter constructs containing deletions of the iNOS promoter showed that sequences located between 8.7 and 10.7 kb upstream of the transcription initiation site are necessary for cytokine responsiveness. This region contains potential binding sites for several cytokine-induced transcription factors and was shown to function in either orientation when placed upstream of a basal iNOS promoter segment terminating at-1.1 kb. The extremely distal location of the cytokine-responsive region contrasts with the reported positions of elements involved in the regulation of iNOS transcription in other cell types. Our data also suggest that posttranscriptional events could play a significant role in regulating iNOS gene expression in human intestinal epithelia.