Abstracts
1997 Digestive Disease Week

The ubiquitin-proteasome pathway regulates IL-1ß-induced IL-6 production in human intestinal epithelial cells.

AA Parikh, MR Moon, AL Salzman, JE Fischer, PO Hasselgren. Department of Surgery, University of Cincinnati, Shriners Burns Institute and Children's Hospital Medical Center, Cincinnati, OH.

Recent studies suggest that IL-1ß induces IL-6 production in human intestinal epithelial cells and that NF-KB may be involved in the transcriptional control of this response. The mechanisms of activation of NF-KB in the enterocyte, however, are unknown. We tested the hypothesis that NF-KB is activated by the ubiquitin-proteasome pathway in response to IL-1ß in the enterocyte, and that this pathway regulates IL-1ß-induced IL-6 production.

Methods: Caco-2 cells, a human intestinal epithelial cell line, were grown to 90% confluence whereafter they were treated with IL-1ß (0.5 ng/ml) alone, or after preincubation with N-Acetyl-Leu-Leu-Norleucinal (LLNL, 1-500 µM), an inhibitor of the 20S proteasome. IL-6 levels in the culture medium were measured by ELISA and NF-KB activity in the cell nuclei was measured by electrophoretic mobility shift assay (EMSA). Results: Pretreatment of the Caco-2 cells with LLNL caused a dose-dependent decrease in IL-1ß-induced IL-6 production without affecting cell viability (Fig. 1[not available]). LLNL also decreased IL-1ß-induced NFKB activity as shown by EMSA (Fig. 2[not available]). Identical results were observed in at least three consecutive experiments.

Conclusions: The results suggest that the ubiquitin-proteasome pathway is involved in the activation of the transcription factor NfKB, probably reflecting breakdown of inhibitory KB, and in IL-1ß- induced IL-6 production in the human enterocyte. Enterocyte production of IL-6 may be an important component of the mucosal response to sepsis and endotoxemia.