Transcription factor NF-kappaB activity in colon epithelial cells: Influence of short-chain fatty acids and specific NF-kappaB subunit combinations

Date of Completion

January 2002

Keywords

Biology, Molecular|Biology, Cell

Degree

Ph.D.

Abstract

Transcriptional factor NF-κB was first found to be involved in activating genes involved in immune and inflammatory responses. Subsequently NF-κB was found to be important for regulating the expression of genes involved in cell proliferation and survival. Consistent with its role in regulating cell proliferation, we found that NF-κB regulates expression of the mouse TERT gene (telomerase reverse transcriptase). NF-κB-dependent TERT expression might serve to maintain telomere length in the conditions like inflammation and infection. ^ Colon epithelial cells are an interesting system to study NF-κB regulation, since they can be subjected to multiple inflammatory and growth regulatory signals. Published data demonstrates that the luminal provision of butyrate can improve symptoms of inflammatory bowel diseases. We found that colon epithelial cells alter their NF-κB activity in presence of butyrate. Our data showed that butyrate blocks translocation of p65 subunit into nucleus following TNF-α activation. Analysis of inhibitory IκBs revealed that the p100 level was increased and IκB-α was stabilized upon butyrate treatment. The proteasome is critical for the degradation of IκBs, and we found that butyrate suppressed proteasome activity up to 40%. The influence of butyrate on proteasome activity and IκB degradation arose from its ability to inhibit histone deacetylases. These results provided new evidence for the role of butyrate modulating colonic inflammation. ^ The major NF-κB complexes found in colonocytes are p50-p50 and p65-p50. Gene expression analysis using nfkb1 knockout mice indicated that p50-p50 homodimer might repress κb-dependent gene activation in the colon. Using adenovirus vectors to increase the p50-p50 activity in the cultured colon cell line, we found that p50-p50 inhibited activation of a subset of κb-regulated genes activated by IL-1β, but not by TNF-α. Selective inhibition of gene activation induced by IL-1β could be explained in part by the ratio of the p50-p50 and p65-p50 complexes: this ratio was higher in IL-1β stimulated cells than in TNF-α-stimulated cells. Although the physiological significance of p50-p50 in colon epithelial cells is not yet clear, regulating the level of the p50-p50 repressor may play a role in colon-related diseases such as colonic inflammation and cancer. ^

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