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Long-Term Exposure of the HT-29 Human Intestinal Epithelial Cell Line to TNF Causes Sustained Up-Regulation of the Polymeric Ig Receptor and Proinflammatory Genes through Transcriptional and Posttranscriptional Mechanisms¹

Departments of Microbiology, Immunology, and Molecular Genetics; and Pathology and Laboratory Medicine, University of Kentucky, Lexington, KY 40536

Transport of IgA Abs across intestinal epithelial cells into gut secretions is mediated by the polymeric Ig receptor (pIgR). The cytokine TNF plays a central role in initiating and amplifying inflammatory reactions, and is implicated in the pathogenesis of inflammatory bowel diseases. Acute exposure of intestinal epithelial cell lines to TNF has been shown to up-regulate transcription of genes encoding pIgR and a number of proinflammatory factors, but the effects of chronic exposure to TNF have not been studied. We found that exposure of HT-29 human colon carcinoma cells to TNF for up to 20 days reduced the rate of cell proliferation, but did not cause gross morphological changes. Expression of mRNA encoding pIgR and several proinflammatory genes increased acutely, and then diminished but remained elevated above control levels throughout the experiment. Changes in gene expression were paralleled by increased expression of the transcription factors IFN regulatory factor-1 and the RelB subunit of NF-B. HT-29 cells activated the endogenous TNF gene in response to TNF treatment, but the level of TNF production was insufficient to maintain pIgR and proinflammatory gene expression after withdrawal of exogenous TNF. Chronic exposure to TNF caused a marked increase in pIgR mRNA stability and a small but significant decrease in TNF mRNA stability, but no change in the half-lives of IL-8, c-Myc, and GAPDH. In summary, we observed different effects of acute vs chronic exposure to TNF on gene expression, and found evidence for transcriptional and posttranscriptional regulation of expression of the pIgR.

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