Tumor necrosis factor α decreases aquaporin 3 expression in intestinal epithelial cells through inhibition of constitutive transcription

Inflammatory diseases of the gut are associated with altered electrolyte and water transport, leading to the development of diarrhea. Epithelially expressed aquaporins (AQPs) are downregulated in inflammation, although the mechanisms involved are not known. We hypothesized that AQP3 expression in intestinal epithelial cells is altered in intestinal inflammation and that these changes are driven by tumor necrosis factor (TNF) α. Human colonic adenocarcinoma (HT‐29) cells were treated with TNFα to investigate signaling mechanisms in vitro. AQP3 expression was assessed by real‐time PCR and radiolabeled glycerol uptake, with select inhibitors and a luciferase reporter construct used to further elucidate intracellular signaling. AQP3 expression was downregulated in HT‐29 cells treated with TNFα. Luciferase reporter construct experiments revealed that TNFα downregulated constitutive transcriptional activity of the AQP3 promoter, and inhibition of MEK/ERK and nuclear factor κB (NF‐κB) signaling prevented the decrease in AQP3 mRNA expression. Constitutive AQP3 expression was suppressed by specificity protein (Sp) 3, and knockdown of this transcription factor bound to the AQP3 promoter was able to partially prevent the TNFα‐induced downregulation of AQP3. TNFα signals through MEK/ERK and NF‐κB to enhance the negative transcriptional control of AQP3 expression exerted by Sp3. Similar mechanisms regulate numerous ion channels, suggesting a common mechanism by which both ion and water transport are altered in inflammation. Aquaporins (AQPs) are water channels critical for a variety of functions in epithelia, including water and small solute transport, proliferation, and apoptosis. AQP3 is downregulated in colonic inflammation, with important physiological consequences, but the mechanism underlying this decreased expression remains unknown. We have discovered the signaling mechanisms whereby tumor necrosis factor suppresses AQP3 expression in intestinal epithelium. TNF activation of MAP kinases and NFB to mediate suppression of gene expression via the Sp3 transcription factor.