Interferon-γ alters downstream signaling originating from epidermal growth factor receptor in intestinal epithelial cells: functional consequences for ion transport.

The epidermal growth factor receptor (EGFr) regulates many cellular functions, such as proliferation, apoptosis, and ion transport. Our aim was to investigate whether long term treatment with interferon-γ (IFN-γ) modulates EGF activation of downstream signaling pathways in intestinal epithelial cells and if this contributes to dysregulation of epithelial ion transport in inflammation. Polarized monolayers of T(84) and HT29/cl.19A colonocytes were preincubated with IFN-γ prior to stimulation with EGF. Basolateral potassium transport was studied in Ussing chambers. We also studied inflamed colonic mucosae from C57BL/6 mice treated with dextran sulfate sodium or mdr1a knock-out mice and controls. IFN-γ increased intestinal epithelial EGFr expression without increasing its phosphorylation. Conversely, IFN-γ caused a significant decrease in EGF-stimulated phosphorylation of specific EGFr tyrosine residues and activation of ERK but not Akt-1. In IFNγ-pretreated cells, the inhibitory effect of EGF on carbachol-stimulated K(+) channel activity was lost. In inflamed colonic tissues, EGFr expression was significantly increased, whereas ERK phosphorylation was reduced. Thus, although it up-regulates EGFr expression, IFN-γ causes defective EGFr activation in colonic epithelial cells via reduced phosphorylation of specific EGFr tyrosine residues. This probably accounts for altered downstream signaling consequences. These observations were corroborated in the setting of colitis. IFN-γ also abrogates the ability of EGF to inhibit carbachol-stimulated basolateral K(+) currents. Our data suggest that, in the setting of inflammation, the biological effect of EGF, including the inhibitory effect of EGF on Ca(2+)-dependent ion transport, is altered, perhaps contributing to diarrheal and other symptoms in vivo.