Fractalkine-mediated signals regulate cell-survival and immune-modulatory responses in intestinal epithelial cells

Background & Aims: In this study, we determined the signal transduction and functional consequences after ligand-specific activation of the fractalkine receptor CX3CR1 in human intestinal epithelial cells. Methods: CX3CR1 expression in human colonic tissues and intestinal epithelial cell lines was determined by immunohistochemistry, immunoblotting, and reverse-transcription polymerase chain reaction. The regulation of mitogen-activated protein kinase (MAPK) activation was assessed by immunoblotting. Regulation of chemokine messenger RNA (mRNA) expression was determined by Northern blotting. NF-kappaB and p53 activation was assessed by electromobility shift assays. Results: Fractalkine mediated the MEK-1 and Galphai-dependent but phosphatidylinositol-3-kinase-independent activation of extracellular signal-regulated kinase-MAPK. Fractalkine activated NF-kappaB and p53 resulting in interleukin 8 and fractalkine mRNA expression. CX3CR1-mediated activation of intestinal epithelial cells was able to induce migration of human neutrophils into but not through the intestinal epithellal cell monolayer. Conclusions: CX3CR1 mediates distinct functional responses in intestinal epithelial cells, which include the autocrine regulation of cell-survival signals and activation of immune modulators, indicating a role of CX3CR1 in host defense mechanisms originating from the intestinal epithelium.