Glucocorticoid suppression of CX3CL1 (fractalkine) by reduced gene promoter recruitment of NF-kB
- The Federation of American Societies for Experimental Biology
- Publication Type:
- Journal Article
- The Journal of the Federation of American Societies for Experimental Biology, 2008, 22 pp. 1807 - 1816
- Issue Date:
Respiratory epithelial cells are a source of CX3CL1 (fractalkine), which mediates cell adhesion and acts as a chemoattractant for monocytes, T cells, and mast cells. We show, in lung A549 epithelial cells, that the tumor necrosis factor-Î± (TNF-Î±) and IFNÎ³ synergistically induced protein release and mRNA expression of CX3CL1 is inhibited by dexamethasone, without interfering with cytokine-induced nuclear translocation of NF-ÎºB, and by an inhibitor of IÎºB kinase 2, AS602868. DNA binding assays confirmed the ability of NF-ÎºB to bind to the proximal CX3CL1 promoter. Chromatin immunoprecipitation assays showed a 5-fold increase in the recruitment of NF-ÎºB to the CX3CL1 gene promoter in response to IFNÎ³/TNF-Î±; this too was reversed by dexamethasone. In contrast, dexamethasone did not displace NF-ÎºB from the granulocyte-macrophage colony-stimulating factor gene promoter. We conclude that CX3CL1 expression is regulated through the NF-ÎºB pathway and that dexamethasone inhibits CX3CL1 expression through a glucocorticoid receptor-dependent (RU486 sensitive) mechanism. This study also provides support for the action of glucocorticoids mediating their suppressive effects on expression by interfering with the binding of transcriptional activators at native gene promoters.
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