The Role of IκB Kinase 2, but Not Activation of NF-κB, in the Release of CXCR3 Ligands from IFN-γ-Stimulated Human Bronchial Epithelial Cells

Abstract

The severity of chronic obstructive pulmonary disease correlates with increased numbers of cytotoxic CD8+ T lymphocytes in the lung parenchyma. CD8+ T lymphocytes release IFN-γ which stimulates airway epithelial cells to produce CXCR3 chemokines leading to further recruitment of CD8+ T lymphocytes. To evaluate the signaling pathways involved in regulation of CXCR3 ligands, the human bronchial epithelial cell line BEAS-2B was stimulated with IFN-γ and the release of the CXCR3 ligands was measured by ELISA. The release of CXCL9, CXCL10, and CXCL11 was inhibited by an IκB kinase 2 (IKK2) selective inhibitor 2-[(Aminocarbonyl)amino]-5-[4-fluorophenyl]-3-thiophenecarboxamide (TPCA-1) (EC50 values were 0.50 ± 0.03, 0.17 ± 0.06, and 0.45 ± 0.10 μM, respectively (n = 6)) and an IKK1/2 selective inhibitor 2-amino-6-(2′cyclopropylemethoxy-6′-hydroxy-phenyl)-4-piperidin-3-yl-pyridine-3-carbonitrile (EC50 values 0.74 ± 0.40, 0.27 ± 0.06, and 0.88 ± 0.29 μM, respectively (n = 6)). The glucocorticosteroid dexamethasone had no effect on CXCR3 ligand release. The release of CXCL10 was most sensitive to inhibition by IKK2 and a role for IKK2 in CXCL10 release was confirmed by overexpression of dominant-negative adenoviral constructs to IKK2 (68.2 ± 8.3% n = 5), but not of IKK1. Neither phosphorylation of IκBα, translocation of p65 to the nucleus, or activation of a NF-κB-dependent reporter (Ad-NF-κB-luc) were detected following stimulation of BEAS-2B cells with IFN-γ. These data suggest that IKK2 is also involved in the IFN-γ-stimulated release of the CXCR3 ligands through a novel mechanism that is independent NF-κB.