Stimulation of the human intercellular adhesion molecule-1 promoter by interleukin-6 and interferon-γ involves binding of distinct factors to a palindromic response element

Intercellular adhesion molecule-1 (ICAM-1) is a transmembrane glycoprotein that promotes adhesion in immunological and inflammatory reactions. ICAM-1 is expressed on cells of many lineages and is induced by interleukin-6 (IL-6) and interferon-γ (IFN-γ). Functional analysis of ICAM-1 promoter-luciferase constructs in HepG2 cells enabled us to identify a region between -110 and - 37 mediating IL-6 and IFN-γ responsiveness and containing a palindromic IL- 6/IFN-γ response element (pIRE). Site-directed mutagenesis of key nucleotides in the ICAM-1 pIRE abolished the effect of both IL-6 and IFN-γ stimulation, while this pIRE element was sufficient to confer IL-6 and IFN- γ responsiveness to a heterologous promoter. We further show by gel retardation analysis that distinct nuclear factors induced by both IL-6 or IFN-γ specifically bind to this pIRE. Furthermore, treatment with IL-6 results in the formation of multiple complexes while IFN-γ induces a single binding complex, both in HepG2 and monocytic U937 cells. Differentiation of U937 cells by exposure to 12-O-tetradecanoyl phorbol-13-acetate abolishes response to IL-6 but not IFN-γ. Supershift data utilizing the ICAM-1 pIRE revealed that IFN-γ and IL-6 both induce a factor antigenically related to IFN-γ activation factor. We further provide data suggesting that IL-6 additionally activates an ICAM-1 pIRE binding factor related to the previously described acute-phase response factor in disparate cell types. We therefore conclude that the activation of these related nuclear factors by IL-6 and IFN-γ is important in the regulation of ICAM-1 gene expression.