Regulatory elements and transcription factors controlling basal and cytokine-induced expression of the gene encoding...

The gene encoding intercellular adhesion molecule 1 (ICAM-1) is transcriptionally induced in response to inflammatory and immunomodulatory cytokines. To investigate the mechanisms controlling ICAM-1 gene expression, we have identified regulatory DNA sequences responsible for maintaining basal and mediating induced transcription in response to tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma). Regulatory elements centered 115, 60, and 40 bp upstream from the ICAM-1 transcription start site were implicated in cytokine-independent gene expression. Regulatory elements dedicated to TNF-alpha and IFN-gamma were identified 190 and 90 bp, respectively, upstream from the ICAM-1 transcription start site. A combination of mutagenesis and DNA-binding assays revealed that the TNF-alpha response element is composite, consisting of binding sites for both C/EBP and NF-kappa B. The IFN-gamma response element behaved as a simple regulatory element that selectively binds to an IFN-gamma-inducible activity composed, at least in part, of p91. These observations provide a framework for understanding how extracellular signals dynamically regulate the adhesive properties of mammalian cells.