IFN-gamma up-regulates IL-18 gene expression via IFN consensus sequence-binding protein and activator protein-1 elements in macrophages

Constitutive IL-18 expression is detected from many different cells, including macrophages, keratinocytes, and osteoblasts. It has been known that IL-18 gene expression is regulated by two different promoters (p1 promoter and p2 promoter). When RAW 264.7 macrophages were treated with IFN-gamma, IL-18 gene expression was increased in a dose- and time-dependent manner. IFN-gamma activated the inducible promoter 1, but not the constitutive promoter 2. Mutagenesis studies indicated that an IFN consensus sequence-binding protein (ICSBP) binding site between -39 and -22 was critical for the IFN-gamma inducibility. EMSA using an ICSBP oligonucleotide probe showed that IFN-gamma treatment increased the formation of DNA-binding complex, which was supershifted with anti-IFN regulatory factor-1 Ab and anti-ICSBP Ab. Another element, an AP-1 site between -1120 and -1083, was important. EMSA using an AP-1-specific oligonucleotide demonstrated that IFN-gamma or LPS treatment increased the AP-1-binding activity. The addition of anti-c-Jun Ab or anti-c-Fos Ab to IFN-gamma- or LPS-treated nuclear extracts resulted in the reduction of AP-1 complex or the formation of a supershifted complex. Taken together, these results indicate that IFN-gamma increased IL-18 gene expression via ICSBP and AP-1 elements.