Synergistic induction of the Tap-1 gene by IFN-gamma and lipopolysaccharide in macrophages is regulated by STAT1

Proper regulation of the Tap-1 gene is critical for the initiation and continuation of a cellular immune response. Analysis of the Tap-1/low molecular mass polypeptide 2 bidirectional promoter showed that the IFN-gamma activation site element is critical for the rapid induction of the promoter by IFN-gamma following transfection into the human macrophage cell line THP-1. Furthermore, activation of STAT1 binding to this site was important for the synergistic response seen following the stimulation with both IFN-gamma and LPS. Mutation of an IFN-stimulated regulatory element that binds IFN regulatory factor 1 appeared to enhance the response to IFN-gamma and LPS. These data show that STAT1 is necessary for the activation of Tap-1 gene expression in APCs and initiation of cellular immune responses. Furthermore, our data suggest that bacterial products such as LPS may enhance cellular immune responses through augmenting the ability of STAT1 to regulate IFN-gamma-inducible genes.