A unique ISRE, in the TATA-less human Isg20 promoter, confers IRF-1-mediated responsiveness to both interferon type I and type II

Interferons (IFNs) encode a family of secreted proteins involved in a numbe r of regulatory functions such as control of cell proliferation, differenti ation and regulation of the immune system. Their diverse biological actions are thought to be mediated by the products of specific but usually overlap ping sets of cellular genes induced in the target cells. We have recently i solated a human cDNA encoding a new nuclear bodies-associated protein (PML- NBs), which we have termed lsg20. In this report, we describe the cloning a nd functional characterization of the lsg20 promoter region and the identif ication of sequence elements and trans-acting factors implicated in its reg ulation, In the absence of any recognizable TATA or CAAT elements, lsg20 pr omoter basal activity is dependent upon the positive transcription factors Sp-1 and USF-1. Interestingly, we demonstrate that a unique interferon stim ulated response element (ISRE) mediates both IFN type I and type II lsg20 i nduction in the absence of functional gamma-activated sequence. These induc tions are strictly dependent upon of the IFN regulatory factor 1 (IRF-1). I n addition, we show that the ISRE is also implicated in the constitutive tr anscriptional activity of lsg20 gene.