DOUBLE-STRANDED-RNA ACTIVATES NOVEL FACTORS THAT BIND TO THE INTERFERON-STIMULATED RESPONSE ELEMENT

Infection of cells with adenovirus or transfection of cells with doubl e-stranded RNA (dsRNA) activates transcription of the alpha/beta inter feron-stimulated genes (ISGs). Induction of ISG expression by adenovir us appears to be mediated through the same DNA target that is responsi ve to alpha/beta interferons, the interferon-stimulated response eleme nt (ISRE). Transcriptional induction by alpha/beta interferons has bee n shown previously to be mediated by the activation of a latent cytopl asmic transcription factor, ISGF3, that translocates to the nucleus an d binds to the ISRE. However, ISG expression induced by adenovirus or dsRNA appears to be mediated by unique dsRNA-activated factors (DRAFs) that bind to the ISRE. The activation of these preexisting factors by dsRNA does not require new protein synthesis. Two DRAFs, DRAF1 and DR AF2, have been identified in our studies as ISRE-binding complexes in gel mobility shift assays. The ISRE-binding specificity of DRAF1 is si milar to that of ISGF3; however, the ISRE-binding specificity of DRAF2 is distinct. Activation of DRAF1 and DRAF2 is independent of interfer on action since it occurs in cells that are nonresponsive to interfero n and in cells that lack the alpha/beta interferon locus. The activati on pathway of DRAF1 and DRAF2 is blocked by the protein kinase inhibit ors staurosporine and genistein. This is analogous to the interferon s ignal transduction pathway and suggests that phosphorylation, possibly tyrosine phosphorylation, is involved in activation of these factors.