Investigations of the formation of a multicomponent transcription complex: Interferon stimulated gene factor 3

Interferon-$\alpha$ (IFN-$\alpha$) induces the transcription of a large set of genes through activation of a multimeric transcription complex, interferon-stimulated gene factor 3 (ISGF3). This complex is composed of three ISGF3$\alpha$ proteins and a single DNA binding ISGF3$\gamma$ component. It forms, in response to treatment by type I IFNs, from constitutive cytoplasmic proteins that must be activated prior to nuclear translocation. Although IFNs are well-described inhibitors of cell growth, the role of known signaling events in this action has not been clearly defined. In this study lymphoblastoid Daudi cells were analyzed to detect the formation of ISGF3, which was detected in cell extracts by an electrophoretic mobility shift assay (EMSA). The ISGF3 linearly increased from 1-30 hours, then gradually declined until 48 hours. This signal did not require the continuous presence of IFN, was partially inhibited by cycloheximide (an inhibitor of protein synthesis), and was prevented by staurosporine (a potent inhibitor of protein tyrosine kinase). These findings suggested that IFN signal generation depended upon the activity of a relatively stable tyrosine kinase-receptor complex.