Activation of the transcription factor ISGF3 by interferon-gamma.

The interferon-stimulated gene factor 3 (ISGF3) transcription factor has been extensively studied in the context of the type I interferon (IFN-alpha/beta)-mediated antiviral response; it consists of the major DNA-binding component p48, and the signal transducers and activators of transcription (Stat)1 and Stat2. We show here that type II IFN (IFN-gamma) can also invoke the activation of ISGF3 in mouse primary embryonic fibroblasts. In fact, the two Stat proteins were tyrosine phosphorylated in IFN-gamma stimulated cells. Our present findings reveal an additional mechanism by which these two distinct types of cytokines, IFN-alpha/beta and -gamma, can commonly elicit antiviral activities.