Regulation of IFN-α/β genes: Evidence for a dual function of the transcription factor complex ISGF3 in the production and action of IFN-α/β

Background: Efficient production of interferons (IFNs) in virally infected cells is an essential aspect of the host defence. The transcription factor complex ISGF3 (IFN-stimulated gene factor 3) was originally identified as a critical mediator of the IFN signal; it is formed upon IFN receptor (IFNR) stimulation and binds to ISREs (IFN-stimulated response elements) to activate IFN-inducible genes. It has recently been shown that the DNA binding component of ISGF3, p48 (ISGF3γ) also binds to virus-inducible elements in the IFN-α/β genes, suggesting a potential new role of p48 in IFN production. Results: Primary cells from mice with a targeted disruption of the p48 gene show severe defects in virus-induced IFN-α/β gene expression. A similar defect was also observed in cells lacking type I IFNR or Stat1, further demonstrating the role of IFN signalling in the induction of these IFN genes. ISGF3 in fact binds to the virus-inducible elements within the IFN-α/β promoters. We also provide evidence showing that these elements are additionally controlled by an unidentified factor(s) which presumably triggers the primary phase of IFN gene induction. Conclusions: Our results demonstrate that the IFN signal transducing complex ISGF3 plays a crucial role in IFN production and suggest that ISGF3 may participate directly in the activation of IFN-α/β promoters. This dual function of ISGF3 may insure the efficient operation of this cytokine system in the host defence.