Possible involvement of the transcription factor ISGF3γ in virus-induced expression of the IFN-β gene

Two virus-inducible transcription factors, IRF-1 and IRF-2 have been identified as an activator and a repressor, respectively, of the type I interferon (IFN) genes. Recent studies with mice carrying null mutations for the IRF-1 or IRF-2 alleles have revealed the existence of IRF-1-dependent and -independent pathways mediating IFN-β gene induction. Here we report that the expression of an IRF family member ISGF3γ is induced upon viral infection in IRF-1-/-, IRF-2-/- embryonic fibroblasts. Furthermore, ISGF3γ can bind to a virus-inducible promoter element in the IFN-β gene. These results suggest that ISGF3γ or complex containing ISGF3γ is involved in the IRF-1-independent pathway mediating IFN-β gene regulation.