Differential viral induction of distinct interferon-α genes by positive feedback through interferon regulatory factor-7

Interferon (IFN) genes are among the earliest transcriptional responses to virus infection of mammalian cells. Although the regulation of the IFN beta gene has been well characterized, the induction of the large family of IFN alpha genes has remained obscure, We report that the IFN alpha genes can be divided into two groups: an immediate-early response gene (IFN alpha 4) which is induced rapidly and without the need for ongoing protein synthesis; and a set of genes that display delayed induction, consisting of at least IFN alpha 2, 5, 6 and 8, which are induced more slowly and require cellular protein synthesis. One protein that must be synthesized for induction of the delayed gene set is IFN itself, presumably IFN alpha 4 or IFN beta, which stimulates the Jak-Stat pathway through the IFN receptor, resulting in activation of the transcription factor interferon-stimulated gene factor 3 (ISGF3), Among the IFN-stimulated genes induced through this positive feedback loop is the IFN regulatory factor (IRF) protein, IRF7, Induction of IRF7 protein in response to IFN and its subsequent activation by phosphorylation in response to virus-specific signals, involving two C-terminal serine residues, are required for induction of the delayed IFN alpha gene set.