IRF1 Tunes Basal Immunity and Antiviral Readiness in a Context-Dependent Manner

Interferon Regulatory Factor 1 (IRF1) plays a pivotal role in interferon (IFN) signaling, yet its context-dependent regulatory functions remain incompletely understood. Here, we dissect the impact of IRF1 on gene regulation in HeLa cells, by targeted knockout (KO) or overexpression (OE) of IRF1. IRF1 KO did not impair interferon stimulated gene (ISG) expression regulation upon IFN-{beta} stimulation, but partially diminished IFN-{psi} induced gene regulation. IRF1 KO did show a homeostatic role in basal gene abundance, including increasing the abundance of some antiviral genes. RNA-seq analysis showed altered expression of both ISGs and immune signaling genes, implicating IRF1 as a dual regulator that fine-tunes gene abundance through both activation and repression. IRF1 OE induced potent antiviral protection in the absence of exogenous IFN, mediated by type I IFN secretion, particularly of IFN- subtypes. This paracrine effect was confirmed by transcriptomics, cytokine profiling, and mass spectrometry, and was functional even in JAK1-deficient or Ruxolitinib-treated cells but not type I IFN receptor KO cells, suggesting the involvement of non-canonical signaling pathways. Hierarchical clustering of RNA-seq data revealed distinct IFN-independent gene clusters activated or repressed by IRF1, including pathways related to adaptive immunity and T cell function. Using protein-binding microarrays and predictive modeling, we mapped IRF1 binding across promoters and validated functional motifs in the IFIT2 gene promoter by a reporter assay. Our integrative approach establishes IRF1 as a central regulator of antiviral immunity, capable of shaping gene expression both through cytokine signaling and direct promoter binding.