Distinct Roles for the NF-κB RelA Subunit during Antiviral Innate Immune Responses

Production of type I interferons (IFNs; prominently, IFN-alpha/beta) following virus infection is a pivotal antiviral innate immune response in higher vertebrates. The synthesis of IFN-beta proceeds via the virus-induced assembly of the transcription factors IRF-3/7, ATF-2/c-Jun, and NF-kappa B on the ifn beta promoter. Surprisingly, recent data indicate that the NF-kappa B subunit RelA is not essential for virus-stimulated ifn beta expression. Here, we show that RelA instead sustains autocrine IFN-beta signaling prior to infection. In the absence of RelA, virus infection results in significantly delayed ifn beta induction and consequently defective secondary antiviral gene expression. While RelA is not required for ifn beta expression after infection, it is nonetheless essential for fully one-fourth of double-stranded RNA (dsRNA)-activated genes, including several mediators of inflammation and immune cell recruitment. Further, RelA directly regulates a small subset of interferon-stimulated genes (ISGs). Finally, RelA also protects cells from dsRNA-triggered RIP1-dependent programmed necrosis. Taken together, our findings suggest distinct roles for RelA in antiviral innate immunity: RelA maintains autocrine IFN-beta signaling in uninfected cells, facilitates inflammatory and adaptive immune responses following infection, and promotes infected-cell survival during this process.