IFIT1 exerts opposing regulatory effects on the inflammatory and interferon gene programs in LPS-activated human macrophages

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Abstract Activation of the TLR4 signaling pathway by LPS leads to activation of both inflammatory and interferon stimulated genes, however the mechanisms through which these coordinately activated transcriptional programs are balanced to promote an optimal innate immune response remains poorly understood. In a genome-wide siRNA screen of the LPS-induced TNF-a response in macrophages, we identified the interferon-stimulated protein IFIT1 as a negative regulator of the inflammatory gene program. Transcriptional profiling further identified an unexpected positive regulatory role for IFIT1 in type I interferon expression, implicating IFIT1 as a reciprocal modulator of LPS-induced inflammatory and interferon gene expression. We demonstrate that these effects of IFIT1 are mediated through modulation of a Sin3a-HDAC2 transcriptional regulatory complex at LPS-induced gene loci. Beyond the well-studied role of cytosolic IFIT1 in restricting viral replication, our data demonstrate an unappreciated function for nuclear IFIT1 in differential transcriptional regulation of separate branches of the LPS-induced gene program. IFIT1 depletion led to a significant increase in the replication of B. cenocepacia. Prior treatment of IFIT1 depleted cells with recombinant IFN-β reversed the enhanced replication of B. cenocepacia, indicating a role for autocrine IFN-β in controlling B. cenocepacia infection and a requirement for IFIT1 in interferon induction in response to bacterial infection. We also observed reduced expression of IFNβ1 in response to viral and bacterial infection in IFIT1 depleted cells, suggesting a broad role for IFIT1 in supporting IFNβ1 expression.

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