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

Activation of the TLR4 signaling pathway by LPS leads to induction 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 remain poorly understood. In a genome-wide siRNA screen of the LPS-induced TNF- 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 gene classes. 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. Wild type THP1 and IFIT1 shRNA cells were transfected with NT siRNA and IFIT1 siRNA respectively in 24-well plates, and differentiated with 10 ng/ml PMA for 72 hours. Cells were stimulated with 100 ng/ml LPS for 0h, 1h, 2h, 4h, 6h and 24h. All but two of the conditions were tested in two biological replicates