A genome-wide siRNA screen identifies a novel role for IFIT1 in regulation of the LPS-induced gene program in macrophages

Authors

• SP John
• J Sun
• ID Fraser

Abstract

LPS stimulation in macrophages leads to the expression of both pro-inflammatory cytokines such as TNF-α, and also type-I interferons such as IFN-β. Interferon Induced Tetratricopeptide repeat protein-1 (IFIT1), an LPS-induced gene, has been characterized as an important host anti-viral gene through its specific recognition of viral RNA. In the course of a genome-wide siRNA screen of the LPS response in human macrophages, we identified IFIT1 as a negative regulator of TNF-α, as its perturbation led to significant increases in TNF-α transcription and secretion in both THP1 cells and primary human macrophages. We generated a THP1 cell line stably expressing IFIT1 shRNA to assess IFIT1 regulation of the broader LPS-induced gene program by microarray. We find that IFIT1 not only has a specific role in negative feedback regulation of the early inflammatory cytokine response (including but not limited to TNF-α), but is also required to ‘license’ the expression of IFN pathway genes induced by LPS. We observed a dramatic attenuation of IFN-β and numerous ISGs when IFIT1 expression is perturbed. Comparison of transcription factor motifs in the promoters of the gene sets enhanced or suppressed in IFIT1 perturbed cells shows enrichment of selective transcription factor subsets. Our data suggest that IFIT1 could be an important control point in the transition from early activation of inflammatory genes to later induction of IFN-dependent genes in TLR-activated macrophages. We identify a novel role for IFIT1 in the regulation of the LPS-induced inflammatory gene program, distinct from its previously established function in blocking viral replication.

Scientific Focus Area: Immunology

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