A Distal Locus Element Mediates IFN-γ Priming of Lipopolysaccharide- Stimulated TNF Gene Expression

Interferon gamma (IFN-gamma) priming sensitizes monocytes and macrophages to lipopolysaccharide (LPS) stimulation, resulting in augmented expression of a set of genes including TNF. Here, we demonstrate that IFN-gamma priming of LPS-stimulated TNF transcription requires a distal TNF/LT locus element 8 kb upstream of the TNF transcription start site (hHS-8). IFN-gamma stimulation leads to increased DNase I accessibility of hHS-8 and its recruitment of interferon regulatory factor 1 (IRF1), and subsequent LPS stimulation enhances H3K27 acetylation and induces enhancer RNA synthesis at hHS-8. Ablation of IRF1 or targeting the hHS-8 IRF1 binding site in vivo with Cas9 linked to the KRAB repressive domain abolishes IFN-gamma priming, but does not affect LPS induction of the gene. Thus, IFN-gamma poises a distal enhancer in the TNF/LT locus by chromatin remodeling and IRF1 recruitment, which then drives enhanced TNF gene expression in response to a secondary toll-like receptor (TLR) stimulus.