Priming of regulatory DNA elements activates inflammatory cytokine genes synergistically with TLR signaling to increase transcription (P1230)

Abstract

Abstract Synergistic activation of inflammatory cytokine genes by IFN-γ and Toll-like receptor signaling is important for innate immunity and inflammatory disease pathogenesis. Enhancement of Toll-like receptor signaling events, a previously proposed mechanism, is insufficient to explain massive activation of cytokine production in human macrophages. We found that IFN-γ induced sustained occupancy of STAT1 and IRF1 at proximal and distal regulatory regions of the TNF, IL6 and IL12B gene loci in human macrophages, which was associated with increased histone acetylation, an indicator of an active histone state. This opening of chromatin greatly facilitated further recruitment of other transcription factors and the assembly of the RNA polymerase II complex upon Toll-like receptor activation, which resulted in increased and prolonged transcription of these inflammatory cytokines. Genome-wide analysis revealed pervasive priming of regulatory elements by IFN-γ and linked coordinate priming of promoters and enhancers with synergistic induction of transcription. Furthermore, IFN-γ-mediated priming conferred sensitivity of cytokine gene transcription to inhibitors of Jak kinases or chromatin regulators of the bromo and extra terminal protein family. Our results provide a synergy mechanism whereby IFN-γ creates a primed chromatin environment to augment Toll-like receptor-induced gene transcription, and suggest therapeutic approaches that selectively target priming mechanisms.