IFN-g Induces Histone 3 Lysine 27 Trimethylation in a Small Subset of Promoters to Stably Silence Gene Expression in Human Macrophages

The mechanisms by which IFN-g activates expression of interferon-stimulated genes that have inflammatory and host defense functions are well understood. In contrast, little is known about how IFN-g represses gene expression. By using transcriptomic and epigenomic analysis, we found that stable repression of a small group of genes by IFN-g is associated with recruitment of the histone methyltransferase EZH2 and deposition of the negative mark histone 3 lysine 27 trimethylation (H3K27me3) at their promoters. Repressed genes included MERTK, PPARG, and RANK, which have anti-inflammatory functions and promote osteoclast differentiation. Gene repression and H3K27me3 persisted after IFN-g signaling was terminated, and these silenced genes were no longer responsive to glucocorticoids, IL-4, and M-CSF. These results identify cytokineinduced H3K27 trimethylation as a mechanism that stabilizes gene silencing in macrophages. IFN-ginduced macrophage activation is thus reinforced by a chromatin-based mechanism that blocks antiinflammatory and opposing pathways