Tight control of inflammatory gene expression by antagonistic environmental cues is key to ensure immune protection while preventing tissue damage. Prostaglandin E 2 (PGE 2 ) modulates macrophage activation during homeostasis and disease, but the underlying mechanisms remain incompletely characterized. Here we dissected the genomic properties of lipopolysaccharide (LPS)-induced genes whose expression is antagonized by PGE 2 . The latter molecule targeted a set of inflammatory gene enhancers that, already in unstimulated macrophages, displayed poorly permissive chromatin organization and were marked by the transcription factor myocyte enhancer factor 2A (MEF2A). Deletion of MEF2A phenocopied PGE 2 treatment and abolished type I interferon (IFN I) induction upon exposure to innate immune stimuli. Mechanistically, PGE 2 interfered with LPSmediated activation of ERK5, a known transcriptional partner of MEF2. This study highlights principles of plasticity and adaptation in cells exposed to a complex environment and uncovers a transcriptional circuit for IFN I induction with relevance for infectious diseases or cancer.
The tumor microenvironment (TME) is a complex architecture of cells, including those of the immune system, of matrix components, and of their interactions within the unique physical traits of the cancer tissue. 1,2 Many elements influence the composition and cellular dynamics of the TME, such as the anatomical site, the type, and stage of the disease, the therapeutic regimen as well as host factors like age, sex, and comorbidities. 2 Within the extreme diversity of TMEs, parameters integrating the relative composition, spatial arrangement, and functional properties of infiltrating immune cells are useful indicators of disease progression and response to therapies. 2,3 For instance, high tumor infiltration of cytotoxic CD8 + T cells engaging inhibitory crosstalk in the TME via the programmed death (PD)1:PD-L1/PD-L2 axis often predicts efficient response to immune checkpoint blockade therapy. 3 In some cases, CD8 + T cells form organized assemblies with antigen-presenting cells such as dendritic cells (DCs), B cells, and macrophages within the tumor stroma; these so-called tertiary lymphoid structures are considered sites of efficient T-cell priming, and their presence is associated with good response to immunotherapy. 4 In this context, a subset of conventional DCs, termed cDC1, can efficiently cross-present tumor antigens for the induction of a durable immune response. 5-7 Accumulation of cDC1 at the tumor site is mediated at least in part by chemokines released by infiltrating natural killer (NK) cells, 8 a
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