Interleukin-15 induces IL-12 receptor beta1 gene expression through PU.1 and IRF 3 by targeting chromatin remodeling

Interleukin-12 receptor beta1 (IL12RB1) is expressed on a variety of immune cells, including T and natural killer (NK) cells and macrophages, and is involved in innate and adaptive immune responses. Levels of IL12RB1 mRNA are dynamically regulated by various cytokines, including interferon-gamma (IFN-gamma) and IL-15. To reveal the regulatory mechanisms governing IL12RB1 gene expression, we analyzed the transcriptional regulatory region of the mouse IL12RB1 gene. Promoter analyses in a mouse macrophage cell line, RAW264.7, revealed that the 2508-bp region upstream of the transcriptional start site is sufficient for the full transcriptional activation of the IL12RB1 gene by IFN-gamma or IL-15. Analyses of the deletion mutants revealed critical roles of IRE/ISRE and ETS/PU.1 elements, to which IRF3 and PU.1, respectively, bound. Notably, chromatin immunoprecipitation (ChIP) assays revealed IL-15 rapidly induced histone H3 acetylation at the IL12RB1 promoter. Consistently, IL-15, as a histone deacetylase inhibitor, synergistically enhanced IL12RB1 gene expression and promoter activation by IFN-gamma through increased protein binding to ETS/PU.1 and IRE/ISRE sites. Additionally, IL12RB1 promoter activation by IFN-gamma was enhanced by the coexpression of a coactivator protein, CBP. Thus, IL-15 induces chromatin remodeling of the IL12RB1 gene promoter, increasing IL12RB1 mRNA expression in synergy with IFN-gamma through the recruitment of PU.1 and IRF3.