IL-12 induces IFN regulating factor-1 (IRF-1) gene expression in human NK and T cells.
IL-12 is a critical immunoregulatory cytokine that promotes cell-mediated immune responses and the differentiation of naive CD4+ cells to Th1 cells; however, relatively few IL-12 target genes have been identified. To better clarify the molecular basis of IL-12 action, we set out to characterize genes up-regulated by IL-12, first by contrasting IL-12- and IFN-alpha-inducible genes. We identified several genes up-regulated by IL-12, namely, MIP-1alpha, MIP-1beta, IL-1RA, and IFN regulatory factor-1 (IRF-1). IRF-1 is a transcription factor regulated by IFNs that is also essential for Th1 responses. We demonstrated that IL-12 directly up-regulates IRF-1 to the same extent as IFN-alpha in normal human T cells and in NK cells. We showed that IL-12 had a direct effect on IRF-1, an effect not mediated indirectly by the induction of IFN-gamma production. Furthermore, IL-2 and IL-12 synergistically induced IRF-1, whereas IFN-alpha and IL-12 did not. The participation of STAT4 in the regulation of IRF-1 was demonstrated in two ways. First, STAT4 was required for the IL-12-dependent transactivation of an IRF-1 reporter construct, and second, STAT4 binding to the IRF-1 promoter was shown using EMSA. In contrast to IL-12, no up-regulation of IRF-1 was found in IL-4-stimulated cells, and IL-4 did not block IL-12-dependent up-regulation of IRF-1. Therefore, IRF-1 may be an important contributor to IL-12 signaling, and we speculate that the defective IL-12 responses seen in IRF-1-/- mice might be attributable, in part, to the absence of this transcription factor.
Galon
J
J
Lymphocyte Cell Biology Section, Arthritis and Rheumatism Branch, National Institute of Arthritis and Musculoskeletal Diseases, Bethesda, MD 20892, USA.
Sudarshan
C
C
Ito
S
S
Finbloom
D
D
O'Shea
J J
JJ
D016475:3T3 Cells; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D005786:Gene Expression Regulation / Q000276:immunology*; D006801:Humans; D050856:Interferon Regulatory Factor-1; D016898:Interferon-alpha / Q000502:physiology; D007372:Interferons / Q000502:physiology*; D018664:Interleukin-12 / Q000037:antagonists & inhibitors / Q000502:physiology*; D007694:Killer Cells, Natural / Q000378:metabolism*; D051379:Mice; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*; D050797:STAT4 Transcription Factor; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D013601:T-Lymphocytes / Q000378:metabolism*; D015534:Trans-Activators / Q000502:physiology; D015854:Up-Regulation / Q000235:genetics / Q000276:immunology
D004268:DNA-Binding Proteins; C494257:IRF1 protein, human; D050856:Interferon Regulatory Factor-1; D016898:Interferon-alpha; C494258:Irf1 protein, mouse; D010750:Phosphoproteins; D050797:STAT4 Transcription Factor; C494090:STAT4 protein, human; C494091:Stat4 protein, mouse; D015534:Trans-Activators; D018664:Interleukin-12; D007372:Interferons