The interleukin 12 p40 gene promoter is primed by interferon gamma in monocytic cells.

TitleThe interleukin 12 p40 gene promoter is primed by interferon gamma in monocytic cells.
Publication TypeJournal Article
Year of Publication1996
AuthorsMa X, Chow JM, Gri G, Carra G, Gerosa F, Wolf SF, Dzialo R, Trinchieri G
JournalJ Exp Med
Date Published1996 Jan 01
KeywordsAnimals, Base Sequence, Cloning, Molecular, DNA Mutational Analysis, Drug Interactions, Gene Expression Regulation, Humans, Interferon-gamma, Interleukin-12, Lipopolysaccharides, Macrophages, Mice, Molecular Sequence Data, Monocytes, Promoter Regions, Genetic, Restriction Mapping, RNA, Messenger, Sequence Deletion, Species Specificity, Transcription, Genetic, Transfection

Interleukin (IL) 12 is a proinflammatory cytokine produced by phagocytic cells, B cells, and other antigen-presenting cells that modulates adaptive immune responses by favoring the generation of T helper type 1 cells. IL-12 mediates some of its physiological activities by acting as a potent inducer of interferon (IFN) gamma production by T and natural killer cells. IFN-gamma enhances the ability of the phagocytic cells to produce IL-12 and other proinflammatory cytokines. Thus, IL-12-induced IFN-gamma acts in a positive feedback loop that represents an important amplifying mechanism in the inflammatory response to infections. We show here that IFN-gamma enhances IL-12 production mostly by priming phagocytic cells for lipopolysaccharide (LPS)-induced transcription of the IL-12 p40 gene, which encodes the heavy chain of the IL-12 heterodimer; furthermore, IFN-gamma directly induces transcription of the IL-12 p35 gene, which encodes the light chain of IL-12, and has at least an additive effect with LPS stimulation in inducing its transcription. The priming effect of IFN-gamma on the LPS-induced p40 gene transcription requires preincubation of the cells with IFN-gamma for at least 8 h to obtain a maximal effect. The priming effect of IFN-gamma for IL-12 production is predominantly at the transcriptional level for both the p40 and the p35 gene, and no evidence for a major role of posttranscriptional or translational mechanisms was found. A 3.3-kb human IL-12 p40 promoter construct transfected into cell lines recapitulated the tissue specificity of the endogenous gene, being silent in two human T cell lines, constitutively active in two human Epstein-Barr virus-positive B lymphoblastoid cell lines, and LPS inducible in the human THP-1 and mouse RAW264.7 monocytic cell lines. Because the RAW264.7 cell line is easily transfectable and regulates the endogenous IL-12 p40 gene in response to IFN-gamma or LPS similarly to human monocytes, it was used for analysis of the regulation of the cloned human IL-12 p40 promoter. A requirement for the region between -222 and -204 in both LPS responsiveness and IFN-gamma priming was established. This region contains an ets consensus sequence that was shown to mediate activation of the promoter by IFN-gamma and LPS, as well as by a cotransfected ets-2. The -222 construct was also regulated in a tissue-specific manner. Two other elements, IRF-1 located at -730 to -719, and NF-IL6 at -520 to -512, were also studied by deletion analysis, which did not result in decreased response to IFN-gamma and LPS stimulation.

Alternate JournalJ Exp Med
PubMed ID8551218
PubMed Central IDPMC2192398
Grant ListCA-10815 / CA / NCI NIH HHS / United States
CA-20833 / CA / NCI NIH HHS / United States
CA-32898 / CA / NCI NIH HHS / United States

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