ABSTRACT
Expression of the anti-inflammatory cytokine IL-10 is suppressed by the pro-inflammatory interferon gamma but the mechanism of this action is unknown. We analysed activity of IL-10 promoter luciferase reporter constructs in transfected RPMI 8226.1 B cells that were treated at -2 h with IFNgamma (1000 U/ml) followed by stimulation with LPS (100 ng/ml) at 0 h. IFNgamma treatment suppressed LPS-induced IL-10 promoter activity in a construct carrying the -1044 promoter and also one containing the -195 promoter. The suppression was independent of the IRF-motif at -182 but involved the Stat-motif at -120. In gelshift analysis this Stat motif did bind LPS-induced Stat3 and with IFNgamma treatment it did, in addition, bind Stat1. ChIP analysis for detection of transcription factor binding to chromatin in intact cells demonstrated Stat3 binding to the proximal IL-10 promoter when cells are stimulated with LPS only. Treatment with IFNgamma only led to Stat1 binding in ChIP analysis and treatment with IFNgamma plus LPS led to reduced Stat3 binding while Stat1 binding remained high. Finally, LPS-induced activity of the trimeric Stat-motif in front of the luciferase reporter was suppressed by IFNgamma. These data demonstrate that IFNgamma down-regulates expression of the IL-10 gene by a novel mechanism that involves displacement of transactiving Stat3 by IFNgamma-induced Stat1.
Subject(s)
Interferon-gamma/pharmacology , Interleukin-10/genetics , Cell Nucleus/drug effects , Cell Nucleus/metabolism , Cells, Cultured , Down-Regulation/drug effects , Down-Regulation/genetics , Humans , Interleukin-10/metabolism , Models, Biological , Promoter Regions, Genetic/drug effects , Protein Binding/drug effects , RNA, Messenger/metabolism , STAT1 Transcription Factor/metabolism , STAT3 Transcription Factor/metabolism , Signal Transduction/drug effects , Signal Transduction/geneticsABSTRACT
In the present report we have determined the molecular mechanisms, which govern the expression of the human IL-10 gene when induced by the glucocorticoid Methyl-Prednisolone (MP). Treatment of cells with MP at 10(-6) M will readily induce IL-10 in CD19+ primary B cells and in a human B cell line. Analysis of the IL-10 promoter showed a robust 18-fold induction and demonstrated that a potential GRE motif was not required, while mutation of the -120 STAT-motif strongly reduced MP-induced trans-activation. A strong induction was also seen with a trimeric STAT-motif and over-expression of dominant-negative STAT3 could block MP induction of IL-10 mRNA. Finally, MP treatment induced binding of STAT3 to the promoter as shown by gelshift, supershift and by chromatin-immunoprecipitation. These data show that glucocorticoid-induced expression of the IL-10 gene is mediated by the transcription factor STAT3.
Subject(s)
Gene Expression Regulation/drug effects , Interleukin-10/genetics , Methylprednisolone/pharmacology , STAT3 Transcription Factor/metabolism , Adenoviridae , Cell Line , Chromatin Immunoprecipitation , Genes, Dominant , Genes, Reporter , Humans , Interleukin-10/metabolism , Luciferases/metabolism , Promoter Regions, Genetic/drug effects , Protein Binding/drug effects , RNA, Messenger/genetics , RNA, Messenger/metabolism , Sequence DeletionABSTRACT
Little is known about determinants regulating expression of Mannan-binding lectin associated serine protease-2 (MASP-2), the effector component of the lectin pathway of complement activation. Comparative bioinformatic analysis of the MASP2 promoter regions in human, mouse, and rat, revealed conservation of two putative Stat binding sites, termed StatA and StatB. Site directed mutagenesis specific for these sites was performed. Transcription activity was decreased 5-fold when StatB site was mutated in the wildtype reporter gene construct. Gel retardation and competition assays demonstrated that proteins contained in the nuclear extract prepared from HepG2 specifically bound double-stranded StatB oligonucleotides. Supershift analysis revealed Stat3 to be the major specific binding protein. We conclude that Stat3 binding is important for MASP2 promoter activity.
