title: Epigenetic and Transcriptional Regulation of IRAK-M Expression in Macrophages.
abstract: During macrophage activation, expression of IL-1R-associated kinase (IRAK)-M is induced to suppress TLR-mediated responses and is a hallmark of endotoxin tolerance. Endotoxin tolerance requires tight regulation of genes occurring at the transcriptional and epigenetic levels. To identify novel regulators of IRAK-M, we used RAW 264.7 macrophages and performed a targeted RNA interference screen of genes encoding chromatin-modifying enzymes, signaling molecules, and transcription factors involved in macrophage activation. Among these, the transcription factor CCAAT/enhancer binding protein (C/EBP)β, known to be involved in macrophage inactivation, was necessary for the induction of IRAK-M expression. Chromatin immunoprecipitation showed that C/EBPβ was recruited to the IRAK-M promoter following LPS stimulation and was indispensable for IRAK-M transcriptional activation. Among histone 3-modifying enzymes, our screen showed that knockdown of the histone 3 lysine 27 (H3K27) methyltransferase and part of the polycomb recessive complex 2, enhancer of Zeste 2, resulted in IRAK-M overexpression. In contrast, knockdown of the H3K27 demethylase ubiquitously transcribed tetratricopeptide repeat X chromosome suppressed the induction of IRAK-M in response to LPS stimulation. Accordingly, we demonstrated that H3K27 on the IRAK-M promoter is trimethylated in unstimulated cells and that this silencing epigenetic mark is removed upon LPS stimulation. Our data propose a mechanism for IRAK-M transcriptional regulation according to which, in the naive state, polycomb recessive complex 2 repressed the IRAK-M promoter, allowing low levels of expression; following LPS stimulation, the IRAK-M promoter is derepressed, and transcription is induced to allow its expression.
authors.affiliation: Laboratory of Clinical Chemistry, Medical School, University of Crete, Heraklion 71003, Crete, Greece.
authors.forename: Konstantina
authors.identifier: 0000-0001-7446-0999
authors.initials: K
authors.lastname: Lyroni
authors.affiliation: Laboratory of Clinical Chemistry, Medical School, University of Crete, Heraklion 71003, Crete, Greece.
authors.forename: Andreas
authors.identifier: 0000-0002-9022-4985
authors.initials: A
authors.lastname: Patsalos
authors.affiliation: Laboratory of Biochemistry, Medical School, University of Crete, Heraklion 71003, Crete, Greece; and.
authors.forename: Maria G
authors.initials: MG
authors.lastname: Daskalaki
authors.affiliation: Laboratory of Clinical Chemistry, Medical School, University of Crete, Heraklion 71003, Crete, Greece.
authors.forename: Christina
authors.initials: C
authors.lastname: Doxaki
authors.affiliation: Cenix Bioscience GmbH, D01307 Dresden, Germany.
authors.forename: Birte
authors.initials: B
authors.lastname: Soennichsen
authors.affiliation: Cenix Bioscience GmbH, D01307 Dresden, Germany.
authors.forename: Mike
authors.initials: M
authors.lastname: Helms
authors.affiliation: Laboratory of Clinical Chemistry, Medical School, University of Crete, Heraklion 71003, Crete, Greece.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Liapis
authors.affiliation: Laboratory of Clinical Chemistry, Medical School, University of Crete, Heraklion 71003, Crete, Greece.
authors.forename: Vassiliki
authors.initials: V
authors.lastname: Zacharioudaki
authors.affiliation: Laboratory of Biochemistry, Medical School, University of Crete, Heraklion 71003, Crete, Greece; and tsatsani@med.uoc.gr s.kampranis@med.uoc.gr.
authors.forename: Sotirios C
authors.identifier: 0000-0001-6208-1684
authors.initials: SC
authors.lastname: Kampranis
authors.affiliation: Laboratory of Clinical Chemistry, Medical School, University of Crete, Heraklion 71003, Crete, Greece; tsatsani@med.uoc.gr s.kampranis@med.uoc.gr.
authors.forename: Christos
authors.identifier: 0000-0003-1214-4151
authors.initials: C
authors.lastname: Tsatsanis
mesh_terms: D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000502:physiology; D002478:Cells, Cultured; D003640:Dealkylation; D044127:Epigenesis, Genetic; D053592:Interleukin-1 Receptor-Associated Kinases / Q000235:genetics*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D016328:NF-kappa B / Q000502:physiology; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; D008070:Lipopolysaccharides; D016328:NF-kappa B; D053592:Interleukin-1 Receptor-Associated Kinases; C507772:Irak3 protein, mouse