TY - JOUR

T1 - Epigenetic and Transcriptional Regulation of IRAK-M Expression in Macrophages

AU - Lyroni, Konstantina

AU - Patsalos, Andreas

AU - Daskalaki, Maria G

AU - Doxaki, Christina

AU - Soennichsen, Birte

AU - Helms, Mike

AU - Liapis, Ioannis

AU - Zacharioudaki, Vassiliki

AU - Kampranis, Sotirios C

AU - Tsatsanis, Christos

N1 - Copyright © 2017 by The American Association of Immunologists, Inc.

PY - 2017

Y1 - 2017

N2 - 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.

AB - 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.

KW - Animals

KW - CCAAT-Enhancer-Binding Protein-beta/physiology

KW - Cells, Cultured

KW - Dealkylation

KW - Epigenesis, Genetic

KW - Interleukin-1 Receptor-Associated Kinases/genetics

KW - Lipopolysaccharides/pharmacology

KW - Macrophages/metabolism

KW - Mice

KW - NF-kappa B/physiology

KW - Promoter Regions, Genetic

KW - Transcription, Genetic

U2 - 10.4049/jimmunol.1600009

DO - 10.4049/jimmunol.1600009

M3 - Journal article

C2 - 28011933

VL - 198

SP - 1297

EP - 1307

JO - Journal of Immunology

JF - Journal of Immunology

SN - 0022-1767

IS - 3

ER -