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 - 2017/2/1
Y1 - 2017/2/1
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
SN - 0022-1767
VL - 198
SP - 1297
EP - 1307
JO - Journal of Immunology
JF - Journal of Immunology
IS - 3
ER -