Involvement of IRAK-M in peptidoglycan-induced tolerance in macrophages.
The molecular mechanisms by which pathogen-associated molecular patterns recognized by TLR2, such as peptidoglycan (PGN), induce homotolerance are largely unknown. It was recently reported that IRAK-M negatively regulates TLR signaling. In this study, we elucidate the molecular mechanisms of tolerance induced by PGN, with a focus on the role of IRAK-M. We demonstrate that pretreatment of macrophage RAW264.7 cells with a high concentration (30 microg/ml) of PGN for 16 h effectively induces tolerance against following stimulation with 30 microg/ml of PGN; while pretreatment with a low concentration (1 microg/ml) of PGN does not. IRAK-M is induced in cells treated with the high concentration of PGN 4-24 h after PGN stimulation, but not in cells treated with the low concentration of PGN up to 24 h after stimulation. Phosphorylation of MAPKs and IkappaBalpha is inhibited after the second PGN stimulation in tolerant cells. Kinase activity of IRAK-1 and association between IRAK-1 and MyD88 are also suppressed in PGN-induced tolerant cells. Furthermore, down-regulation of IRAK-M expression by small interfering RNAs specific for IRAK-M reinstates the production of TNF-alpha after PGN restimulation. These results suggest that induction of IRAK-M and inhibition of kinase activity of IRAK-1 are crucial to PGN-induced tolerance in macrophages.
Nakayama
Kuniko
K
Department of Infectious Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo 113-8655, Japan.
Okugawa
Shu
S
Yanagimoto
Shintaro
S
Kitazawa
Takatoshi
T
Tsukada
Kunihisa
K
Kawada
Miki
M
Kimura
Satoshi
S
Hirai
Koichi
K
Takagaki
Yohtaroh
Y
Ota
Yasuo
Y
D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D015151:Immunoblotting; D053592:Interleukin-1 Receptor-Associated Kinases; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D010457:Peptidoglycan / Q000737:chemistry* / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011494:Protein Kinases / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D010457:Peptidoglycan; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; D011494:Protein Kinases; D053592:Interleukin-1 Receptor-Associated Kinases; C507772:Irak3 protein, mouse