Endotoxin tolerance dysregulates MyD88- and Toll/IL-1R domain-containing adapter inducing IFN-beta-dependent pathways and increases expression of negative regulators of TLR signaling.
Endotoxin tolerance reprograms cell responses to LPS by repressing expression of proinflammatory cytokines, while not inhibiting production of anti-inflammatory cytokines and antimicrobial effectors. Molecular mechanisms of induction and maintenance of endotoxin tolerance are incompletely understood, particularly with regard to the impact of endotoxin tolerization on signalosome assembly, activation of adaptor-kinase modules, and expression of negative regulators of TLR signaling in human cells. In this study, we examined LPS-mediated activation of MyD88-dependent and Toll-IL-1R-containing adaptor inducing IFN-beta (TRIF)-dependent pathways emanating from TLR4 and expression of negative regulators of TLR signaling in control and endotoxin-tolerant human monocytes. Endotoxin tolerization suppressed LPS-inducible TLR4-TRIF and TRIF-TANK binding kinase (TBK)1 associations, induction of TBK1 kinase activity, activation of IFN regulatory factor (IRF)-3, and expression of RANTES and IFN-beta. Tolerance-mediated dysregulation of the TLR4-TRIF-TBK1 signaling module was accompanied by increased levels of suppressor of IkappaB kinase-epsilon (SIKE) and sterile alpha and Armadillo motif-containing molecule (SARM). LPS-tolerant cells showed increased expression of negative regulators Toll-interacting protein (Tollip), suppressor of cytokine signaling (SOCS)-1, IL-1R-associated kinase-M, and SHIP-1, which correlated with reduced p38 phosphorylation, IkappaB-alpha degradation, and inhibited expression of TNF-alpha, IL-6, and IL-8. To examine functional consequences of increased expression of Tollip in LPS-tolerized cells, we overexpressed Tollip in 293/TLR4/MD-2 transfectants and observed blunted LPS-inducible activation of NF-kappaB and RANTES, while TNF-alpha responses were not affected. These data demonstrate dysregulation of TLR4-triggered MyD88- and TRIF-dependent signaling pathways and increased expression of negative regulators of TLR signaling in endotoxin-tolerant human monocytes.
Piao
Wenji
W
Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Song
Chang
C
Chen
Haiyan
H
Diaz
Marco A Quevedo
MA
Wahl
Larry M
LM
Fitzgerald
Katherine A
KA
Li
Liwu
L
Medvedev
Andrei E
AE
D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051186:Armadillo Domain Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D002460:Cell Line; D016207:Cytokines / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D006801:Humans; D050838:Interferon Regulatory Factor-3 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology / Q000494:pharmacology*; D009000:Monocytes / Q000276:immunology / Q000378:metabolism*; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D011493:Protein Kinase C / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects* / Q000276:immunology; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000276:immunology / Q000378:metabolism
D033942:Adaptor Proteins, Vesicular Transport; D051186:Armadillo Domain Proteins; D016207:Cytokines; D003598:Cytoskeletal Proteins; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; D008070:Lipopolysaccharides; C507779:MYD88 protein, human; D053594:Myeloid Differentiation Factor 88; C435689:SARM1 protein, human; C108944:SOCS1 protein, human; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; C470409:TICAM1 protein, human; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D017346:Protein Serine-Threonine Kinases; C403191:TBK1 protein, human; D011493:Protein Kinase C; D048051:p38 Mitogen-Activated Protein Kinases