title: Bacterial lipoprotein-induced self-tolerance and cross-tolerance to LPS are associated with reduced IRAK-1 expression and MyD88-IRAK complex formation.
abstract: Tolerance to bacterial cell-wall components may represent an essential regulatory mechanism during bacterial infection. We have demonstrated previously that the inhibition of nuclear factor (NF)-kappaB and mitogen-activated protein kinase activation was present in bacterial lipoprotein (BLP) self-tolerance and its cross-tolerance to lipopolysaccharide (LPS). In this study, the effect of BLP-induced tolerance on the myeloid differentiation factor 88 (MyD88)-dependent upstream signaling pathway for NF-kappaB activation in vitro was examined further. When compared with nontolerant human monocytic THP-1 cells, BLP-tolerant cells had a significant reduction in tumor necrosis factor alpha (TNF-alpha) production in response to a high-dose BLP (86+/-12 vs. 6042+/-245 ng/ml, P < 0.01) or LPS (341+/-36 vs. 7882+/-318 ng/ml, P < 0.01) stimulation. The expression of Toll-like receptor 2 (TLR2) protein was down-regulated in BLP-tolerant cells, whereas no significant differences in TLR4, MyD88, interleukin-1 receptor-associated kinase 4 (IRAK-4), and TNF receptor-associated factor 6 expression were observed between nontolerant and BLP-tolerant cells, as confirmed by Western blot analysis. The IRAK-1 protein was reduced markedly in BLP-tolerant cells, although IRAK-1 mRNA expression remained unchanged as revealed by real-time reverse transcriptase-polymerase chain reaction analysis. Furthermore, decreased MyD88-IRAK immunocomplex formation, as demonstrated by immunoprecipitation, was observed in BLP-tolerant cells following a second BLP or LPS stimulation. BLP pretreatment also resulted in a marked inhibition in total and phosphorylated inhibitor of kappaB-alpha (IkappaB-alpha) expression, which was not up-regulated by subsequent BLP or LPS stimulation. These results demonstrate that in addition to the down-regulation of TLR2 expression, BLP tolerance is associated with a reduction in IRAK-1 expression, MyD88-IRAK association, and IkappaB-alpha phosphorylation. These findings further elucidate the molecular mechanisms underlying bacterial peptide tolerance.
authors.affiliation: Department of Academic Surgery, National University of Ireland (NUI)/University College Cork, Cork University Hospital, Cork, Ireland.
authors.forename: Chong Hui
authors.initials: CH
authors.lastname: Li
authors.forename: Jiang Huai
authors.initials: JH
authors.lastname: Wang
authors.forename: H Paul
authors.initials: HP
authors.lastname: Redmond
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000096:biosynthesis / Q000187:drug effects*; D002460:Cell Line; D002478:Cells, Cultured; D006801:Humans; D007108:Immune Tolerance / Q000187:drug effects* / Q000276:immunology; D053592:Interleukin-1 Receptor-Associated Kinases; D047908:Intracellular Signaling Peptides and Proteins / Q000187:drug effects*; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D008074:Lipoproteins / Q000494:pharmacology*; D009000:Monocytes / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D046912:Multiprotein Complexes / Q000096:biosynthesis / Q000276:immunology; D053594:Myeloid Differentiation Factor 88; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000187:drug effects*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology; D013997:Time Factors; D051195:Toll-Like Receptor 2 / Q000096:biosynthesis / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000096:biosynthesis / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis / Q000187:drug effects
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D047908:Intracellular Signaling Peptides and Proteins; D008070:Lipopolysaccharides; D008074:Lipoproteins; C507779:MYD88 protein, human; D046912:Multiprotein Complexes; D053594:Myeloid Differentiation Factor 88; D009363:Neoplasm Proteins; D012333:RNA, Messenger; C120635:TAX1BP1 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D053592:Interleukin-1 Receptor-Associated Kinases; D017346:Protein Serine-Threonine Kinases