title: Pellino-1 Positively Regulates Toll-like Receptor (TLR) 2 and TLR4 Signaling and Is Suppressed upon Induction of Endotoxin Tolerance.
abstract: Endotoxin tolerance reprograms Toll-like receptor (TLR) 4-mediated macrophage responses by attenuating induction of proinflammatory cytokines while retaining expression of anti-inflammatory and antimicrobial mediators. We previously demonstrated deficient TLR4-induced activation of IL-1 receptor-associated kinase (IRAK) 4, IRAK1, and TANK-binding kinase (TBK) 1 as critical hallmarks of endotoxin tolerance, but mechanisms remain unclear. In this study, we examined the role of the E3 ubiquitin ligase Pellino-1 in endotoxin tolerance and TLR signaling. LPS stimulation increased Pellino-1 mRNA and protein expression in macrophages from mice injected with saline and in medium-pretreated human monocytes, THP-1, and MonoMac-6 cells, whereas endotoxin tolerization abrogated LPS inducibility of Pellino-1. Overexpression of Pellino-1 in 293/TLR2 and 293/TLR4/MD2 cells enhanced TLR2- and TLR4-induced nuclear factor κB (NF-κB) and expression of IL-8 mRNA, whereas Pellino-1 knockdown reduced these responses. Pellino-1 ablation in THP-1 cells impaired induction of myeloid differentiation primary response protein (MyD88), and Toll-IL-1R domain-containing adapter inducing IFN-β (TRIF)-dependent cytokine genes in response to TLR4 and TLR2 agonists and heat-killed Escherichia coli and Staphylococcus aureus, whereas only weakly affecting phagocytosis of heat-killed bacteria. Co-expressed Pellino-1 potentiated NF-κB activation driven by transfected MyD88, TRIF, IRAK1, TBK1, TGF-β-activated kinase (TAK) 1, and TNFR-associated factor 6, whereas not affecting p65-induced responses. Mechanistically, Pellino-1 increased LPS-driven K63-linked polyubiquitination of IRAK1, TBK1, TAK1, and phosphorylation of TBK1 and IFN regulatory factor 3. These results reveal a novel mechanism by which endotoxin tolerance re-programs TLR4 signaling via suppression of Pellino-1, a positive regulator of MyD88- and TRIF-dependent signaling that promotes K63-linked polyubiquitination of IRAK1, TBK1, and TAK1.
authors.affiliation: From the Department of Immunology, University of Connecticut Health Center, Farmington, Connecticut 06030 and.
authors.forename: Michael
authors.initials: M
authors.lastname: Murphy
authors.affiliation: the Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland 21201.
authors.forename: Yanbao
authors.initials: Y
authors.lastname: Xiong
authors.affiliation: From the Department of Immunology, University of Connecticut Health Center, Farmington, Connecticut 06030 and.
authors.forename: Goutham
authors.initials: G
authors.lastname: Pattabiraman
authors.affiliation: the Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland 21201.
authors.forename: Fu
authors.initials: F
authors.lastname: Qiu
authors.affiliation: From the Department of Immunology, University of Connecticut Health Center, Farmington, Connecticut 06030 and medvedev@uchc.edu.
authors.forename: Andrei E
authors.initials: AE
authors.lastname: Medvedev
mesh_terms: D000818:Animals; D057809:HEK293 Cells; D006801:Humans; D053592:Interleukin-1 Receptor-Associated Kinases / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D008810:Mice, Inbred C57BL; D009000:Monocytes / Q000276:immunology / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D009687:Nuclear Proteins / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction; D048029:TNF Receptor-Associated Factor 6 / Q000378:metabolism; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D015533:Transcriptional Activation / Q000276:immunology; D044767:Ubiquitin-Protein Ligases / Q000502:physiology*; D054875:Ubiquitination; D000099151:MAP Kinase Kinase Kinase 7
chemical_list: D053592:Interleukin-1 Receptor-Associated Kinases; D008070:Lipopolysaccharides; D020930:MAP Kinase Kinase Kinases; D016328:NF-kappa B; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; D048029:TNF Receptor-Associated Factor 6; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D044767:Ubiquitin-Protein Ligases; D000099151:MAP Kinase Kinase Kinase 7; C495342:TLR2 protein, human; C495345:TLR4 protein, human; C485959:PELI1 protein, human; C507768:IRAK1 protein, human; C403191:TBK1 protein, human
keywords: Toll receptor; innate immunity; lipopolysaccharide (LPS); post-translational modification (PTM); signal transduction; ubiquitin ligase