title: MyD88-dependent SHIP1 regulates proinflammatory signaling pathways in dendritic cells after monophosphoryl lipid A stimulation of TLR4.
abstract: We previously showed that monophosphoryl lipid A (MLA) activates TLR4 in dendritic cells (DCs) in a Toll/IL-1R domain-containing adaptor inducing IFN-β (TRIF)-biased manner: MLA produced from Salmonella minnesota Re595 induced signaling events and expression of gene products that were primarily TRIF dependent, whereas MyD88-dependent signaling was impaired. Moreover, when tested in TRIF-intact/MyD88-deficient DCs, synthetic MLA of the Escherichia coli chemotype (sMLA) showed the same activity as its diphosphoryl, inflammatory counterpart (synthetic diphosphoryl lipid A), indicating that TRIF-mediated signaling is fully induced by sMLA. Unexpectedly, we found that the transcript level of one proinflammatory cytokine was increased in sMLA-treated cells by MyD88 deficiency to the higher level induced by synthetic diphosphoryl lipid A, which suggested MyD88 may paradoxically help restrain proinflammatory signaling by TRIF-biased sMLA. In this article, we demonstrate that sMLA induces MyD88 recruitment to TLR4 and activates the anti-inflammatory lipid phosphatase SHIP1 in an MyD88-dependent manner. At the same time, MyD88-dependent signaling activity at the level of IL-1R-associated kinase 1 is markedly reduced. Increased SHIP1 activity is associated with reductions in sMLA-induced IκB kinase α/β and IFN regulatory factor 3 activation and with restrained expression of their downstream targets, endothelin-1 and IFN-β, respectively. Results of this study identify a pattern that is desirable in the context of vaccine adjuvant design: TRIF-biased sMLA can stimulate partial MyD88 activity, with MyD88-dependent SHIP1 helping to reduce proinflammatory signaling in DCs.
authors.affiliation: Department of Microbiology and Immunology, University of Louisville School of Medicine, Louisville, KY 40202, USA.
authors.forename: Caglar
authors.initials: C
authors.lastname: Cekic
authors.forename: Carolyn R
authors.initials: CR
authors.lastname: Casella
authors.forename: Duygu
authors.initials: D
authors.lastname: Sag
authors.forename: Frann
authors.initials: F
authors.lastname: Antignano
authors.forename: Joseph
authors.initials: J
authors.lastname: Kolb
authors.forename: Jill
authors.initials: J
authors.lastname: Suttles
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hughes
authors.forename: Gerald
authors.initials: G
authors.lastname: Krystal
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Mitchell
mesh_terms: D000276:Adjuvants, Immunologic / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001854:Bone Marrow Cells / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D003713:Dendritic Cells / Q000276:immunology* / Q000382:microbiology / Q000473:pathology; D004926:Escherichia coli / Q000276:immunology; D018836:Inflammation Mediators / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D000072181:Inositol Polyphosphate 5-Phosphatases; D008050:Lipid A / Q000031:analogs & derivatives* / Q000502:physiology; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D053594:Myeloid Differentiation Factor 88 / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D012475:Salmonella / Q000276:immunology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000819:agonists / Q000378:metabolism* / Q000502:physiology
chemical_list: D000276:Adjuvants, Immunologic; D018836:Inflammation Mediators; D008050:Lipid A; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; C049596:diphosphoryl lipid A; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases; C000606433:Inpp5d protein, mouse; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; C048436:monophosphoryl lipid A