title: Selective activation of the p38 MAPK pathway by synthetic monophosphoryl lipid A.
abstract: TLR4 stimulation by lipopolysaccharide can cause both MAL/MyD88- and TRAM/TRIF (Toll IL-1 receptor domain-containing adaptor-inducing IFNbeta)-dependent signaling events. Monophosphoryl lipid A (MPLA), a low toxicity derivative of endotoxic lipopolysaccharide, enhances antibody responses, T cell expansion, and recall responses against antigens without causing excessive inflammatory side effects. Previously, we proposed that TRIF-biased activation of TLR4 by MPLA is responsible for its reduced toxicity while retaining potent adjuvant effects. However, some TRIF-associated genes, such as MCP-1, are only weakly expressed, and some MyD88-associated inflammatory and anti-inflammatory cytokines, such as tumor necrosis factor alpha and interleukin-10, are strongly activated after MPLA stimulation despite weak NF-kappaB but strong IRF3 activation. We now report that synthetic derivatives of MPLA retained TRIF bias as compared with synthetic diphosphoryl lipid A, indicating a change in a single phosphoryl group is sufficient for TRIF-biased TLR4 stimulation. We extend our previous observations by showing that sMLA induces strong p38 MAPK but weak JNK activation, resulting in high IP-10 (interferon-inducible protein 10), tumor necrosis factor alpha, and interleukin-10 but low MCP-1 transcript levels. Results of this study identify a novel biochemical mechanism for regulation of sMLA-induced gene expression.
authors.affiliation: Department of Microbiology and Immunology, University of Louisville School of Medicine, Louisville, Kentucky 40202, USA.
authors.forename: Caglar
authors.initials: C
authors.lastname: Cekic
authors.forename: Carolyn R
authors.initials: CR
authors.lastname: Casella
authors.forename: Chelsea A
authors.initials: CA
authors.lastname: Eaves
authors.forename: Atsushi
authors.initials: A
authors.lastname: Matsuzawa
authors.forename: Hidenori
authors.initials: H
authors.lastname: Ichijo
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Mitchell
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000502:physiology*; D000276:Adjuvants, Immunologic / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D001853:Bone Marrow / Q000378:metabolism; D054357:Chemokine CXCL10 / Q000235:genetics / Q000378:metabolism; D003713:Dendritic Cells / Q000378:metabolism*; D008050:Lipid A / Q000031:analogs & derivatives* / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D000276:Adjuvants, Immunologic; D054357:Chemokine CXCL10; D008050:Lipid A; D053594:Myeloid Differentiation Factor 88; D012333:RNA, Messenger; D051197:Toll-Like Receptor 4; D048051:p38 Mitogen-Activated Protein Kinases; C507780:Myd88 protein, mouse; C476286:Ticam1 protein, mouse; C493487:Tlr4 protein, mouse; C048436:monophosphoryl lipid A