Abstract
Mannose-capped lipoarabinomannans (Man-LAMs) are members of the repertoire of Mycobacterium tuberculosis modulins that the bacillus uses to subvert the host innate immune response. Interleukin-12 (IL-12) production is critical for mounting an effective immune response by the host against M. tuberculosis. We demonstrate that Man-LAM inhibits IL-12 p40 production mediated by subsequent challenge with lipopolysaccharide (LPS). Man-LAM inhibits LPS-induced IL-12 p40 expression in an IL-10-independent manner. It attenuates LPS-induced NF-kappaB-driven luciferase gene expression, suggesting that its effects are likely directly related to inhibition of NF-kappaB. This is probably because of dampening of the Toll-like receptor signaling. Man-LAM inhibits IL-1 receptor-associated kinase (IRAK)-TRAF6 interaction as well as IkappaB-alpha phosphorylation. It directly attenuates nuclear translocation and DNA binding of c-Rel and p50. Man-LAM exerts these effects by inducing the expression of Irak-M, a negative regulator of TLR signaling. Knockdown of Irak-M expression by RNA interference reinstates LPS-induced IL-12 production in Man-LAM-pretreated cells. The fact that Irak-M expression could be elicited by yeast mannan suggested that ligation of the mannose receptor by the mannooligosaccharide caps of LAM was the probable trigger for IRAK-M induction.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Active Transport, Cell Nucleus
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Animals
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Blotting, Western
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Cell Line
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Dose-Response Relationship, Drug
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Enzyme-Linked Immunosorbent Assay
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Gene Expression Regulation
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Gene Silencing
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Genes, Reporter
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I-kappa B Proteins / metabolism
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Immunoprecipitation
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Interleukin-1 Receptor-Associated Kinases
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Interleukin-10 / metabolism
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Interleukin-12 / metabolism*
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Interleukin-12 Subunit p40
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Intracellular Signaling Peptides and Proteins / chemistry*
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Intracellular Signaling Peptides and Proteins / metabolism
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Lipopolysaccharides / chemistry*
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Lipopolysaccharides / metabolism
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Luciferases / metabolism
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Macrophages / metabolism*
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Macrophages / microbiology*
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Mannose / chemistry
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Mice
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Mycobacterium tuberculosis / metabolism*
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NF-KappaB Inhibitor alpha
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NF-kappa B / metabolism
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Oligosaccharides / chemistry
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Phenotype
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Phosphorylation
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Plasmids / metabolism
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Promoter Regions, Genetic
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Protein Binding
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Protein Serine-Threonine Kinases / chemistry*
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Protein Serine-Threonine Kinases / metabolism
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Protein Subunits / metabolism*
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RNA, Small Interfering / metabolism
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Reverse Transcriptase Polymerase Chain Reaction
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Signal Transduction
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TNF Receptor-Associated Factor 6 / metabolism
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Toll-Like Receptors / metabolism*
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Transfection
Substances
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I-kappa B Proteins
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Interleukin-12 Subunit p40
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Intracellular Signaling Peptides and Proteins
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Lipopolysaccharides
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NF-kappa B
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Nfkbia protein, mouse
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Oligosaccharides
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Protein Subunits
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RNA, Small Interfering
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TNF Receptor-Associated Factor 6
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Toll-Like Receptors
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lipoarabinomannan
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Interleukin-10
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NF-KappaB Inhibitor alpha
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Interleukin-12
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Luciferases
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Interleukin-1 Receptor-Associated Kinases
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Irak3 protein, mouse
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Protein Serine-Threonine Kinases
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Mannose