Abstract
LPS-activated neutrophils secrete IL-1β by activation of TLR-4. Based on studies in macrophages, it is likely that ROS and lysosomal destabilization regulated by Syk activation may also be involved. Since neutrophils have abundant expression of the ITIM-containing co-receptor CEACAM1 and Gram-negative bacteria such as Neisseria utilize CEACAM1 as a receptor that inhibits inflammation, we hypothesized that the overall production of IL-1β in LPS treated neutrophils may be negatively regulated by CEACAM1. We found that LPS treated neutrophils induced phosphorylation of Syk resulting in the formation of a complex including TLR4, p-Syk, and p-CEACAM1, which in turn, recruited the inhibitory phosphatase SHP-1. LPS treatment leads to ROS production, lysosomal damage, caspase-1 activation and IL-1β secretion in neutrophils. The absence of this regulation in Ceacam1⁻/⁻ neutrophils led to hyper production of IL-1β in response to LPS. The hyper production of IL-1β was abrogated by in vivo reconstitution of wild type but not ITIM-mutated CEACAM1 bone marrow stem cells. Blocking Syk activation by kinase inhibitors or RNAi reduced Syk phosphorylation, lysosomal destabilization, ROS production, and caspase-1 activation in Ceacam1⁻/⁻ neutrophils. We conclude that LPS treatment of neutrophils triggers formation of a complex of TLR4 with pSyk and pCEACAM1, which upon recruitment of SHP-1 to the ITIMs of pCEACAM1, inhibits IL-1β production by the inflammasome. Thus, CEACAM1 fine-tunes IL-1β production in LPS treated neutrophils, explaining why the additional utilization of CEACAM1 as a pathogen receptor would further inhibit inflammation.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Animals
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Carcinoembryonic Antigen / genetics
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Carcinoembryonic Antigen / immunology
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Carcinoembryonic Antigen / metabolism*
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Caspase 1 / genetics
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Caspase 1 / immunology
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Caspase 1 / metabolism
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Enzyme Activation / drug effects
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Enzyme Activation / genetics
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Enzyme Activation / immunology
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Inflammasomes / genetics
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Inflammasomes / immunology
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Inflammasomes / metabolism
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Inflammation / genetics
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Inflammation / immunology
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Inflammation / metabolism
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Inflammation / pathology
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Interleukin-1beta / biosynthesis*
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Interleukin-1beta / genetics
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Interleukin-1beta / immunology
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Intracellular Signaling Peptides and Proteins / genetics
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Intracellular Signaling Peptides and Proteins / immunology
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Intracellular Signaling Peptides and Proteins / metabolism*
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Lipopolysaccharides / pharmacology*
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Lysosomes / genetics
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Lysosomes / immunology
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Lysosomes / metabolism
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Lysosomes / pathology
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Macrophages / immunology
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Macrophages / metabolism
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Macrophages / pathology
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Mice
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Mice, Knockout
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Multiprotein Complexes / genetics
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Multiprotein Complexes / immunology
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Multiprotein Complexes / metabolism*
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Neisseria / immunology
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Neisseria / metabolism
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Neisseriaceae Infections / genetics
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Neisseriaceae Infections / immunology
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Neisseriaceae Infections / metabolism
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Neisseriaceae Infections / pathology
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Neutrophil Activation / drug effects*
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Neutrophil Activation / genetics
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Neutrophil Activation / immunology
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Neutrophils / immunology
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Neutrophils / metabolism*
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Neutrophils / pathology
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Phosphorylation / drug effects
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Phosphorylation / genetics
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Phosphorylation / immunology
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Protein Tyrosine Phosphatase, Non-Receptor Type 6 / genetics
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Protein Tyrosine Phosphatase, Non-Receptor Type 6 / immunology
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Protein Tyrosine Phosphatase, Non-Receptor Type 6 / metabolism*
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Protein-Tyrosine Kinases / genetics
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Protein-Tyrosine Kinases / immunology
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Protein-Tyrosine Kinases / metabolism*
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Reactive Oxygen Species / immunology
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Reactive Oxygen Species / metabolism
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Syk Kinase
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Toll-Like Receptor 4 / agonists
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Toll-Like Receptor 4 / genetics
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Toll-Like Receptor 4 / immunology
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Toll-Like Receptor 4 / metabolism*
Substances
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Carcinoembryonic Antigen
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Ceacam1 protein, mouse
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Inflammasomes
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Interleukin-1beta
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Intracellular Signaling Peptides and Proteins
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Lipopolysaccharides
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Multiprotein Complexes
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Reactive Oxygen Species
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Tlr4 protein, mouse
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Toll-Like Receptor 4
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Protein-Tyrosine Kinases
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Syk Kinase
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Syk protein, mouse
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Protein Tyrosine Phosphatase, Non-Receptor Type 6
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Ptpn6 protein, mouse
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Caspase 1