Carbon monoxide differentially inhibits TLR signaling pathways by regulating ROS-induced trafficking of TLRs to lipid rafts

Carbon monoxide (CO), a byproduct of heme catabolism by heme oxygenase (HO), confers potent antiinflammatory effects. Here we demonstrate that CO derived from HO-1 inhibited Toll-like receptor (TLR) 2, 4, 5, and 9 signaling, but not TLR3-dependent signaling, in macrophages. Ligand-mediated receptor trafficking to lipid rafts represents an early event in signal initiation of immune cells. Trafficking of TLR4 to lipid rafts in response to LPS was reactive oxygen species (ROS) dependent because it was inhibited by diphenylene iodonium, an inhibitor of NADPH oxidase, and in gp91phox-deficient macrophages. CO selectively inhibited ligand-induced recruitment of TLR4 to lipid rafts, which was also associated with the inhibition of ligand-induced ROS production in macrophages. TLR3 did not translocate to lipid rafts by polyinosine-polycytidylic acid (poly(I:C)). CO had no effect on poly(I:C)-induced ROS production and TLR3 signaling. The inhibitory effect of CO on TLR-induced cytokine production was abolished in gp91phox-deficient macrophages, also indicating a role for NADPH oxidase. CO attenuated LPS-induced NADPH oxidase activity in vitro, potentially by binding to gp91phox. Thus, CO negatively controlled TLR signaling pathways by inhibiting translocation of TLR to lipid rafts through suppression of NADPH oxidase–dependent ROS generation.

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NF-κB, JNK, and TLR Signaling Pathways in Hepatocarcinogenesis

Gastroenterology Research and Practice ◽

10.1155/2010/367694 ◽

2010 ◽

Vol 2010 ◽

pp. 1-10 ◽

Cited By ~ 39

Author(s):

Shin Maeda

Keyword(s):

Hepatocellular Carcinoma ◽

Signaling Pathways ◽

Inflammatory Cell ◽

Prognostic Markers ◽

Tumor Promotion ◽

Neoplastic Cell ◽

Nuclear Factor ◽

Tlr Signaling ◽

The Third

Hepatocellular carcinoma (HCC) is the third largest cause of cancer deaths worldwide. The role of molecular changes in HCC have been used to identify prognostic markers and chemopreventive or therapeutic targets. It seems that toll-like receptors (TLRs) as well as the nuclear factor (NF)-κB, and JNK pathways are critical regulators for the production of the cytokines associated with tumor promotion. The cross-talk between an inflammatory cell and a neoplastic cell, which is instigated by the activation of NF-κB and JNKs, is critical for tumor organization. JNKs also regulate cell proliferation and act as oncogenes, making them the main tumor-promoting protein kinases. TLRs play roles in cytokine and hepatomitogen expression mainly in myeloid cells and may promote liver tumorigenesis. A better understanding of these signaling pathways in the liver will help us understand the mechanism of hepatocarcinogenesis and provide a new therapeutic target for HCC.

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Lysosomal trafficking regulator Lyst links membrane trafficking to toll-like receptor–mediated inflammatory responses

Journal of Experimental Medicine ◽

10.1084/jem.20141461 ◽

2016 ◽

Vol 214 (1) ◽

pp. 227-244 ◽

Cited By ~ 15

Author(s):

Andreas Westphal ◽

Weijia Cheng ◽

Jinbo Yu ◽

Guntram Grassl ◽

Martina Krautkrämer ◽

...

Keyword(s):

Signaling Pathways ◽

Membrane Trafficking ◽

Inflammatory Responses ◽

Functional Integration ◽

Receptor Signaling ◽

Toll Like Receptor ◽

Tlr Signaling ◽

Lysosomal Trafficking ◽

Phagosomal Maturation ◽

Chediak Higashi Syndrome

Subcellular compartmentalization of receptor signaling is an emerging principle in innate immunity. However, the functional integration of receptor signaling pathways into membrane trafficking routes and its physiological relevance for immune responses is still largely unclear. In this study, using Lyst-mutant beige mice, we show that lysosomal trafficking regulator Lyst links endolysosomal organization to the selective control of toll-like receptor 3 (TLR3)– and TLR4-mediated proinflammatory responses. Consequently, Lyst-mutant mice showed increased susceptibility to bacterial infection and were largely resistant to endotoxin-induced septic shock. Mechanistic analysis revealed that Lyst specifically controls TLR3- and TLR4-induced endosomal TRIF (TIR domain–containing adapter-inducing interferon β) signaling pathways. Loss of functional Lyst leads to dysregulated phagosomal maturation, resulting in a failure to form an activation-induced Rab7+ endosomal/phagosomal compartment. This specific Rab7+ compartment was further demonstrated to serve as a major site for active TRIF signaling events, thus linking phagosomal maturation to specific TLR signaling pathways. The immunoregulatory role of Lyst on TLR signaling pathways was confirmed in human cells by CRISPR/Cas9-mediated gene inactivation. As mutations in LYST cause human Chédiak-Higashi syndrome, a severe immunodeficiency, our findings also contribute to a better understanding of human disease mechanisms.

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TLR Signaling Pathways: Opportunities for Activation and Blockade in Pursuit of Therapy

Current Pharmaceutical Design ◽

10.2174/138161206778743466 ◽

2006 ◽

Vol 12 (32) ◽

pp. 4123-4134 ◽

Cited By ~ 40

Author(s):

K. Hoebe ◽

Z. Jiang ◽

P. Georgel ◽

K. Tabeta ◽

E. Janssen ◽

...

Keyword(s):

Signaling Pathways ◽

Tlr Signaling

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IgM+IgD+CD27+ B cells are markedly reduced in IRAK-4–, MyD88-, and TIRAP- but not UNC-93B–deficient patients

Blood ◽

10.1182/blood-2012-07-440776 ◽

2012 ◽

Vol 120 (25) ◽

pp. 4992-5001 ◽

Cited By ~ 63

Author(s):

Sandra Weller ◽

Mélanie Bonnet ◽

Héloïse Delagreverie ◽

Laura Israel ◽

Maya Chrabieh ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Signaling Pathways ◽

Size Distribution ◽

Heavy Chain ◽

Peripheral Blood ◽

Somatic Hypermutation ◽

Key Factors ◽

Tlr Signaling ◽

B Cell Subsets

Abstract We studied the distribution of peripheral B-cell subsets in patients deficient for key factors of the TLR-signaling pathways (MyD88, TIRAP/MAL, IL-1 receptor–associated kinase 4 [IRAK-4], TLR3, UNC-93B, TRIF). All TLRs, except TLR3, which signals through the TRIF adaptor, require MyD88 and IRAK-4 to mediate their function. TLR4 and the TLR2 heterodimers (with TLR1, TLR6, and possibly TLR10) require in addition the adaptor TIRAP, whereas UNC-93B is needed for the proper localization of intracellular TLR3, TLR7, TLR8, and TLR9. We found that IgM+IgD+CD27+ but not switched B cells were strongly reduced in MyD88-, IRAK-4-, and TIRAP-deficient patients. This defect did not appear to be compensated with age. However, somatic hypermutation of Ig genes and heavy-chain CDR3 size distribution of IgM+IgD+CD27+ B cells were not affected in these patients. In contrast, the numbers of IgM+IgD+CD27+ B cells were normal in the absence of TLR3, TRIF, and UNC-93B, suggesting that UNC-93B–dependent TLRs, and notably TLR9, are dispensable for the presence of this subset in peripheral blood. Interestingly, TLR10 was found to be expressed at greater levels in IgM+IgD+CD27+ compared with switched B cells in healthy patients. Hence, we propose a role for TIRAP-dependent TLRs, possibly TLR10 in particular, in the development and/or maintenance of IgM+IgD+CD27+ B cells in humans.

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The Effect of Adenosine on TLR Signaling Pathways in Human Monocytic THP-1 Cells.

Blood ◽

10.1182/blood.v104.11.3828.3828 ◽

2004 ◽

Vol 104 (11) ◽

pp. 3828-3828

Author(s):

Chin-Fu Chen ◽

Chun-Huai Cheng ◽

Seychelle Vos

Keyword(s):

Immune Responses ◽

Signaling Pathways ◽

Immune Cells ◽

Adenosine Receptors ◽

Protein Modification ◽

Map Kinases ◽

Critical Role ◽

Innate Immune ◽

Fcγ Receptors ◽

Tlr Signaling

Abstract Adenosine is an important metabolite that serves as a potent regulator of inflammation and mediates various biological functions in different cell types. Adenosine inhibits the proinflammatory actions of inflammatory and immune cells via interaction with its receptors, particularly A2A receptors. Adenosine receptors belong to the seven-transmembrane G-protein coupled receptors and via the different G proteins transfer signals through different effectors including adenyl cyclase, PKA, PKC, PI3K, and MAP kinases. The mechanisms by which the adenosine regulates immune responses and how adenosine receptor pathways interact with other signaling pathways are currently unknown. Toll-like receptors (TLRs) of the innate immune cells recognize conserved microbial structures, such as bacterial lipopolysaccharide and viral double-stranded RNA, and activate signaling pathways that result in innate immune responses against microbial infections. Fcγ receptors of the innate cells play a critical role in the clearance of pathogens, regulation of inflammation and co-ordination of the immune response. We seek to understand the interaction between adenosine (via adenosine receptors) and TLR- and Fcγ R- mediated signaling pathways. We have initiated study on the effect of adenosine and lipopolysaccharide (LPS) on expression of TLR2, TLR4, FcγRI and Fcγ RII receptors in the human monocytic cell line THP-1. We incubated cells with 100μM adenosine for three hours at 37°C and assayed the expression of receptors using flow cytometry. Our results suggest that adenosine increases the expression of TLR2 and TLR4 in both undifferentiated cells and the cells induced to become macrophages by phorbol ester. Incubation with adenosine for 24 hours further increases the expression of TLR2 and TLR4 in both undifferentiated and differentiated THP-1 cells. Similarly, incubation with LPS for three hours increases the expression TLR2 and TLR4 in both undifferentiated and differentiated THP-1 cells. In contrast, the expression level of FcγRI and FcγRII receptors do not change in the presence of either adenosine or LPS. These observations suggest that adenosine specifically enhances expression of TLRs but not Fcγ receptors. To further understand the interaction between adenosine and TLR pathways, we are continuously investigating the effect of adenosine on expression and the protein modification (e.g. phosphorylation) of TLR2, TLR4, and the molecules in the TLR signaling cascades including MyD88, IRAK and MAP kinases using real-time RT-PCR and western blotting.

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