The Small GTPase Arf6 Is Essential for the Tram/Trif Pathway in TLR4 Signaling

Acker, Tim Van; Eyckerman, Sven; Walle, Lieselotte Vande; Gerlo, Sarah; Goethals, Marc; Lamkanfi, Mohamed; Bovijn, Celia; Tavernier, Jan; Peelman, Frank

doi:10.1074/jbc.m113.499194

Cited by 28 publications

(39 citation statements)

References 63 publications

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“…RAB11A GTPase is involved in the recruitment of TLR4 from the endocytic recycling compartment to E.coli phagosome (32) and affects localization of TICAM-2 to the endocytic recycling compartment and early sorting endosomes (32). The small GTPase ADP-ribosylation factor 6 also regulates transport of the TLR4 adaptor TIRAP and TICAM-2 to distinct signaling platforms (33). In addition, multiple molecules such as CD14, MD-2, PI3K, and Raftlin regulate TLR4 internalization (16,17,31), which is important in shifting the TLR4 signaling axis from MyD88 to TICAM-1, leading to expression of IFN-b and IFNstimulated genes including caspase 4/11, a cytoplasmic LPS receptor (34,35).…”

Section: Discussionmentioning

confidence: 99%

Raftlin Controls Lipopolysaccharide-Induced TLR4 Internalization and TICAM-1 Signaling in a Cell Type–Specific Manner

Tatematsu

Yoshida

Morioka

et al. 2016

The Journal of Immunology

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The clathrin-dependent endocytic pathway is crucial for endosomal TLR3- and TLR4-mediated Toll–IL-1R domain–containing adaptor molecule-1 (TICAM-1) signaling. TLR4 uses a different signaling platform, plasma membrane and endosomes, for activation of TIRAP-MyD88 and TICAM-2–TICAM-1, respectively. LPS-induced endocytosis of TLR4 is mandatory for TICAM-1–mediated signaling including IFN-β production. Several molecules/mechanisms such as CD14, clathrin, and phosphatidylinositol metabolism have been reported to act as inducers of TLR4 translocation. However, the molecular mechanism of spatiotemporal regulation of TLR4 signaling remains unresolved. We have previously shown that Raftlin is essential for clathrin-dependent endocytosis of TLR3 ligand in human epithelial cells and myeloid dendritic cells (DCs). In this article, we demonstrate that Raftlin also mediated LPS-induced TLR4 internalization and TICAM-1 signaling in human monocyte-derived DCs and macrophages (Mo-Mϕs). When Raftlin was knocked down, LPS-induced TLR4-mediated IFN-β promoter activation, but not NF-κB activation, was decreased in HEK293 cells overexpressing TLR4/MD-2 or TLR4/MD-2/CD14. LPS-induced IFN-β production by monocyte-derived DCs and Mo-Mϕs was significantly decreased by knockdown of Raftlin. Upon LPS stimulation, Raftlin moved from the cytoplasm to the plasma membrane in Mo-Mϕs, where it colocalized with TLR4. Raftlin associated with clathrin-associated adaptor protein–2 in resting cells and transiently bound to TLR4 and clathrin at the cell surface in response to LPS. Thus, Raftlin appears to modulate cargo selection as an accessary protein of clathrin-associated adaptor protein–2 in clathrin-mediated endocytosis of TLR3/4 ligands.

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Section: Discussionmentioning

confidence: 99%

Raftlin Controls Lipopolysaccharide-Induced TLR4 Internalization and TICAM-1 Signaling in a Cell Type–Specific Manner

Tatematsu

Yoshida

Morioka

et al. 2016

The Journal of Immunology

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“…Thus far, all of the evidence in animal models, including the present study, suggests that ARF6, while necessary for disease pathology, does not regulate cytokine release (15). In contrast, it has been proposed that inhibition of ARF6 in fibroblasts, macrophages, and dendritic cells decreases LPS-induced cytokine production by preventing the association of MYD88 with TIRAP and TLR4(41, 42). However, LTA-induced cytokine expression, which also requires the association of MYD88 to TIRAP, was not affected by ARF6 inhibition suggesting a greater complexity in these TLR-signaling pathways (42).…”

Section: Discussionmentioning

confidence: 99%

ARF6 Inhibition Stabilizes the Vasculature and Enhances Survival during Endotoxic Shock

Davis

Zhu

Gibson

et al. 2014

The Journal of Immunology

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The vascular endothelium responds to infection by destabilizing endothelial cell-cell junctions to allow fluid and cells to pass into peripheral tissues facilitating clearance of infection and tissue repair. During sepsis, endotoxin and other pro-inflammatory molecules induce excessive vascular leak, which can cause organ dysfunction, shock, and death. Current therapies for sepsis are limited to antibiotics and supportive care, which are often insufficient to reduce morbidity and prevent mortality. Previous attempts at blocking inflammatory cytokine responses in humans have proven ineffective at reducing the pathologies associated with sepsis, thus highlighting the need for a new therapeutic strategy. The small GTPase ARF6 is activated by a MYD88-ARNO interaction to induce vascular leak through disruption of endothelial adherens junctions. Here we show that the MYD88-ARNO-ARF6 signaling axis is responsible for lipopolysaccharide (LPS)-induced endothelial permeability and is a destabilizing convergence point utilized by multiple inflammatory cues. We also show that blocking ARF6 with a peptide construct of its N-terminus is sufficient to reduce vascular leak and enhance survival during endotoxic shock without inhibiting host cytokine response. Our data highlight the therapeutic potential of blocking ARF6 and reducing vascular leak for the treatment of inflammatory conditions such as endotoxemia.

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“…However, the specific mechanism by which TLR4 is transported to the endosome was incompletely defined. The small GTPase ADP ribosylation factor 6 (ARF6) and Rab family of GTPases have been investigated in controlling endocytic transport of receptors (10). Recently, Husebye et al showed that Rab11a, a small GTPase, regulates recruitment of TLR4 and TRAM to E. coli phagosomes and controls both E. coli-and LPSinduced IRF3 activation (9).…”

Section: Cd14-independent Endocytosis Of Tlr4 In Macrophages Renderedmentioning

confidence: 99%

CD14 dependence of TLR4 endocytosis and TRIF signaling displays ligand specificity and is dissociable in endotoxin tolerance

Rajesh

Perkins

Ireland

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

125

104

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Dimerization of Toll-like receptor 4 (TLR4)/myeloid differentiation factor 2 (MD2) heterodimers is critical for both MyD88-and TIRdomain-containing adapter-inducing IFN-β (TRIF)-mediated signaling pathways. Recently, Zanoni et al. [(2011) Cell 147(4):868-880] reported that cluster of differentiation 14 (CD14) is required for LPS-/Escherichia coli-induced TLR4 internalization into endosomes and activation of TRIF-mediated signaling in macrophages. We confirmed their findings with LPS but report here that CD14 is not required for receptor endocytosis and downstream signaling mediated by TLR4/MD2 agonistic antibody (UT12) and synthetic small-molecule TLR4 ligands (1Z105) in murine macrophages. CD14 deficiency completely ablated the LPS-induced TBK1/IRF3 signaling axis that mediates production of IFN-β in murine macrophages without affecting MyD88-mediated signaling, including NF-κB, MAPK activation, and TNF-α and IL-6 production. However, neither the MyD88-nor TRIF-signaling pathways and their associated cytokine profiles were altered in the absence of CD14 in UT12-or 1Z105-treated murine macrophages. Eritoran (E5564), a lipid A antagonist that binds the MD2 "pocket," completely blocked LPS-and 1Z105-driven, but not UT12-induced, TLR4 dimerization and endocytosis. Furthermore, TLR4 endocytosis is induced in macrophages tolerized by exposure to either LPS or UT12 and is independent of CD14. These data indicate that TLR4 receptor endocytosis and the TRIF-signaling pathway are dissociable and that TLR4 internalization in macrophages can be induced by UT12, 1Z105, and during endotoxin tolerance in the absence of CD14. T oll-like receptor 4 (TLR4) signaling plays a crucial role in host defense against Gram-negative bacteria by recognizing the outer membrane component, lipopolysaccharide (LPS) (1-3). TLR4 signaling is initiated by transfer of an LPS monomer from LPS binding protein (LBP) to cluster of differentiation 14 (CD14) (GPI-linked or soluble). In turn, CD14 transfers monomeric LPS to myeloid differentiation factor 2 (MD-2), a protein that associates noncovalently with TLR4 (4). Appropriate ligand binding to MD2 results in dimerization of two TLR4/MD2 complexes (4). TLR4 is unique in that it is the only TLR that activates both myeloid differentiation primary response 88 (MyD88) and TIR-domain-containing adapter-inducing IFN-β (TRIF)-dependent signaling pathways (5, 6). MyD88-mediated, TLR4 signaling occurs mainly at plasma membranes and involves IL-1R-associated kinases phosphorylation, association of TNF-receptor-associated factor 6, and downstream signaling that results in NF-κB activation and induction of proinflammatory mediators such as TNF-α and IL-6 (7). In contrast, TRIF-mediated signaling in response to LPS occurs at the endosomal membrane after internalization of the TLR4 that, in turn, activates IFN regulatory factor 3 (IRF3), resulting in production of IFN-β, IP-10, and other IRF-3-dependent genes, as well as delayed NF-κB activation (8). Recent studies have shown that the endocytosis of TLR4 is tight...

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The Small GTPase Arf6 Is Essential for the Tram/Trif Pathway in TLR4 Signaling

Cited by 28 publications

References 63 publications

Raftlin Controls Lipopolysaccharide-Induced TLR4 Internalization and TICAM-1 Signaling in a Cell Type–Specific Manner

Raftlin Controls Lipopolysaccharide-Induced TLR4 Internalization and TICAM-1 Signaling in a Cell Type–Specific Manner

ARF6 Inhibition Stabilizes the Vasculature and Enhances Survival during Endotoxic Shock

CD14 dependence of TLR4 endocytosis and TRIF signaling displays ligand specificity and is dissociable in endotoxin tolerance

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