Innate recognition and signaling by Toll-like receptors (TLRs) is facilitated by functionally associated coreceptors, although the cooperativity mechanisms involved are poorly understood. As a model we investigated TLR2 interactions with the GD1a ganglioside binding subunit of type IIb Escherichia coli enterotoxin (LT-IIb-B(5)). Both LT-IIb-B(5) and a GD1a binding-defective mutant (LT-IIb-B(5)(T13I)) could modestly bind to TLR2, but only the wild-type molecule displayed a dramatic increase in TLR2 binding activity in the presence of GD1a (although not in the presence of irrelevant gangliosides). Moreover, fluorescence resonance energy transfer experiments indicated that LT-IIb-B(5) induces lipid raft recruitment of TLR2 and TLR1 and their clustering with GD1a, in contrast to the GD1a binding-defective mutant, which moreover fails to activate TLR2 signaling. LT-IIb-B(5)-induced cell activation was critically dependent upon the Toll/IL-1 receptor domain-containing adaptor protein, which was induced to colocalize with TLR2 and GD1a, as shown by confocal imaging. Therefore, GD1a provides TLR2 coreceptor function by enabling the ligand to recruit, bind, and activate TLR2. These findings establish a model of TLR2 coreceptor function and, moreover, suggest novel mechanisms of adjuvanticity by non-toxic derivatives of type II enterotoxins dependent upon GD1a/TLR2 cooperative activity.
"TLR2/1 and TLR2/6 complexes have been linked to proinflammatory and anti-inflammatory responses, respectively , . TLR2 recognition of agonists is also influenced by co-receptors and accessory molecules, such as CD14 , CD36 , MD-2 , lipopolysaccharide-binding protein (LBP) , CD11b-CD18 integrin , and ganglioside GD1a . "
[Show abstract][Hide abstract] ABSTRACT: TLR2 plays a critical role in the protection against Paracoccidioides brasiliensis conferred by ArtinM administration. ArtinM, a D-mannose-binding lectin from Artocarpus heterophyllus, induces IL-12 production in macrophages and dendritic cells, which accounts for the T helper1 immunity that results from ArtinM administration. We examined the direct interaction of ArtinM with TLR2using HEK293A cells transfected with TLR2, alone or in combination with TLR1 or TLR6, together with accessory proteins. Stimulation with ArtinM induced NF-κB activation and interleukin (IL)-8 production in cells transfected with TLR2, TLR2/1, or TLR2/6. Murine macrophages that were stimulated with ArtinM had augmented TLR2 mRNA expression. Furthermore, pre-incubation of unstimulated macrophages with an anti-TLR2 antibody reduced the cell labeling with ArtinM. In addition, a microplate assay revealed that ArtinM bound to TLR2 molecules that had been captured by specific antibodies from a macrophages lysate. Notably,ArtinM binding to TLR2 was selectively inhibited when the lectin was pre-incubated with mannotriose. The biological relevance of the direct interaction of ArtinM with TLR2 glycans was assessed using macrophages from TLR2-KOmice, which produced significantly lower levels of IL-12 and IL-10 in response to ArtinM than macrophages from wild-type mice. Pre-treatment of murine macrophages with pharmacological inhibitors of signaling molecules demonstrated the involvement of p38 MAPK and JNK in the IL-12 production induced by ArtinM and the involvement ofPI3K in IL-10 production. Thus, ArtinM interacts directly with TLR2 or TLR2 heterodimers in a carbohydrate recognition-dependent manner and functions as a TLR2 agonist with immunomodulatory properties.
PLoS ONE 06/2014; 9(6):e98512. DOI:10.1371/journal.pone.0098512 · 3.23 Impact Factor
" immune system . Lipopolysaccharide - induced macrophage ganglioside expression and surface accessibility are dramatically altered with the modification of TLR4 - dependent downstream events ( Yohe et al . 1991 ; Macala and Yohe 1995 ) . TLR2 acts in concert with ganglioside coreceptors to mediate LT - IIb signaling ( Hajishengallis et al . 2005 ; Liang et al . 2007 ) . A TLR2 inter - active motif is found in both LT - IIb and LT - IIc ( Nawar et al . 2010 ) . Our results suggest that ganglioside co - reception for LT - IIc might be facilitated by long - chain fatty acyl ceramides . We further theorize that long - chain fatty acyl ceramide alters the orientation and surface accessibility of carbohy"
[Show abstract][Hide abstract] ABSTRACT: Bacterial heat-labile enterotoxins (LT) signal through tightly regulated interactions with host cell gangliosides. LT-IIa and LT-IIb of E. coli bind preferentially to gangliosides with a NeuAcα2-3Galβ1-3GalNAc terminus, with key distinctions in specificity. LT-IIc, a newly discovered E. coli LT, is comprised of an A polypeptide with high homology, and a B polypeptide with moderate homology, to LT-IIa and LT-IIb. LT-IIc is less cytotoxic than LT-IIa and LT-IIb. We theorized that LT-IIc-host cell interaction is regulated by specific structural attributes of immune cell ganglioside receptors and designed experiments to test this hypothesis. Overlay immunoblotting to a diverse array of neural and macrophage gangliosides, indicated that LT-IIc bound to a restrictive range of gangliosides, each possessing a NeuAcα2-3Galβ1-3GalNAc, with a requisite terminal sialic acid. LT-IIc did not bind to GM1a with short chain fatty acyl ceramides. Affinity overlay immunoblots, constructed to a diverse array of known ganglioside structures of murine peritoneal macrophages, established that LT-IIc bound to GM1a comprised of long chain fatty acyl ceramides. Findings were confirmed with LT-IIc also binding to GM1a of RAW264.7 cells, comprised of long chain fatty acyl ceramide. Thus, LT-IIc-ganglioside binding differs distinctly from that of LT-IIa and LT-IIb. LT-IIc binding is not just dependent on carbohydrate composition, but also upon the orientation of the oligosaccharide portion of GM1a by the ceramide moiety. These studies are the first demonstration of LT-ganglioside dependence upon ceramide composition and underscore the contribution of long chain fatty acyl ceramides to host cell interactions.
"It binds the β subunit of type IIb heat-labile enterotoxin of Escherichia coli, enabling this ligand to induce TLR2/TLR1 signaling within lipid rafts. GD1a does not appear to interact with triacyl molecules (Liang et al., 2007b). Since bacterial porins, which have been shown to be TLR2 ligands (Massari et al., 2002; Liu et al., 2008), are also oligomeric pore forming proteins that bind to the same dimer, there is a possibility that GD1a may also affect or enhance their signaling, but there is no experimental evidence supporting this hypothesis (Massari et al., 2006). "
[Show abstract][Hide abstract] ABSTRACT: Toll-like receptors (TLRs) are recognition molecules for multiple pathogens, including bacteria, viruses, fungi, and parasites. TLR2 forms heterodimers with TLR1 and TLR6, which is the initial step in a cascade of events leading to significant innate immune responses, development of adaptive immunity to pathogens and protection from immune sequelae related to infection with these pathogens. This review will discuss the current status of TLR2 mediated immune responses by recognition of pathogen-associated molecular patterns (PAMPS) on these organisms. We will emphasize both canonical and non-canonical responses to TLR2 ligands with emphasis on whether the inflammation induced by these responses contributes to the disease state or to protection from diseases.
Frontiers in Immunology 04/2012; 3:79. DOI:10.3389/fimmu.2012.00079
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