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Mouse Siglec-F and human Siglec-8 are functionally convergent paralogs that are selectively expressed on eosinophils and recognize 6'-sulfo-sialyl Lewis X as a preferred glycan ligand

Department of Molecular Biology, The Scripps Research Institute, San Diego, CA 92037, USA.
Glycobiology (Impact Factor: 3.14). 12/2005; 15(11):1125-35. DOI: 10.1093/glycob/cwi097
Source: PubMed

ABSTRACT Mouse sialic acid-binding immunoglobulin-like lectin F (Siglec-F) is an eosinophil surface receptor, which contains an immunoreceptor tyrosine-based inhibitory motif (ITIM) in its cytoplasmic domain, implicating it as a regulator of cell signaling as documented for other siglecs. Here, we show that the sialoside sequence 6'-sulfo-sLe(X) (Neu5Acalpha2-3[6-SO4] Galbeta1-4[Fucalpha1-3]GlcNAc) is a preferred ligand for Siglec-F. In glycan array analysis of 172 glycans, recombinant Siglec-F-Fc chimeras bound with the highest avidity to 6'-sulfo-sLe X. Secondary analysis showed that related structures, sialyl-Lewis X (sLe X) and 6-sulfo-sLe X containing 6-GlcNAc-SO4 showed much lower binding avidity, indicating significant contribution of 6-Gal-SO4 on Siglec-F binding to 6'-sulfo-sLe x. The lectin activity of Siglec-F on mouse eosinophils was "masked" by endogenous cis ligands and could be unmasked by treatment with sialidase. Unmasked Siglec-F mediated mouse eosinophil binding and adhesion to multivalent 6'-sulfo-sLe X structure, and these interactions were inhibited by anti-Siglec-F monoclonal antibody (mAb). Although there is no clear-cut human ortholog of Siglec-F, Siglec-8 is encoded by a paralogous gene that is expressed selectively by human eosinophils and has recently been found to recognize 6'-sulfo-sLe X. These observations suggest that mouse Siglec-F and human Siglec-8 have undergone functional convergence during evolution and implicate a role for the interaction of these siglecs with their preferred 6'-sulfo-sLe X ligand in eosinophil biology.

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    • "Despite the remarkably consistent benefits of targeting Siglec-F in mouse models of hypereosinophilia, asthma and gastrointestinal eosinophilia and the exaggerated eosinophilic responses seen in mice deficient in Siglec-F when put through various models of allergic inflammation [12], based on the data presented herein, Siglec-F appears to have a different intracellular mechanism of activity than Siglec-8 in that even under cytokine priming conditions, cell death is always caspase dependent. Given the fact that Siglec-F is a functional paralog rather than a true ortholog of Siglec-8 [17] and that below chimpanzees there is no Siglec-8 ortholog [47], [48] efforts to advance the targeting of Siglec-8 as a potential therapeutic for human diseases will need to consider other strategies besides simply relying on data from studies of Siglec-F. "
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    ABSTRACT: Siglec-F and Siglec-8 are functional paralog proapoptotic cell surface receptors expressed on mouse and human eosinophils, respectively. Whereas Siglec-8 mediated death involves caspases and/or reactive oxygen species (ROS) generation and mitochondrial injury, very little is known about Siglec-F-mediated signaling and apoptosis. Therefore the objective of the current experiments was to better define apoptosis pathways mediated by Siglec-F and Siglec-8. Given that Siglec-F-induced apoptosis is much less robust than Siglec-8-induced apoptosis, we hypothesized that mechanisms involved in cell death via these receptors would differ. Consequences of engagement of Siglec-F on mouse eosinophils were studied by measuring ROS production, and by performing apoptosis assays using eosinophils from normal, hypereosinophilic, NADPH oxidase-deficient, src homology domain-containing protein tyrosine phosphatase (SHP)-1-deficient, and Lyn kinase-deficient mice. Inhibitors of caspase and Src family kinase activity were also used. Engagement of Siglec-F induced mouse eosinophil apoptosis that was modest in magnitude and dependent on caspase activity. There was no detectable ROS generation, or any role for ROS, NADPH oxidase, SHP-1, or Src family kinases in this apoptotic process. These data suggest that Siglec-F-mediated apoptosis is different in both magnitude and mechanisms when compared to published data on Siglec-8-mediated human eosinophil apoptosis. One likely implication of this work is that models targeting Siglec-F in vivo in mice may not provide identical mechanistic predictions for consequences of Siglec-8 targeting in vivo in humans.
    PLoS ONE 06/2013; 8(6):e68143. DOI:10.1371/journal.pone.0068143 · 3.23 Impact Factor
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    • "There are few reports of the expression of Siglecs in rats; thus, the available anti-Siglec-F antibody of the murine type was used for this study. However, murine mast cells do not express Siglec-F [11]. Siglec-F is considered to be the functional ortholog of human Siglec-8, which is expressed selectively in eosinophils, mast cells, and basophils [2,12-15]. "
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    ABSTRACT: Sialic acid-binding Ig-like lectin (Siglec) is an immune inhibitory receptor that plays a role in the negative regulation of the activation of immune cells. This study aimed to evaluate the effects of anti-Siglec-F on plasma and urinary histamine levels in ovalbumin (OVA)-challenged urinary bladder in mice. Thirty BALB/c mice were used. In group I (control group, n=5), mice were sensitized with OVA and challenged with saline. In group II (OVA challenge group, n=5), OVA was used for intraperitoneal sensitization and intravesical challenge. The challenged mice in group III (control immunoglobulin G [IgG] group, n=5) and those in group IV (anti-Siglec-F group, n=5) were intraperitoneally pretreated with rabbit control IgG or anti-Siglec-F antibody, respectively. In groups V (N-acetylcysteine [NAC] in OVA challenge group, n=5) and VI (control NAC only, n=5), mice were pretreated with NAC. Urinary histamine concentrations were significantly higher 7 days after intravesical OVA challenge (P<0.01), whereas plasma histamine levels were not. Pretreatment with anti-Siglec-F antibody significantly prevented the increase in urinary histamine release (P<0.05), whereas pretreatment with the IgG antibody control did not. Also, pretreatment of the OVA challenge group with NAC did not affect the histamine concentration in either urine or plasma. Systemic anti-Siglec-F treatment showed anti-allergic effects at least on local histamine release, particularly in the lower urinary bladder.
    International neurourology journal 09/2012; 16(3):122-5. DOI:10.5213/inj.2012.16.3.122
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    • "When cross-linked by mAbs on hpbMC, Siglec-8 does not lead to apoptosis as it does on eosinophils, but rather to strong inhibition of histamine and prostaglandin D2 secretion and of [Ca 2+ ] influx (Yokoi et al., 2008; Bochner, 2009; Karra et al., 2009). Siglec-8 is known to specifically recognize the sialoside sequence 6 -sulfo-sLex (Tateno et al., 2005). Siglec-8 has been shown to be associated with asthma (Gao et al., 2010). "
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    ABSTRACT: Mast cells (MC) are major participants in the allergic reaction. In addition they possess immunomodulatory roles in the innate and adaptive immune reactions. Their functions are modulated through a number of activating and inhibitory receptors expressed on their surface. This review deals with some of the most recently described receptors, their expression patterns, ligand(s), signal transduction mechanisms, possible cross-talk with other receptors and, last but not least, regulatory functions that the MC can perform based on their receptor expression in health or in disease. Where the receptor role on MC is still not clear, evidences from other hematopoietic cells expressing them is provided as a possible insight for their function on MC. Suggested strategies to modulate these receptors' activity for the purpose of therapeutic intervention are also discussed.
    Frontiers in Immunology 08/2012; 3:238. DOI:10.3389/fimmu.2012.00238
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