Ephrinb1 and Ephrinb2 are associated with interleukin-7 receptor α and retard its internalization from the cell surface.
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ABSTRACT:
SUBMITTER: Luo H
PROVIDER: S-EPMC3247986 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The discovery of African henipaviruses (HNVs) related to pathogenic Hendra virus (HeV) and Nipah virus (NiV) from Southeast Asia and Australia presents an open-ended health risk. Cell receptor use by emerging African HNVs at the stage of host-cell entry is a key parameter when considering the potential for spillover and infection of human populations. The attachment glycoprotein from a Ghanaian bat isolate (GhV-G) exhibits <30% sequence identity with Asiatic NiV-G/HeV-G. Here, through functional and structural analysis of GhV-G, we show how this African HNV targets the same human cell-surface receptor (ephrinB2) as the Asiatic HNVs. We first characterized this virus-receptor interaction crystallographically. Compared with extant HNV-G-ephrinB2 structures, there was significant structural variation in the six-bladed β-propeller scaffold of the GhV-G receptor-binding domain, but not the Greek key fold of the bound ephrinB2. Analysis revealed a surprisingly conserved mode of ephrinB2 interaction that reflects an ongoing evolutionary constraint among geographically distal and phylogenetically divergent HNVs to maintain the functionality of ephrinB2 recognition during virus-host entry. Interestingly, unlike NiV-G/HeV-G, we could not detect binding of GhV-G to ephrinB3. Comparative structure-function analysis further revealed several distinguishing features of HNV-G function: a secondary ephrinB2 interaction site that contributes to more efficient ephrinB2-mediated entry in NiV-G relative to GhV-G and cognate residues at the very C terminus of GhV-G (absent in Asiatic HNV-Gs) that are vital for efficient receptor-induced fusion, but not receptor binding per se. These data provide molecular-level details for evaluating the likelihood of African HNVs to spill over into human populations.
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Project description:The Eph (erythropoietin-producing hepatoma) family of receptor tyrosine kinases and their membrane-bound ligands, the ephrins, have been implicated in regulating cell adhesion and migration during development by mediating cell-to-cell signaling events. The transmembrane ephrinB (Eph receptor interactor B) protein is a bidirectional signaling molecule that sends a forward signal through the activation of its cognate receptor tyrosine kinase, residing on another cell. A reverse signal can be transduced into the ephrinB-expressing cell via tyrosine phosphorylation of its conserved C-terminal cytoplasmic domain. Although some insight has been gained regarding how ephrinB may send signals affecting cytoskeletal components, little is known about how ephrinB1 reverse signaling affects transcriptional processes. Here we report that signal transducer and activator of transcription 3 (STAT3) can interact with ephrinB1 in a phosphorylation-dependent manner that leads to enhanced activation of STAT3 transcriptional activity. This activity depends on the tyrosine kinase Jak2, and two tyrosines within the intracellular domain of ephrinB1 are critical for the association with STAT3 and its activation. The recruitment of STAT3 to ephrinB1, and its resulting Jak2-dependent activation and transcription of reporter targets, reveals a signaling pathway from ephrinB1 to the nucleus.
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Project description:The epidermal growth factor receptor (EGFR) is a cell-surface glycoprotein that is involved mainly in cell proliferation. Overexpression of this receptor is intimately related to the development of a broad spectrum of tumors. In addition, glycans linked to the EGFR are known to affect its EGF-induced activation. Because of the pathophysiological significance of the EGFR, we prepared a fluorescently labeled EGFR (EGFR128-AZDye 488) on the cell surface by employing the genetic code expansion technique and bioorthogonal chemistry. EGFR128-AZDye 488 was initially utilized to investigate time-dependent endocytosis of the EGFR in live cells. The results showed that an EGFR inhibitor and antibody suppress endocytosis of the EGFR promoted by the EGF, and that lectins recognizing glycans of the EGFR do not enhance EGFR internalization into cells. Observations made in studies of the effects of appended glycans on the entry of the EGFR into cells indicate that a de-sialylated or de-fucosylated EGFR is internalized into cells more efficiently than a wild-type EGFR. Furthermore, by using the FRET-based imaging method of cells which contain an EGFR linked to AZDye 488 (a FRET donor) and cellular glycans labeled with rhodamine (a FRET acceptor), sialic acid residues attached to the EGFR were specifically detected on the live cell surface. Taken together, the results suggest that a fluorescently labeled EGFR will be a valuable tool in studies aimed at gaining an understanding of cellular functions of the EGFR.
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Project description:To minimize immune responses against infected cells, HIV-1 has evolved different mechanisms to limit the surface expression of its envelope glycoproteins (Env). Recent observations suggest that the binding of certain broadly neutralizing antibodies (bNAbs) targeting the 'closed' conformation of Env induces its internalization. On the other hand, non-neutralizing antibodies (nNAbs) that preferentially target Env in its 'open' conformation, remain bound to Env on the cell surface for longer periods of time. In this study, we attempt to better understand the underlying mechanisms behind the differential rates of antibody-mediated Env internalization. We demonstrate that 'forcing' open Env using CD4 mimetics allows for nNAb binding and results in similar rates of Env internalization as those observed upon the bNAb binding. Moreover, we can identify distinct populations of Env that are differentially targeted by Abs that mediate faster rates of internalization, suggesting that the mechanism of antibody-induced Env internalization partially depends on the localization of Env on the cell surface.
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Project description:PurposeThe prevalence of food allergy, triggered by T-helper type 2 (Th2) cell-mediated inflammation, is increasing worldwide. Interleukin (IL)-18 plays an important role in inflammatory diseases by binding with the IL-18 receptor. IL-18/IL-18 receptor α (IL-18Rα) is a cofactor for immunoglobulin E (IgE) production and Th2 cell development. Studies have not investigated the association between the IL-18/IL-18Rα signaling pathway and food allergy. Here, we investigated the role of IL-18Rα in food allergy induction and development.MethodsWild-type (WT) and IL-18Rα-null mutant (IL-18Rα-/-) C57BL/6 mice were sensitized and challenged using ovalbumin (OVA) for food allergy induction. Food allergy symptoms, T cell-mediated immune responses, and signal transducer and activator of transcription (STAT)/suppressors of cytokine signaling (SOCS) pathways were analyzed in mice.ResultsIL-18Rα expression was increased in WT mouse intestines after OVA treatment. Food allergy-induced IL-18Rα-/- mice showed attenuated systemic food allergic reactions, OVA-specific IgE and mouse mast cell protease-1 production, inflammatory cell infiltration, and T cell activation. Ex vivo experiments showed that cell proliferation and Th2 cytokine production were lower in IL-18Rα-/- mouse splenocytes than in WT mouse splenocytes. IL-18Rα blockade in WT splenocytes attenuated cell proliferation and Th2 cytokine production. Moreover, STAT3 phosphorylation was reduced in IL-18Rα-/- mice, and SOCS3 and SOCS1 activation were diminished in IL-18Rα-/- intestinal T cells.ConclusionsIL-18Rα regulates allergic reactions and immune responses by regulating T cell responses in food allergies. Moreover, IL-18Rα is involved in the STAT/SOCS signaling pathways. Targeting IL-18Rα signaling might be a novel therapeutic strategy for food allergy.
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Project description:Driving nanomaterials to specific cell populations is still a major challenge for different biomedical applications. Several strategies to improve cell binding and uptake have been tried thus far by intrinsic material modifications or decoration with active molecules onto their surface. In the present work, we covalently bound the chemokine CXCL5 on fluorescently labeled amino-functionalized SiO2 nanoparticles to precisely targeting CXCR2+ immune cells. We synthesized and precisely characterized the physicochemical features of the modified particles. The presence of CXCL5 on the surface was detected by z-potential variation and CXCL5-specific electron microscopy immunogold labeling. CXCL5-amino SiO2 nanoparticle cell binding and internalization performances were analyzed in CXCR2+ THP-1 cells by flow cytometry and confocal microscopy. We showed improved internalization of the chemokine modified particles in the absence or the presence of serum. This internalization was reduced by cell pre-treatment with free CXCL5. Furthermore, we demonstrated CXCR2+ cell preferential targeting by comparing particle uptake in THP-1 vs. low-CXCR2 expressing HeLa cells. Our results provide the proof of principle that chemokine decorated nanomaterials enhance uptake and allow precise cell subset localization. The possibility to aim at selective chemokine receptor-expressing cells can be beneficial for the diverse pathological conditions involving immune reactions.
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Project description:Amyloid aggregates found in the brain of patients with neurodegenerative diseases, including Alzheimer's and Parkinson's disease, are thought to spread to increasingly larger areas of the brain through a prion-like seeding mechanism. Not much is known about which cell surface receptors may be involved in the cell-to-cell transfer, but proteoglycans are of interest due to their well-known propensity to interact with amyloid aggregates. In this study, we investigated the involvement of plasma membrane-bound heparan and chondroitin sulfate proteoglycans in cellular uptake of aggregates consisting of α-synuclein, a protein forming amyloid aggregates in Parkinson's disease. We show, using a pH-sensitive probe, that internalization of α-synuclein amyloid fibrils in neuroblastoma cells is dependent on heparan sulfate, whereas internalization of smaller non-amyloid oligomers is not. We also show that α-synuclein fibril uptake in an oligodendrocyte-like cell line is equally dependent on heparan sulfate, while astrocyte- and microglia-like cell lines have other means to internalize the fibrils. In addition, we analyzed the interaction between the α-synuclein amyloid fibrils and heparan sulfate and show that overall sulfation of the heparan sulfate chains is more important than sulfation at particular sites along the chains.
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