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1.  Novel Innate Immune Functions for Galectin-1: Galectin-1 Inhibits Cell Fusion by Nipah Virus Envelope Glycoproteins and Augments Dendritic Cell Secretion of Proinflammatory Cytokines1 
Galectin-1 (gal-1), an endogenous lectin secreted by a variety of cell types, has pleiotropic immunomodulatory functions, including regulation of lymphocyte survival and cytokine secretion in autoimmune, transplant disease, and parasitic infection models. However, the role of gal-1 in viral infections is unknown. Nipah virus (NiV) is an emerging pathogen that causes severe, often fatal, febrile encephalitis. The primary targets of NiV are endothelial cells. NiV infection of endothelial cells results in cell-cell fusion and syncytia formation triggered by the fusion (F) and attachment (G) envelope glycoproteins of NiV that bear glycan structures recognized by gal-1. In the present study, we report that NiV envelope-mediated cell-cell fusion is blocked by gal-1. This inhibition is specific to the Paramyxoviridae family because gal-1 did not inhibit fusion triggered by envelope glycoproteins of other viruses, including two retroviruses and a pox virus, but inhibited fusion triggered by envelope glycoproteins of the related Hendra virus and another paramyxovirus. The physiologic dimeric form of gal-1 is required for fusion inhibition because a monomeric gal-1 mutant had no inhibitory effect on cell fusion. gal-1 binds to specific N-glycans on NiV glycoproteins and aberrantly oligomerizes NiV-F and NiV-G, indicating a mechanism for fusion inhibition. gal-1 also increases dendritic cell production of proinflammatory cytokines such as IL-6, known to be protective in the setting of other viral diseases such as Ebola infections. Thus, gal-1 may have direct antiviral effects and may also augment the innate immune response against this emerging pathogen.
PMCID: PMC4428613  PMID: 15972675
2.  CD45 mediated fodrin cleavage during galectin-1 mediated T cell death promotes phagocytic clearance of dying cells 
Disassembly and phagocytic removal of dying cells is critical to maintain immune homeostasis. The factors regulating fragmentation and uptake of dying lymphocytes are not well understood. Degradation of fodrin, a cytoskeletal linker molecule that attaches CD45 to the actin cytoskeleton, has been described in apoptotic cells, although no specific initiator of fodrin degradation has been identified. CD45 is a glycoprotein receptor for galectin-1, an endogenous lectin that can trigger lymphocyte apoptosis. CD45 is not required for membrane changes or DNA degradation during galectin-1 death. However, here we show that fodrin degradation occurs during galectin-1 T cell death, and CD45 is essential for fodrin degradation to occur. In the absence of CD45 and fodrin degradation, cell death is not accompanied by membrane blebbing, indicating that fodrin degradation occurs via a distinct pathway compared to the pathway that initiates apoptotic membrane changes and DNA degradation. Moreover, there is slower phagocytic uptake of cells in which fodrin degradation is blocked relative to cells in which CD45-mediated fodrin degradation occurs. These studies identify a novel role for CD45 in regulating cellular disassembly and promoting phagocytic clearance during galectin-1 induced T cell death.
PMCID: PMC3541008  PMID: 19454697
3.  Structural aspects of binding of α-linked digalactosides to human galectin-1 
Glycobiology  2011;21(12):1627-1641.
By definition, adhesion/growth-regulatory galectins are known for their ability to bind β-galactosides such as Galβ(1 → 4)Glc (lactose). Indications for affinity of human galectin-1 to α-linked digalactosides pose questions on the interaction profile with such bound ligands and selection of the galactose moiety for CH–π stacking. These issues are resolved by a combination of 15N–1H heteronuclear single quantum coherence (HSQC) chemical shift and saturation transfer difference nuclear magnetic resonance (STD NMR) epitope mappings with docking analysis, using the α(1 → 3/4)-linked digalactosides and also Galα(1 → 6)Glc (melibiose) as test compounds. The experimental part revealed interaction with the canonical lectin site, and this preferentially via the non-reducing-end galactose moiety. Low-energy conformers appear to be selected without notable distortion, as shown by molecular dynamics simulations. With the α(1 → 4) disaccharide, however, the typical CH–π interaction is significantly diminished, yet binding appears to be partially compensated for by hydrogen bonding. Overall, these findings reveal that the type of α-linkage in digalactosides has an impact on maintaining CH–π interactions and the pattern of hydrogen bonding, explaining preference for the α(1 → 3) linkage. Thus, this lectin is able to accommodate both α- and β-linked galactosides at the same site, with major contacts to the non-reducing-end sugar unit.
PMCID: PMC3219418  PMID: 21712397
agglutinin; glycolipid; glycoprotein; lectin; sugar code
4.  High Throughput Screening for Compounds That Alter Muscle Cell Glycosylation Identifies New Role for N-Glycans in Regulating Sarcolemmal Protein Abundance and Laminin Binding* 
The Journal of Biological Chemistry  2012;287(27):22759-22770.
Background: Genetic alteration of muscle cell glycosylation in muscular dystrophy models has ameliorated disease.
Results: A high throughput screen identified a small molecule, lobeline, which altered muscle cell glycosylation and improved laminin binding.
Conclusion: Lobeline increased abundance of sarcolemmal glycoproteins and increased laminin binding in an N-glycan-dependent manner.
Significance: A novel approach revealed an unexpected role for N-glycans in muscle cell function.
Duchenne muscular dystrophy is an X-linked disorder characterized by loss of dystrophin, a cytoskeletal protein that connects the actin cytoskeleton in skeletal muscle cells to extracellular matrix. Dystrophin binds to the cytoplasmic domain of the transmembrane glycoprotein β-dystroglycan (β-DG), which associates with cell surface α-dystroglycan (α-DG) that binds laminin in the extracellular matrix. β-DG can also associate with utrophin, and this differential association correlates with specific glycosylation changes on α-DG. Genetic modification of α-DG glycosylation can promote utrophin binding and rescue dystrophic phenotypes in mouse dystrophy models. We used high throughput screening with the plant lectin Wisteria floribunda agglutinin (WFA) to identify compounds that altered muscle cell surface glycosylation, with the goal of finding compounds that increase abundance of α-DG and associated sarcolemmal glycoproteins, increase utrophin usage, and increase laminin binding. We identified one compound, lobeline, from the Prestwick library of Food and Drug Administration-approved compounds that fulfilled these criteria, increasing WFA binding to C2C12 cells and to primary muscle cells from wild type and mdx mice. WFA binding and enhancement by lobeline required complex N-glycans but not O-mannose glycans that bind laminin. However, inhibiting complex N-glycan processing reduced laminin binding to muscle cell glycoproteins, although O-mannosylation was intact. Glycan analysis demonstrated a general increase in N-glycans on lobeline-treated cells rather than specific alterations in cell surface glycosylation, consistent with increased abundance of multiple sarcolemmal glycoproteins. This demonstrates the feasibility of high throughput screening with plant lectins to identify compounds that alter muscle cell glycosylation and identifies a novel role for N-glycans in regulating muscle cell function.
PMCID: PMC3391114  PMID: 22570487
Glycobiology; Glycosylation Inhibitors; Laminin; Lectin; Muscular Dystrophy; Duchenne Muscular Dystrophy; N-Glycan; Dystroglycan; Lobeline; Muscle
5.  Suppression Of Autoimmune Diabetes By Soluble Galectin-1 
Type 1 diabetes (T1D) is a T-cell-mediated autoimmune disease that targets the β-cells of the pancreas. We investigated the ability of soluble galectin-1 (gal-1), an endogenous lectin that promotes T-cell apoptosis, to down-regulate the T-cell response that destroys the pancreatic β-cells. We demonstrated that in NOD mice, gal-1-therapy reduces significantly the amount of Th1 cells and augments the number of T-cells secreting IL-4 or IL-10 specific for islet cell-Ag, and causes peripheral deletion of β-cell-reactive T-cells. Administration of gal-1 prevented onset of hyperglycemia in NOD mice at early and sub-clinical stages of T1D. Preventive gal-1-therapy shifted the composition of the insulitis into an infiltrate that did not invade the islets, and that contained a significantly reduced number of Th1 cells and a higher percentage of CD4+ T-cells with content of IL-4, IL-5 or IL-10. The beneficial effects of gal-1 correlated with the ability of the lectin to trigger apoptosis of the T-cell subsets that cause β-cell damage, while sparing naïve T-cells, Th2 lymphocytes and regulatory T-cells in NOD mice. Importantly, gal-1 reversed β-cell autoimmunity in NOD mice with ongoing T1D, with reversal of hyperglycemia. Since gal-1-therapy did not cause major side effects or β-cell toxicity in NOD mice, the use of gal-1 to control β-cell autoimmunity represents a novel alternative for treatment of sub-clinical or ongoing T1D.
PMCID: PMC2929001  PMID: 19234158
Diabetes; Autoimmunity; Th1/Th2 cells
6.  Galectin-1 induces nuclear translocation of Endonuclease G in caspase- and cytochrome c-independent T cell death1 
Cell death and differentiation  2004;11(12):1277-1286.
Galectin-1, a mammalian lectin expressed in many tissues, induces death of diverse cell types, including lymphocytes and tumor cells. The galectin-1 T cell death pathway is novel and distinct from other death pathways, including those initiated by Fas and corticosteroids. We have found that galectin-1 binding to human T cell lines triggered rapid translocation of endonuclease G from mitochondria to nuclei. However, endonuclease G nuclear translocation occurred without cytochrome c release from mitochondria, without nuclear translocation of apoptosis inducing factor, and prior to loss of mitochondrial membrane potential. Galectin-1 treatment did not result in caspase activation, nor was death blocked by caspase inhibitors. However, galectin-1 cell death was inhibited by intracellular expression of galectin-3, and galectin-3 expression inhibited the eventual loss of mitochondrial membrane potential. Galectin-1 induced cell death proceeds via a caspase-independent pathway that involves a unique pattern of mitochondrial events, and different galectin family members can coordinately regulate susceptibility to cell death.
PMCID: PMC1201488  PMID: 15297883
galectin; apoptosis; T lymphocyte; Endonuclease G; human; phosphatidylserine (PS); z-Val-Ala-Asp(OMe)-CH2F (zVAD-fmk); z-Asp-Glu-Val-Asp(OMe)-CH2F (zDEVD-fmk); poly(ADP-ribose)polymerase (PARP); 7-amino-actinomycin D (7AAD); z-Asp-Glu-Val-Asp-7-amino-4-trifluoromethylcoumarin (zDEVD-AFC); mitochondrial membrane potential (Δψm); endonuclease G (EndoG); 10-N-nonyl acridine orange (NAO); Apoptosis inducing factor (AIF); truncated Bid (tBid); propidium iodide (PI); fluorescein isothiocyanate (FITC)
7.  θ Defensins Protect Cells from Infection by Herpes Simplex Virus by Inhibiting Viral Adhesion and Entry 
Journal of Virology  2004;78(10):5147-5156.
We tested the ability of 20 synthetic θ defensins to protect cells from infection by type 1 and type 2 herpes simplex viruses (HSV-1 and -2, respectively). The peptides included rhesus θ defensins (RTDs) 1 to 3, originally isolated from rhesus macaque leukocytes, and three peptides (retrocyclins 1 to 3) whose sequences were inferred from human θ-defensin (DEFT) pseudogenes. We also tested 14 retrocyclin analogues, including the retro, enantio, and retroenantio forms of retrocyclin 1. Retrocyclins 1 and 2 and RTD 3 protected cervical epithelial cells from infection by both HSV serotypes, but only retrocyclin 2 did so without causing cytotoxicity or requiring preincubation with the virus. Surface plasmon resonance studies revealed that retrocyclin 2 bound to immobilized HSV-2 glycoprotein B (gB2) with high affinity (Kd, 13.3 nM) and that it did not bind to enzymatically deglycosylated gB2. Temperature shift experiments indicated that retrocyclin 2 and human α defensins human neutrophil peptide 1 (HNP 1) to HNP 3 protected human cells from HSV-2 by different mechanisms. Retrocyclin 2 blocked viral attachment, and its addition during the binding or penetration phases of HSV-2 infection markedly diminished nuclear translocation of VP16 and expression of ICP4. In contrast, HNPs 1 to 3 had little effect on binding but reduced both VP16 transport and ICP4 expression if added during the postbinding (penetration) period. We recently reported that θ defensins are miniature lectins that bind gp120 of human immunodeficiency virus type 1 (HIV-1) with high affinity and inhibit the entry of R5 and X4 isolates of HIV-1. Given its small size (18 residues), minimal cytotoxicity, lack of activity against vaginal lactobacilli, and effectiveness against both HSV-2 and HIV-1, retrocyclin 2 provides an intriguing prototype for future topical microbicide development.
PMCID: PMC400355  PMID: 15113897

Results 1-7 (7)