Galectin-1 and HIV-1 Infection

Membrane organization by tetraspanins and galectins shapes lymphocyte function

Immune receptors are not randomly distributed at the plasma membrane of lymphocytes but are segregated into specialized domains that function as platforms to initiate signalling, as exemplified by the B cell or T cell receptor complex and the immunological synapse. 'Membrane-organizing proteins' and, in particular, tetraspanins and galectins, are crucial for controlling the spatiotemporal organization of immune receptors and other signalling proteins. Deficiencies in specific tetraspanins and galectins result in impaired immune synapse formation, lymphocyte proliferation, antibody production and migration, which can lead to impaired immunity, tumour development and autoimmunity. In contrast to conventional ligand-receptor interactions, membrane organizers interact in cis (on the same cell) and modulate receptor clustering, receptor dynamics and intracellular signalling. New findings have uncovered their complex and dynamic nature, revealing shared binding partners and collaborative activity in determining the composition of membrane domains. Therefore, immune receptors should not be envisaged as independent entities and instead should be studied in the context of their spatial organization in the lymphocyte membrane. We advocate for a novel approach to study lymphocyte function by globally analysing the role of membrane organizers in the assembly of different membrane complexes and discuss opportunities to develop therapeutic approaches that act via the modulation of membrane organization.

O-glycan structures in apo(a) subunit of human lipoprotein(a) suppresses the pro-angiogenic activity of galectin-1 on human umbilical vein endothelial cells

Apolipoprotein(a) [apo(a)] is a highly polymorphic O-glycoprotein circulating in human plasma as lipoprotein(a) [Lp(a)]. The O-glycan structures of apo(a) subunit of Lp(a) serve as strong ligands of galectin-1, an O-glycan binding pro-angiogenic lectin abundantly expressed in placental vascular tissues. But the pathophysiological significance of apo(a)-galectin-1 binding is not yet been revealed. Carbohydrate-dependent binding of galectin-1 to another O-glycoprotein, neuropilin-1 (NRP-1) on endothelial cells activates vascular endothelial growth factor receptor 2 (VEGFR2) and mitogen-activated protein kinase (MAPK) signaling. Using apo(a), isolated from human plasma, we demonstrated the potential of the O-glycan structures of apo(a) in Lp(a) to inhibit angiogenic properties such as proliferation, migration, and tube-formation in human umbilical vein endothelial cells (HUVECs) as well as neovascularization in chick chorioallantoic membrane. Further, in vitro protein-protein interaction studies have confirmed apo(a) as a superior ligand to NRP-1 for galectin-1 binding. We also demonstrated that the protein levels of galectin-1, NRP-1, VEGFR2, and downstream proteins in MAPK signaling were reduced in HUVECs in the presence of apo(a) with intact O-glycan structures compared to that of de-O-glycosylated apo(a). In conclusion, our study shows that apo(a)-linked O-glycans prevent the binding of galectin-1 to NRP-1 leading to the inhibition of galectin-1/neuropilin-1/VEGFR2/MAPK-mediated angiogenic signaling pathway in endothelial cells. As higher plasma Lp(a) level in women is an independent risk factor for pre-eclamsia, a pregnancy-associated vascular complication, we propose that apo(a) O-glycans-mediated inhibition of the pro-angiogenic activity of galectin-1 may be one of the underlying molecular mechanism of pathogenesis of Lp(a) in pre-eclampsia.

GPI-anchored ligand-BioID2-tagging system identifies Galectin-1 mediating Zika virus entry

Identification of host factors facilitating pathogen entry is critical for preventing infectious diseases. Here, we report a tagging system consisting of a viral receptor-binding protein (RBP) linked to BioID2, which is expressed on the cell surface via a GPI anchor. Using VSV or Zika virus (ZIKV) RBP, the system (BioID2- RBP(V)-GPI; BioID2-RBP(Z)-GPI) faithfully identifies LDLR and AXL, the receptors of VSV and ZIKV, respectively. Being GPI-anchored is essential for the probe to function properly. Furthermore, BioID2-RBP(Z)-GPI expressed in human neuronal progenitor cells identifies galectin-1 on cell surface pivotal for ZIKV entry. This conclusion is further supported by antibody blocking and galectin-1 silencing in A549 and mouse neural cells. Importantly, Lgals1^−/− mice are significantly more resistant to ZIKV infection than Lgals1^+/+ littermates are, having significantly lower virus titers and fewer pathologies in various organs. This tagging system may have broad applications for identifying protein-protein interactions on the cell surface.

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A tagging system for identifying ligand-receptor interactions is developed

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Receptor binding domain determines the specificity of the system

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Being GPI-anchored is pivotal for the tagging system to function properly

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Galectin-1 is identified as an entry factor essential for ZIKV infection

An updated patent review of galectin-1 and galectin-3 inhibitors and their potential therapeutic applications (2016-present)

INTRODUCTION

Galectins are ubiquitous in nature. They have established themselves as a protein family of high therapeutic potential and play a role in a wide variety of diseases like cancer, fibrosis, and Alzheimer's. Within the galectin family, galectin- 1 and galectin- 3 have been widely studied and their roles and functions have now been well established.

AREAS COVERED

In this review, we discuss the important advancements in the development of galectin-1 & 3 inhibitors. All patents filed detailing the divergent strategies to inhibit galectin-1 & 3 from 2016 to present have been covered and discussed.

EXPERT OPINION

Over the past couple of decades, distinct galectin inhibitors have been synthesized, reported and studied. Among all, the mono and disaccharide-based antagonists have been found to be considerably successful. However, the cumbersome synthetic route followed to develop this class of inhibitors, in addition to complexity involved in making selective modifications within these molecules has posed a significant challenge. Recently, there have been numerous reports on heterocyclic-based galectin inhibitors. If these are established as potent galectin inhibitors, their ease of synthesis and tunability could overcome the potential drawbacks of carbohydrate-based inhibitors and could thus be exploited to develop efficient and highly specific galectin inhibitors.

Andrographis paniculata (Burm. f.) Wall. ex Nees: An Updated Review of Phytochemistry, Antimicrobial Pharmacology, and Clinical Safety and Efficacy

Infectious disease (ID) is one of the top-most serious threats to human health globally, further aggravated by antimicrobial resistance and lack of novel immunization options. Andrographis paniculata (Burm. f.) Wall. ex Nees and its metabolites have been long used to treat IDs. Andrographolide, derived from A. paniculata, can inhibit invasive microbes virulence factors and regulate the host immunity. Controlled clinical trials revealed that A. paniculata treatment is safe and efficacious for acute respiratory tract infections like common cold and sinusitis. Hence, A. paniculata, mainly andrographolide, could be considered as an excellent candidate for antimicrobial drug development. Considering the importance, medicinal values, and significant role as antimicrobial agents, this study critically evaluated the antimicrobial therapeutic potency of A. paniculata and its metabolites, focusing on the mechanism of action in inhibiting invasive microbes and biofilm formation. A critical evaluation of the secondary metabolites with the aim of identifying pure compounds that possess antimicrobial functions has further added significant values to this study. Notwithstanding that A. paniculata is a promising source of antimicrobial agents and safe treatment for IDs, further empirical research is warranted.

Sugar Codes Conjugated Alginate: An Innovative Platform to Make a Strategic Breakthrough in Simultaneous Prophylaxis of GERD and Helicobacter pylori Infection

INTRODUCTION

Currently, gastroesophageal reflux disease (GERD) is one of the most ubiquitous problems in clinical practice. An antacid-alginate combination (under the trade name Gaviscon) is a natural-based product that effectively suppresses GERD. This product acts via the formation of viscous gel that floats on the top of the gastric content. On the other hand, efficient management of Helicobacter pylori infection with minimal side effects is an important goal for gastroenterologists. Furthermore, some H. pylori-positive patients suffer from GERD.

METHODS

Here, we present the results of investigations on alginate conjugated to sugar codes in order to find initial clues regarding the potential ability of this conjugate in the simultaneous prophylaxis of GERD and H. pylori infection in an in vitro assay.

RESULTS

It is noteworthy that our results reveal that sugar codes conjugated alginate considerably decrease (approximately 74%) the adhesion of H. pylori to gastric epithelial cells in vitro. Moreover, surprisingly after conjugation of sugar codes, alginate can maintain its ability to create gel. Our results demonstrate that alginate conjugated to sugar codes is not cytotoxic.

CONCLUSION

The preparation of these conjugates can be regarded as the first step to establish a new roadmap for the simultaneous prevention of GERD and H. pylori infection in future studies on in vivo models.

Human Galectin-1 and Its Inhibitors: Privileged Target for Cancer and HIV

Galectin 1(Gal-1), a β-galactoside binding mammalian lectin of 14KDa, is implicated in many signalling pathways, immune responses associated with cancer progression and immune disorders. Inhibition of human Gal-1 has been regarded as one of the potential therapeutic approaches for the treatment of cancer, as it plays a major role in tumour development and metastasis by modulating various biological functions viz. apoptosis, angiogenesis, migration, cell immune escape. Gal-1 is considered as a biomarker in diagnosis, prognosis and treatment condition. The overexpression of Gal-1 is well established and seen in many types of cancer progression like osteosarcoma, breast, lung, prostate, melanoma, etc. Gal-1 greatly accelerates the binding kinetics of HIV-1 to susceptible cells, leading to faster viral entry and a more robust viral replication by specific binding of CD4 cells. Hence, the Gal-1 is considered a promising molecular target for the development of new therapeutic drugs for cancer and HIV. The present review laid emphasis on structural insights and functional role of Gal-1 in the disease, current Gal-1 inhibitors and future prospects in the design of specific Gal-1 inhibitors.

Gal-1 regulates dendritic cells-induced Treg/Th17 balance though NF-κB/RelB-IL-27 pathway

Background

This study aimed to investigate the mechanism of galectin (Gal)-1 of regulating Treg/Th17 in pathogenesis of acute rejection after liver transplantation in rat.

Methods

Mononuclear cells were induced to immature dendritic cells (imDCs), which were transfected with or without NF-κB/RelB. Western Blot was performed to detect the expression of NF-κB/RelB. the expression of CD11c, CD45RB, CD80 and MHC II were detected by flow cytometry. Enzyme-linked immunosorbent assay (ELISA) was employed to detect cytokines IL-27 and TGF-β. Lewis and dark agouti (DA) rats were generally anaesthetized by isoflurane inhalation to establish liver transplant models.

Results

We demonstrate that Gal-1 disturbs maturation of imDCs by downregulating NF-κB/RelB expression, and Gal-1 negatively controls CD4⁺ proliferation though IL-27 pathway.

Conclusions

In aggregate, Gal-1 promotes Treg differentiation in CD4⁺ T cells though NF-κB/RelB-IL-27 pathway. These findings suggest a new therapeutic target to mediate Treg population.

Galectin-1 interacts with the human endogenous retroviral envelope protein syncytin-2 and potentiates trophoblast fusion in humans

Syncytin (Syn)-2 is an important fusogenic protein that contributes to the formation of the placental syncytiotrophoblast. Galectin (Gal)-1, a soluble lectin, is also involved in trophoblast cell fusion and modulates the interaction of certain retroviral envelopes with their cellular receptor. This study aimed to investigate the association between Syn-2 and Gal-1 during human trophoblast cell fusion. This association was evaluated in vitro on primary villous cytotrophoblasts (vCTBs) and cell lines using recombinant Gal-1 and Syn-2-pseudotyped viruses. Using lactose, a Gal antagonist, and Gal-1-specific small interfering RNA (siRNA) transfections, we confirmed the implication of Gal-1 in vCTBs and BeWo cell fusion, although RT-PCR and ELISA analyses suggested that Gal-1 alone did not induce syncytialization. Infection assays showed a specific and significant effect of Gal-1 on the infectivity of Syn-2-pseudotyped viruses that depended on the expression of major facilitator superfamily domain-containing 2A (MFSD2a). Moreover, Gal-3, another placental Gal, did not modulate the infectivity of Syn-2-positive viruses, strengthening the specific association between Gal-1 and Syn-2. Interestingly, Gal-1 significantly reduced the infectivity of Syn-1-pseudotyped viruses, suggesting the opposite effects of Gal-1 on Syn-1 and -2. Finally, coimmunoprecipitation experiments showed a glycan-dependent interaction between Syn-2-bearing virions and Gal-1. We conclude that Gal-1 specifically interacts with Syn-2 and possibly regulates Syn-2/MFSD2a interaction during syncytialization of trophoblastic cells.-Toudic, C., Vargas, A., Xiao, Y., St-Pierre, G., Bannert, N., Lafond, J., Rassart, É., Sato, S., Barbeau, B. Galectin-1 interacts with the human endogenous retroviral envelope protein syncytin-2 and potentiates trophoblast fusion in humans.

Delayed Galectin-3-Mediated Reprogramming of Microglia After Stroke is Protective

Galectin-3 (Gal-3), a β-galactoside-binding lectin, has recently emerged as a molecule with immunoregulatory functions. We investigated the effects of Gal-3 on microglia morphology, migration, and secretory profile under physiological conditions and in the context of ischemic injury. We show that in the control conditions, exposure to recombinant Gal-3 increases microglial ramification and motility in vitro and in vivo via an IL-4-dependent mechanism. Importantly, after stroke, Gal-3 exerted marked immune-modulatory properties. Delivery of Gal-3 at 24 h after middle cerebral artery occlusion (MCAO) was associated with an increase in Ym1-positive microglia and decrease in iNOS. Analysis of cytokine profiles at the protein level revealed downregulation of pro-inflammatory cytokines and a marked upregulation of the anti-inflammatory cytokine, IL-4, 24 h after i.c.v. injection of Gal-3. Importantly, the observed shift in cytokines in microglia was associated with a significant decrease in the infarct size. Taken together, our results suggest that when delivered well after ischemic injury, Gal-3 might fine tune innate immunity and induce a therapeutic shift in microglia polarization.

Galectin-3 and N-acetylglucosamine promote myogenesis and improve skeletal muscle function in the mdx model of Duchenne muscular dystrophy

The muscle membrane, sarcolemma, must be firmly attached to the basal lamina. The failure of proper attachment results in muscle injury, which is the underlying cause of Duchenne muscular dystrophy (DMD), in which mutations in the dystrophin gene disrupts the firm adhesion. In patients with DMD, even moderate contraction causes damage, leading to progressive muscle degeneration. The damaged muscles are repaired through myogenesis. Consequently, myogenesis is highly active in patients with DMD, and the repeated activation of myogenesis leads to the exhaustion of the myogenic stem cells. Therefore, approaches to reducing the risk of the exhaustion are to develop a treatment that strengthens the interaction between the sarcolemma and the basal lamina and increases the efficiency of the myogenesis. Galectin-3 is an oligosaccharide-binding protein and is known to be involved in cell-cell interactions and cell-matrix interactions. Galectin-3 is expressed in myoblasts and skeletal muscle, although its function in muscle remains elusive. In this study, we found evidence that galectin-3 and the monosaccharide N-acetylglucosamine, which increases the synthesis of binding partners (oligosaccharides) of galectin-3, promote myogenesis in vitro. Moreover, in the mdx mouse model of DMD, treatment with N-acetylglucosamine increased muscle-force production. The results suggest that treatment with N-acetylglucosamine might mitigate the burden of DMD.-Rancourt, A., Dufresne, S. S., St-Pierre, G., Lévesque, J.-C., Nakamura, H., Kikuchi, Y., Satoh, M. S., Frenette, J., Sato, S. Galectin-3 and N-acetylglucosamine promote myogenesis and improve skeletal muscle function in the mdx model of Duchenne muscular dystrophy.

Multivalent effect of glycopolypeptide based nanoparticles for galectin binding

Synthetic glycopolypeptides are versatile glycopolymers used to conceive bioinspired nanoassemblies. In this work, novel amphiphilic glycopolypeptides were designed to incorporate lactose or galactan in order to prepare polymeric nanoassemblies with sizes below 50 nm. The bioactivity of the two different outer surface sugar units was evaluated by defining glycan relative binding affinities to human galectins 1 and 3. A specific multivalent effect was found only for polymeric nanoparticles displaying galactan with a significant increase of the binding activity as compared to free glycan in solution. Such synthetic designs present great potential as therapeutic tools to address galectin related pathologies.

Exosomes Derived from HIV-1 Infected DCs Mediate Viral trans-Infection via Fibronectin and Galectin-3

Exosomes are membrane enclosed nano-sized vesicles actively released into the extracellular milieu that can harbor genomic, proteomic and lipid cargos. Functionally, they are shown to regulate cell-cell communication and transmission of pathogens. Though studies have implicated a role for exosomes in HIV-1 pathogenesis, their mechanisms are not well defined. Here, we characterized exosomes derived from uninfected or HIV-1 infected T-cells and DCs. We demonstrate substantial differences in morphological, molecular and biogenesis machinery between exosomes derived from these two immune cell types. In addition, exosomes derived from HIV-1 infected DCs were 4 fold more infective than either cell free HIV-1 or exosomes derived from T-cells. Molecular analysis of exosomes detected the presence of fibronectin and galectin-3 in those derived from DCs, whereas T-cell exosomes lacked these molecules. Addition of anti-fibronectin antibody and β-lactose, a galectin-3 antagonist, significantly blocked DC exosome-mediated HIV-1 infection of T-cells. We also observed increased gene expression of the pro-inflammatory cytokines IFN-γ, TNF-α, IL-1β and RANTES and activation of p38/Stat pathways in T-cells exposed to exosomes derived from HIV-1 infected DCs. Our study provides insight into the role of exosomes in HIV pathogenesis and suggests they can be a target in development of novel therapeutic strategies against viral infection.

Characterization of galectin-1 from Chinese giant salamanders Andrias davidianus and its involvements during immune response

Galectins are considered as a multifunctional protein which play essential roles in cell adhesion and apoptosis, inflammation, tumor progression and immune response. In spite of extensive studies of galectin importance in immune system among different animals, few studies have been devoted to their functions in amphibian. In the present study, we characterized one proto type of galectin (named AdGal1) from Chinese giant salamander Andrias davidianus and studied its function in immune response. AdGal1 cDNA possesses an open reading frame of 598 bp, which encodes a putative galectin of 134 amino acids containing one carbohydrate recognition domains (CRDs). The constitutive expression of mRNA transcripts was detected in a wide range of tissues, with the highest expression in kidney. Immune challenges with Aeromonas hydrophila and Chinese giant salamander iridovirus (GSIV), the transcript level of AdGal1 in kidney was significantly upregulated. The mature protein of AdGal1 was successfully expressed and purified in Escherichia coli BL21 (DE3). The recombinant AdGal1 (rAdGal1) could show bind activity to different Gram negative and Gram positive bacteria. It could also strongly agglutinate different kinds of bacteria at different concentrations. Collectively, these data from the present study indicate that AdGal1 is a vital pattern recognition receptor to recognize different microbes in the innate immune system of Andrias davidianus.

Trichomonas vaginalis Lipophosphoglycan Exploits Binding to Galectin-1 and -3 to Modulate Epithelial Immunity

Trichomoniasis is the most common non-viral sexually transmitted infection caused by the vaginotropic extracellular protozoan parasite Trichomonas vaginalis. The infection is recurrent, with no lasting immunity, often asymptomatic, and linked to pregnancy complications and risk of viral infection. The molecular mechanisms of immune evasion by the parasite are poorly understood. We demonstrate that galectin-1 and -3 are expressed by the human cervical and vaginal epithelial cells and act as pathogen-recognition receptors for the ceramide phosphoinositol glycan core (CPI-GC) of the dominant surface protozoan lipophosphoglycan (LPG). We used an in vitro model with siRNA galectin knockdown epithelial clones, recombinant galectins, clinical Trichomonas isolates, and mutant protozoan derivatives to dissect the function of galectin-1 and -3 in the context of Trichomonas infection. Galectin-1 suppressed chemokines that facilitate recruitment of phagocytes, which can eliminate extracellular protozoa (IL-8) or bridge innate to adaptive immunity (MIP-3α and RANTES (regulated on activation normal T cell expressed and secreted)). Silencing galectin-1 increased and adding exogenous galectin-1 suppressed chemokine responses to Trichomonas or CPI-GC/LPG. In contrast, silencing galectin-3 reduced IL-8 response to LPG. Live Trichomonas depleted the extracellular levels of galectin-3. Clinical isolates and mutant Trichomonas CPI-GC that had reduced affinity to galectin-3 but maintained affinity to galectin-1 suppressed chemokine expression. Thus via CPI-GC binding, Trichomonas is capable of regulating galectin bioavailability and function to the benefit of its parasitic survival. These findings suggest novel approaches to control trichomoniasis and warrant further studies of galectin-binding diversity among clinical isolates as a possible source for symptom disparity in parasitic infections.

Enterovirus 71 virion-associated galectin-1 facilitates viral replication and stability

Enterovirus 71 (EV71) infection causes a myriad of diseases from mild hand-foot-and-mouth disease or herpangina to fatal brain stem encephalitis complicated with pulmonary edema. Several severe EV71 endemics have occurred in Asia-Pacific region, including Taiwan, and have become a serious threat to children’s health. EV71 infection is initiated by the attachment of the virion to the target cell surface. Although this process relies primarily upon interaction between viruses and cell surface receptors, soluble factors may also influence the binding of EV71 to host cells.Galectin-1 has been reported to participate in several virus infections, but is not addressed in EV71. In this study, we found that the serum levels of galectin-1 in EV71-infected children were higher than those in non-infected people. In EV71 infected cells, galectin-1 was found to be associated with the EV71 VP1 and VP3 via carbohydrate residues and subsequently released and bound to another cell surface along with the virus. EV71 propagated from galectin-1 knockdown SK-N-SH cells exhibited lower infectivity in cultured cells and less pathogenicity in mice than the virus propagated from parental cells. In addition, this galectin-1-free EV71 virus was sensitive to high temperature and lost its viability after long-term storage, which could be restored following supplement of recombinant galectin-1. Taken together, our findings uncover a new role of galectin-1 in facilitating EV71 virus infection.

The roles of direct recognition by animal lectins in antiviral immunity and viral pathogenesis

Lectins are a group of proteins with carbohydrate recognition activity. Lectins are categorized into many families based on their different cellular locations as well as their specificities for a variety of carbohydrate structures due to the features of their carbohydrate recognition domain (CRD) modules. Many studies have indicated that the direct recognition of particular oligosaccharides on viral components by lectins is important for interactions between hosts and viruses. Herein, we aim to globally review the roles of this recognition by animal lectins in antiviral immune responses and viral pathogenesis. The different classes of mammalian lectins can either recognize carbohydrates to activate host immunity for viral elimination or can exploit those carbohydrates as susceptibility factors to facilitate viral entry, replication or assembly. Additionally, some arthropod C-type lectins were recently identified as key susceptibility factors that directly interact with multiple viruses and then facilitate infection. Summarization of the pleiotropic roles of direct viral recognition by animal lectins will benefit our understanding of host-virus interactions and could provide insight into the role of lectins in antiviral drug and vaccine development.

Effect of galectins on viral transmission

Recent reports suggest that some galectins bind to enveloped viruses. They include influenza virus, human immunodeficiency virus-1 (HIV-1), human T-cell leukemia virus-1 (HTLV-1), and Nipah virus. It is also suggested that the interaction between viruses and galectins influences viral attachment to their susceptible cells, affecting the viral infectivity. Our work suggests that galectin-1 increases the infectivity of HIV-1 and HTVL-1. Indeed, galectin-1 promotes the initial adsorption of HIV-1 to CD4(+) cells through its binding to viral envelope gp120 and facilitates HIV-1 infection in a manner that is dependent on its recognition of β-galactoside residues. Thus, as galectin-1 can be considered as a pattern recognition receptor, HIV-1 exploits this host factor to promote its transmission or replication. In this chapter, we describe methods used to investigate this potential role of galectins in HIV-1 infection as a case in point for future studies on galectin-virus interactions.

Affinofile profiling: how efficiency of CD4/CCR5 usage impacts the biological and pathogenic phenotype of HIV

HIV-1 envelope (Env) uses CD4 and a coreceptor (CCR5 and/or CXCR4) for viral entry. The efficiency of receptor/coreceptor mediated entry has important implications for HIV pathogenesis and transmission. The advent of CCR5 inhibitors in clinical use also underscores the need for quantitative and predictive tools that can guide therapeutic management. Historically, measuring the efficiency of CD4/CCR5 mediated HIV entry has relied on surrogate and relatively slow throughput assays that cannot adequately capture the full spectrum of Env phenotypes. In this review, we discuss the details of the Affinofile receptor affinity profiling system that has provided a quantitative and higher throughput method to characterize viral entry efficiency as a function of CD4 and CCR5 expression levels. We will then review how the Affinofile system has been used to reveal the distinct pathophysiological properties associated with Env entry phenotypes and discuss potential shortcomings of the current system.

Nanoparticle based galectin-1 gene silencing, implications in methamphetamine regulation of HIV-1 infection in monocyte derived macrophages

Galectin-1, an adhesion molecule, is expressed in macrophages and implicated in human immunodeficiency virus (HIV-1) viral adsorption. In this study, we investigated the effects of methamphetamine on galectin-1 production in human monocyte derived macrophages (MDM) and the role of galectin-1 in methamphetamine potentiation of HIV-1 infection. Herein we show that levels of galectin-1 gene and protein expression are significantly increased by methamphetamine. Furthermore, concomitant incubation of MDM with galectin-1 and methamphetamine facilitates HIV-1 infection compared to galectin-1 alone or methamphetamine alone. We utilized a nanotechnology approach that uses gold nanorod (GNR)-galectin-1 siRNA complexes (nanoplexes) to inhibit gene expression for galectin-1. Nanoplexes significantly silenced gene expression for galectin-1 and reversed the effects of methamphetamine on galectin-1 gene expression. Moreover, the effects of methamphetamine on HIV-1 infection were attenuated in the presence of the nanoplex in MDM.

Biochemical and biologic characterization of exosomes and microvesicles as facilitators of HIV-1 infection in macrophages

Exosomes and microvesicles (MV) are cell membranous sacs originating from multivesicular bodies and plasma membranes that facilitate long-distance intercellular communications. Their functional biology, however, remains incompletely understood. Macrophage exosomes and MV isolated by immunoaffinity and sucrose cushion centrifugation were characterized by morphologic, biochemical, and molecular assays. Lipidomic, proteomic, and cell biologic approaches uncovered novel processes by which exosomes and MV facilitate HIV-1 infection and dissemination. HIV-1 was "entrapped" in exosome aggregates. Robust HIV-1 replication followed infection with exosome-enhanced fractions isolated from infected cell supernatants. MV- and exosome-facilitated viral infections are affected by a range of cell surface receptors and adhesion proteins. HIV-1 containing exosomes readily completed its life cycle in human monocyte-derived macrophages but not in CD4(-) cells. The data support a significant role for exosomes as facilitators of viral infection.

Hepatitis C virus attachment mediated by apolipoprotein E binding to cell surface heparan sulfate

Viruses are known to use virally encoded envelope proteins for cell attachment, which is the very first step of virus infection. In the present study, we have obtained substantial evidence demonstrating that hepatitis C virus (HCV) uses the cellular protein apolipoprotein E (apoE) for its attachment to cells. An apoE-specific monoclonal antibody was able to efficiently block HCV attachment to the hepatoma cell line Huh-7.5 as well as primary human hepatocytes. After HCV bound to cells, however, anti-apoE antibody was unable to inhibit virus infection. Conversely, the HCV E2-specific monoclonal antibody CBH5 did not affect HCV attachment but potently inhibited HCV entry. Similarly, small interfering RNA-mediated knockdown of the key HCV receptor/coreceptor molecules CD81, claudin-1, low-density lipoprotein receptor (LDLr), occludin, and SR-BI did not affect HCV attachment but efficiently suppressed HCV infection, suggesting their important roles in HCV infection at postattachment steps. Strikingly, removal of heparan sulfate from the cell surface by treatment with heparinase blocked HCV attachment. Likewise, substitutions of the positively charged amino acids with neutral or negatively charged residues in the receptor-binding region of apoE resulted in a reduction of apoE-mediating HCV infection. More importantly, mutations of the arginine and lysine to alanine or glutamic acid in the receptor-binding region ablated the heparin-binding activity of apoE, as determined by an in vitro heparin pulldown assay. HCV attachment could also be inhibited by a synthetic peptide derived from the apoE receptor-binding region. Collectively, these findings demonstrate that apoE mediates HCV attachment through specific interactions with cell surface heparan sulfate.

Morphine and galectin-1 modulate HIV-1 infection of human monocyte-derived macrophages

Morphine is a widely abused, addictive drug that modulates immune function. Macrophages are a primary reservoir of HIV-1; therefore, they play a role in the development of this disease, as well as impact the overall course of disease progression. Galectin-1 is a member of a family of β-galactoside-binding lectins that are soluble adhesion molecules and that mediate direct cell-pathogen interactions during HIV-1 viral adhesion. Because the drug abuse epidemic and the HIV-1 epidemic are closely interrelated, we propose that increased expression of galectin-1 induced by morphine may modulate HIV-1 infection of human monocyte-derived macrophages (MDMs). In this article, we show that galectin-1 gene and protein expression are potentiated by incubation with morphine. Confirming previous studies, morphine alone or galectin-1 alone enhance HIV-1 infection of MDMs. Concomitant incubation with exogenous galectin-1 and morphine potentiated HIV-1 infection of MDMs. We used a nanotechnology approach that uses gold nanorod-galectin-1 small interfering RNA complexes (nanoplexes) to inhibit gene expression for galectin-1. We found that nanoplexes silenced gene expression for galectin-1, and they reversed the effects of morphine on galectin-1 expression. Furthermore, the effects of morphine on HIV-1 infection were reduced in the presence of the nanoplex.

Galectin-1-specific inhibitors as a new class of compounds to treat HIV-1 infection

Despite significant improvements, antiretroviral therapies against HIV-1 are plagued by a high frequency of therapeutic failures that have been associated with acquisition of drug resistance. We recently reported that HIV-1 exploits a host glycan binding protein, galectin-1, to increase its attachment to host cells, thereby increasing its overall infectivity in susceptible cells. This finding suggests that host molecules such as galectin-1 could reduce the expected efficiency of HIV-1 drugs targeting early steps of the replicative cycle, such as attachment and entry processes. Thus, new classes of drugs that would interfere with galectin-1/HIV-1 interactions could benefit the current antiretroviral therapy. To further explore this possibility, experiments were conducted to discover leading compounds showing specific inhibition of galectin-1 activity in a cellular model of HIV-1 infection. Three lactoside compounds were found to modestly inhibit the interaction of galectin-1 with primary human CD4(+) T cells. Interestingly, these same inhibitors reduced the galectin-1-mediated increase in HIV-1 attachment to target cells in a much more efficient manner. More important, the tested lactoside derivatives also significantly decreased the galectin-1-dependent enhancement of HIV-1 infection. These observations deserve further attention when considering that the development of new drugs to prevent and treat HIV-1 infection remains a priority.

Host-soluble galectin-1 promotes HIV-1 replication through a direct interaction with glycans of viral gp120 and host CD4

Sexual transmission of HIV-1 requires virus adsorption to a target cell, typically a CD4(+) T lymphocyte residing in the lamina propria, beneath the epithelium. To escape the mucosal clearance system and reach its target cells, HIV-1 has evolved strategies to circumvent deleterious host factors. Galectin-1, a soluble lectin found in the underlayers of the epithelium, increases HIV-1 infectivity by accelerating its binding to susceptible cells. By comparison, galectin-3, a family member expressed by epithelial cells and part of the mucosal clearance system, does not perform similarly. We show here that galectin-1 directly binds to HIV-1 in a β-galactoside-dependent fashion through recognition of clusters of N-linked glycans on the viral envelope gp120. Unexpectedly, this preferential binding of galectin-1 does not rely on the primary sequence of any particular glycans. Instead, glycan clustering arising from the tertiary structure of gp120 hinders its binding by galectin-3. Increased polyvalency of a specific ligand epitope is a common strategy for glycans to increase their avidity for lectins. In this peculiar occurrence, glycan clustering is instead exploited to prevent binding of gp120 by galectin-3, which would lead to a biological dead-end for the virus. Our data also suggest that galectin-1 binds preferentially to CD4, the host receptor for gp120. Together, these results suggest that HIV-1 exploits galectin-1 to enhance gp120-CD4 interactions, thereby promoting virus attachment and infection events. Since viral adhesion is a rate-limiting step for HIV-1 entry, modulation of the gp120 interaction with galectin-1 could thus represent a novel approach for the prevention of HIV-1 transmission.

Viral induction and targeted inhibition of galectin-1 in EBV+ posttransplant lymphoproliferative disorders

Posttransplant lymphoproliferative disorders (PTLDs) are potentially fatal, EBV-driven B-cell malignancies that develop in immunocompromised solid organ or hematopoietic stem cell recipients. In PTLD, the expression of EBV proteins, including latent membrane protein 1 (LMP1) and LMP2A, viral immune evasion strategies, and impaired host immune surveillance foster the proliferation of EBV-transformed B cells. Current PTLD treatment strategies include reduction of immunosuppression, which increases the risk of graft rejection, anti-CD20 treatment, combination chemotherapy, and administration of EBV-specific cytotoxic T cells. In the present study, we report that EBV-transformed lymphoblastoid B-cell lines (LCLs) and primary PTLDs overexpress galectin-1 (Gal1), a carbohydrate-binding lectin that induces tolerogenic dendritic cells and triggers the selective apoptosis of CD4(+) Th1 and Th17 cells and cytotoxic T cells. In transcriptional reporter assays, LMP2A and LMP1 each increased Gal1-driven luciferase expression, and the combination of LMP2A and LMP1 was additive. In addition, small interfering RNA (siRNA)-mediated depletion of LMP2A decreased Gal1 protein abundance in EBV-transformed LCLs. Gal1 expression in LCLs was dependent on both activating protein 1 (AP-1) and PI3K. A newly developed neutralizing Gal1 mAb selectively inhibited Gal1-mediated apoptosis of EBV-specific CD8(+) T cells. Given the tolerogenic and immunosuppressive function of Gal1, antibody-mediated Gal1 neutralization may represent a novel immunotherapeutic strategy for PTLD and other Gal1-expressing tumors.