6-o- and N-sulfated syndecan-1 promotes baculovirus binding and entry into Mammalian cells

The underlying mechanisms of arenaviral entry through matriglycan

Matriglycan, a recently characterized linear polysaccharide, is composed of alternating xylose and glucuronic acid subunits bound to the ubiquitously expressed protein α-dystroglycan (α-DG). Pathogenic arenaviruses, like the Lassa virus (LASV), hijack this long linear polysaccharide to gain cellular entry. Until recently, it was unclear through what mechanisms LASV engages its matriglycan receptor to initiate infection. Additionally, how matriglycan is synthesized onto α-DG by the Golgi-resident glycosyltransferase LARGE1 remained enigmatic. Recent structural data for LARGE1 and for the LASV spike complex informs us about the synthesis of matriglycan as well as its usage as an entry receptor by arenaviruses. In this review, we discuss structural insights into the system of matriglycan generation and eventual recognition by pathogenic viruses. We also highlight the unique usage of matriglycan as a high-affinity host receptor compared with other polysaccharides that decorate cells.

The role of glycosylation patterns of viral glycoproteins and cell entry receptors in arenavirus infection

Mammarenaviruses are enveloped RNA viruses that can be associated with rodent-transmitted diseases in humans. Their virions are composed of a nucleocapsid surrounded by a lipid bilayer with glycoprotein (GP) spikes interacting with receptors on target cells. Both the GP and receptors are highly glycosylated, with glycosylation patterns being crucial for virus binding and cell entry, viral tropism, immune responses, or therapy strategies. These effects have been previously described for several different viruses. In case of arenaviruses, they remain insufficiently understood. Thus, it is important to determine the mechanisms of glycosylation of viral proteins and receptors responsible for infection, in order to fully understand the biology of arenaviruses. In this article, we have summarized and critically evaluated the available literature data on the glycosylation of mammarenavirus-associated proteins to facilitate further research in this field.

Evaluation of Baculoviruses as Gene Therapy Vectors for Brain Cancer

We aimed to assess the potential of baculoviral vectors (BV) for brain cancer gene therapy. We compared them with adenoviral vectors (AdV), which are used in neuro-oncology, but for which there is pre-existing immunity. We constructed BVs and AdVs encoding fluorescent reporter proteins and evaluated their transduction efficiency in glioma cells and astrocytes. Naïve and glioma-bearing mice were intracranially injected with BVs to assess transduction and neuropathology. Transgene expression was also assessed in the brain of BV-preimmunized mice. While the expression of BVs was weaker than AdVs in murine and human glioma cell lines, BV-mediated transgene expression in patient-derived glioma cells was similar to AdV-mediated transduction and showed strong correlation with clathrin expression, a protein that interacts with the baculovirus glycoprotein GP64, mediating BV endocytosis. BVs efficiently transduced normal and neoplastic astrocytes in vivo, without apparent neurotoxicity. BV-mediated transgene expression was stable for at least 21 days in the brain of naïve mice, but it was significantly reduced after 7 days in mice systemically preimmunized with BVs. Our findings indicate that BVs efficiently transduce glioma cells and astrocytes without apparent neurotoxicity. Since humans do not present pre-existing immunity against BVs, these vectors may constitute a valuable tool for the delivery of therapeutic genes into the brain.

Evaluation of Malarial Var2CSA-Displaying Baculovirus Vector in Transduction Efficiency in Human Cancer Cells

Baculovirus vectors (BVs) are able to use for gene transduction in mammalian cells and are recognized as growing viral vectors for cancer gene therapy applications. The transduction efficiency of BVs varies among cancer cell types. To improve the transduction efficiency of BVs in human cancer cells, BV displaying malarial variant surface antigen 2-chondroitin sulfate A (var2CSA) molecules was developed in this study. Var2CSA plays a critical role in the sequestration of Plasmodium falciparum-infected erythrocytes in the placenta. Moreover, var2CSA binds to cancer cells via placenta-like chondroitin sulfate A (CSA), but not to non-cancer cells. Var2CSA BV showed significantly higher gene transduction than control BV in HepG2 and Huh7 cells, human hepatic cancer cells as well as AsPC-1 cells, human pancreatic cancer cells. The transduction efficiency of var2CSA BV was significantly inhibited by the anti-gp64 antibody, free heparin, and CSA. The results of this study suggest that var2CSA BV would be an improved vector for cancer gene therapies, especially in the treatment of hepatic and pancreatic cancers.

The Magic Staff: A Comprehensive Overview of Baculovirus-Based Technologies Applied to Human and Animal Health

Baculoviruses are enveloped, insect-specific viruses with large double-stranded DNA genomes. Among all the baculovirus species, Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is the most studied. Due to its characteristics regarding biosafety, narrow host range and the availability of different platforms for modifying its genome, AcMNPV has become a powerful biotechnological tool. In this review, we will address the most widespread technological applications of baculoviruses. We will begin by summarizing their natural cycle both in larvae and in cell culture and how it can be exploited. Secondly, we will explore the different baculovirus-based protein expression systems (BEVS) and their multiple applications in the pharmaceutical and biotechnological industry. We will focus particularly on the production of vaccines, many of which are either currently commercialized or in advanced stages of development (e.g., Novavax, COVID-19 vaccine). In addition, recombinant baculoviruses can be used as efficient gene transduction and protein expression vectors in vertebrate cells (e.g., BacMam). Finally, we will extensively describe various gene therapy strategies based on baculoviruses applied to the treatment of different diseases. The main objective of this work is to provide an extensive up-to-date summary of the different biotechnological applications of baculoviruses, emphasizing the genetic modification strategies used in each field.

Potential Proteins Interactions with Bombyx mori Nucleopolyhedrovirus Revealed by Co-Immunoprecipitation

Virus–host interactions are critical for virus replication, virulence, and pathogenicity. The Bombyx mori nucleopolyhedrovirus (BmNPV) is a typical model baculovirus, representing one of the most common and harmful pathogens in sericulture. Herein, we used co-immunoprecipitation to identify candidate proteins with potential interactions with BmNPV. First, a recombinant BV virus particle rBmBV-egfp-p64-3×flag-gp64sp was constructed using a MultiBac baculovirus multigene expression system. Co-immunoprecipitation experiments were then performed with the recombinant BV virus infected with BmN cells and Dazao silkworms. LC-MS/MS analysis revealed a total of 845 and 1368 candidate proteins were obtained from BmN cells and silkworm samples, respectively. Bioinformatics analysis (Gene Ontology, KEGG Pathway) was conducted for selection of proteins with significant enrichment for further confirmation of the effects on BmNPV replication. Overall, the results showed that SEC61 and PIC promoted the replication of BmNPV, while FABP1 inhibited the replication of BmNPV. In summary, this study reveals the potential proteins involved in BmNPV invasion and proliferation in the host and provides a platform for identifying the potential receptor proteins of BmNPV.

Heparan sulfate proteoglycans serve as alternative receptors for low affinity LCMV variants

Members of the Old World Arenaviruses primarily utilize α-dystroglycan (α-DAG1) as a cellular receptor for infection. Mutations within the glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV) reduce or abrogate the binding affinity to α-DAG1 and thus influence viral persistence, kinetics, and cell tropism. The observation that α-DAG1 deficient cells are still highly susceptible to low affinity variants, suggests the use of an alternative receptor(s). In this study, we used a genome-wide CRISPR Cas9 knockout screen in DAG1 deficient 293T cells to identify host factors involved in α-DAG1-independent LCMV infection. By challenging cells with vesicular stomatitis virus (VSV), pseudotyped with the GP of LCMV WE HPI (VSV-GP), we identified the heparan sulfate (HS) biosynthesis pathway as an important host factor for low affinity LCMV infection. These results were confirmed by a genetic approach targeting EXTL3, a key factor in the HS biosynthesis pathway, as well as by enzymatic and chemical methods. Interestingly, a single point mutation within GP1 (S153F or Y155H) of WE HPI is sufficient for the switch from DAG1 to HS binding. Furthermore, we established a simple and reliable virus-binding assay, using directly labelled VSV-GP by intramolecular fusion of VSV-P and mWasabi, demonstrating the importance of HS for virus attachment but not entry in Burkitt lymphoma cells after reconstitution of HS expression. Collectively, our study highlights the essential role of HS for low affinity LCMV infection in contrast to their high affinity counterparts. Residual LCMV infection in double knockouts indicate the use of (a) still unknown entry receptor(s).

Baculoviruses in Gene Therapy and Personalized Medicine

This review will outline the role of baculoviruses in gene therapy and future potential in personalized medicine. Baculoviruses are a safe, non-toxic, non-integrative vector with a large cloning capacity. Baculoviruses are also a highly adaptable, low-cost vector with a broad tissue and host tropism due to their ability to infect both quiescent and proliferating cells. Moreover, they only replicate in insect cells, not mammalian cells, improving their biosafety. The beneficial properties of baculoviruses make it an attractive option for gene delivery. The use of baculoviruses in gene therapy has advanced significantly, contributing to vaccine production, anti-cancer therapies and regenerative medicine. Currently, baculoviruses are primarily used for recombinant protein production and vaccines.  This review will also discuss methods to optimize baculoviruses protein production and mammalian cell entry, limitations and potential for gene therapy and personalized medicine. Limitations such as transient gene expression, complement activation and virus fragility are discussed in details as they can be overcome through further genetic modifications and other methods. This review concludes that baculoviruses are an excllent candidate for gene therapy, personalized medicine and other biotherapeutic applications.

Glycan-dependent cell adhesion mechanism of Tc toxins

Toxin complex (Tc) toxins are virulence factors of pathogenic bacteria. Tcs are composed of three subunits: TcA, TcB and TcC. TcA facilitates receptor-toxin interaction and membrane permeation, TcB and TcC form a toxin-encapsulating cocoon. While the mechanisms of holotoxin assembly and pore formation have been described, little is known about receptor binding of TcAs. Here, we identify heparins/heparan sulfates and Lewis antigens as receptors for different TcAs from insect and human pathogens. Glycan array screening reveals that all tested TcAs bind negatively charged heparins. Cryo-EM structures of Morganella morganii TcdA4 and Xenorhabdus nematophila XptA1 reveal that heparins/heparan sulfates unexpectedly bind to different regions of the shell domain, including receptor-binding domains. In addition, Photorhabdus luminescens TcdA1 binds to Lewis antigens with micromolar affinity. Here, the glycan interacts with the receptor-binding domain D of the toxin. Our results suggest a glycan dependent association mechanism of Tc toxins on the host cell surface.

Induction of mucosal immunity against pathogens by using recombinant baculoviral vectors: Mechanisms, advantages, and limitations

Over 90% of pathogens of medical importance invade the organism through mucosal surfaces, which makes it urgent to develop safe and effective mucosal vaccines and mucosal immunization protocols. Besides, parenteral immunization does not provide adequate protective immunity in mucosal surfaces. Effective mucosal vaccination could protect local and systemic compartments and favor herd immunity. Although various mucosal adjuvants and Ag-delivery systems have been developed, none has filled the gap to control diseases caused by complex mucosal pathogens. Among the strategies to counteract them, recombinant virions from the baculovirus Autographa californica multiple nucleopolyhedrovirus (rAcMNPV) are useful vectors, given their safety and efficacy to produce mucosal and systemic immunity in animal infection models. Here, we review the immunogenic properties of rAcMNPV virions from the perspectives of mucosal immunology and vaccinology. Some features, which are analyzed and extrapolated from studies with different particulate antigens, include size, shape, surface molecule organization, and danger signals, all needed to break the tolerogenic responses of the mucosal immune tissues. Also, we present a condensed discussion on the immunity provided by rAcMNPV virions against influenza virus and human papillomavirus in animal models. Through the text, we highlight the advantages and limitations of this experimental immunization platform.

The spatiotemporal expression pattern of Syndecans in murine embryonic teeth

The hierarchical interactions between the dental epithelium and dental mesenchyme represent a common paradigm for organogenesis. During tooth development, various morphogens interact with extracellular components in the extracellular matrix and on the cell surfaces to transmit regulatory signaling into cells. We recently found pivotal roles of FAM20B-catalyzed proteoglycans in the control of murine tooth number at embryonic stages. However, the expression pattern of proteoglycans in embryonic teeth has not been well understood. We extracted total RNA from E14.5 murine tooth germs for semi-quantitative RT-PCR analysis of 29 proteoglycans, and identified 23 of them in the embryonic teeth. As a major subfamily of FAM20B-catalyzed proteoglycans, Syndecans are important candidates being potentially involved in the tooth development of mice. We examined the expression pattern of Syndecans in embryonic teeth using in situ hybridization (ISH) and immunohistochemistry (IHC) approaches. Syndecan-1 is mainly present in the dental mesenchyme at early embryonic stages. Subsequently, its expression expands to both dental epithelium and dental mesenchyme. Syndecan-2 is strongly expressed in the dental mesenchyme at early embryonic stages, then shifts to the stratum intermedium and inner dental epithelium at cap stages. Syndecan-3 shows a gradually increased expression that initially in the dental epithelium of both incisors and molars and then in the inner dental epithelium and stratum intermedium in molars alone. Syndecan-4 is localized in the dental epithelium in incisors and the dental follicle mesenchyme in molars at early cap stage. The spatiotemporal expression pattern of Syndecans in murine embryonic teeth suggest potential roles of these proteoglycans in murine tooth morphogenesis.

Baculovirus-Derived Vectors for Immunization and Therapeutic Applications

Baculoviruses are arthropod-specific, enveloped viruses with circular, supercoiled double-stranded deoxyribonucleic acid genomes. While many viruses are studied to seek solutions for their adverse impact on human, veterinary, and plant health, the study of baculoviruses was stimulated initially by their potential utility to control insect pests. Later, the utility of baculovirus as gene expression vectors was evidenced leading to numerous applications. Several strategies are employed to obtain recombinant viruses that express large quantities of heterologous proteins. A major step forward was the development of bacmid technology (the construction of bacterial artificial chromosomes containing the genome of the baculovirus) which allows the manipulation of the baculovirus genome in bacteria. With this technology, foreign genes can be introduced into the bacmid by homologous and site-directed recombination or by transposition. Baculoviruses have been used to explore fundamental questions in molecular biology such as the nature of programmed cell-death. Moreover, the ability of baculoviruses to transduce mammalian cells led to the consideration of their use as gene-therapy and vaccine vectors. Strategies for genetic engineering of baculoviruses have been developed to meet the requirements of new application areas. Display of foreign proteins on the surface of virions or in nucleocapsid structures, the assembly of expressed proteins to form virus-like particles or protein complexes have been explored and validated as vaccines. The aim of this chapter is to update the areas of application of the baculoviruses in protein expression, alternative vaccine designs and gene therapy of infectious diseases and genetic disorders. Finally, we review the baculovirus-derived products on the market and in the pipeline for biomedical and veterinary use.

New SDC function prediction based on protein-protein interaction using bioinformatics tools

The precise roles for SDC have been complex to specify. Assigning and reanalyzing protein and peptide identification to novel protein functions is one of the most important challenges in postgenomic era. Here, we provide SDC molecular description to support, contextualize and reanalyze the corresponding protein-protein interaction (PPI). From SDC-1 data mining, we discuss the potential of bioinformatics tools to predict new biological rules of SDC. Using these methods, we have assembled new possibilities for SDC biology from PPI data, once, the understanding of biology complexity cannot be capture from one simple question.

Protection of Baculovirus Vectors Expressing Complement Regulatory Proteins against Serum Complement Attack

Baculovirus vectors (BVs) enable safe and efficient gene delivery to mammalian cells and are useful in a wide range of applications, including gene therapy and in vivo analysis of gene functions. We previously developed BVs expressing malaria sporozoite surface proteins for targeting liver cells or hepatocytes. However, BVs are known to be very vulnerable to complement attack and efforts to overcome their inactivation based on complement are important. In this study, BVs expressing complement regulatory proteins (CRPs) on the surfaces of virions were developed to inhibit complement reactions. Decay accelerating factor (DAF; CD55)-type BVs exhibited significantly higher complement resistance than control BVs without any CRPs in HepG2 cells transduction, although the transduction efficacy of DAF-type BV was low. In contrast, CD46-DAF-CD59 fusion type BVs showed significantly higher transduction efficacy and complement resistance than both control and DAF-type BVs. DAF-type and CD46-DAF-CD59 type BVs repressed formation of the membrane attack complex, a terminal product of complement reaction cascades, induced by BVs. These results suggest that the CD46-DAF-CD59 fusion construct confers complement protection ability superior to that of the DAF construct in gene delivery under complement active serum.

Sulfotransferase and Heparanase: Remodeling Engines in Promoting Virus Infection and Disease Development

An extraordinary binding site generated in heparan sulfate (HS) structures, during its biosynthesis, provides a unique opportunity to interact with multiple protein ligands including viral proteins, and therefore adds tremendous value to this master molecule. An example of such a moiety is the sulfation at the C3 position of glucosamine residues in HS chain via 3-O sulfotransferase (3-OST) enzymes, which generates a unique virus-cell fusion receptor during herpes simplex virus (HSV) entry and spread. Emerging evidence now suggests that the unique patterns in HS sulfation assist multiple viruses in invading host cells at various steps of their life cycles. In addition, sulfated-HS structures are known to assist in invading host defense mechanisms and initiating multiple inflammatory processes; a critical event in the disease development. All these processes are detrimental for the host and therefore raise the question of how HS-sulfation is regulated. Epigenetic modulations have been shown to be implicated in these reactions during HSV infection as well as in HS modifying enzyme sulfotransferases, and therefore pose a critical component in answering it. Interestingly, heparanase (HPSE) activity is shown to be upregulated during virus infection and multiple other diseases assisting in virus replication to promote cell and tissue damage. These phenomena suggest that sulfotransferases and HPSE serve as key players in extracellular matrix remodeling and possibly generating unique signatures in a given disease. Therefore, identifying the epigenetic regulation of OST genes, and HPSE resulting in altered yet specific sulfation patterns in HS chain during virus infection, will be a significant a step toward developing potential diagnostic markers and designing novel therapies.

Baculovirus as a Tool for Gene Delivery and Gene Therapy

Based on its ability to express high levels of protein, baculovirus has been widely used for recombinant protein production in insect cells for more than thirty years with continued technical improvements. In addition, baculovirus has been successfully applied for foreign gene delivery into mammalian cells without any viral replication. However, several CpG motifs are present throughout baculoviral DNA and induce an antiviral response in mammalian cells, resulting in the production of pro-inflammatory cytokines and type I interferon through a Toll-like receptor (TLR)-dependent or -independent signaling pathway, and ultimately limiting the efficiency of transgene expression. On the other hand, by taking advantage of this strong adjuvant activity, recombinant baculoviruses encoding neutralization epitopes can elicit protective immunity in mice. Moreover, immunodeficient cells, such as hepatitis C virus (HCV)- or human immunodeficiency virus (HIV)-infected cells, are more susceptible to baculovirus infection than normal cells and are selectively eliminated by the apoptosis-inducible recombinant baculovirus. Here, we summarize the application of baculovirus as a gene expression vector and the mechanism of the host innate immune response induced by baculovirus in mammalian cells. We also discuss the future prospects of baculovirus vectors.

Specific glycosaminoglycan chain length and sulfation patterns are required for cell uptake of tau versus α-synuclein and β-amyloid aggregates

Transcellular propagation of protein aggregate "seeds" has been proposed to mediate the progression of neurodegenerative diseases in tauopathies and α-synucleinopathies. We previously reported that tau and α-synuclein aggregates bind heparan sulfate proteoglycans (HSPGs) on the cell surface, promoting cellular uptake and intracellular seeding. However, the specificity and binding mode of these protein aggregates to HSPGs remain unknown. Here, we measured direct interaction with modified heparins to determine the size and sulfation requirements for tau, α-synuclein, and β-amyloid (Aβ) aggregate binding to glycosaminoglycans (GAGs). Varying the GAG length and sulfation patterns, we next conducted competition studies with heparin derivatives in cell-based assays. Tau aggregates required a precise GAG architecture with defined sulfate moieties in the N- and 6-O-positions, whereas the binding of α-synuclein and Aβ aggregates was less stringent. To determine the genes required for aggregate uptake, we used CRISPR/Cas9 to individually knock out the major genes of the HSPG synthesis pathway in HEK293T cells. Knockouts of the extension enzymes exostosin 1 (EXT1), exostosin 2 (EXT2), and exostosin-like 3 (EXTL3), as well as N-sulfotransferase (NDST1) or 6-O-sulfotransferase (HS6ST2) significantly reduced tau uptake, consistent with our biochemical findings, and knockouts of EXT1, EXT2, EXTL3, or NDST1, but not HS6ST2 reduced α-synuclein uptake. In summary, tau aggregates display specific interactions with HSPGs that depend on GAG length and sulfate moiety position, whereas α-synuclein and Aβ aggregates exhibit more flexible interactions with HSPGs. These principles may inform the development of mechanism-based therapies to block transcellular propagation of amyloid protein-based pathologies.

Production and Purification of Baculovirus for Gene Therapy Application

Baculovirus has traditionally been used for the production of recombinant protein and vaccine. However, more recently, baculovirus is emerging as a promising vector for gene therapy application. Here, baculovirus is produced by transient transfection of the baculovirus plasmid DNA (bacmid) in an adherent culture of Sf9 cells. Baculovirus is subsequently expanded in Sf9 cells in a serum-free suspension culture until the desired volume is obtained. It is then purified from the culture supernatant using heparin affinity chromatography. Virus supernatant is loaded onto the heparin column which binds baculovirus particles in the supernatant due to the affinity of heparin for baculovirus envelop glycoprotein. The column is washed with a buffer to remove contaminants and baculovirus is eluted from the column with a high-salt buffer. The eluate is diluted to an isotonic salt concentration and baculovirus particles are further concentrated using ultracentrifugation. Using this method, baculovirus can be concentrated up to 500-fold with a 25% recovery of infectious particles. Although the protocol described here demonstrates the production and purification of the baculovirus from cultures up to 1 L, the method can be scaled-up in a closed-system suspension culture to produce a clinical-grade vector for gene therapy application.

Malaria sporozoite protein expression enhances baculovirus-mediated gene transfer to hepatocytes

BACKGROUND

Baculovirus vector (BV) is able to transduce foreign genes into mammalian cells efficiently and safely by incorporating a mammalian promoter. In the present study, we tailored the surface proteins expressed by malaria sporozoites to enhance hepatocyte transduction. Sporozoites infect hepatocytes within minutes of initial entry into the blood circulation. Infectivity and hepatocyte-specific selectivity are mediated by the interplay between hepatocytes and sporozoite surface proteins. The circumsporozoite protein (CSP) and the thrombospondin-related anonymous protein (TRAP) bind to the heparan sulfate proteoglycan on the hepatocyte surface and contribute to sporozoite infection and hepatocyte selectivity.

METHODS

BVs displaying an ectodomain consisting of three different CSP variants (full-length, N-terminal and C-terminal) or TRAP on the virus envelope were constructed, and the resulting in vitro hepatocyte transduction efficiency was evaluated.

RESULTS

We demonstrated improved hepatocyte transduction efficiency in BVs expressing CSP or TRAP ectodomains compared to BVs without malaria surface proteins. In addition, gene transduction efficiencies for BVs displaying CSP or TRAP are higher than those expressing the preS1 antigen of the hepatitis B virus.

CONCLUSIONS

BVs expressing CSP or TRAP in the ectodomain could represent a promising hepatocyte-specific gene delivery methodology. Copyright © 2016 John Wiley & Sons, Ltd.

A comparative review of viral entry and attachment during large and giant dsDNA virus infections

Viruses enter host cells via several mechanisms, including endocytosis, macropinocytosis, and phagocytosis. They can also fuse at the plasma membrane and can spread within the host via cell-to-cell fusion or syncytia. The mechanism used by a given viral strain depends on its external topology and proteome and the type of cell being entered. This comparative review discusses the cellular attachment receptors and entry pathways of dsDNA viruses belonging to the families Adenoviridae, Baculoviridae, Herpesviridae and nucleocytoplasmic large DNA viruses (NCLDVs) belonging to the families Ascoviridae, Asfarviridae, Iridoviridae, Phycodnaviridae, and Poxviridae, and giant viruses belonging to the families Mimiviridae and Marseilleviridae as well as the proposed families Pandoraviridae and Pithoviridae. Although these viruses have several common features (e.g., topology, replication and protein sequence similarities) they utilize different entry pathways to infect wide-range of hosts, including humans, other mammals, invertebrates, fish, protozoa and algae. Similarities and differences between the entry methods used by these virus families are highlighted, with particular emphasis on viral topology and proteins that mediate viral attachment and entry. Cell types that are frequently used to study viral entry are also reviewed, along with other factors that affect virus-host cell interactions.

Heparan sulfate proteoglycans (HSPGs) and chondroitin sulfate proteoglycans (CSPGs) function as endocytic receptors for an internalizing anti-nucleic acid antibody

A subset of monoclonal anti-DNA autoantibodies enters a variety of living cells. Here, we aimed to identify the endocytic receptors recognized by an internalizing anti-nucleic acid autoantibody, the 3D8 single-chain variable fragment (scFv). We found that cell surface binding and internalization of 3D8 scFv were inhibited markedly in soluble heparan sulfate (HS)/chondroitin sulfate (CS)-deficient or -removed cells and in the presence of soluble HS and CS. 3D8 scFv colocalized intracellularly with either HS proteoglycans (HSPGs) or CSPGs in HeLa cells. 3D8 scFv was co-endocytosed and co-precipitated with representative individual HSPG and CSPG molecules: syndecan-2 (a transmembrane HSPG), glypican-3 (a glycosylphosphatidylinositol (GPI)-anchored HSPG); CD44 (a transmembrane CSPG); and brevican (a GPI-anchored CSPG). Collected data indicate that 3D8 scFv binds to the negatively charged sugar chains of both HSPGs and CSPGs and is then internalized along with these molecules, irrespective of how these proteoglycans are associated with the cell membrane. This is the first study to show that anti-DNA antibodies enter cells via both HSPGs and CSPGs simultaneously. The data may aid understanding of endocytic receptors that bind anti-DNA autoantibodies. The study also provides insight into potential cell membrane targets for macromolecular delivery.

Glycosaminoglycans are involved in bacterial adherence to lung cells

Background

Lower respiratory infections are among the top ten causes of death worldwide. Since pathogen to cell adhesion is a crucial step in the infection progress, blocking the interaction between eukaryotic receptors and bacterial ligands may enable the pathogenesis process to be stopped. Cell surface glycosaminoglycans (GAGs) are known to be mediators in the adhesion of diverse bacteria to different cell types, making it of interest to examine their involvement in the attachment of various pathogenic bacteria to lung cells, including epithelial cells and fibroblasts.

Methods

The function of cell surface GAGs in bacterial adhesion was studied by reducing their levels through inhibiting their biosynthesis and enzymatic degradation, as well as in binding competition experiments with various species of GAGs. The participation of the different bacterial adhesins in attachment was evaluated through competition with two peptides, both containing consensus heparin binding sequences. Blocking inhibition assays using anti-syndecans and the enzymatic removal of glypicans were conducted to test their involvement in bacterial adhesion. The importance of the fine structure of GAGs in the interaction with pathogens was investigated in competition experiments with specifically desulfated heparins.

Results

The binding of all bacteria tested decreased when GAG levels in cell surface of both lung cells were diminished. Competition experiments with different types of GAGs showed that heparan sulfate chains are the main species involved. Blocking or removal of cell surface proteoglycans evidenced that syndecans play a more important role than glypicans. The binding was partially inhibited by peptides including heparin binding sequences. Desulfated heparins also reduced bacterial adhesion to different extents depending on the bacterium and the sulfated residue, especially in fibroblast cells.

Conclusions

Taken together, these data demonstrate that the GAG chains of the cell surface are involved in the adhesion of bacterial adhesins to lung cells. Heparan sulfate seems to be the main species implicated, and binding is dependent on the sulfation pattern of the molecule. These data could facilitate the development of new anti-infective strategies, enabling the development of new procedures for blocking the interaction between pathogens and lung cells more effectively.

Purification of baculovirus vectors using heparin affinity chromatography

Baculoviruses are commonly used for recombinant protein and vaccine production. Baculoviruses are nonpathogenic to vertebrates, have a large packaging capacity, display broad host and cell type tropism, infect both dividing and nondividing cells, and do not elicit strong immune or allergic responses in vivo. Hence, their use as gene delivery vehicles has become increasingly popular in recent years. Moreover, baculovirus vectors carrying mammalian regulatory elements can efficiently transduce and express transgenes in mammalian cells. Based on the finding that heparan sulfate, which is structurally similar to heparin, is an attachment receptor for baculovirus, we developed a novel scalable baculovirus purification method using heparin-affinity chromatography. Baculovirus supernatants were loaded onto a POROS heparin column, washed to remove unbound materials, and eluted with 1.5 mol/l NaCl, which yielded a recovery of purified baculovirus of 85%. After ultracentrifugation, baculovirus titers increased from 200- to 700-fold with overall yields of 26–29%. We further show that baculovirus particles were infectious, normal in morphology and size, despite high-salt elution and shear forces used during purification and concentration. Our chromatography-based purification method is scalable and, together with ultracentrifugation and/or tangential flow filtration, will be suitable for large-scale manufacturing of baculovirus stocks for protein and vaccine production and in gene therapy applications.

Identification of AcMNPV GP64-binding proteins through a combinational use of a self-biotinylated virus and the cross-linking method

Baculoviruses are potential vectors of gene therapy for the ability to transfer gene high efficiently into mammalian cells. However, cell membrane proteins which interact with baculoviral glycoproteins have not been identified. In this study, we developed a self-biotinylated AcMNPV bearing biotinylated GP64 glycoproteins. This recombinant virus demonstrated the capability to infect insect cells and to transduct mammalian cells. Using this biotinylated virus, a protein >170Kda which could specifically interact with GP64 proteins was identified from virus transducted BHK-21 cells through cross-linking and streptavidin purification. Our study provides a useful approach for identifying cell membrane proteins that interact with baculovirus surface proteins or proteins involved in virus attachment.

Baculovirus-mediated gene delivery and RNAi applications

Baculoviruses are widely encountered in nature and a great deal of data is available about their safety and biology. Recently, these versatile, insect-specific viruses have demonstrated their usefulness in various biotechnological applications including protein production and gene transfer. Multiple in vitro and in vivo studies exist and support their use as gene delivery vehicles in vertebrate cells. Recently, baculoviruses have also demonstrated high potential in RNAi applications in which several advantages of the virus make it a promising tool for RNA gene transfer with high safety and wide tropism.

Diversity of heparan sulfate and HSV entry: basic understanding and treatment strategies

A modified form of heparan sulfate (HS) known as 3-O-sulfated heparan sulfate (3-OS HS) generates fusion receptor for herpes simplex virus (HSV) entry and spread. Primary cultures of corneal fibroblasts derived from human eye donors have shown the clinical significance of this receptor during HSV corneal infection. 3-OS HS- is a product of a rare enzymatic modification at C3 position of glucosamine residue which is catalyzed by 3-O-sulfotransferases (3-OSTs) enzymes. From humans to zebrafish, the 3-OST enzymes are highly conserved and widely expressed in cells and tissues. There are multiple forms of 3-OSTs each producing unique subset of sulfated HS making it chemically diverse and heterogeneous. HSV infection of cells or zebrafish can be used as a unique tool to understand the structural-functional activities of HS and 3-OS HS and likewise, the infection can be used as a functional assay to screen phage display libraries for identifying HS and 3-OS HS binding peptides or small molecule inhibitors. Using this approach over 200 unique 12-mer HS and 3-OS HS recognizing peptides were isolated and characterized against HSV corneal infection where 3-OS HS is known to be a key receptor. In this review we discuss emerging role of 3-OS HS based therapeutic strategies in preventing viral infection and tissue damage.

Heparan sulfate proteoglycan as a cell-surface endocytosis receptor

How various macromolecules are exchanged between cells and how they gain entry into recipient cells are fundamental questions in cell biology with important implications e.g. non-viral drug delivery, infectious disease, metabolic disorders, and cancer. The role of heparan sulfate proteoglycan (HSPG) as a cell-surface receptor of diverse macromolecular cargo has recently been manifested. Exosomes, cell penetrating peptides, polycation-nucleic acid complexes, viruses, lipoproteins, growth factors and morphogens among other ligands enter cells through HSPG-mediated endocytosis. Key questions that partially have been unraveled over recent years include the respective roles of HSPG core protein and HS chain structure specificity for macromolecular cargo endocytosis, the down-stream intracellular signaling events involved in HSPG-dependent membrane invagination and vesicle formation, and the biological significance of the HSPG transport pathway. Here, we discuss the intriguing role of HSPGs as a major entry pathway of macromolecules in mammalian cells with emphasis on recent in vitro and in vivo data that provide compelling evidence of HSPG as an autonomous endocytosis receptor.