Processing and secretion of envelope glycoproteins of human immunodeficiency virus type 1 in the presence of trimming glucosidase inhibitor deoxynojirimycin

1-Deoxynojirimycin and its Derivatives: A Mini Review of the Literature

1-Deoxynojirimycin (1-DNJ) is a naturally occurring sugar analogue with unique bioactivities. It is found in mulberry leaves and silkworms, as well as in the metabolites of certain microorganisms, including Streptomyces and Bacillus. 1-DNJ is a potent α-glucosidase inhibitor and it possesses anti-hyperglycemic, anti-obese, anti-viral and anti-tumor properties. Some derivatives of 1-DNJ, like miglitol, miglustat and migalastat, were applied clinically to treat diseases such as diabetes and lysosomal storage disorders. The present review focused on the extraction, determination, pharmacokinetics and bioactivity of 1-DNJ, as well as the clinical application of 1-DNJ derivatives.

Mechanisms of Antiviral Activity of Iminosugars Against Dengue Virus

The antiviral mechanism of action of iminosugars against many enveloped viruses, including dengue virus (DENV), HIV, influenza and hepatitis C virus, is believed to be mediated by inducing misfolding of viral N-linked glycoproteins through inhibition of host endoplasmic reticulum-resident α-glucosidase enzymes. This leads to reduced secretion and/or infectivity of virions and hence lower viral titres, both in vitro and in vivo. Free oligosaccharide analysis from iminosugar-treated cells shows that antiviral activity correlates with production of mono- and tri-glucosylated sugars, indicative of inhibition of ER α-glucosidases. We demonstrate that glucose-mimicking iminosugars inhibit isolated glycoprotein and glycolipid processing enzymes and that this inhibition also occurs in primary cells treated with these drugs. Galactose-mimicking iminosugars that have been tested do not inhibit glycoprotein processing but do inhibit glycolipid processing, and are not antiviral against DENV. By comparison, the antiviral activity of glucose-mimetic iminosugars that inhibit endoplasmic reticulum-resident α-glucosidases, but not glycolipid processing, demonstrates that inhibition of α-glucosidases is responsible for iminosugar antiviral activity against DENV. This monograph will review the investigations of many researchers into the mechanisms of action of iminosugars and the contribution of our current understanding of these mechanisms for optimising clinical delivery of iminosugars. The effects of iminosugars on enzymes other than glucosidases, the induction of ER stress and viral receptors will be also put into context. Data suggest that inhibition of α-glucosidases results in inhibited release of virus and is the primary antiviral mechanism of action of iminosugars against DENV.

The C-terminal tail of the gp41 transmembrane envelope glycoprotein of HIV-1 clades A, B, C, and D may exist in two conformations: an analysis of sequence, structure, and function

In addition to the major ectodomain, the gp41 transmembrane glycoprotein of HIV-1 is now known to have a minor ectodomain that is part of the long C-terminal tail. Both ectodomains are highly antigenic, carry neutralizing and non-neutralizing epitopes, and are involved in virus-mediated fusion activity. However, data have so far been biologically based, and derived solely from T cell line-adapted (TCLA), B clade viruses. Here we have carried out sequence and theoretically based structural analyses of 357 gp41 C-terminal sequences of mainly primary isolates of HIV-1 clades A, B, C, and D. Data show that all these viruses have the potential to form a tail loop structure (the minor ectodomain) supported by three, β-sheet, membrane-spanning domains (MSDs). This means that the first (N-terminal) tyrosine-based sorting signal of the gp41 tail is situated outside the cell membrane and is non-functional, and that gp41 that reaches the cell surface may be recycled back into the cytoplasm through the activity of the second tyrosine-sorting signal. However, we suggest that only a minority of cell-associated gp41 molecules – those destined for incorporation into virions – has 3 MSDs and the minor ectodomain. Most intracellular gp41 has the conventional single MSD, no minor ectodomain, a functional first tyrosine-based sorting signal, and in line with current thinking is degraded intracellularly. The gp41 structural diversity suggested here can be viewed as an evolutionary strategy to minimize HIV-1 envelope glycoprotein expression on the cell surface, and hence possible cytotoxicity and immune attack on the infected cell.

Additive effect of tunicamycin and dextran sulfate on the binding of monoclonal antibody to the V2 domain of the envelope glycoprotein 120 of human immunodeficiency virus type 1

Using flow cytometry or immunoprecipitation analysis in cells chronically infected with HIV-1 IIIB Supt-1, we noticed an additive effect of tunicamycin and low molecular weight dextran (LMDS) on the binding of the G3-4 monoclonal antibody to monomeric and oligomeric forms of glycoprotein 120 (gp120). The inhibition of glycosylation by tunicamycin reduced the number of monomeric and oligomeric forms of gp120. The inhibition of the binding of the G3-4 antibody to monomeric and oligomeric forms of gp120 was more pronounced in the presence of LMDS. We also found that the G3-4 antibody can not recognise the nascent polypeptide chain of the envelope glycoprotein.

Application of monoclonal antibodies to monitor the synthesis of a glycoprotein core of envelope glycoproteins of human immunodeficiency virus (HIV-1)

Using monoclonal antibodies 0.5 beta or G3-42, directed against V3 and C4 domains of glycoprotein 120 (gp120), we monitored the synthesis of oligomeric and monomeric forms of HIV-1 envelope glycoprotein 120 by flow cytometry or immunoprecipitation analysis in chronically infected MoIT-4 cells, cultured in the presence of tunicamycin. We observed that the inhibition of glycosylation by high concentrations of tunicamycin results in the reduction of an oligomeric gp120 on the surface of infected MoIT 4 cells as well as the decrease in the concentration of a monomeric form in the cytoplasm. Our studies revealed that the antibody 0.5 beta (exhibited higher sensitivity in the detection of gp120 than the antibody G3-42). We also observed that both antibodies did not recognise nonglycosylated precursor core envelope protein.

Effect of changes in the glycosylation of the human immunodeficiency virus type 1 envelope on the immunoreactivity and sensitivity to thrombin of its third variable domain

The influence of HIV Env glycosylation on the conformation of the third variable domain (V3) of Env was studied by both deglycosylation of mature Env and the use of Env produced by recombinant systems in which alpha-glucosidase activity was inhibited by either deoxynojirimycin (DNM) or mutation. Selective deglycosylation affected anti-V3 antibody binding. The immunoreactivity and sensitivity to thrombin cleavage of V3 presented on Env produced in baby hamster kidney cells were changed by DNM treatment. In contrast, Env expressed in alpha-glucosidase I-deficient Chinese hamster ovary cells or in their parental cells treated by DNM fully retained these V3 properties. These results are discussed in relation to the inconsistent data obtained on V3 property changes resulting from Env glycosylation changes.

Megalomicin inhibits HIV-1 replication and interferes with gp160 processing

The inhibitory effects on HIV replication of megalomicin (MGM, an inhibitor of intra-Golgi vesicle transport, have been studied. In experiments at low multiplicity of infection on Jurkat and MT2 cell lines. MGM inhibited the production of p24 antigen, the formation of syncytia, and the induction of apoptosis at concentrations below 5 microM. Furthermore, PCR analysis of genomic DNA showed that, in the presence of MGM, HIV-1 had been eradicated from the culture. MGM also inhibited replication of primary isolates of HIV-1 in blood lymphoblasts and more importantly, at 1 microM, MGM inhibited depletion of CD4+ T cells in cultures of blood lymphocytes from seropositive patients. Finally, MGM inhibited the generation of infectious virions and the processing of the envelope protein precursor gp160 to its mature forms, resulting in the rapid degradation of gp 160. These data suggest that MGM induces a powerful inhibitory effect on HIV-1 replication at nontoxic concentrations by preventing the processing of HIV-1 gp160 envelope protein and the subsequent formation of infectious viral particles.

Recombinant HIV envelope expressed in an alpha-glucosidase I-deficient CHO cell line and its parental cell line in the presence of 1-deoxynojirimycin is functional

alpha-Glucosidase inhibitors-e.g., 1-deoxynojirimycin (DNM)-interfere with HIV infectivity in CD4+ cell cultures but have proven unsuccessful in clinical trials. In vitro, several HIV Env properties, including the cleavage of the Env precursor gp 160, the immunoreactivity of the third variable domain (V3) of Env, the binding to the CD4 receptor, and the induction of the membrane fusion between the virus and the host cell, have been reported to be altered by such inhibitors. We have studied these properties for Env expressed via a recombinant vaccinia virus in two Chinese hamster ovary cell lines, an alpha-glucosidase I-deficient cell line and its parental cell line, treated with DNM under conditions that have been reported to alter Env properties. The glycosylation of Env, but not the quantity produced, varied in accordance with the experimental conditions. However, irrespective of these conditions, Env cleavage, V3 immunoreactivity, CD4 binding, membrane expression, and ability to induce syncytium formation were similar. Thus, neither the alpha-glucosidase I deficiency nor DNM treatment had a significant effect on the properties of Env produced here. Cellular mechanisms that may allow the normal expression of Env are discussed and may offer an explanation for the many discrepant results obtained to date on the effects of DNM on HIV Env.

Processing of the envelope glycoprotein gp160 in immunotoxin-resistant cell lines chronically infected with human immunodeficiency virus type 1

We describe the isolation and characterization of variant cell lines which are chronically infected with the human immunodeficiency virus (HIV) and resistant to the action of immunotoxins directed against the HIV envelope protein. These variants all produce normal levels of HIV proteins, budding virions, and the envelope protein precursor gp160. Two of the variants, 10E and 11E, contain a mutation within the env gene which results in the production of a truncated precursor and altered processing and transport of the protein to the cell surface. Variants B9 and G4 are defective in gp160 cleavage and do not efficiently transport the envelope protein to the cell surface. There are no mutations in the expressed viruses of B9 and G4. These cell lines express higher levels of CD4 protein and mRNA than H9/NL4-3. Thus, 10E, 11E, B9, and G4 have escaped immunotoxin action by downmodulating the envelope protein from their cell surfaces. None of these variants produce infectious HIV. Two other immunotoxin-resistant variants, E9-3 and 41-17, produce normal levels of gp160, efficiently transport the cleaved and processed subunits to the cell surface, and secrete infectious HIV. These studies identify alterations in gp160 processing that underscore the importance of the relationship between HIV and the cell that it infects.

Antiviral therapy for human immunodeficiency virus infections

Depending on the stage of their intervention with the viral replicative cycle, human immunodeficiency virus inhibitors could be divided into the following groups: (i) adsorption inhibitors (i.e., CD4 constructs, polysulfates, polysulfonates, polycarboxylates, and polyoxometalates), (ii) fusion inhibitors (i.e., plant lectins, succinylated or aconitylated albumins, and betulinic acid derivatives), (iii) uncoating inhibitors (i.e., bicyclams), (iv) reverse transcription inhibitors acting either competitively with the substrate binding site (i.e., dideoxynucleoside analogs and acyclic nucleoside phosphonates) or allosterically with a nonsubstrate binding site (i.e., non-nucleoside reverse transcriptase inhibitors), (v) integration inhibitors, (vi) DNA replication inhibitors, (vii) transcription inhibitors (i.e., antisense oligodeoxynucleotides and Tat antagonists), (viii) translation inhibitors (i.e., antisense oligodeoxynucleotides and ribozymes), (ix) maturation inhibitors (i.e., protease inhibitors, myristoylation inhibitors, and glycosylation inhibitors), and finally, (x) budding (assembly/release) inhibitors. Current knowledge, including the therapeutic potential, of these various inhibitors is discussed. In view of their potential clinical the utility, the problem of virus-drug resistance and possible strategies to circumvent this problem are also addressed.

Identification of three N-linked glycans in the V4-V5 region of HIV-1 gp 120, dispensable for CD4-binding and fusion activity of gp 120

Site-directed mutagenesis was used to study the biological significance of three N-linked glycans (linked to Asn406, Asn448, and Asn463), situated in the CD4-binding region of gp120. Mutagenesis was carried out in a phage M13 system, and the mutated env genes were inserted into recombinant vaccinia virus (r-vaccinia virus). To evaluate if the level of expression affected the biological phenotype of mutant gp120, we expressed the envelope glycoproteins using either a weak (7.5 K) or a strong (11 K) promoter of vaccinia virus. The expression of mutated env proteins was analyzed after infecting CD4-expressing HeLa cells with the r-vaccinia virus, by monitoring the ability of the infected cells to generate CD4-dependent syncytia. Env gene products lacking all three glycans as well as env gene products lacking different permutations of one or two glycans were analyzed. All mutated gp120 species had the expected electrophoretical mobility as anticipated from elimination of one, two, and three N-linked glycans, respectively. Moreover, all mutant env gene products demonstrated the same capacity to induce formation of syncytia, irrespective of using the weak or strong promoter for expression. These data indicate that the three N-linked glycans studied are dispensable for HIV env gene products to function in CD4-binding and the subsequent fusion step.

Inhibition of alpha-glucosidase I of the glycoprotein-processing enzymes by 6-O-butanoyl castanospermine (MDL 28,574) and its consequences in human immunodeficiency virus-infected T cells

The 6-O-butanoyl derivative of castanospermine (MDL 28,574) was previously shown to be approximately 30-fold more potent than the naturally occurring molecule at inhibiting the replication of human immunodeficiency virus (HIV) (D. L. Taylor, P. S. Sunkara, P. S. Liu, M. S. Kang, T. L. Bowlin, and A. S. Tyms, AIDS 5:693-698, 1991). We now report that consistent with its improved anti-HIV activity, MDL 28,574 is more effective (50% inhibitory concentration [IC50], 20 microM) than the parent molecule (IC50, 254 microM) at causing the accumulation of glucosylated oligosaccharides in HIV-infected cells by inhibition of glycoprotein processing. These were predominantly of the glucose 3 type, as determined by P4 Bio-Gel analysis after digestion with purified alpha-glucosidase I, indicating that, intracellularly, this enzyme is the major target for inhibition. MDL 28,574, however, was less active (IC50, 1.27 microM) than castanospermine (IC50, 0.12 microM) against the mutual target enzyme, cellular alpha-glucosidase I, in a cell-free assay system. The increased effects of MDL 28,574 against alpha-glucosidase I in cell culture were attributed to the improved cellular uptake of the more lipophilic derivative. Inhibition of this enzyme activity in HIV-infected H9 cells impaired viral glycoprotein processing and resulted in the expression of abnormally configured gp120. This did not affect virus production, but the virions had decreased infectivity which was partially related to a reduced ability to bind to CD4+ T cells.

Functions of HIV envelope glycans

The unusually highly glycosylated state of the major envelope glycoprotein (gp160) of the human immunodeficiency virus has offered a challenge to both glycobiologists and virologists. What is the functional significance of such a mass of glycans and how might they be manipulated to disadvantage virus pathogenesis? Some answers to each of these questions have already been obtained: N-linked glycans are necessary for the creation, but not the maintenance, of a bioactive conformation, and drug-induced alteration of the glycosylation pattern can lead to impaired virus infectivity. As a model for studying glycan function and as a target for antiviral therapy, gp160 represents a unique candidate.

Site-specific N-glycosylation and oligosaccharide structures of recombinant HIV-1 gp120 derived from a baculovirus expression system

We report the complete structures of the N-linked oligosaccharides and the site-specificity of the N-glycosylation of recombinant gp120 (rgp120) of the HIV-1 BH8 isolate produce by a baculovirus expression system. Glycopeptides derived from the tryptic digests of intact rgp120 or of cyanogen bromide-generated fragments of rgp120 were isolated by their binding to concanavalin A-Sepharose and were purified by reversed-phase HPLC. The isolated glycopeptides were treated with PNGase F, releasing the carbohydrate moiety while converting Asn to Asp, and identified by amino acid analysis and/or peptide sequencing. Our results indicate that all 22 potential N-glycosylation sites in the rgp120 sequence are utilized. We did not detect N-acetylgalactosamine in rgp120, indicating that the glycoprotein lacks typical O-linked oligosaccharides. To investigate the oligosaccharide structures at the sites of glycosylation, we determined the carbohydrate composition for each site and characterized the oligosaccharides by 1H-NMR spectroscopy and by oligosaccharide mapping using high pH anion-exchange chromatography. Mannose and N-acetylglucosamine were the only sugars observed in the intact rgp120 and likewise in individual glycopeptides. All glycopeptides derived from rgp120 contained high mannose-type N-linked oligosaccharides, ranging from GlcNAc2Man5 to GlcNAc2Man9. However, different glycosylation sites showed varied degrees of processing of the high mannose-type oligosaccharides, as characterized by the ratio of GlcNAc2Man8-9 to GlcNAc2Man5-7. These results demonstrate that N-glycosylation of rgp120 in the baculovirus expression system occurs at all potential sites and is site specific in terms of oligosaccharide structures.

Legitimate and illegitimate cleavage of human immunodeficiency virus glycoproteins by furin

Coexpression of human immunodeficiency virus type 1 glycoproteins with the subtilisin-like protease furin leads to processing of gp160 and gp140, a truncated form of gp160, to gp120. In addition, we show that gp120 itself is further cleaved by furin at sites near the primary cleavage site and within the V3 loop.

Screening for inhibitors of HIV gp120-CD4 binding using an enzyme-linked immunoabsorbent assay

Binding of the HIV-1 major viral surface glycoprotein, gp120, to the major cell receptor, CD4, is essential for HIV infection of the target cell and syncytium formation. An enzyme-linked immunoassay using solid phase CD4 was used to quantitate the binding of HIV-1 gp120 to CD4, and to assess the activity and mechanism of action of putative inhibitors of that reaction. Monoclonal antibodies to the gp120 binding site on CD4 (e.g., Leu3a) blocked gp120 binding, while monoclonal antibodies to other portions of CD4 (e.g. OKT4) did not. Both aurintricarboxylic acid and sulfonated polysaccharides (e.g., dextran sulfate) blocked CD4-gp120 interactions by binding to the CD4 component. Human polyclonal antibodies to gp120 also blocked gp120-CD4 binding, but none of the monoclonal antibodies tested (including several with neutralizing activity) were effective. In contrast, several lectins (including mannose binding protein) bound to gp120 and blocked CD4-gp120 interactions. Enzymatic deglycosylation of gp120 only minimally affected its CD4 binding capacity, while non-glycosylated gp120 (produced in Escherichia coli)-bound CD4 about 10-fold less well than fully-glycosylated material. The results demonstrate that this assay system can be used to measure the activity of inhibitors of CD4-gp120 binding, and to determine the mechanism of action of those inhibitors.

Mechanism of action of N-butyl deoxynojirimycin in inhibiting HIV-1 infection and activity in combination with nucleoside analogs

The effects on HIV-1 infection of a glucosidase inhibitor, N-butyl deoxynojirimycin (N-buDNJ), were examined. The combinations of N-buDNJ and nucleoside analogs dideoxyinosine (DDI), dideoxycytidine (DDC), or azidothymidine (AZT) were examined in an acute infection assay. The combination of N-buDNJ and nucleoside analog reduced the yield of reverse transcriptase activity more than did either agent alone, and the effects on the number of infectious virus particles were additive or synergistic. In studies of the mechanism whereby N-buDNJ alters HIV-1 envelope fusion activity, no effects on CD4 binding were detected. However, cleavage within the V3 loop of gp120 was reduced by N-buDNJ treatment, possibly reflecting an altered conformation of this region of the envelope protein.

Nonrandom distribution of gp120 N-linked glycosylation sites important for infectivity of human immunodeficiency virus type 1

More than 20 consensus N-linked glycosylation sites occur in the gp120 coding sequence of most isolates of human immunodeficiency virus type 1. Based on the N-linked glycosylation pattern of a well-characterized recombinant gp120, it is likely that N-linked sugars are present at most, if not all, of the consensus glycosylation sites of the heavily glycosylated gp120. In this study, we evaluated the relative importance of each of the 24 N-linked glycosylation sites of gp120 in the molecular clone HXB2 to viral infectivity. The ability of HXB2-derived mutants, each having 1 of the 24 N-linked glycosylation sites mutated by site-directed mutagenesis, to infect CD4-positive SupT1 cells was compared with that of the wild-type virus. We found that most of the individual consensus N-linked glycosylation sites are dispensable for viral infectivity. The five consensus N-linked glycosylation sites that are likely to have important roles in infectivity are all located in the amino-terminal half of gp120, indicating that the N-linked glycosylation sites that are important for infectivity of human immunodeficiency virus type 1 are not randomly distributed in gp120. We predict that a partially glycosylated gp120 with most of the dispensable N-linked glycosylation sites removed may be a better vaccine candidate than the fully glycosylated gp120.

Mutational analysis of conserved N-linked glycosylation sites of human immunodeficiency virus type 1 gp41

Amino acid substitutions were introduced into four conserved N-linked glycosylation sites of the human immunodeficiency virus type 1 envelope transmembrane glycoprotein, gp41, to alter the canonical N-linked glycosylation sequences. One altered site produced a severe impairment of viral infectivity, which raises the possibility that N-linked sugars at this site may have an important role in the human immunodeficiency virus type 1 life cycle.

Role of asparagine-linked glycosylation in human immunodeficiency virus type 1 transmembrane envelope function

Transmembrane envelope protein (TM) residues 100, 105, and 128 of human immunodeficiency virus type 1 (HIV-1) strain HXB2 are potential sites for asparagine-linked oligosaccharide additions which are conserved among HIV-1 isolates, and all other lentivirus TM proteins. Site-specific mutants of each of the asparagine residues did not eliminate the ability of the virus to infect and replicate in CD4+ cells, but infectivity was reduced with all of these mutants, and syncytia induction was attenuated with two of these mutants. Studies of envelope expression of the mutant with the most severe defect demonstrated no significant effects on envelope protein synthesis, conformation, processing, multimerization, or release into the culture medium, suggesting that N-linked oligosaccharides are important in the specific fusion activity of TM.

Human T-cell leukemia virus type I envelope protein maturation process: requirements for syncytium formation

The human T-cell leukemia virus type I (HTLV-I) envelope protein is synthesized as a gp61 precursor product cleaved into two mature proteins, a gp45 exterior protein and a gp20 anchoring the envelope at the cell membrane. Using N-glycosylation inhibitors and site-directed mutagenesis of the potential glycosylation sites, we have studied the HTLV-I envelope intracellular maturation requirements for syncytium formation. We show here that experimental conditions resulting in the absence of precursor cleavage (tunicamycin, monensin treatments, and use of inhibitors of the reticulum steps of the N glycosylations) also result in no cell surface expression of envelope protein. The lack of syncytium formation observed in these cases is thus explained by incorrect intracellular transport. When the precursor is cleaved in the Golgi stack (no treatment or treatment with inhibitors of the Golgi steps of the N glycosylations), it is transported to the cell surface in all the cases examined. Syncytium formation is markedly reduced, however, when Golgi glycosylations are incorrect, which shows that the sugar moieties are involved in the envelope functions. Site-directed mutagenesis demonstrates that each of the five potential glycosylation sites is actually glycosylated. Glycosylation of sites 1 and 5 is required for normal maturation, whereas that of sites 2, 3, and 4 is dispensable. Glycosylation of each site, however, is required for normal syncytium formation. Altogether, the restraints exerted by the cell for the HTLV-I envelope to be transported and functional are very high, which might play a role in the observed conservation of the envelope amino acid sequence between various strains.

Glucosidase inhibitors for treatment of HIV-1 infection

The HIV-1 envelope protein is a glycoprotein composed of 120 kD and 41 kD subunits. It contains 30-38 potential asparagine-linked glycosylation sites which have been shown to play a role in CD4 binding, virus uptake, and cytopathogenicity. Several inhibitors of oligosaccharide attachment or modification have been tested. An agent which inhibits glucosidases, N-butyl deoxynojirimycin was found to inhibit HIV-1 and SIVmac infectivity, and is currently in clinical trials.

Brefeldin A inhibits the processing and secretion of envelope glycoproteins of human immunodeficiency virus type 1

The processing and secretion of the envelope glycoproteins of human immunodeficiency virus type 1 (HIV-1) were studied in chronically infected T cells and in primary macrophages treated with an antiviral antibiotic brefeldin A (BFA). BFA blocks the egress of proteins from the endoplasmic reticulum and has a profound effect on the structure of cis/medial Golgi. In MOLT-3 cells infected with the IIIB strain of HIV-1 (MOLT-3/IIIB), BFA inhibited the intracellular processing of gp160. The secretion of envelope proteins from these cells was significantly inhibited in the presence of BFA. The gag proteins, on the other hand, were processed and secreted normally. BFA also inhibited the proteolytic processing of gp160 in primary macrophages infected with HIV-1. The infectivity of virus pelleted from the medium of MOLT-3/IIIB cells treated with BFA was markedly lower than that obtained from untreated cells. These results demonstrate that the proteolytic processing of gp160 in HIV-1-infected cells takes place after the glycoprotein exists the endoplasmic reticulum and that the transport of glycoprotein to the cell surface is required for assembly of complete HIV-1 particles.

Effect of N-(3-phenyl-2-propenyl)-1-deoxynojirimycin on the lectin binding to HIV-1 glycoproteins

The effect of N-(3-phenyl-2-propenyl)-1-deoxynojirimycin (ppDNM) on the lectin binding to HIV-1 glycoprotein was analyzed by using biotinylated lectins of various sugar specificities as probes. ppDNM potentially inhibited HIV-1-induced syncytium formation and viral infectivity of HIV-1 without cytotoxicity. The lectin binding assay showed that ppDNM treatment reduced Con A binding to gp120 of HIV-1.

Role of oligosaccharides in the processing and maturation of envelope glycoproteins of human immunodeficiency virus type 1

The processing and maturation of envelope glycoproteins of human immunodeficiency virus type 1 (HIV-1) were studied in infected cells treated with inhibitors of oligosaccharide processing. In MOLT-3 cells chronically infected with HIV-1 (strain HTLV-IIIB), tunicamycin severely inhibited the glycosylation of envelope proteins. Deoxynojirimycin, an inhibitor of glucosidase I in the rough endoplasmic reticulum, inhibited the proteolytic processing of gp160, whereas no such effect was noted with either deoxymannojirimycin or swainsonine, inhibitors of mannosidase I and II, respectively, in the Golgi complex. The processed gp120 and gp41 synthesized in the presence of deoxymannojirimycin were found to contain mannose-rich oligosaccharide cores as evidenced by their susceptibility to endoglycosidase H digestion. The formation of syncytia normally observed when CEM cells are cocultured with HIV-1-infected cells was markedly inhibited in the presence of deoxynojirimycin, but such inhibition was not observed in cells treated with deoxymannojirimycin or swainsonine. The infectivity of virions released from MOLT-3/HTLV-IIIB cells treated with deoxynojirimycin or deoxymannojirimycin was significantly lower than the infectivity of virions released from untreated cells. On the other hand, treatment with swainsonine did not affect the infectivity of the progeny virus. These results suggest that the proteolytic processing of gp160 takes place in infected cells when the glycoprotein has mannose-rich oligosaccharide structures. Trimming of glucose residues and the primary trimming of mannose residues are necessary for the release of infectious virus.