Mediation of human immunodeficiency virus type 1 binding by interaction of cell surface heparan sulfate proteoglycans with the V3 region of envelope gp120-gp41

The CC-chemokine RANTES increases the attachment of human immunodeficiency virus type 1 to target cells via glycosaminoglycans and also activates a signal transduction pathway that enhances viral infectivity

We have studied the mechanisms by which the CC-chemokine RANTES can enhance the infectivities of human immunodeficiency virus type 1 (HIV-1) and other enveloped viruses, when present at concentrations in excess of 500 ng/ml in vitro. Understanding the underlying mechanisms might throw light on fundamental processes of viral infection, in particular for HIV-1. Our principal findings are twofold: firstly, that oligomers of RANTES can cross-link enveloped viruses, including HIV-1, to cells via glycosaminoglycans (GAGs) present on the membranes of both virions and cells; secondly, that oligomers of RANTES interact with cell-surface GAGs to transduce a herbimycin A-sensitive signal which, over a period of several hours, renders the cells more permissive to infection by several viruses, including HIV-1. The enhancement mechanisms require that RANTES oligomerize either in solution or following binding to GAGs, since no viral infectivity enhancement is observed with a mutant form of the RANTES molecule that contains a single-amino-acid change (glutamic acid to serine at position 66) which abrogates oligomerization.

HIV-1 attachment: another look

HIV-1 attachment to host cells is generally considered to take place via high-affinity binding between CD4 and gp120. However, the binding of virion-associated gp120 to cellular CD4 is often weak, and most cell types that are permissive for HIV-1 infection express little CD4. Thus, other interactions between the virion and the cell surface could dominate the attachment process.

Proteoglycan receptor binding by Neisseria gonorrhoeae MS11 is determined by the HV-1 region of OpaA

The interaction of the OpaA protein of Neisseria gonorrhoeae MS11mk with heparan sulphate-containing proteoglycan receptors on Chang conjunctiva epithelial cells was examined using isolated receptor binding and cell adherence/internalization assays. OpaA deletion proteins, in which the four surface-exposed regions of the protein were deleted individually, and chimeric OpaA/B proteins, in which the surface-exposed regions of the OpaA and OpaB proteins were exchanged, were expressed in N. gonorrhoeae. The recombinant deletion proteins and the chimeric OpaA/B proteins were surface exposed in the outer membrane of N. gonorrhoeae. Isolated receptor-binding assays and Chang cell infection assays with OpaA deletion variants indicated that hypervariable region 1 was essential for the interaction of N. gonorrhoeae with the proteoglycan receptor. Expression of chimeric OpaA/B proteins confirmed the central role of hypervariable region 1 in receptor binding and demonstrated that this domain alone confers the invasive biological phenotype in a non-heparan sulphate proteoglycan-binding Opa protein. The other variable regions of OpaA enhanced receptor binding in the presence of region 1, but did not constitute binding domains on their own. The results indicate that proteoglycan receptor binding results from a hierarchical interaction between the variable domains of the OpaA protein of MS11mk.

Cell-surface heparan sulfate facilitates human immunodeficiency virus Type 1 entry into some cell lines but not primary lymphocytes

Many viruses have evolved to exploit cell-surface glycosaminoglycans (GAG), particularly heparan sulfate, to facilitate their attachment and infection of host cells. Here, the case for the involvement of heparan sulfate GAG in cellular infection by human immunodeficiency virus Type 1 (HIV-1) compared with herpes simplex virus Type 1 (HSV-1) is re-examined. It is shown that HIV-1 infection is facilitated by heparan sulfate GAG in only one of three highly permissive cell lines tested, whereas HSV-1 infection is facilitated to varying extents in all three. To evaluate the physiological relevance of these findings, primary peripheral blood lymphocytes (PBL), the physiological host for HIV-1, were examined. It was found that treatment of PBL with heparitinase, to remove any traces of heparan sulfate GAG, did not alter their sensitivity to infection by either lymphocyte-tropic, X4-type strain HIV-1IIIB, nor the monocyte-tropic, R5-type strain, HIV-1Ba-L. It is concluded that heparan sulfate GAG has little physiological role in the infection of lymphocytes by HIV-1 and that evidence derived from studies on immortalized cell lines suggesting a significant role must be interpreted with caution.

Tyrosine sulfation of the amino terminus of CCR5 facilitates HIV-1 entry

Chemokine receptors and related seven-transmembrane-segment (7TMS) receptors serve as coreceptors for entry of human and simian immunodeficiency viruses (HIV-1, HIV-2, and SIV) into target cells. Each of these otherwise diverse coreceptors contains an N-terminal region that is acidic and tyrosine rich. Here, we show that the chemokine receptor CCR5, a principal HIV-1 coreceptor, is posttranslationally modified by O-linked glycosylation and by sulfation of its N-terminal tyrosines. Sulfated tyrosines contribute to the binding of CCR5 to MIP-1 alpha, MIP-1 beta, and HIV-1 gp120/CD4 complexes and to the ability of HIV-1 to enter cells expressing CCR5 and CD4. CXCR4, another important HIV-1 coreceptor, is also sulfated. Tyrosine sulfation may contribute to the natural function of many 7TMS receptors and may be a modification common to primate immunodeficiency virus coreceptors.

Baculovirus vector requires electrostatic interactions including heparan sulfate for efficient gene transfer in mammalian cells

BACKGROUND

Recently, several reports have described the ability of recombinant baculoviruses to transduce a variety of mammalian cells. Yet, mechanisms involved in baculovirus entry in those cells remain largely unexplored, particularly at the primary binding step of the virions to the cell membrane.

METHODS

This report focused on the primary virus-cell interactions that lead to in vitro transduction of human 293 cells using a polyhedrin-deleted baculovirus harboring a CMV-driven beta-galactosidase gene (BacLacZ).

RESULTS

Infection rate monitored for 8 h and transduction rate with a multiplicity of infection of up to 800 were, both, non-saturable. Temperatures from 37 degrees C to 4 degrees C dramatically impaired BacLacZ but not adenovirus cell attachment. Competitive infections performed with an excess of a non LacZ-expressing baculovirus hardly competed at a 1/1 ratio. Consistent with an adsorptive binding process onto the cell surface, interactions through electrostatic charges between both viral and cell membranes appeared to be critical for BacLacZ transduction. The addition of polybrene to the cells prior to or during the infection prevented both virus binding and LacZ gene transfer, suggesting the involvement of negatively charged epitopes exposed at the cell surface. The simultaneous presence of the highly charged heparin abrogated BacLacZ binding to the cell surface and subsequent gene transfer. Lastly, direct in vitro binding of BacLacZ to heparin but not BSA columns could be demonstrated after elution of infectious BacLacZ virus in high salt molarity.

CONCLUSION

Electrostatic charges play a critical role during the first step in mammalian cell transduction mediated by a recombinant baculovirus.

The V3 loop-mimicking pseudopeptide 5[Kpsi(CH2N)PR]-TASP inhibits HIV infection in primary macrophage cultures

The V3 loop-mimicking pseudopeptide 5[Kpsi(CH2N)PR]-TASP [psi(CH2N) representing a reduced peptide bond], which presents pentavalently the tripeptide Kpsi(CH2N)PR, is a potent inhibitor of HIV entry. By its capacity to bind specifically protein components on the cell surface, 5[Kpsi(CH2N)PR]-TASP blocks the attachment of virus particles to permissive CD4+ cells. Here, the inhibitory effect of 5[Kpsi(CH2N)PR]-TASP was investigated in monocyte-derived macrophages (MDMs) infected by the monocytotropic HIV-1(Ba-L) isolate. We show that 5[Kpsi(CH2N)PR]-TASP inhibits HIV-1(Ba-L) infection in a dose-dependent manner, with more than 90% inhibition at 2 microM concentration. On the other hand, the control 5[QPQ]-TASP construct and the monovalent Kpsi(CH2N)PR tripeptide have no effect even at high concentrations. Under such experimental conditions, the biotin-labeled 5[Kpsi(CH2N)PR]-TASP, but not the Kpsi(CH2N)PR construct, binds specifically to the surface of MDMs and forms a stable complex with the cell surface-expressed nucleolin, as has been demonstrated to be the case in peripheral blood mononuclear cells. Infection of MDMs by HIV-1(Ba-L) could also be inhibited by beta-chemokines RANTES and MIP-1beta. Interestingly, association of low concentrations of 5[Kpsi(CH2N)PR]-TASP and beta-chemokines results in a synergistic inhibitory effect on HIV infection compared with the effect observed with each reagent alone. The inhibitory effect of 5[Kpsi(CH2N)PR]-TASP in primary macrophage cultures point out its potential as an anti-HIV drug in cells, which are the natural viral targets.

Adaptation of Sindbis virus to BHK cells selects for use of heparan sulfate as an attachment receptor

Attachment of Sindbis virus to the cell surface glycosaminoglycan heparan sulfate (HS) and the selection of this phenotype by cell culture adaptation were investigated. Virus (TR339) was derived from a cDNA clone representing the consensus sequence of strain AR339 (K. L. McKnight, D. A. Simpson, S. C. Lin, T. A. Knott, J. M. Polo, D. F. Pence, D. B. Johannsen, H. W. Heidner, N. L. Davis, and R. E. Johnston, J. Virol. 70:1981-1989, 1996) and from mutant clones containing either one or two dominant cell culture adaptations in the E2 structural glycoprotein (Arg instead of Ser at E2 position 1 [designated TRSB]) or this mutation plus Arg for Ser at E2 114 [designated TRSB-R114]). The consensus virus, TR339, bound to baby hamster kidney (BHK) cells very poorly. The mutation in TRSB increased binding 10- to 50-fold, and the additional mutation in TRSB-R114 increased binding 3- to 5-fold over TRSB. The magnitude of binding was positively correlated with the degree of cell culture adaptation and with attenuation of these viruses in neonatal mice. HS was identified as the attachment receptor for the mutant viruses by the following experimental results. (i) Low concentrations of soluble heparin inhibited plaque formation on and binding of mutant viruses to BHK cells by >95%. In contrast, TR339 showed minimal inhibition at high concentrations. (ii) Binding and infectivity of TRSB-R114 was sensitive to digestion of cell surface HS with heparinase III, and TRSB was sensitive to both heparinase I and heparinase III. TR339 infectivity was only slightly affected by either digestion. (iii) Radiolabeled TRSB and TRSB-R114 attached efficiently to heparin-agarose beads in binding assays, while TR339 showed virtually no binding. (iv) Binding and infectivity of TRSB and TRSB-R114, but not TR339, were greatly reduced on Chinese hamster ovary cells deficient in HS specifically or all glycosaminoglycans. (v) High-multiplicity-of-infection passage of TR339 on BHK cell cultures resulted in rapid coselection of high-affinity binding to BHK cells and attachment to heparin-agarose beads. Sequencing of the passaged virus population revealed a mutation from Glu to Lys at E2 70, a mutation common to many laboratory strains of Sindbis virus. These results suggest that TR339, the most virulent virus tested, attaches to cells through a low-affinity, primarily HS-independent mechanism. Adaptive mutations, selected during cell culture growth of Sindbis virus, enhance binding and infectivity by allowing the virus to attach by an alternative mechanism that is dependent on the presence of cell surface HS.

Antiviral effect of bovine lactoferrin saturated with metal ions on early steps of human immunodeficiency virus type 1 infection

Lactoferrin is a mammalian iron-binding glycoprotein present in many biological secretions, such as milk, tears, semen and plasma and a major component of the specific granules of polymorphonuclear leucocytes. The effect of bovine lactoferrin (BLf) in apo-form or saturated with ferric, manganese or zinc ions, on human immunodeficiency virus type 1 (HIV-1) infection in the C8166 T-cell line was studied. Both HIV-1 replication and syncytium formation were efficiently inhibited, in a dose-dependent manner, by lactoferrins. BLf in apo and saturated forms markedly inhibited HIV-1 replication when added prior to HIV infection or during the virus adsorption step, thus suggesting a mechanism of action on the HIV binding to or entry into C8166 cells. Likewise, the addition of Fe3+BLf prior to HIV infection and during the attachment step resulted in a marked reduction of the HIV-1 DNA in C8166 cells 20 h after infection. The potent antiviral effect and the high selectivity index exhibited by BLf suggest for this protein, in apo or saturated forms, an important role in inhibiting the early HIV-cell interaction, even though a post adsorption effect cannot be ruled out.

Interactions among HIV gp120, CD4, and CXCR4: dependence on CD4 expression level, gp120 viral origin, conservation of the gp120 COOH- and NH2-termini and V1/V2 and V3 loops, and sensitivity to neutralizing antibodies

The binding of HIV-derived recombinant soluble (s)gp120 to the CD4(+)/CXCR4(+) A3.01 T cell line inhibits the binding of the CXCR4-specific monoclonal antibodies 12G5, which interacts with the second extracellular loop, and 6H8, which binds the NH2 terminus. We have used this as an assay to analyse the interaction of recombinant sgp120 from diverse viral origins with CXCR4. The strength of the interaction between sgp120 and CXCR4 correlated with sgp120 affinity for the CD4-CXCR4 complex, and the interaction of sgp120MN and sgp120IIIB with CXCR4 was highly dependent on the level of CD4 expressed on a variety of different T cell lines. sgp120 from X4, R5X4, and R5 viruses interacted with CXCR4, although the R5 sgp120-CXCR4 interactions were weaker than those of the other gp120s. The interaction of sgp120IIIB or sgp120MN with CXCR4 was inhibited by neutralizing monoclonal antibodies that prevent the sgp120-CD4 interaction but also by antibodies specific for the gp120 V2 and V3 loops, the CD4-induced epitope and the 2G12 epitope, which interfere weakly or not at all with CD4-sgp120 binding. The binding to A3.01 cells of wild-type sgp120HxB2, but not of sgp120 deleted in the COOH and NH2 termini, interfered with 12G5 binding in a dose-dependent manner. Further deletion of the V1 and V2 loops restored CXCR4 binding activity, but additional removal of the V3 loop eliminated the gp120-CXCR4 interaction, without decreasing the affinity between mutated sgp120 and CD4. Taken together, these results demonstrate that the interactions between sgp120 and CXCR4 are globally similar to those previously observed between sgp120 and CCR5, with some apparent differences in the strength of the sgp120-CXCR4 interactions and their dependence on CD4.

Cytokine regulation of human immunodeficiency virus type 1 entry and replication in human monocytes/macrophages through modulation of CCR5 expression

Human macrophages express chemokine receptors that act as coreceptors for human immunodeficiency virus type 1 (HIV-1) and are major targets for HIV-1 infection in vivo. The effects of cytokines on HIV-1 infection of macrophages and on the expression of CCR5, the principal coreceptor for macrophage-tropic viruses, have now been investigated. Expression of CCR5 on the surface of freshly isolated human monocytes was virtually undetectable by flow cytometry with the monoclonal antibody 5C7. However, after culture of monocytes for 48 h in serum-free medium, approximately 30% of the resulting macrophages expressed CCR5 and the cells were susceptible to infection by macrophage-tropic HIV-1. Addition of either macrophage colony-stimulating factor (M-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF) to the cultures markedly increased both the extent of HIV-1 entry and replication as well as surface expression of CCR5. In contrast, addition of the T-helper 2 (Th2) cell-derived cytokine interleukin-4 (IL-4) or IL-13 prevented the expression of CCR5 induced by culture in medium alone, and IL-4 inhibited virus entry, replication, and cytopathicity under these conditions. IL-4 or IL-13 also prevented the stimulatory effects of M-CSF or GM-CSF on CCR5 expression as well as HIV-1 entry and replication. In addition, IL-4 reversed the increase in CCR5 expression induced by pretreatment of cells with M-CSF. Although IL-10 also inhibits HIV-1 replication in macrophages, it did not suppress surface CCR5 expression induced by colony-stimulating factors. These results indicate that the cytokine environment determines the susceptibility of macrophages to HIV-1 infection by various mechanisms, one of which is the regulation of HIV-1 coreceptor expression.

Identification of V3 loop-binding proteins as potential receptors implicated in the binding of HIV particles to CD4(+) cells

The binding of human immunodeficiency virus (HIV) type 1 particles to CD4(+) cells could be blocked either by antibodies against the V3 loop domain of the viral external envelope glycoprotein gp120, or by the V3 loop mimicking pseudopeptide 5[Kpsi(CH2N)PR]-TASP, which forms a stable complex with a cell-surface-expressed 95-kDa protein. Here, by using an affinity matrix containing 5[Kpsi(CH2N)PR]-TASP and cytoplasmic extracts from human CEM cells, we purified three V3 loop-binding proteins of 95, 40, and 30 kDa, which after microsequencing were revealed to be as nucleolin, putative HLA class II-associated protein (PHAP) II, and PHAP I, respectively. The 95-kDa cell-surface protein was also isolated and found to be nucleolin. We show that recombinant preparations of gp120 bind the purified preparations containing the V3 loop-binding proteins with a high affinity, comparable to the binding of gp120 to soluble CD4. Such binding is inhibited either by 5[Kpsi(CH2N)PR]-TASP or antibodies against the V3 loop. Moreover, these purified preparations inhibit HIV entry into CD4(+) cells as efficiently as soluble CD4. Taken together, our results suggest that nucleolin, PHAP II, and PHAP I appear to be functional as potential receptors in the HIV binding process by virtue of their capacity to interact with the V3 loop of gp120.

Infection of human primary renal epithelial cells with HIV-1 from children with HIV-associated nephropathy

Children affected with human immunodefficiency virus (HIV)-associated nephropathy (HIVAN) usually develop significant renal glomerular and tubular epithelial cell injury. The pathogenesis of these changes is not clearly understood. Human renal tubular epithelial cells (RTEc) do not express CD4 surface receptors, and it is not clear whether these cells can be infected by HIV-1. Certain strains of HIV-1, however, have been shown capable of infecting CD4-negative epithelial cell lines. We hypothesized that the inability of laboratory strains of HIV-1 to infect renal epithelial cells may be due to a limited tropism, as opposed to wild-type viruses derived from children with HIVAN, and that viruses derived from these children are capable of infecting RTEc from the same patient. Here, we have demonstrated that HIV-1 isolates from children with HIVAN can productively infect RTEc through a CD4 independent pathway, and that infected mononuclear cells can transfer the virus to human RTEc. Human RTEc sustained low levels of viral replication and HIV-1 inhibited the growth and survival of cultured human RTEc. Thus, HIV-1 may directly induce degenerative changes in RTEc of children with HIVAN. Infected macrophages may play a relevant role in this process by transferring viruses to RTEc.

Human immunodeficiency virus type 1 attachment to HeLa CD4 cells is CD4 independent and gp120 dependent and requires cell surface heparans

The binding of human immunodeficiency virus type 1 (HIV-1) (Hx10) virions to two different cell lines was analyzed by using a novel assay based on the detection, by anti-HLA-DR-specific antibodies, of HLA-DR+ virus binding to HLA-DR- cells. Virion attachment to the CD4+-T-cell line A3.01 was highly CD4 dependent in that it was potently inhibited by CD4 monoclonal antibodies (MAbs), and little virus binding to the CD4- sister A2.01 line was observed. By contrast, virion binding to HeLa cells expressing moderate or high levels of CD4 was equivalent to, or lower than, binding to wild-type CD4- HeLa cells. Moreover, several CD4 MAbs did not reduce, but enhanced, HIV-1 attachment to HeLa-CD4 cells. CD4 was required for infection of HeLa cells, however, demonstrating a postattachment role for this receptor. MAbs specific for the V2 and V3 loops and the CD4i epitope of gp120 strongly inhibited virion binding to HeLa-CD4 cells, whereas MAbs specific for the CD4bs and the 2G12 epitopes enhanced attachment. Despite this, all gp120- and gp41-specific MAbs tested neutralized infectivity on HeLa-CD4 cells. HIV-1 attachment to HeLa cells was only partially inhibited by MAbs specific for adhesion molecules present on the virus or target cells but was completely blocked by polyanions such as heparin, dextran sulfate, and pentosan sulfate. Treatment of HeLa-CD4 cells with heparinases completely eliminated HIV attachment and infection, strongly implicating cell surface heparans in the attachment process. CD4 dependence for HIV-1 attachment to target cells is thus highly cell line specific and may be replaced by other ligand-receptor interactions.

Simple and rapid purification of alphaherpesviruses by chromatography on a cation exchange membrane

A simple and rapid method is described for the purification of two alphaherpesviruses, pseudorabies virus (PrV) and bovine herpesvirus 1, by chromatography on a cation exchange membrane. Cell culture supernatants were passed over a sulfonic-acid modified filter membrane and virions were eluted with a potassium chloride-containing buffer. Over 85% of the virus was eluted within a single fraction and specific infectivity of the resulting virus preparation was over 10-fold higher than that of sucrose gradient-purified virions. Cation exchange was also used for purification of PrV mutants deleted in several glycoproteins which grow in cell culture to titers 10- to 100-fold lower than those obtained by wildtype PrV. For PrV, the presence of non-essential glycoprotein gC, which mediates interaction of virions with cell surface heparin sulfate during attachment, was crucial for the successful purification by cation exchange.

Heparin and its derivatives bind to HIV-1 recombinant envelope glycoproteins, rather than to recombinant HIV-1 receptor, CD4

We have employed a direct radiolabel binding assay to investigate the interaction between3H-heparin and recombinant envelope glycoproteins, rgp120s, derived from several different isolates of HIV-1. Comparable dose-dependent binding is exhibited by rgp120s from isolates IIIB, GB8, MN and SF-2. Under identical experimental conditions the binding of3H-heparin to a recombinant soluble form of the cellular receptor for gp120, CD4, is negligible. The binding of3H-heparin to rgp120 is competed for by excess unlabeled heparin and certain other, but not all, glycosaminoglycan and chemically modified heparins. Of a range of such polysaccharides tested, ability to compete with3H-heparin for binding was strictly correlated with inhibition of HIV-1 replication in vitro. Those possessing potent anti-HIV-1 activity were effective competitors, whereas those having no or little anti-HIV-1 activity were poor competitors. Scatchard analysis indicates that the K d of the interaction between heparin and rgp120 is 10 nM. Binding studies conducted in increasing salt concentrations confirm that the interaction is ionic in nature. Synthetic 33-35 amino acid peptides based on the sequence of the V3 loop of gp120 also bind to heparin with high affinity. V3 loop peptides that are cyclized due to terminal cysteine residues show more selective binding than their uncyclized counterparts. Overall, these data demonstrate further that heparin exerts its anti-HIV-1 activity by binding to the envelope glycoprotein of HIV-1, rather than its cellular receptor, CD4. This study confirms that the V3 loop of gp120 is the site at which heparin exerts its anti-HIV-1 activity. Moreover, it reveals that high affinity binding to heparin is shared by all four rgp120s examined, despite amino acid substitutions within the V3 loop.

Heparin interferes with translocation of Yop proteins into HeLa cells and binds to LcrG, a regulatory component of the Yersinia Yop apparatus

Yersiniae are equipped with the Yop virulon, an apparatus that allows extracellular bacteria to deliver toxic Yop proteins inside the host cell cytosol in order to sabotage the communication networks of the host cell or even to cause cell death. LcrG is a component of the Yop virulon involved in the regulation of secretion of the Yops. In this paper, we show that LcrG can bind HeLa cells, and we analyse the role of proteoglycans in this phenomenon. Treatment of the HeLa cells with heparinase I, but not chondroitinase ABC, led to inhibition of binding. Competition assays indicated that heparin and dextran sulphate strongly inhibited binding, but that other glycosaminoglycans did not. This demonstrated that binding of HeLa cells to purified LcrG is caused by heparan sulphate proteoglycans. LcrG could bind directly to heparin-agarose beads and, in agreement with these results, analysis of the protein sequence of Yersinia enterocolitica LcrG revealed heparin-binding motifs. In vitro production and secretion by Y. enterocolitica of the Yops was unaffected by the addition of heparin. However, the addition of exogenous heparin decreased the level of YopE-Cya translocation into HeLa cells. A similar decrease was seen with dextran sulphate, whereas the other glycosaminoglycans tested had no significant effect. Translocation was also decreased by treatment of HeLa cells with heparinitase, but not with chondroitinase. Thus, heparan sulphate proteoglycans have an important role to play in translocation. The interaction between LcrG and heparan sulphate anchored at the surface of HeLa cells could be a signal triggering deployment of the Yop translocation machinery. This is the first report of a eukaryotic receptor interacting with the type III secretion and associated translocation machinery of Yersinia or of other bacteria.

Sulfated carbohydrate compounds prevent microbial adherence by sexually transmitted disease pathogens

Heparan sulfate (HS) serves as a receptor for adherence of herpes simplex viruses, Chlamydia trachomatis, Neisseria gonorrhoeae, and, indirectly, human immunodeficiency virus. Using primary human culture systems, we identified sulfated carbohydrate compounds that resemble HS and competitively inhibit infection by these pathogens. These compounds are candidates for intravaginal formulations for the prevention of sexually transmitted diseases.

Antiviral activity of derivatized dextrans on HIV-1 infection of primary macrophages and blood lymphocytes

The present study demonstrates at the molecular level that dextran derivatives carboxymethyl dextran benzylamine (CMDB) and carboxymethyl dextran benzylamine sulfonate (CMDBS), characterized by a statistical distribution of anionic carboxylic groups, hydrophobic benzylamide units, and/or sulfonate moieties, interact with HIV-1 LAI gp120 and V3 consensus clades B domain. Only limited interaction was observed with carboxy-methyl dextran (CMD) or dextran (D) under the same conditions. CMDBS and CMDB (1 microM) strongly inhibited HIV-1 infection of primary macrophages and primary CD4+ lymphocytes by macrophage-tropic and T lymphocyte-tropic strains, respectively, while D or CMD had more limited effects on M-tropic infection of primary macrophages and exert no inhibitory effect on M- or T-tropic infection of primary lymphocytes. CMDBS and CMDB (1 microM) had limited but significant effect on oligomerized soluble recombinant gp120 binding to primary macrophages while they clearly inhibit (> 50%) such binding to primary lymphocytes. In conclusion, the inhibitory effect of CMDB and the CMDBS, is observed for HIV M- and T-tropic strain infections of primary lymphocytes and macrophages which indicates that these compounds interfere with steps of HIV replicative cycle which neither depend on the virus nor on the cell.

Neutralizing antibodies against the V3 loop of human immunodeficiency virus type 1 gp120 block the CD4-dependent and -independent binding of virus to cells

The CD4 molecule is an essential receptor for human immunodeficiency virus type 1 (HIV-1) through high-affinity interactions with the viral external envelope glycoprotein gp120. Previously, neutralizing monoclonal antibodies (MAbs) specific to the third hypervariable domain of gp120 (the V3 loop) have been thought to block HIV infection without affecting the binding of HIV particles to CD4-expressing human cells. However, here we demonstrate that this conclusion was not correct and was due to the use of soluble gp120 instead of HIV particles. Indeed, neutralizing anti-V3 loop MAbs inhibited completely the binding and entry of HIV particles into CD4+ human cells. In contrast, the binding of virus was only partially inhibited by neutralizing anti-CD4 MAbs against the gp120 binding site in CD4, which, like the anti-V3 loop MAbs, completely inhibited HIV entry and infection. Nonneutralizing control MAbs against either the V3 loop or the N or C terminus of gp120 had no significant effect on HIV binding and entry. HIV-1 particles were also found to bind human and murine cells expressing or not expressing the human CD4 molecule. Interestingly, the binding of HIV to CD4+ murine cells was inhibited by both anti-V3 and anti-CD4 MAbs, whereas the binding to human and murine CD4- cells was affected only by anti-V3 loop MAbs. The effect of anti-V3 loop neutralizing MAbs on the HIV binding to cells appears not to be the direct consequence of gp120 shedding from HIV particles or of a decreased affinity of CD4 or gp120 for binding to its surface counterpart. Taken together, our results suggest the existence of CD4-dependent and -independent binding events involved in the attachment of HIV particles to cells; in both of these events, the V3 loop plays a critical role. As murine cells lack the specific cofactor CXCR4 for HIV-1 entry, other cell surface molecules besides CD4 might be implicated in stable binding of HIV particles to cells.

HIV-1 envelope gp120 and viral particles block adenosine deaminase binding to human CD26

CD26, known to be the adenosine deaminase (ADA) binding protein, has been implicated in HIV infection. In human B and T cell lines we show that, irrespective of CD4 expression, 125I-labeled ADA binding to CD26 is inhibited by recombinant soluble HIV-1 envelope glycoprotein gp120 and by HIV-1 infectious particles. Overlapping synthetic peptides covering the entire gp120 sequence were tested to map the region in gp120 responsible for ADA binding inhibition. Only peptides in the C3 region significantly inhibited the binding of ADA to CD26. These results indicate that a specific function of gp120 is the inhibition of ADA binding to CD26 in both CD4+ and CD4- cells. Since the interaction ecto-ADA/CD26 is required for the activation of T cells, it remains possible that HIV particle-mediated blockade of ecto-ADA/CD26 interaction may have significant consequences in the pathogenesis of AIDS disease.

Inhibition of human immunodeficiency virus type 1 infection in a T-cell line (CEM) by new dipeptidyl-peptidase IV (CD26) inhibitors

Phenylalanyl-pyrrolidine-2 nitrile (Phe-pyrr-2-CN) and arginyl(PMC)-pyrrolidine-2-nitrile (Arg(PMC)-pyrr-2-CN) are two dipeptidyl peptidase IV/CD26 (DPP-IV/CD26) inhibitors designed and synthesized by our group. These two compounds suppress the enzymatic activity of DPP-IV/CD26 in a competitive and reversible manner. Pretreatment of CEM cells with either of the compounds yielded a marked albeit transient reduction of HIV infection, as measured by HIV1 p24 production, RT activity and syncytium formation. The ID50 value of the Phe-Pyrr-2-CN and Arg(PMC)-pyrr-2-CN in HIV1 inhibition was 5.3 microM and 2.4 microM, respectively. Administration of either of the DPP-IV/CD26 inhibitors 1 h after HIV1 infection did not suppress HIV1 production. An analog whose inhibitory activity toward DPP-IV/CD26 was abolished by blocking the N-terminal of Phe-pyrr-2-CN with the 9-fluorenymethyloxycarbonyl (Fmoc) group had no effect on HIV1 infection. An additive effect of HIV1 inhibition was observed in combinations of either of the DPP-IV/CD26 inhibitors with CD4 monoclonal antibody. These results suggest that DPP-IV/CD26 enzymatic activity may play a role in facilitating HIV1 infection of human CD4+T cells at the entry process. DPP-IV/CD26 inhibitors may therefore have potential use in combination with other drugs to prevent HIV1 transmission.

HIV type 1 V3 peptide constructs act differently on HIV type 1 infection of peripheral blood lymphocytes and macrophages

We have previously shown that a multibranched peptide construct derived from the tip of the B clade V3 loop consensus sequence (MPBC1: [GPGRAF]8-[K]4-[K]2-K-beta A-OH), but not V3 monomer peptides, inhibit human immunodeficiency virus type 1 (HIV-1) infection and syncytium formation of CD4+ T cells from immortalized lines. Here, we show that MBPC1 attaches to normal peripheral blood lymphocytes (PBLS) and monocytes but not to erythrocytes. While treatment with 5 microM MBPC1 had no significant antiviral effect on HIV-1Ba-L infection of monocyte-derived macrophages as assessed by p24 production in culture supernatants, this dose inhibited both HIV-1Ba-L and HIV-1LAI infection of PBLs. Virus production was inhibited up to 90% when MBPC1 was added to PBLs immediately after the virus, and was inhibited about 50% when it was added after 3 days; no effect was noted when it was added 7 days postinfection. MBPC1 did not affect PBL growth or IL-2 receptor and CD4 surface expression level. These observations suggest a selective antiviral effect of MBPC1 on CD4+ T lymphocytes and they provide additional circumstantial evidence that HIV-1 enters lymphocytes and monocytes by different mechanisms.

Role of cell surface glycosaminoglycans of human T cells in human immunodeficiency virus type-1 (HIV-1) infection

To investigate the role of cell surface glycosaminoglycans (GAGs), including heparan sulfate (HS), on HIV-1 infection in human T cells, HIV-1 binding and infection were determined after treatment of T-cell lines and CD4+ T cells from normal peripheral blood mononuclear cells (PBMC) with GAG-degrading enzyme or a GAG metabolic sulfation inhibitor. Heparitinase I (hep I) and sodium chlorate prevented binding of HIV-1/IIIB to MT-4 cells as revealed by indirect immunofluorescence procedures, thereby inhibiting infection. Hep I was less effective in the binding inhibition of the macrophage-tropic strain HIV-1/SF162 than that of the T-cell line-tropic strain HIV-1/IIIB. The binding of HIV-1/SF162 was about 100-fold less dependent on cell surface HS than HIV-1/IIIB. Human HTLV-I positive T-cell lines expressed more HS than HTLV-I negative T-cell lines or normal CD4+ T cells when stained with anti-HS mAbs against either native or heparitinase-treated HS. With the exception of endo-beta-galactosidase (endo-beta-gal), GAG-degrading enzymes, including hep I, chondroitinase ABC (chon ABC), chondroitinase AC II (chon AC II) and keratanase, did not prevent the binding of HIV-1/IIIB to CD4+ T cells from normal PBMC. These results indicate that the cell surface HS of human T cells participates in HIV-1 infection by facilitating HIV-1/IIIB binding to MT-4 cells. In particular, the sulfation of HS chains is critical. Since the expression of cell surface HS varies among T cells, which are not consistently sensitive to hep I treatment in HIV-1 binding inhibition, other GAG-like molecules may also be involved.

Proline-rich tandem repeats of antibody complementarity-determining regions bind and neutralize human immunodeficiency virus type 1 particles

The proline-rich tandem repeat domain of human mucin MUC1 forms an extended structure containing large repeating loops that are crested by a turn. We show that the repeating-loop structure of MUC1 can be replaced by an antibody complementarity-determining region loop of a human immunodeficiency virus type 1 (HIV-1)-specific neutralizing antibody to create a chimeric, multivalent, mucin-like, anti-HIV-1 compound. We used 8 residues of an antibody molecule to replace 8 of 20 residues of the MUC1 tandem-repeat sequence. The antiviral peptide discussed here contains three copies of a 20-residue tandem repeat, (IYYDYEEDPAPGSTAPPAHG)3, for a total of 60 residues. We demonstrate that the mucin-antibody chimera retains the binding specificity of the parent antibody (monoclonal antibody F58), GPGR of the HIV-1 gp120 V3 neutralizing epitope, and the ability to neutralize virus particles. In inhibition enzyme-linked immunosorbent assay, the mucin-antibody chimeric peptide could inhibit 71 to 84% of binding to a V3 loop peptide by monoclonal antibodies known to be specific for GPGR in the V3 loop. The mucin-antibody chimeric peptide could also inhibit monoclonal antibody binding to native gp120 captured from virus particles. In addition, the chimeric peptide neutralized the homologous HIV-IIIB virus in a standard neutralization assay. The methods of antiviral peptide design and construction presented here are general and theoretically limited only by the size of the antibody repertoire. This approach could be used to synthesize peptides for a variety of therapeutic applications.

Relative resistance to HIV-1 infection of CD4 lymphocytes from persons who remain uninfected despite multiple high-risk sexual exposure

Some individuals remain uninfected with human immunodeficiency virus type-1 (HIV-1) despite multiple high-risk sexual exposures. We studied a cohort of 25 subjects with histories of multiple high-risk sexual exposures to HIV-1 and found that their CD8+ lymphocytes had greater anti-HIV-1 activity than did CD8+ lymphocytes from nonexposed controls. Further studies indicated that their purified CD4+ lymphocytes were less susceptible to infection with multiple primary isolates of HIV-1 than were CD4+ lymphocytes from the nonexposed controls. This relative resistance to HIV-1 infection did not extend to T-cell line-adapted strains, was restricted by the envelope glycoprotein, was not explained by the cell surface density of CD4 molecules, but was associated with the activity of the C-C chemokines RANTES, MIP-1alpha, and MIP-1beta. This relative resistance of CD4+ lymphocytes may contribute to protection from HIV-1 in multiply exposed persons.

Identification of cell surface molecules that interact with pseudorabies virus

The alphaherpesvirus pseudorabies virus (PrV) has been shown to attach to cells by interaction between the viral glycoprotein gC and cell membrane proteoglycans carrying heparan sulfate chains (HSPGs). A secondary binding step requires gD and presumably another, hitherto unidentified cellular receptor. By use of a virus overlay protein binding assay (VOPBA), cosedimentation analyses, and affinity chromatography, we identified three species of cell membrane constituents that bind PrV. By treatment with EDTA, peripheral HSPGs of very high apparent molecular mass (>200 kDa) could be extracted from Madin-Darby bovine kidney cells. Binding of PrV to these HSPGs in the VOPBA was sensitive to enzymatic digestion with heparinase or papain. Cosedimentation analyses indicated that binding between PrV and high-molecular-weight HSPG depended on the presence of gC in the virion. In addition, adsorption of radiolabeled PrV virions to cells could be inhibited by the addition of purified high-molecular-weight HSPG. By using urea extraction buffer, a second species of HSPG of approximately 140 kDa could be solubilized. Binding of PrV to this HSPG in the VOPBA was also dependent on the presence of heparan sulfate, since reactivity was abolished after suppression of glycosaminoglycan biosynthesis with NaClO3 and after heparinase treatment. In addition to HSPG, in cellular membrane extracts obtained by treatment with mild detergent, a 85-kDa membrane protein was demonstrated to bind PrV in the VOPBA and affinity chromatography. In summary, we identified three species of cell membrane constituents that bind PrV: a peripheral HSPG of high molecular weight, an integral HSPG of approximately 140 kDa, and an integral membrane protein of 85 kDa. It is tempting to speculate that interaction between PrV and the two species of HSPG mediates primary attachment of PrV and that the 85-kDa protein is involved in a subsequent attachment step.

The receptor-binding domain of pseudorabies virus glycoprotein gC is composed of multiple discrete units that are functionally redundant

Many herpesviruses attach to cells in a two-step process, using the glycoprotein gC family of homologs to bind the primary receptor, heparan sulfate (HS) proteoglycan, and glycoprotein gD homologs to bind an unknown secondary receptor. We have previously shown by deletion analysis that the amino-terminal one-third of gC from pseudorabies virus (PRV), a swine herpesvirus, includes at least the principal HS receptor-binding domain. This portion of PRV gC contains three discrete clusters of basic residues that exactly or nearly match proposed consensus sequences for heparin-binding domains (HBDs); four additional potential HBDs lie in the distal two-thirds of the glycoprotein. We now specifically implicate each of the three amino-terminal HBDs in virus attachment. Mutational analysis demonstrated that any one of the three HBDs could mediate efficient virus infectivity; HS-dependent PRV attachment to cells was eliminated only after all three amino-terminal HBDs were altered. Furthermore, the binding dysfunction was due to a disruption of the specific HBDs and not to total charge loss. Thus, unlike previously described viral receptor-binding domains, the PRV gC receptor-binding domain is composed of multiple, discrete units that can function independently of one another. These units may function redundantly either to increase binding affinity or perhaps to effectively increase the virus's host range.

Soluble CD4 induces the binding of human immunodeficiency virus type 1 to cells via the V3 loop of glycoprotein 120 and specific sites in glycoprotein 41

We have previously reported that incubation of human immunodeficiency virus type 1 (HIV-1) at 4 degrees C with soluble CD4 (sCD4) does not block but increases the binding of virions to CD4-positive H9 cells. In this study, we investigated the mechanism of this effect. It appears that sCD4 can induce the binding of HIV-1IIIB to CD4-negative human cells and to H9 cells with downregulated expression of CD4 at both 4 and 37 degrees C. The binding is proportional to the amount of sCD4 associated with virions, and requires the presence of heparan sulfate proteoglycans on the surface of cells. Monoclonal antibody (MAb) 9284 directed at an epitope overlapping with a putative heparin binding motif in the V3 loop of gp120 almost completely blocked the sCD4-induced binding of virions, while MAbs recognizing other sites of V2 or V3 loops had no effect. The binding of sCD4-coated virions to cells was also inhibited by MAbs 50-69 and 98-6 directed at extracellular epitopes of gp41, whose exposure is increased on binding of sCD4 to virions. Therefore, sCD4 potentiates the binding of HIV-1IIIB virions to cells by inducing conformational changes that enable envelope gp120 and gp41 to interact with cell surface components other than the CD4 receptor.

Polydeoxyguanine motifs in a 12-mer phosphorothioate oligodeoxynucleotide augment binding to the v3 loop of HIV-1 gp120 and potency of HIV-1 inhibition independency of G-tetrad formation

Phosphorothioate oligodeoxynucleotides belong to a class of polyanions that bind to the third variable domain (v3) of HIV-1 gp120 and inhibit infectivity of a wide variety of HIV-1 isolates. This potent v3 binding of phosphorothioate oligodeoxynucleotides, which is relatively independent of the nucleotide sequence of the oligodeoxynucleotides, decreases with chain length (below 18-mers) and is low for 8-mers. However, recent studies have observed a nucleotide sequence-dependent augmentation of phosphorothioate oligodeoxynucleotide binding to v3 for 8-mers that contain the S-dG4 motif (e.g., SdT2G4T2) and have suggested that formation of quadruple helical tetraplexes (G-tetrads) is associated with the acquisition of v3 binding ability by small phosphorothioate oligodeoxynucleotides. In the current study, a series of SdG4-containing oligodeoxynucleotides were synthesized with varying tandem length (including the 8-mer SdT2G4T2, the 12-mer SdG4T4G4, and the 28-mer SdG4(T4G4)3) and compared with phosphorothioate oligodeoxynucleotides (with similar lengths or related sequences) for (1) their inhibition of the binding of mAb 9284, which binds to the N-terminal portion of the v3 loop, (2) the values of Kc when these compounds are used as competitors of the rgp120-binding of an alkylating phosphodiester oligodeoxynucleotide probe, and (3) inhibition of HIV-1 infectivity in a cell-cell transmission model. The presence of S-dG4 motifs and the number of tandem motifs augmented v3 binding and anti-HIV-1 infectivity for small (8-mer or 12-mer oligodeoxynucleotides) but did not significantly augment the potency of 28-mers. Whereas tetraplex formation of SdT2G4T2 may contribute to its v3 binding, the 12-mer SdG4T4G4 does not migrate as the tetraplex on nonreducing gels, suggesting that S-dG4 motifs may augment anti-HIV activity by multiple mechanisms.

Inhibition of human immunodeficiency virus infection of CD4+ cells by CD4-free glycopeptides from monocytic U937 cells

We have previously demonstrated that human immunodeficiency virus (HIV) envelope glycoproteins have specific carbohydrate-binding properties for mannosyl/N-acetylglucosaminyl residues presented at high density on a carrier in vitro. Here, we investigated whether HIV envelope glycoprotein gp120 was able to interact with surface membrane carbohydrates of CD4+ cells by means of such lectin-carbohydrate interactions. CD4-free tryptic glycopeptides, prepared from the membrane of CD4+ monocytic U937 cells and partially purified by ConA-agarose affinity chromatography, could be eluted by mannan but not by methyl-alpha-mannose or methyl-alpha-glucose, which strongly suggests that they displayed oligomannosidic structures. These glycopeptides bound in a mannosyl-specific manner to radiolabeled recombinant gp120. Deglycosylation with N-glycanase which, as expected, strongly diminished binding of the glycopeptides to concanavalin A also abolished their interaction with gp120. In addition, the glycopeptides inhibited HIV infection of both U937 and CD4+ lymphoid CEM cells when preincubated with the virus. These findings indicate that, independently of the binding to CD4, mannosyl structures on CD4+ cells may play a role through lectin-carbohydrate interactions in envelope glycoprotein binding to a putative coreceptor(s) of HIV.

Human immunodeficiency virus type 1 infection of SK-N-MC cells: domains of gp120 involved in entry into a CD4-negative, galactosyl ceramide/3' sulfo-galactosyl ceramide-positive cell line

The primary receptor for human immunodeficiency virus (HIV) is the CD4 molecule; however, in vitro evidence suggests that a neutral glycolipid, galactosyl ceramide (GalCer) or a derivative molecule, 3' sulfogalactosyl ceramide (GalS), may serve as an alternative receptor for HIV type 1 (HIV-1) in cells of neural and colonic origin. Biochemical studies have demonstrated that recombinant gp120 envelope protein binds to GalCer/GalS in both solid-phase enzyme-linked immunosorbent assay and high-performance thin-layer chromatography overlays. We have used the SK-N-MC cell line, a CD4-negative, GalCer/GalS-positive cell line previously characterized as susceptible to HIV-1 infection, to identify virus isolates with either a positive infection phenotype, HIVHxB2, or a negative infection phenotype, HIV-1(89.6). Using a solid-phase virus binding assay, we determined the level of restriction in HIV-1(89.6) infection to be at the level of virus-glycolipid binding. Furthermore, using HIV-1HxB2-HIV-1(89.6) chimeras, we have identified a 193-amino-acid fragment from the envelope region of HIV-1HxB2 containing the V3, V4, and V5 regions which confers a positive infection phenotype on the HIV-1(89.6) background. Recombinant viruses which separate this 193-amino-acid fragment into two distinct chimeras are each able to confer a positive infection phenotype on the background of HIV89.6, suggesting that a stable GalCer/GalS-envelope interaction is dependent on the conformation of the envelope protein in the context of the viral membrane. Alternatively, the GalCer/GalS-gp120 bond may involve multiple sites on the oligomeric envelope protein.

CD26 expression correlates with entry, replication and cytopathicity of monocytotropic HIV-1 strains in a T-cell line

Experiments to identify cell determinants involved in HIV-1 tropism revealed a specific decrease in the expression of the T-cell activation antigen CD26 after monocytotropic (M-tropic) but not T-cell line-tropic (T-tropic) virus infection of the PM1 T-cell line. The level of CD26 expression in single-cell clones of PM1 correlated with the entry rate and cytopathicity of M-tropic HIV-1 variants, resulting in preferential survival of cells with low CD26 levels after infection. Experiments with recombinant viruses showed that the third hypervariable region of the envelope gp120 plays an important role in this selection process. This study identifies CD26 as a key marker for M-tropic human immunodeficiency virus type 1 (HIV-1) infection and suggests a mechanism for the early loss of CD26-expressing cells in HIV-1-infected individuals.