Pseudopeptide TASP inhibitors of HIV entry bind specifically to a 95-kDa cell surface protein

Transactive Response DNA-Binding Protein (TARDBP/TDP-43) Regulates Cell Permissivity to HIV-1 Infection by Acting on HDAC6

The transactive response DNA-binding protein (TARDBP/TDP-43) influences the processing of diverse transcripts, including that of histone deacetylase 6 (HDAC6). Here, we assessed TDP-43 activity in terms of regulating CD4+ T-cell permissivity to HIV-1 infection. We observed that overexpression of wt-TDP-43 increased both mRNA and protein levels of HDAC6, resulting in impaired HIV-1 infection independently of the viral envelope glycoprotein complex (Env) tropism. Consistently, using an HIV-1 Env-mediated cell-to-cell fusion model, the overexpression of TDP-43 levels negatively affected viral Env fusion capacity. Silencing of endogenous TDP-43 significantly decreased HDAC6 levels and increased the fusogenic and infection activities of the HIV-1 Env. Using pseudovirus bearing primary viral Envs from HIV-1 individuals, overexpression of wt-TDP-43 strongly reduced the infection activity of Envs from viremic non-progressors (VNP) and rapid progressors (RP) patients down to the levels of the inefficient HIV-1 Envs observed in long-term non-progressor elite controllers (LTNP-EC). On the contrary, silencing endogenous TDP-43 significantly favored the infectivity of primary Envs from VNP and RP individuals, and notably increased the infection of those from LTNP-EC. Taken together, our results indicate that TDP-43 shapes cell permissivity to HIV-1 infection, affecting viral Env fusion and infection capacities by altering the HDAC6 levels and associated tubulin-deacetylase anti-HIV-1 activity.

Subcellular fractionation and localization studies reveal a direct interaction of the fragile X mental retardation protein (FMRP) with nucleolin

Fragile X mental Retardation Protein (FMRP) is a well-known regulator of local translation of its mRNA targets in neurons. However, despite its ubiquitous expression, the role of FMRP remains ill-defined in other cell types. In this study we investigated the subcellular distribution of FMRP and its protein complexes in HeLa cells using confocal imaging as well as detergent-free fractionation and size exclusion protocols. We found FMRP localized exclusively to solid compartments, including cytosolic heavy and light membranes, mitochondria, nuclear membrane and nucleoli. Interestingly, FMRP was associated with nucleolin in both a high molecular weight ribosomal and translation-associated complex (≥6 MDa) in the cytosol, and a low molecular weight complex (∼200 kDa) in the nucleoli. Consistently, we identified two functional nucleolar localization signals (NoLSs) in FMRP that are responsible for a strong nucleolar colocalization of the C-terminus of FMRP with nucleolin, and a direct interaction of the N-terminus of FMRP with the arginine-glycine-glycine (RGG) domain of nucleolin. Taken together, we propose a novel mechanism by which a transient nucleolar localization of FMRP underlies a strong nucleocytoplasmic translocation, most likely in a complex with nucleolin and possibly ribosomes, in order to regulate translation of its target mRNAs.

Pleiotrophin expression and role in physiological angiogenesis in vivo: potential involvement of nucleolin

Background

Pleiotrophin (PTN) is a heparin-binding growth factor with significant role(s) in tumour growth and angiogenesis. Although implication of endogenous PTN has been studied in several in vivo models of tumour angiogenesis, its role in physiological angiogenesis has not been addressed. In the present work, we studied expression and functional significance of endogenous PTN during angiogenesis in the chicken embryo chorioallantoic membrane (CAM).

Methods

Using molecular, cellular and biochemical assays, we studied the expression pattern of PTN in CAM and human endothelial cells and its possible interaction with nucleolin (NCL). CAM cells were transfected with a pCDNA3.1 vector, empty (PC) or containing full length cDNA for PTN in antisense orientation (AS-PTN). Angiogenesis was estimated by measuring total vessel length. In vitro, human endothelial cells migration was studied by using a transwell assay, and down-regulation of NCL was performed by using a proper siRNA.

Results

Endogenous PTN mRNA and protein levels, as well as protein levels of its receptor protein tyrosine phosphatase beta/zeta (RPTPβ/ζ) were maximal at early stages, when CAM angiogenesis is active. Application of AS-PTN onto CAM at days of active angiogenesis was not toxic to the tissue and led to dose-dependent decreased expression of endogenous PTN, ERK1/2 activity and angiogenesis. Interestingly, endogenous PTN was also immunolocalized at the endothelial cell nucleus, possibly through interaction with NCL, a protein that has a significant role in the nuclear translocation of many proteins. Down-regulation of NCL by siRNA in human endothelial cells significantly decreased nuclear PTN, verifying this hypothesis. Moreover, it led to abolishment of PTN-induced endothelial cell migration, suggesting, for the first time, that PTN-NCL interaction has a functional significance.

Conclusions

Expression of endogenous PTN correlates with and seems to be involved in angiogenesis of the chicken embryo CAM. Our data suggest that NCL may have a role, increasing the number of growth factors whose angiogenic/tumorigenic activities are mediated by NCL.

Targeting surface nucleolin with multivalent HB-19 and related Nucant pseudopeptides results in distinct inhibitory mechanisms depending on the malignant tumor cell type

BACKGROUND

Nucleolin expressed at the cell surface is a binding protein for a variety of ligands implicated in tumorigenesis and angiogenesis. By using a specific antagonist that binds the C-terminal RGG domain of nucleolin, the HB-19 pseudopeptide, we recently reported that targeting surface nucleolin with HB-19 suppresses progression of established human breast tumor cells in the athymic nude mice, and delays development of spontaneous melanoma in the RET transgenic mice.

METHODS

By the capacity of HB-19 to bind stably surface nucleolin, we purified and identified nucleolin partners at the cell surface. HB-19 and related multivalent Nucant pseudopeptides, that present pentavalently or hexavalently the tripeptide Lysψ(CH2N)-Pro-Arg, were then used to show that targeting surface nucleolin results in distinct inhibitory mechanisms on breast, prostate, colon carcinoma and leukemia cells.

RESULTS

Surface nucleolin exists in a 500-kDa protein complex including several other proteins, which we identified by microsequencing as two Wnt related proteins, Ku86 autoantigen, signal recognition particle subunits SRP68/72, the receptor for complement component gC1q-R, and ribosomal proteins S4/S6. Interestingly, some of the surface-nucleolin associated proteins are implicated in cell signaling, tumor cell adhesion, migration, invasion, cell death, autoimmunity, and bacterial infections. Surface nucleolin in the 500-kDa complex is highly stable. Surface nucleolin antagonists, HB-19 and related multivalent Nucant pseudopeptides, exert distinct inhibitory mechanisms depending on the malignant tumor cell type. For example, in epithelial tumor cells they inhibit cell adhesion or spreading and induce reversion of the malignant phenotype (BMC cancer 2010, 10:325) while in leukemia cells they trigger a rapid cell death associated with DNA fragmentation. The fact that these pseudopeptides do not cause cell death in epithelial tumor cells indicates that cell death in leukemia cells is triggered by a specific signaling mechanism, rather than nonspecific cellular injury.

CONCLUSIONS

Our results suggest that targeting surface nucleolin could change the organization of the 500-kDa complex to interfere with the proper functioning of surface nucleolin and the associated proteins, and thus lead to distinct inhibitory mechanisms. Consequently, HB-19 and related Nucant pseudopeptides provide novel therapeutic opportunities in treatment of a wide variety of cancers and related malignancies.

Surface expressed nucleolin is constantly induced in tumor cells to mediate calcium-dependent ligand internalization

BACKGROUND

Nucleolin is one of the major proteins of the nucleolus, but it is also expressed on the cell surface where is serves as a binding protein for variety of ligands implicated in tumorigenesis and angiogenesis. Emerging evidence suggests that the cell-surface expressed nucleolin is a strategic target for an effective and nontoxic cancer therapy.

METHODOLOGY/PRINCIPAL FINDINGS

By monitoring the expression of nucleolin mRNA, and by measuring the level of nucleolin protein recovered from the surface and nucleus of cells, here we show that the presence of nucleolin at the cell surface is dependent on the constant induction of nucleolin mRNA. Indeed, inhibitors of RNA transcription or translation block expression of surface nucleolin while no apparent effect is observed on the level of nucleolin in the nucleus. The estimated half-life of surface nucleolin is less than one hour, whereas that of nuclear nucleolin is more than 8 hours. Nucleolin mRNA induction is reduced markedly in normal fibroblasts that reach confluence, while it occurs continuously even in post-confluent epithelial tumor cells consistent with their capacity to proliferate without contact inhibition. Interestingly, cold and heat shock induce nucleolin mRNA concomitantly to enhanced mRNA expression of the heat shock protein 70, thus suggesting that surface nucleolin induction also occurs in response to an environmental insult. At the cell surface, one of the main functions of nucleolin is to shuttle specific extracellular ligands by an active transport mechanism, which we show here to be calcium dependent.

CONCLUSION/SIGNIFICANCE

Our results demonstrate that the expression of surface nucleolin is an early metabolic event coupled with tumor cell proliferation and stress response. The fact that surface nucleolin is constantly and abundantly expressed on the surface of tumor cells, makes them a preferential target for the inhibitory action of anticancer agents that target surface nucleolin.

The spliceosomal phosphopeptide P140 controls the lupus disease by interacting with the HSC70 protein and via a mechanism mediated by gammadelta T cells

The phosphopeptide P140 issued from the spliceosomal U1-70K snRNP protein is recognized by lupus CD4(+) T cells, transiently abolishes T cell reactivity to other spliceosomal peptides in P140-treated MRL/lpr mice, and ameliorates their clinical features. P140 modulates lupus patients' T cell response ex vivo and is currently included in phase IIb clinical trials. Its underlying mechanism of action remains elusive. Here we show that P140 peptide binds a unique cell-surface receptor, the constitutively-expressed chaperone HSC70 protein, known as a presenting-protein. P140 induces apoptosis of activated MRL/lpr CD4(+) T cells. In P140-treated mice, it increases peripheral blood lymphocyte apoptosis and decreases B cell, activated T cell, and CD4(-)CD8(-)B220(+) T cell counts via a specific mechanism strictly depending on gammadelta T cells. Expression of inflammation-linked genes is rapidly regulated in CD4(+) T cells. This work led us to identify a powerful pathway taken by a newly-designed therapeutic peptide to immunomodulate lupus autoimmunity.

Midkine, a cytokine that inhibits HIV infection by binding to the cell surface expressed nucleolin

The growth factor midkine (MK) is a cytokine that inhibits HIV infection in cell cultures in an autocrine and paracrine manner by blocking the attachment of HIV particles to permissive cells. MK mRNA is systematically expressed in adult peripheral blood lymphocytes from healthy donors, while its expression becomes markedly but transiently increased upon in vitro treatment of lymphocytes with IL-2 or IFN-gamma and activation of T lymphocytes by PHA or through the engagement of the CD28 antigen. The binding of MK to cells occurs specifically at a high and a low affinity binding site. This low affinity-binding site is the cell-surface expressed nucleolin, which is implicated in the mechanism of the initial attachment of HIV particles to cells. Accordingly, the nucleolin-binding HB-19 pseudopeptide has no effect on the MK binding to the high affinity binding site, whereas it prevents the binding of MK to the low affinity binding site, thus suggesting the low affinity receptor of MK is the cell-surface-expressed nucleolin. Confocal immunofluorescence laser microscopy revealed the colocalization of MK and the cell-surface-expressed nucleolin at distinct spots. The use of various deletion constructs of nucleolin then indicates that the extreme C-terminal end of nucleolin, containing repeats of the amino acid motif RGG, as the domain that binds MK. The specific binding of MK to the surface nucleolin is independent of heparan sulfate and chondroitin sulfate proteoglycans. After binding to cells, MK enters cells by an active process in which nucleolin and lipid rafts appear to be implicated. The potent and the distinct anti-HIV action of MK along with its enhanced expression in lymphocytes by various physiological stimuli, point out that MK is a cytokine that could be involved in HIV pathogenesis.

The anti-HIV cytokine midkine binds the cell surface-expressed nucleolin as a low affinity receptor

The growth factor midkine (MK) is a cytokine that inhibits the attachment of human immunodeficiency virus particles by a mechanism similar to the nucleolin binding HB-19 pseudopeptide. Here we show that the binding of MK to cells occurs specifically at a high and a low affinity binding site. HB-19 prevents the binding of MK to the low affinity binding site only. Confocal immunofluorescence laser microscopy revealed the colocalization of MK and the cell-surface-expressed nucleolin at distinct spots. The use of various deletion constructs of nucleolin then indicated that the extreme C-terminal end of nucleolin, containing repeats of the amino acid motif RGG, is the domain that binds MK. The specific binding of MK to cells is independent of heparan sulfate and chondroitin sulfate expression. After binding to cells, MK enters cells by an active process. Interestingly, the cross-linking of surface-bound MK with a specific antibody results in the clustering of surface nucleolin along with glycosylphosphatidylinositol-linked proteins CD90 and CD59, thus, pointing out that MK binding induces lateral assemblies of nucleolin with specific membrane components of lipid rafts. Our results suggest that the cell surface-expressed nucleolin serves as a low affinity receptor for MK and could be implicated in its entry process.

Effects of L- and D-REKR amino acid-containing peptides on HIV and SIV envelope glycoprotein precursor maturation and HIV and SIV replication

The aim of the present study was to evaluate the capacity of synthetic l- and d-peptides encompassing the HIV-1(BRU) gp160 REKR cleavage site to interfere with HIV and simian immuno-deficiency virus (SIV) replication and maturation of the envelope glycoprotein (Env) precursors. To facilitate their penetration into cells, a decanoyl (dec) group was added at the N-terminus. The sequences synthesized included dec5d or dec5l (decREKRV), dec9d or dec9l (decRVVQREKRV) and dec14d or dec14l (TKAKRRVVQREKRV). The peptide dec14d was also prepared with a chloromethane (cmk) group as C-terminus. Because l-peptides exhibit significant cytotoxicity starting at 35 microM, further characterization was conducted mostly with d-peptides, which exhibited no cytotoxicity at concentrations higher than 70 microM. The data show that only dec14d and dec14dcmk could inhibit HIV-1(BRU), HIV-2(ROD) and SIV(mac251) replication and their syncytium-inducing capacities. Whereas peptides dec5d and dec9d were inactive, dec14dcmk was at least twice as active as peptide dec14d. At the molecular level, our data show a direct correlation between anti-viral activity and the ability of the peptides to interfere with maturation of the Env precursors. Furthermore, we show that when tested in vitro the dec14d peptide inhibited PC7 with an inhibition constant K(i)=4.6 microM, whereas the peptide dec14l preferentially inhibited furin with a K(i)=28 microM. The fact that PC7 and furin are the major prohormone convertases reported to be expressed in T4 lymphocytes, the principal cell targets of HIV, suggests that they are involved in the maturation of HIV and SIV Env precursors.

The anti-HIV pentameric pseudopeptide HB-19 binds the C-terminal end of nucleolin and prevents anchorage of virus particles in the plasma membrane of target cells

The multivalent pseudopeptide HB-19 that binds the cell-surface-expressed nucleolin is a potent inhibitor of human immunodeficiency virus (HIV) infection by blocking virus particle attachment and thus anchorage in the plasma membrane. We show that cross-linking of surface-bound HB-19A (like HB-19 but with a modified template) results in aggregation of HB-19A with surface nucleolin. Consistent with its specific action, HB-19A binding to different types of cells reaches saturation at concentrations that have been reported to result in inhibition of HIV infection. By using Chinese hamster ovary mutant cell lines, we confirm that the binding of HB-19A to surface nucleolin is independent of heparan and chondroitin sulfate proteoglycans. In vitro generated full-length nucleolin was found to bind HB-19A, whereas the N-terminal part containing the acidic amino acid stretches of nucleolin did not. The use of various deletion constructs of the C-terminal part of nucleolin then permitted the identification of the extreme C-terminal end of nucleolin, containing repeats of the amino acid motif, RGG, as the domain that binds HB-19A. Finally, a synthetic peptide corresponding to the last C-terminal 63 amino acids was able to inhibit HIV infection at the stage of HIV attachment to cells, thus suggesting that this domain could be functional in the HIV anchorage process.

The anti-HIV pentameric pseudopeptide HB-19 is preferentially taken up in vivo by lymphoid organs where it forms a complex with nucleolin

The HB-19 pseudopeptide 5[Kpsi(CH(2)N)PR]-TASP, psi(CH(2)N) for reduced peptide bond, is a specific inhibitor of HIV infection in different CD4(+) cell lines and in primary T-lymphocytes and macrophages. It blocks virus-particle attachment to permissive cells by binding and forming a stable complex with nucleolin expressed on the cell surface. Here, we have investigated the tissue distribution of the tritiated HB-19 by using beta-radio imager whole-body mapping in rats. A rapid, selective, and stable distribution and accumulation of the systematically administered HB-19 was demonstrated within the spleen, liver, bone, and kidney as soon as 5 min following its administration. No apparent uptake of HB-19 occurred in the brain and the muscle tissue. Interestingly and despite its rapid clearance from the blood, at 24 h postexposure a significant proportion of HB-19 was still recovered from target organs, of which 16-37% could be accounted for intact pseudopeptide. The elimination of HB-19 mainly occurred by renal glomerular filtration and most of the excreted radioactivity appeared to be HB-19 metabolites. Finally, injection of the biotin-labeled HB-19 pseudopeptide but not its control counterpart allowed the recovery of the HB-19-nucleolin complex from the liver, spleen, thymus, and bone marrow, thus indicating that the in vivo molecular target of HB-19 is surface nucleolin. Our results demonstrate the preferential uptake and stability of HB-19 in lymphoid organs that are the site of HIV propagation.

Characterization of interaction between C-domain on HIV-1 gp41 and the putative receptor protein p62

Based on the fact that the binding of HIV-1 gp41 to the putative cellular receptor protein p62 could be inhibited by the C-domain peptide of gp41, we wanted to confirm the interaction of the C-domain with p62 and to characterize the receptor-binding site on the C-domain. We attempted to isolate the putative receptor protein p62 from cell lysates of the human B cell line Raji by affinity chromatography using sepharose-columns which were conjugated with three different peptides of the C-domain respectively. A protein of 62 kDa was isolated by peptide (NP2)-sepharose-column, while none of the proteins was identified in eluates of the other two overlapped peptides of C-domain, indicating that HIV-1 gp41 by the region aa635-664 of C-domain binds to the putative receptor protein p62. Besides, CD spectroscopy analysis revealed that only a NP2 peptide could induce significant conformational change of P62. In addition, the interaction between P62 and three peptides of the C-domain was characterized by the surface plasma resonance (SPR) measurement. It was indicated that only the NP2 peptide significantly inhibited the interaction between rsgp41 and the putative receptor P62, confirming that the protein p62 may serve as a potential receptor for gp41 binding, and the peptide NP2 contains an integrate binding site for gp41 binding to p62.

Calreticulin, a potential cell surface receptor involved in cell penetration of anti-DNA antibodies

A 50-kDa protein was purified as a potential receptor, using an affinity matrix containing biotinylated F14.6 or H9.3 anti-DNA mAbs derived from autoimmune (New Zealand Black x New Zealand White)F(1) mouse and membrane extracts from cells. This protein was identified as calreticulin (CRT) by microsequencing. Confocal microscopy and FACS analysis showed that CRT was present on the surface of various cells. CRT protein was recognized by a panel of anti-DNA mAbs in ELISA. The binding of F14.6 to lymphocytes and Chinese hamster ovary cells was inhibited by soluble CRT or SPA-600. Thus, the anti-DNA mAbs used in this study bound to CRT, suggesting that CRT may mediate their penetration into the cells and play an important role in lupus pathogenesis.

Inhibition of HIV infection by the cytokine midkine

The growth factor midkine (MK) has been reported to bind heparan sulfate and nucleolin, two components of the cell surface implicated in the attachment of HIV-1 particles. Here we show that synthetic and recombinant preparations of MK inhibit in a dose-dependent manner infection of cells by T-lymphocyte- and macrophage-tropic HIV-1 isolates. The binding of labeled MK to cells is prevented by excess unlabeled MK or by the anti-HIV pseudopeptide HB-19 that blocks HIV entry by forming a stable complex with the cell-surface-expressed nucleolin. MK mRNA is systematically expressed in adult peripheral blood lymphocytes from healthy donors, while its expression becomes markedly but transiently increased upon in vitro treatment of lymphocytes with IL-2 or IFN-gamma and activation of T-lymphocytes by PHA or antibodies specific to CD3/CD28. In MK-producing lymphocytes, MK is detectable at the cell surface where it colocalizes with the surface-expressed nucleolin. Finally, by using MK-producing CD4(+) and CD4(-) cell clones we show that HIV infection in cell cultures could be inhibited in both an autocrine and a paracrine manner. The potent and distinct anti-HIV action of MK along with its enhanced expression in lymphocytes by various physiological stimuli suggests that MK is a cytokine that could be implicated in HIV-induced pathogenesis.

The HB-19 pseudopeptide 5[Kpsi(CH2N)PR]-TASP inhibits attachment of T lymophocyte- and macrophage-tropic HIV to permissive cells

The HB-19 pseudopeptide 5[Kpsi(CH2N)PR]-TASP[psi(CH2N) indicating a reduced peptide bond], which binds the cell surface-expressed nucleolin, is a potent inhibitor of HIV infection. Here, by using primary T lymphocyte cultures and an experimental cell model to monitor HIV entry, we show that HB-19 inhibits in a dose-dependent manner both T lymphocyte- and macrophage-tropic HIV isolates. Similar positively charged control pseudopeptides have no effect on HIV infection even at high concentrations. These observations, and the fact that HB-19 has no effect on SIV-mac and HIV-1 pseudotyped with VSV envelope glycoproteins, confirm the specific nature of this inhibitor against the entry process mediated by the HIV envelope glycoproteins. Finally, association of low doses of HB-19 with beta-chemokines or AZT results in an increased inhibitory effect on HIV infection. HB-19 has no inhibitory effect when added to cells a few hours after HIV entry. On the other hand, in HB-19-pretreated cells, the inhibitory effect persists for several hours, even after washing cells to remove away the unbound pseudopeptide. Under such conditions, the attachment of HIV particles to cells is inhibited as efficiently as by neutralizing monoclonal antibodies directed against the V3 loop. In view of its specific mode of action on various HIV isolates, HB-19 represents a potential anti-HIV drug.

The anti-HIV pseudopeptide HB-19 forms a complex with the cell-surface-expressed nucleolin independent of heparan sulfate proteoglycans

The HB-19 pseudopeptide 5[Kpsi(CH(2)N)PR]-TASP, psi(CH(2)N) for reduced peptide bond, is a specific inhibitor of human immunodeficiency virus (HIV) infection in different CD4(+) cell lines and in primary T-lymphocytes and macrophages. Here, by using an experimental CD4(+) cell model to monitor HIV entry and infection, we demonstrate that HB-19 binds the cell surface and inhibits attachment of HIV particles to permissive cells. At concentrations that inhibit HIV attachment, HB-19 binds cells irreversibly, becomes complexed with the cell-surface-expressed nucleolin, and eventually results in its degradation. Accordingly, by confocal immunofluorescence microscopy, we demonstrate the drastic reduction of the cell-surface-expressed nucleolin following treatment of cells with HB-19. HIV particles can prevent the binding of HB-19 to cells and inhibit complex formation with nucleolin. Such a competition between viral particles and HB-19 is consistent with the implication of nucleolin in the process of HIV attachment to target cells. We show that another inhibitor of HIV infection, the fibroblast growth factor-2 (FGF-2) that uses cell-surface-expressed heparan sulfate proteoglycans as low affinity receptors, binds cells and blocks attachment of HIV to permissive cells. FGF-2 does not prevent the binding of HB-19 to cells and to nucleolin, and similarly HB-19 has no apparent effect on the binding of FGF-2 to the cell surface. The lack of competition between these two anti-HIV agents rules out the potential involvement of heparan sulfate proteoglycans in the mechanism of anti-HIV effect of HB-19, thus pointing out that nucleolin is its main target.

Peptide and glycopeptide dendrimers. Part II

Recent progress in peptide and glycopeptide chemistry make the preparation of peptide and glycopeptide dendrimers of acceptable purity, with designed structural and immunochemical properties reliable. New methodologies using unprotected peptide building blocks have been developed to further increase the possibilities of their design and improve their preparation and separation. The sophisticated design of peptide and glycopeptide dendrimers has led to their use as antigens and immunogens, for serodiagnosis and other biochemical uses including drug delivery. Dendrimers bearing peptide with predetermined secondary structures are useful tools in protein de novo design. This article covers synthesis and applications of multiple antigen peptides (MAPs), multiple antigen glycopeptides (MAGs), multiple antigen peptides based on sequential oligopeptide carriers (MAP-SOCs), glycodendrimers and template-assembled synthetic proteins (TASPs). In part II the preparation of MAPs, and the utility of glycodendrimers and TASPs are discussed.

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.

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.

Increased rate of HIV-1 entry and its cytopathic effect in CD4+/CXCR4+ T cells expressing relatively high levels of CD26

The role of the T-cell activation antigen CD26 was evaluated in viral entry and infection of CD4(+)/CXCR4(+) cells by the lymphotropic HIV-1 Lai isolate. For this purpose, CEM T cells, which are permissive to HIV infection and express low levels of CD26, were used to establish by transfection four groups of cell clones expressing either low, high, and very high levels of CD26, or expressing the anti-sense RNA of CD26. Entry was monitored by the detection of proviral DNA synthesis and the kinetics of virus production, whereas the cytopathic effect was demonstrated by the occurrence of apoptosis. HIV entry and infection were consistently accelerated by at least 24 to 48 h in clones expressing high levels of CD26 compared to the parental cells or to the clones expressing low levels of CD26. Interestingly, infection of clones expressing very high levels of CD26 was not accelerated and showed a kinetics of infection similar to that of low CD26 expressing clones. Moreover, HIV infection was significantly reduced in the clones expressing CD26 anti-sense RNA. In the different clones, apoptosis was dependent on the severity of virus infection and occurred after the accumulation of HIV envelope glycoproteins. Our results demonstrate that with equivalently expressed levels of CD4 and CXCR4 in cell lines established from CEM cells, relatively high levels of CD26 contribute to an increased rate of HIV entry, infection, and apoptosis. Furthermore, they point out that overexpression of CD26 in a given cell line may lead to a negative effect on HIV infection. Consequently, CD26 appears to regulate HIV entry and apoptosis, processes which are critical for viral pathogenesis.

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.