Characterization of V3 loop-binding protein(s) of Molt-4 and U937 cells

The N-terminal of the V3 loop in HIV type 1 gp120 is responsible for its conformation-dependent interaction with cell surface molecules

The V3 loop of HIV-1 gp120 plays an important role in the interaction of the viral envelope with cellular coreceptors and/or with other cell surface molecules. To clarify this interaction we used a panel of monoclonal antibodies (MAbs) against V3 loop and synthetic looped V3 peptides V3-BH10, V3-ADA, and V3-89.6, derived from the V3 regions of the BH10 clone of IIIB (X4-tropic), ADA (R5-tropic), and 89.6 (R5X4-tropic), respectively. A linear mutant peptide, V3-BH10/CA, was also synthesized as a control. Biotinylated V3-BH10, -BH10/CA, and-ADA were also made. The binding abilities of the biotinylated and nonbiotinylated peptides to various types of cells were investigated by using flow cytometry. Subsequently, the principal region of the V3 loop involved in cell surface binding was analyzed by using MAbs against the tip (447-52D and 694-98D), N-termini (IIIB-V3-21) or C-termini (IIIB-V3-01) of the V3 loop in flow cytometry and enzyme-linked immunoabsorbent assay. We demonstrate that looped V3 peptides of both X4 and R5X4 HIV (V3-BH10 and V3-89.6) can bind to various types of cells irrespective of their CD4 and/or coreceptor expression in a conformation-dependent manner. In contrast, the V3 loop of R5 HIV (V3-ADA) can scarcely bind to the cells. Using MAbs whose epitopes cover the entire V3 loop we found that MAb IIIB-V3-21 can react with platebound but not cell-bound peptides, and the MAb blocked biotin-V3-BH10 binding suggesting that the N-terminal of the V3 loop interacts directly with cell surface molecule(s).

Marked increase in anti-HIV activity, as well as inhibitory activity against HIV entry mediated by CXCR4, linked to enhancement of the binding ability of tachyplesin analogs to CXCR4

T22 ([Tyr5,12, Lys7]-polyphemusin II) is a strong anti-HIV compound. Six analogs of T22 and two natural forms were synthesized. Of them, all downsized peptides (14 residues; TW70, T131, T134, and T140) showed a higher selectivity index than did other, 17- or 18-residue peptides. In particular, T134 and T140 showed both lower cytotoxicity and higher antiviral activity than did T22 against HIV infection of MT-4 cells, an HTLV-I-bearing T cell line. To clarify the inhibitory mode of T22 and its analogs, we used a single-round replication assay (luciferase assay), in which different envelope-bearing pseudotypes were used to infect CXCR4- or CCR5-bearing U87 cells via CD4. All of the analogs inhibited T cell line-tropic strain HXB-2 (X4) and dual-tropic strain 89.6 (R5X4) HIV infections mediated by CXCR4, but had no effect on macrophage-tropic strain ADA (R5) or 89.6 HIV infections mediated by CCR5. The inhibition by T134 (IC50 of 2.70 nM) and T140 (IC50 of 0.432 nM) was also stronger than that by T22 (IC50 of 5.05 nM). The binding of anti-CXCR4 monoclonal antibody 12G5 to lymphoma-derived T cell line Sup-T1 was more efficiently blocked by T134 and T140 than by T22. Taken together, T22 and its analogs T134 and T140 exerted their inhibition by specific binding to CXCR4. The marked increase in the anti-HIV activity of T134 and T140 was ascribed to an enhancement in their ability to bind to CXCR4.

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.

V3 loop of human immunodeficiency virus type 1 reduces cyclin E expression and induces G1 arrest in interleukin 2-dependent T cells

We previously described that V3 loop derived from the HTLV-III BH10 clone V3-BH10 markedly suppressed IL-2-driven T cell proliferation and produced G1 arrest of the cells. Here, we tested the effect of V3-BH10 on the molecules that are involved in transition from the G1 to S phase of the cell cycle. The effect of V3-BH10 on the IL-2-induced expression of G1 cyclins, Cdk inhibitors, and phosphorylation of retinoblastoma protein (pRb) was tested by immunoblotting, using the IL-2-dependent CD4-positive cell line Kit 225. Furthermore, IL-2-dependent kinase activity of the cyclin E-Cdk2 complex was investigated with histone H1 as a substrate. V3-BH10 reduced the IL-2-dependent expression of cyclin E, but not that of cyclin D and Cdk inhibitors such as p21 and p27. As the result of reduction of cyclin E, histone H1 kinase activity of the cyclin E-Cdk2 complex was markedly reduced even in the presence of rIL-2, followed by incomplete phosphorylation of pRb. The reduction in hyperphosphorylation of pRb by V3-BH10 led to G1 arrest of the cell cycle. Thus, V3-BH10 induced G1 arrest in IL-2-dependent cell cycle progression by reducing cyclin E expression, which may be one of the mechanisms underlying the dysfunction of T cells in HIV-1-infected people.

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

The template assembled synthetic peptide constructs (TASP), pentavalently presenting the tripeptide KPR or RPK, are potent and specific inhibitors of human immunodeficiency virus (HIV) infection by preventing viral entry into permissive cells. Here the 5[KPsi(CH2N)PR]-TASP construct, Psi(CH2N) for reduced peptide bond, was used in studies to demonstrate its specific binding to a 95-kDa cell surface protein ligand. Compared to its nonreduced 5[KPR]-TASP counterpart, the pseudopeptide 5[KPsi(CH2N)PR]-TASP manifested higher affinity to bind to its cell surface ligand, increased activity to inhibit HIV infection, and resistance to degradation when incubated in serum from an HIV-1 seropositive individual. In ligand blotting experiments, the biotin-labeled 5[KPsi(CH2N)PR]-TASP identified a single 95-kDa protein in crude cell extracts. This 95-kDa protein (p95) is expressed on the cell surface since surface iodination of cells resulted in its labeling, and moreover, following incubation of cells with the biotin-labeled 5[KPsi(CH2N)PR]-TASP, the p95.TASP complex was recovered by affinity chromatography using avidin-agarose. All anti-HIV TASP constructs but not their control derivatives affected the binding of biotin-labeled 5[KPsi(CH2N)PR]-TASP to p95, thus emphasizing the specific nature of this binding. Since 5[KPsi(CH2N)PR]-TASP does not interact with HIV-envelope glycoproteins, our results suggest that TASP inhibitors mediate directly or indirectly a block in HIV-mediated membrane fusion process by binding to the cell surface expressed p95.

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.

V3 loop of human immunodeficiency virus type 1 suppresses interleukin 2-induced T cell growth

We tested the effect of three linear or two loop peptides derived from the V3 region of the HTLV-III BH10 clone or the SF2 strain of human immunodeficiency virus type 1 on IL-2-driven T cell proliferation. V3-BH10, which consists of 42 amino acids and has a loop structure, suppressed IL-2-driven proliferation of all IL-2-dependent cells [Kit225, ED-40515(+), KT-3, 7-day PHA-blasts, and fresh peripheral blood mononuclear cells] tested, whereas it did not suppress the cell growth of IL-2-independent cell lines (Hut102, Molt-4, and Jurkat). This suppressive effect was also seen in IL-2-driven cell growth of CD8-positive lymphocytes purified from 7-day PHA-blasts, indicating that CD4 molecules were not required for the suppression. The treatment with anti-V3 loop monoclonal antibody (902 antibody) completely abolished the suppressive effect of V3-BH10. In addition, V3-BH10 generated the arrest of Kit225 cells and also purified CD8-positive lymphocytes in G1 phase in the presence of IL-2. Neither chromatin condensation nor DNA fragmentation was detected in Kit225 cells cultured with V3-BH10 and IL-2. V3-BH10 neither blocked radiolabeled IL-2 binding to IL-2 receptors nor affected tyrosyl phosphorylation of several cellular proteins (p120, p98, p96, p54, and p38), which is immediately induced by IL-2 stimulation. However, V3-BH10 enhanced IL-2-induced mRNA expression of c-fos but not c-myc or junB. Thus, the binding of V3 loop of gp120 to the cell surface molecule(s) appears to affect intracellular IL-2 signaling, which leads to the suppression of IL-2-induced T cell growth.

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.