Applications of biotinylated V3 loop peptides of human immunodeficiency virus type 1 to flow cytometric analyses and affinity chromatographic techniques

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).

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.

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.

Relationship of HIV-1 envelope V2 and V3 sequences of the primary isolates to the viral phenotype

We examined the relationship between the amino acid sequences of the V2 and V3 regions of the envelope protein and the biological properties of ten human immunodeficiency virus type 1 (HIV-1) primary isolates. The infectivity, cytopathic effect (CPE), and syncytium forming activity of these primary isolates were tested against three T cell lines (CEM, MT2, and MOLT4/CL.8 cells), CD8-depleted peripheral blood mononuclear cells (PBMC), and primary monocyte-derived macrophages (MDM) from seronegative donors. In addition to the viral groups which had the syncytium inducing/T-cell line tropic (SI/TT) phenotype or non-syncytium inducing/non-T cell line tropic (NSI/NT) phenotype (including the NSI/macrophage tropic (NSI/MT) phenotype), there was a group of viruses that infected one or two T cell lines and PBMC but could not mediate syncytium formation. We therefore classified this group of viruses as a non-syncytium inducing/partial T-cell line tropic (NSI/pTT) virus. To investigate the relationship between these viral phenotypes and the sequence variability of the V2 and V3 regions of the envelope, we cloned the viral gene segment and sequenced the individual isolates. The sequence data suggested that the SI/TT type changes in the V3 sequence alone mediate a partial T cell line tropism and mild cytopathic effect and that an isolate became more virulent (SI/TT phenotype) if there were additional changes in the V2 or other regions. On the other hand, sequence changes in the V2 region alone could not mediate phenotypic changes but some additional changes in the other variable regions (for example, V3) might be required for the phenotypic changes in combination with changes in V2. These findings also suggested that amino acid changes in both the V2 and V3 region are required for the development of virulent variants of HIV-1 that outgrow during advanced stages of the disease.

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

The V3 loop in gp120 of human immunodeficiency virus type 1 (HIV-1) is known as a principal neutralizing and cell-tropic determinant. Biotinylated synthetic V3 loop peptides derived from three different HIV-1 strains were used as ligands to identify the cell surface counterreceptor, which may participate in the infection of HIV-1. Two different cell lines, Molt-4 and U937, and three V3 loop peptides derived from LAVELI, HTLV-IIIMN, and HTLV-IIIB strains were used. The binding of HTLV-IIIB-derived peptide to the cell surface was confirmed using 125I-labeled surface proteins of both cell lines. The relative molecular mass of the major radioactive band on the autoradiogram was 32-33 kDa in both cell lines. A protein was purified from the plasma membrane fraction of Molt-4 cells using affinity columns coupled with three different V3 loop peptides. Two major polypeptides (32 and 33 kDa) were eluted from the affinity column. Size-exclusion chromatography showed that the protein migrated as a single peak with a molecular mass of 130 kDa. These proteins were separated by reversed-phase chromatography, which indicated that the 32-kDa protein is more hydrophobic than the 33-kDa protein in Molt-4 cells. A similar but not identical 130-kDa protein with 32- and 33-kDa polypeptides were also purified from U937 cells. These findings indicate that HIV-1 utilizes a tetrameric protein on the surface of Molt-4 and U937 cells on infection.

Synergistic effect of recombinant CD4-immunoglobulin in combination with azidothymidine, dideoxyinosine and 0.5 beta-monoclonal antibody on human immunodeficiency virus infection in vitro

Data are presented which indicate that combinations of rCD4 immunoglobulin with azidothymidine, dideoxyinosine or 0.5 beta mouse monoclonal antibodies directed against the V3 region of HIV-1, were more effective in treatment of acute HIV infection in vitro than each compound alone. It is suggested that combination therapy with these compounds is more beneficial in treatment of HIV-infected patients than monotherapy, especially with respect to a reduction of the known side effects and the formation of resistant HIV strains after treatment with nucleoside analogues.