scholarly journals A rat CD4 mutant containing the gp120-binding site mediates human immunodeficiency virus type 1 infection.

1993 ◽  
Vol 177 (4) ◽  
pp. 949-954 ◽  
Author(s):  
J H Simon ◽  
C Somoza ◽  
G A Schockmel ◽  
M Collin ◽  
S J Davis ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Syncytium Formation ◽  
Gp120 Binding ◽  
Ability To Act ◽  
Immunodeficiency Virus ◽  
Inhibitory Antibodies ◽  
Hiv 1

CD4 is the primary receptor for the human immunodeficiency virus type 1 (HIV-1). Early mutational studies implicated a number of residues of CD4, centered in the region 41-59, in binding to gp120. However, further mutational analyses, together with studies using inhibitory antibodies or CD4-derived peptides, have suggested that other regions of CD4 are also involved in binding or postbinding events during infection. To resolve these ambiguities, we used rat CD4 mutants in which particular regions were replaced with the corresponding sequence of human CD4. We have previously shown that some of these are able to bind HIV-1 gp120, and here we test their ability to act as functional receptors. We find that the presence of human CD4 residues 33-62 is enough to confer efficient receptor function to rat CD4, and we conclude that it is unlikely that regions of CD4 outside this sequence are involved in specific interactions with HIV-1 during either infection or syncytium formation.

scholarly journals Differential CD4/CCR5 Utilization, gp120 Conformation, and Neutralization Sensitivity between Envelopes from a Microglia-Adapted Human Immunodeficiency Virus Type 1 and Its Parental Isolate

2001 ◽  
Vol 75 (8) ◽  
pp. 3568-3580 ◽  
Author(s):  
Julio Martı́n ◽  
Celia C. LaBranche ◽  
Francisco González-Scarano
Keyword(s):  
Human Immunodeficiency Virus ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Syncytium Formation ◽  
Luciferase Reporter ◽  
Recombinant Viruses ◽  
Amino Terminal ◽  
Immunodeficiency Virus ◽  
Hiv 1

ABSTRACT Human immunodeficiency virus type 1 (HIV-1) infects and induces syncytium formation in microglial cells from the central nervous system (CNS). A primary isolate (HIV-1BORI) was sequentially passaged in cultured microglia, and the isolate recovered (HIV-1BORI-15) showed high levels of fusion and replicated more efficiently in microglia (J. M. Strizki, A. V. Albright, H. Sheng, M. O'Connor, L. Perrin, and F. González-Scarano, J. Virol. 70:7654–7662, 1996). The parent and adapted viruses used CCR5 as coreceptor. Recombinant viruses demonstrated that the syncytium-inducing phenotype was associated with four amino acid differences in the V1/V2 region of the viral gp120 (J. T. C. Shieh, J. Martin, G. Baltuch, M. H. Malim, and F. González-Scarano, J. Virol. 74:693–701, 2000). We produced luciferase-reporter, env-pseudotyped viruses using plasmids containing env sequences from HIV-1BORI, HIV-1BORI-15, and the V1/V2 region of HIV-1BORI-15 in the context of HIV-1BORI env (named rBORI, rB15, and rV1V2, respectively). The pseudotypes were used to infect cells expressing various amounts of CD4 and CCR5 on the surface. In contrast to the parent recombinant, the rB15 and rV1V2 pseudotypes retained their infectability in cells expressing low levels of CD4 independent of the levels of CCR5, and they infected cells expressing CD4 with a chimeric coreceptor containing the third extracellular loop of CCR2b in the context of CCR5 or a CCR5 Δ4 amino-terminal deletion mutant. The VH-rB15 and VH-rV1V2 recombinant viruses were more sensitive to neutralization by a panel of HIV-positive sera than was VH-rBORI. Interestingly, the CD4-induced 17b epitope on gp120 was more accessible in the rB15 and rV1V2 pseudotypes than in rBORI, even before CD4 binding, and concomitantly, the rB15 and rV1V2 pseudotypes were more sensitive to neutralization with the human 17b monoclonal antibody. Adaptation to growth in microglia—cells that have reduced expression of CD4 in comparison with other cell types—appears to be associated with changes in gp120 that modify its ability to utilize CD4 and CCR5. Changes in the availability of the 17b epitope indicate that these affect conformation. These results imply that the process of adaptation to certain tissue types such as the CNS directly affects the interaction of HIV-1 envelope glycoproteins with cell surface components and with humoral immune responses.

scholarly journals Determinants of Syncytium Formation in Microglia by Human Immunodeficiency Virus Type 1: Role of the V1/V2 Domains

2000 ◽  
Vol 74 (2) ◽  
pp. 693-701 ◽  
Author(s):  
Joseph T. C. Shieh ◽  
Julio Martín ◽  
Gordon Baltuch ◽  
Michael H. Malim ◽  
Francisco González-Scarano
Keyword(s):  
Human Immunodeficiency Virus ◽  
Amino Acid ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Syncytium Formation ◽  
Single Amino Acid ◽  
Single Amino Acid Change ◽  
Immunodeficiency Virus ◽  
Hiv 1

ABSTRACT Microglia are the main reservoir for human immunodeficiency virus type 1 (HIV-1) in the central nervous system (CNS), and multinucleated giant cells, the result of fusion of HIV-1-infected microglia and brain macrophages, are the neuropathologic hallmark of HIV dementia. One potential explanation for the formation of syncytia is viral adaptation for these CD4+ CNS cells. HIV-1BORI-15, a virus adapted to growth in microglia by sequential passage in vitro, mediates high levels of fusion and replicates more efficiently in microglia and monocyte-derived-macrophages than its unpassaged parent (J. M. Strizki, A. V. Albright, H. Sheng, M. O'Connor, L. Perrin, and F. Gonzalez-Scarano, J. Virol. 70:7654–7662, 1996). Since the interaction between the viral envelope glycoprotein and CD4 and the chemokine receptor mediates fusion and plays a key role in tropism, we have analyzed the HIV-1BORI-15 env as a fusogen and in recombinant and pseudotyped viruses. Its syncytium-forming phenotype is not the result of a switch in coreceptor use but rather of the HIV-1BORI-15envelope-mediated fusion of CD4+CCR5+ cells with greater efficiency than that of its parental strain, either by itself or in the context of a recombinant virus. Genetic analysis indicated that the syncytium-forming phenotype was due to four discrete amino acid differences in V1/V2, with a single-amino-acid change between the parent and the adapted virus (E153G) responsible for the majority of the effect. Additionally, HIV-1BORI-15 env-pseudotyped viruses were less sensitive to decreases in the levels of CD4 on transfected 293T cells, leading to the hypothesis that the differences in V1/V2 alter the interaction between this envelope and CD4 or CCR5, or both. In sum, the characterization of the envelope of HIV-1BORI-15, a highly fusogenic glycoprotein with genetic determinants in V1/V2, may lead to a better understanding of the relationship between HIV replication and syncytium formation in the CNS and of the importance of this region of gp120 in the interaction with CD4 and CCR5.

scholarly journals Formation of Syncytia Is Repressed by Tetraspanins in Human Immunodeficiency Virus Type 1-Producing Cells

2009 ◽  
Vol 83 (15) ◽  
pp. 7467-7474 ◽  
Author(s):  
Jia Weng ◽  
Dimitry N. Krementsov ◽  
Sandhya Khurana ◽  
Nathan H. Roy ◽  
Markus Thali
Keyword(s):  
Human Immunodeficiency Virus ◽  
Cell Fusion ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Syncytium Formation ◽  
Target Cells ◽  
Immunodeficiency Virus ◽  
Hiv 1

ABSTRACT In vitro propagation studies have established that human immunodeficiency virus type 1 (HIV-1) is most efficiently transmitted at the virological synapse that forms between producer and target cells. Despite the presence of the viral envelope glycoprotein (Env) and CD4 and chemokine receptors at the respective surfaces, producer and target cells usually do not fuse with each other but disengage after the viral particles have been delivered, consistent with the idea that syncytia, at least in vitro, are not required for HIV-1 spread. Here, we tested whether tetraspanins, which are well known regulators of cellular membrane fusion processes that are enriched at HIV-1 exit sites, regulate syncytium formation. We found that overexpression of tetraspanins in producer cells leads to reduced syncytium formation, while downregulation has the opposite effect. Further, we document that repression of Env-induced cell-cell fusion by tetraspanins depends on the presence of viral Gag, and we demonstrate that fusion repression requires the recruitment of Env by Gag to tetraspanin-enriched microdomains (TEMs). However, sensitivity to fusion repression by tetraspanins varied for different viral strains, despite comparable recruitment of their Envs to TEMs. Overall, these data establish tetraspanins as negative regulators of HIV-1-induced cell-cell fusion, and they start delineating the requirements for this regulation.

scholarly journals Characterization of DC-SIGN/R Interaction with Human Immunodeficiency Virus Type 1 gp120 and ICAM Molecules Favors the Receptor's Role as an Antigen-Capturing Rather than an Adhesion Receptor

2005 ◽  
Vol 79 (8) ◽  
pp. 4589-4598 ◽  
Author(s):  
Greg A. Snyder ◽  
Jennifer Ford ◽  
Parizad Torabi-Parizi ◽  
James A. Arthos ◽  
Peter Schuck ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Cell Surface ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Trojan Horse ◽  
Gp120 Binding ◽  
Immunodeficiency Virus ◽  
Cell Surface Glycoproteins ◽  
Hiv 1

ABSTRACT The dendritic cell (DC)-specific intercellular adhesion molecule 3 (ICAM-3)-grabbing nonintegrin binding receptor (DC-SIGN) was shown to bind human immunodeficiency virus type 1 (HIV-1) viral envelope protein gp120 and proposed to function as a Trojan horse to enhance trans-virus infection to host T cells. To better understand the mechanism by which DC-SIGN and DC-SIGNR selectively bind HIV-1 gp120, we constructed a series of deletion mutations in the repeat regions of both receptors. Different truncated receptors exist in different oligomeric forms. The carbohydrate binding domain without any repeats was monomeric, whereas the full extracellular receptors existed as tetramers. All reconstituted receptors retained their ability to bind gp120. The dissociation constant, however, differed drastically from micromolar values for the monomeric receptors to nanomolar values for the tetrameric receptors, suggesting that the repeat region of these receptors contributes to the avidity of gp120 binding. Such oligomerization may provide a mechanism for the receptor to selectively recognize pathogens containing multiple high-mannose-concentration carbohydrates. In contrast, the receptors bound to ICAMs with submicromolar affinities that are similar to those of two nonspecific cell surface glycoproteins, FcγRIIb and FcγRIII, and the oligomerization of DC-SIGNR resulted in no increase in binding affinity to ICAM-3. These findings suggest that DC-SIGN may not discriminate other cell surface glycoproteins from ICAM-3 binding. The pH dependence in DC-SIGN binding to gp120 showed that the receptor retained high-affinity gp120 binding at neutral pH but lost gp120 binding at pH 5, suggesting a release mechanism of HIV in the acidic endosomal compartment by DC-SIGN. Our work contradicts the function of DC-SIGN as a Trojan horse to facilitate HIV-1 infection; rather, it supports the function of DC-SIGN/R (a designation referring to both DC-SIGN and DC-SIGNR) as an antigen-capturing receptor.

scholarly journals Rational Site-Directed Mutations of the LLP-1 and LLP-2 Lentivirus Lytic Peptide Domains in the Intracytoplasmic Tail of Human Immunodeficiency Virus Type 1 gp41 Indicate Common Functions in Cell-Cell Fusion but Distinct Roles in Virion Envelope Incorporation

2003 ◽  
Vol 77 (6) ◽  
pp. 3634-3646 ◽  
Author(s):  
Vandana Kalia ◽  
Surojit Sarkar ◽  
Phalguni Gupta ◽  
Ronald C. Montelaro
Keyword(s):  
Human Immunodeficiency Virus ◽  
Cell Fusion ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Syncytium Formation ◽  
Immunodeficiency Virus ◽  
Arginine Residues ◽  
Hiv 1 ◽  
Cell Cell

ABSTRACT Two highly conserved cationic amphipathic α-helical motifs, designated lentivirus lytic peptides 1 and 2 (LLP-1 and LLP-2), have been characterized in the carboxyl terminus of the transmembrane (TM) envelope glycoprotein (Env) of lentiviruses . Although various properties have been attributed to these domains, their structural and functional significance is not clearly understood. To determine the specific contributions of the Env LLP domains to Env expression, processing, and incorporation and to viral replication and syncytium induction, site-directed LLP mutants of a primary dualtropic infectious human immunodeficiency virus type 1 (HIV-1) isolate (ME46) were examined. Substitutions were made for highly conserved arginine residues in either the LLP-1 or LLP-2 domain (MX1 or MX2, respectively) or in both domains (MX4). The HIV-1 mutants with altered LLP domains demonstrated distinct phenotypes. The LLP-1 mutants (MX1 and MX4) were replication defective and showed an average of 85% decrease in infectivity, which was associated with an evident decrease in gp41 incorporation into virions without a significant decrease in Env expression or processing in transfected 293T cells. In contrast, MX2 virus was replication competent and incorporated a full complement of Env into its virions, indicating a differential role for the LLP-1 domain in Env incorporation. Interestingly, the replication-competent MX2 virus was impaired in its ability to induce syncytia in T-cell lines. This defect in cell-cell fusion did not correlate with apparent defects in the levels of cell surface Env expression, oligomerization, or conformation. The lack of syncytium formation, however, correlated with a decrease of about 90% in MX2 Env fusogenicity compared to that of wild-type Env in quantitative luciferase-based cell-cell fusion assays. The LLP-1 mutant MX1 and MX4 Envs also exhibited an average of 80% decrease in fusogenicity. Altogether, these results demonstrate for the first time that the highly conserved LLP domains perform critical but distinct functions in Env incorporation and fusogenicity.

scholarly journals Unique Monoclonal Antibody Recognizing the Third Extracellular Loop of CXCR4 Induces Lymphocyte Agglutination and Enhances Human Immunodeficiency Virus Type 1-Mediated Syncytium Formation and Productive Infection

2001 ◽  
Vol 75 (23) ◽  
pp. 11534-11543 ◽  
Author(s):  
Reiko Tanaka ◽  
Atsushi Yoshida ◽  
Tsutomu Murakami ◽  
Eishi Baba ◽  
Julliane Lichtenfeld ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Syncytium Formation ◽  
Productive Infection ◽  
Extracellular Loop ◽  
The Third ◽  
Immunodeficiency Virus ◽  
Hiv 1

ABSTRACT To increase insight into the structural basis of CXCR4 utilization in human immunodeficiency virus type 1 (HIV-1) infection, a new generation of three monoclonal antibodies (MAbs) was developed in WKA rats. The A80 MAb, which binds an epitope in the third extracellular loop (ECL3) of CXCR4, has unique biologic properties that provide novel insights into CXCR4 function. This agent enhanced syncytium formation in activated human peripheral blood mononuclear cells (PBMC) infected with X4 or R5 and CEM cells infected with X4 HIV-1 strains. Exposure to A80 increased the productive infection of activated CD4+ T cells and CEM cells with R5 and X4 viruses, respectively. This antibody uniquely induced agglutination of PBMC and CEM cells but did not activate calcium mobilization. Agglutination induced by A80 was inhibited by stromal cell-derived factor 1, T22, and phorbol 12-myristate 13-acetate but was not significantly altered by pretreatment of cells with pertussis toxin, wortmannin, or MAbs to LFA-1, ICAM-1, ICAM-2, and ICAM-3. The binding of the A145 and A120 MAbs was mapped to the N-terminal extracellular domain and a conformational epitope involving ECL1 and ECL2, respectively. Both of these MAbs inhibited HIV-1 infection and lacked the novel properties of A80. These results suggest a new role for CXCR4 in homologous lymphocyte adhesion that is ligand independent and in HIV-1 infection.

scholarly journals Loss of a Single N-Linked Glycan Allows CD4-Independent Human Immunodeficiency Virus Type 1 Infection by Altering the Position of the gp120 V1/V2 Variable Loops

2001 ◽  
Vol 75 (7) ◽  
pp. 3435-3443 ◽  
Author(s):  
Peter Kolchinsky ◽  
Enko Kiprilov ◽  
Peter Bartley ◽  
Roee Rubinstein ◽  
Joseph Sodroski
Keyword(s):  
Human Immunodeficiency Virus ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Glycosylation Site ◽  
Ccr5 Chemokine Receptor ◽  
Gp120 Binding ◽  
Immunodeficiency Virus ◽  
Variable Loops ◽  
Hiv 1

ABSTRACT The gp120 envelope glycoprotein of primary human immunodeficiency virus type 1 (HIV-1) promotes virus entry by sequentially binding CD4 and the CCR5 chemokine receptor on the target cell. Previously, we adapted a primary HIV-1 isolate, ADA, to replicate in CD4-negative canine cells expressing human CCR5. The gp120 changes responsible for CD4-independent replication were limited to the V2 loop-V1/V2 stem. Here we show that elimination of a single glycosylation site at asparagine 197 in the V1/V2 stem is sufficient for CD4-independent gp120 binding to CCR5 and for HIV-1 entry into CD4-negative cells expressing CCR5. Deletion of the V1/V2 loops also allowed CD4-independent viral entry and gp120 binding to CCR5. The binding of the wild-type ADA gp120 to CCR5 was less dependent upon CD4 at 4°C than at 37°C. In the absence of the V1/V2 loops, neither removal of the N-linked carbohydrate at asparagine 197 nor lowering of the temperature increased the CD4-independent phenotypes. A CCR5-binding conformation of gp120, achieved by CD4 interaction or by modification of temperature, glycosylation, or variable loops, was preferentially recognized by the monoclonal antibody 48d. These results suggest that the CCR5-binding region of gp120 is occluded by the V1/V2 variable loops, the position of which can be modulated by temperature, CD4 binding, or an N-linked glycan in the V1/V2 stem.

scholarly journals Alanine Substitutions of Polar and Nonpolar Residues in the Amino-Terminal Domain of CCR5 Differently Impair Entry of Macrophage- and Dualtropic Isolates of Human Immunodeficiency Virus Type 1

1998 ◽  
Vol 72 (4) ◽  
pp. 3464-3468 ◽  
Author(s):  
Gwénaël E. E. Rabut ◽  
Jason A. Konner ◽  
Francis Kajumo ◽  
John P. Moore ◽  
Tatjana Dragic
Keyword(s):  
Human Immunodeficiency Virus ◽  
Human Immunodeficiency Virus Type ◽  
Virus Type ◽  
Amino Terminal ◽  
Terminal Domain ◽  
Gp120 Binding ◽  
Immunodeficiency Virus ◽  
Amino Terminal Domain ◽  
Hiv 1

ABSTRACT Multiple extracellular domains of the CC-chemokine receptor CCR5 are important for its function as a human immunodeficiency virus type 1 (HIV-1) coreceptor. We have recently demonstrated by alanine scanning mutagenesis that the negatively charged residues in the CCR5 amino-terminal domain are essential for gp120 binding and coreceptor function. We have now extended our analysis of this domain to include most polar and nonpolar amino acids. Replacement of alanine with all four tyrosine residues and with serine-17 and cysteine-20 decrease or abolish gp120 binding and CCR5 coreceptor activity. Tyrosine-15 is essential for viral entry irrespective of the test isolate. Substitutions at some of the other positions impair the entry of dualtropic HIV-1 isolates more than that of macrophagetropic ones.

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