1
|
Andrianov AM, Kornoushenko YV, Kashyn IA, Kisel MA, Tuzikov AV. In silico design of novel broad anti-HIV-1 agents based on glycosphingolipid β-galactosylceramide, a high-affinity receptor for the envelope gp120 V3 loop. J Biomol Struct Dyn 2014; 33:1051-66. [PMID: 24942968 DOI: 10.1080/07391102.2014.926832] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Novel anti-Human immunodeficiency virus (HIV)-1 agents targeting the V3 loop of envelope protein gp120 were designed by computer modeling based on glycosphingolipid β-galactosylceramide (β-GalCer), which is an alternative receptor allowing HIV-1 entry into CD4-negative cells of neural and colonic origin. Models of these β-GalCer analogs bound to the V3 loops from five various HIV-1 variants were generated by molecular docking and their stability was estimated by molecular dynamics (MDs) and binding free energy simulations. Specific binding to the V3 loop was accomplished primarily by non-conventional XH…π interactions between CH/OH sugar groups of the glycolipids and the conserved V3 residues with π-conjugated side chains. The designed compounds were found to block the tip and/or the base of the V3 loop, which form invariant structural motifs that contain residues critical for cell tropism. With the MDs calculations, the docked models of the complexes of the β-GalCer analogs with V3 are energetically stable in all of the cases of interest and exhibit low values of free energy of their formation. Based on the data obtained, these compounds are considered as promising basic structures for the rational design of novel, potent, and broad-spectrum anti-HIV-1 therapeutics.
Collapse
Affiliation(s)
- Alexander M Andrianov
- a Institute of Bioorganic Chemistry , National Academy of Sciences of Belarus , Kuprevich Street 5/2, Minsk 220141 , Republic of Belarus
| | | | | | | | | |
Collapse
|
2
|
Andrianov AM, Kashyn IA, Tuzikov AV. Discovery of novel anti-HIV-1 agents based on a broadly neutralizing antibody against the envelope gp120 V3 loop: a computational study. J Biomol Struct Dyn 2013; 32:1993-2004. [DOI: 10.1080/07391102.2013.848825] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
|
3
|
Yokoyama M, Naganawa S, Yoshimura K, Matsushita S, Sato H. Structural dynamics of HIV-1 envelope Gp120 outer domain with V3 loop. PLoS One 2012; 7:e37530. [PMID: 22624045 PMCID: PMC3356331 DOI: 10.1371/journal.pone.0037530] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 04/20/2012] [Indexed: 01/18/2023] Open
Abstract
BACKGROUND The net charge of the hypervariable V3 loop on the HIV-1 envelope gp120 outer domain plays a key role in modulating viral phenotype. However, the molecular mechanisms underlying the modulation remain poorly understood. METHODOLOGY/PRINCIPAL FINDINGS By combining computational and experimental approaches, we examined how V3 net charge could influence the phenotype of the gp120 interaction surface. Molecular dynamics simulations of the identical gp120 outer domain, carrying a V3 loop with net charge of +3 or +7, showed that the V3 change alone could induce global changes in fluctuation and conformation of the loops involved in binding to CD4, coreceptor and antibodies. A neutralization study using the V3 recombinant HIV-1 infectious clones showed that the virus carrying the gp120 with +3 V3, but not with +7 V3, was resistant to neutralization by anti-CD4 binding site monoclonal antibodies. An information entropy study shows that otherwise variable surface of the gp120 outer domain, such as V3 and a region around the CD4 binding loop, are less heterogeneous in the gp120 subpopulation with +3 V3. CONCLUSIONS/SIGNIFICANCE These results suggest that the HIV-1 gp120 V3 loop acts as an electrostatic modulator that influences the global structure and diversity of the interaction surface of the gp120 outer domain. Our findings will provide a novel structural basis to understand how HIV-1 adjusts relative replication fitness by V3 mutations.
Collapse
Affiliation(s)
- Masaru Yokoyama
- Laboratory of Viral Genomics, Pathogen Genomics Center, National Institute of Infectious Diseases, 4-7-1 Gakuen, Musashi Murayama-shi, Tokyo, Japan
- * E-mail: (MY); (HS)
| | - Satoshi Naganawa
- Department of Microbiology and Cell Biology, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo, Japan
| | - Kazuhisa Yoshimura
- Division of Clinical Retrovirology and Infectious Diseases, Center for AIDS Research, Kumamoto University, 2-2-1 Honjo, Kumamoto, Japan
| | - Shuzo Matsushita
- Division of Clinical Retrovirology and Infectious Diseases, Center for AIDS Research, Kumamoto University, 2-2-1 Honjo, Kumamoto, Japan
| | - Hironori Sato
- Laboratory of Viral Genomics, Pathogen Genomics Center, National Institute of Infectious Diseases, 4-7-1 Gakuen, Musashi Murayama-shi, Tokyo, Japan
- * E-mail: (MY); (HS)
| |
Collapse
|
4
|
Kong L, Sattentau QJ. Antigenicity and Immunogenicity in HIV-1 Antibody-Based Vaccine Design. ACTA ACUST UNITED AC 2012; S8:3. [PMID: 23227445 DOI: 10.4172/2155-6113] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Neutralizing antibodies can protect from infection by immunodeficiency viruses. However, the induction by active vaccination of antibodies that can potently neutralize a broad range of circulating virus strains is a goal not yet achieved, despite more than 2 decades of research. Here we review progress made in the field, from early empirical studies to today's rational structure-based vaccine antigen design. We discuss the existence of broadly neutralizing antibodies, their implications for epitope discovery and recent progress made in antigen design. Finally, we consider the relationship between antigenicity and immunogenicity for B cell recognition and antibody production, a major hurdle for rational vaccine design to overcome.
Collapse
Affiliation(s)
- Leopold Kong
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, UK ; The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | | |
Collapse
|
5
|
Melikyan GB. Membrane fusion mediated by human immunodeficiency virus envelope glycoprotein. CURRENT TOPICS IN MEMBRANES 2011; 68:81-106. [PMID: 21771496 DOI: 10.1016/b978-0-12-385891-7.00004-0] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Gregory B Melikyan
- Department of Pediatrics, Infectious Diseases, Emory University, Atlanta, GA, USA
| |
Collapse
|
6
|
Lynch RM, Rong R, Li B, Shen T, Honnen W, Mulenga J, Allen S, Pinter A, Gnanakaran S, Derdeyn CA. Subtype-specific conservation of isoleucine 309 in the envelope V3 domain is linked to immune evasion in subtype C HIV-1 infection. Virology 2010; 404:59-70. [PMID: 20494390 DOI: 10.1016/j.virol.2010.04.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2010] [Revised: 03/17/2010] [Accepted: 04/10/2010] [Indexed: 11/19/2022]
Abstract
The V3 region of the HIV-1 envelope (Env) glycoprotein gp120 is a key functional domain yet it exhibits distinct mutational patterns across subtypes. Here an invariant residue (Ile 309) was replaced with Leu in 7 subtype C patient-derived Envs from recent infection and 4 related neutralizing antibody escape variants that emerged later. For these 11 Envs, I309L did not alter replication in primary CD4 T cells; however, replication in monocyte-derived macrophages was enhanced. Infection of cell lines with low CD4 or CCR5 revealed that I309L enhanced utilization of CD4 but did not affect the ability to use CCR5. This CD4-enhanced phenotype tracked with sensitivity to sCD4, indicating increased exposure of the CD4 binding site. The results suggest that Ile 309 preserves a V3-mediated masking function that occludes the CD4 binding site. The findings point to an immune evasion strategy in subtype C Env to protect this vulnerable immune target.
Collapse
Affiliation(s)
- Rebecca M Lynch
- Immunology and Molecular Pathogenesis Program, Emory University, Atlanta, GA 30329, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Miyauchi K, Kozlov MM, Melikyan GB. Early steps of HIV-1 fusion define the sensitivity to inhibitory peptides that block 6-helix bundle formation. PLoS Pathog 2009; 5:e1000585. [PMID: 19763181 PMCID: PMC2736578 DOI: 10.1371/journal.ppat.1000585] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2009] [Accepted: 08/24/2009] [Indexed: 11/18/2022] Open
Abstract
The HIV envelope (Env) glycoprotein mediates membrane fusion through sequential interactions with CD4 and coreceptors, followed by the refolding of the transmembrane gp41 subunit into the stable 6-helix bundle (6HB) conformation. Synthetic peptides derived from the gp41 C-terminal heptad repeat domain (C-peptides) potently inhibit fusion by binding to the gp41 pre-bundle intermediates and blocking their conversion into the 6HB. Our recent work revealed that HIV-1 enters cells by fusing with endosomes, but not with the plasma membrane. These studies also showed that, for the large part, gp41 pre-bundles progress toward 6HBs in endosomal compartments and are thus protected from external fusion inhibitors. Here, we examined the consequences of endocytic entry on the gp41 pre-bundle exposure and on the virus' sensitivity to C-peptides. The rates of CD4 and coreceptor binding, as well as the rate of productive receptor-mediated endocytosis, were measured by adding specific inhibitors of these steps at varied times of virus-cell incubation. Following the CD4 binding, CCR5-tropic viruses recruited a requisite number of coreceptors much faster than CXCR4-tropic viruses. The rate of subsequent uptake of ternary Env-CD4-coreceptor complexes did not correlate with the kinetics of coreceptor engagement. These measurements combined with kinetic analyses enabled the determination of the lifetime of pre-bundle intermediates on the cell surface. Overall, these lifetimes correlated with the inhibitory potency of C-peptides. On the other hand, the basal sensitivity to peptides varied considerably among diverse HIV-1 isolates and ranked similarly with their susceptibility to inactivation by soluble CD4. We conclude that both the longevity of gp41 intermediates and the extent of irreversible conformational changes in Env upon CD4 binding determine the antiviral potency of C-peptides. The human immunodeficiency virus (HIV) envelope glycoprotein (Env) mediates fusion between the viral and cell membranes. The fusion is initiated by Env-receptor interactions and is followed by coreceptor binding and refolding of the transmembrane gp41 subunit. The gp41 refolding proceeds through several distinct intermediates, culminating in the formation of a final helical bundle structure which is blocked by inhibitory peptides targeting the complementary domains of gp41. We have recently shown that the exposure time of gp41 intermediates on the cell surface is limited by productive HIV endocytosis leading to fusion with endosomes. Here, we measured the rates of progression of different HIV isolates through distinct intermediate steps accessible to fusion inhibitors and correlated these rates with the inhibitory potency of peptides against these viruses. Whereas the potency of peptides was proportional to the lifetime of gp41 intermediates on the cell surface, the baseline sensitivity of the virus was also Env context-dependent. Higher concentrations of these inhibitors were required to block fusion induced by glycoproteins that were more resistant to inactivation by the soluble receptor. Collectively, these findings imply that both the kinetic factors and the stability of Env-receptor complexes control the HIV sensitivity to inhibitory peptides.
Collapse
Affiliation(s)
- Kosuke Miyauchi
- Institute of Human Virology and Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
| | - Michael M. Kozlov
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Gregory B. Melikyan
- Institute of Human Virology and Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- * E-mail:
| |
Collapse
|
8
|
Melikyan GB. Common principles and intermediates of viral protein-mediated fusion: the HIV-1 paradigm. Retrovirology 2008; 5:111. [PMID: 19077194 PMCID: PMC2633019 DOI: 10.1186/1742-4690-5-111] [Citation(s) in RCA: 135] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2008] [Accepted: 12/10/2008] [Indexed: 12/20/2022] Open
Abstract
Enveloped viruses encode specialized fusion proteins which promote the merger of viral and cell membranes, permitting the cytosolic release of the viral cores. Understanding the molecular details of this process is essential for antiviral strategies. Recent structural studies revealed a stunning diversity of viral fusion proteins in their native state. In spite of this diversity, the post-fusion structures of these proteins share a common trimeric hairpin motif in which the amino- and carboxy-terminal hydrophobic domains are positioned at the same end of a rod-shaped molecule. The converging hairpin motif, along with biochemical and functional data, implies that disparate viral proteins promote membrane merger via a universal "cast-and-fold" mechanism. According to this model, fusion proteins first anchor themselves to the target membrane through their hydrophobic segments and then fold back, bringing the viral and cellular membranes together and forcing their merger. However, the pathways of protein refolding and the mechanism by which this refolding is coupled to membrane rearrangements are still not understood. The availability of specific inhibitors targeting distinct steps of HIV-1 entry permitted the identification of key conformational states of its envelope glycoprotein en route to fusion. These studies provided functional evidence for the direct engagement of the target membrane by HIV-1 envelope glycoprotein prior to fusion and revealed the role of partially folded pre-hairpin conformations in promoting the pore formation.
Collapse
Affiliation(s)
- Gregory B Melikyan
- Institute of Human Virology, Department of Microbiology and Immunology, University of Maryland School of Medicine, 725 W, Lombard St, Baltimore, MD 21201, USA.
| |
Collapse
|
9
|
Chien MP, Jiang S, Chang DK. The function of coreceptor as a basis for the kinetic dissection of HIV type 1 envelope protein-mediated cell fusion. FASEB J 2007; 22:1179-92. [PMID: 18032634 DOI: 10.1096/fj.07-9576com] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The function of HIV-1 HXB2 envelope (Env) glycoprotein (gp) was investigated by surface plasmon resonance and fluorescence imaging techniques. Strikingly, it was found that gp120 shedding requires the presence of the X4 coreceptor. A similar coreceptor requirement was observed for the membrane mixing and the Env recruitment on the cell surface. However, exposure and membrane penetration of the fusion peptide do not require X4 and occur within the first minute after incubation of Env with CD4 and/or X4. Analogously X4 was not required but enhanced binding of the fusion inhibitor. In contrast, bundle formation of the gp41 ectodomain, as monitored by NC-1, was accelerated by the presence of X4. The kinetics of these key post-Env binding events as determined in real time by fluorescence microscopic imaging, coupled with the differential coreceptor requirement, led to the proposition that gp120 shedding, which takes place from 1 to 10 min after engagement of receptor and coreceptor to Env, is a primary function of the coreceptor. The shedding of the surface subunits is needed for the subsequent processes including hemifusion, full fusion, and Env recruitment. The temporal order of these fusogenic steps allows construction of a refined model on the Env-mediated cell fusion event.
Collapse
Affiliation(s)
- Miao-Ping Chien
- Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Republic of China
| | | | | |
Collapse
|
10
|
Bellamy-McIntyre AK, Lay CS, Baär S, Maerz AL, Talbo GH, Drummer HE, Poumbourios P. Functional links between the fusion peptide-proximal polar segment and membrane-proximal region of human immunodeficiency virus gp41 in distinct phases of membrane fusion. J Biol Chem 2007; 282:23104-16. [PMID: 17526486 DOI: 10.1074/jbc.m703485200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The binding of CD4 and chemokine receptors to the gp120 attachment glycoprotein of human immunodeficiency virus triggers refolding of the associated gp41 fusion glycoprotein into a trimer of hairpins with a 6-helix bundle (6HB) core. These events lead to membrane fusion and viral entry. Here, we examined the functions of the fusion peptide-proximal polar segment and membrane-proximal Trp-rich region (MPR), which are exterior to the 6HB. Alanine substitution of Trp(666), Trp(672), Phe(673), and Ile(675) in the MPR reduced entry by up to 120-fold without affecting gp120-gp41 association or cell-cell fusion. The L537A polar segment mutation led to the loss of gp120 from the gp120-gp41 complex, reduced entry by approximately 10-fold, but did not affect cell-cell fusion. Simultaneous Ala substitution of Leu(537) with Trp(666), Trp(672), Phe(673), or Ile(675) abolished entry with 50-80% reductions in cell-cell fusion. gp120-gp41 complexes of fusion-defective double mutants were resistant to soluble CD4-induced shedding of gp120, suggesting that their ability to undergo receptor-induced conformational changes was compromised. Consistent with this idea, a representative mutation, L537A/W666A, led to an approximately 80% reduction in lipophilic fluorescent dye transfer between gp120-gp41-expressing cells and receptor-expressing targets, indicating a block prior to the lipid-mixing phase. The L537A/W666A double mutation increased the chymotrypsin sensitivity of the polar segment in a trimer of hairpins model, comprising the 6HB core, the polar segment, and MPR linked N-terminally to maltose-binding protein. The data indicate that the polar segment and MPR of gp41 act synergistically in forming a fusion-competent gp120-gp41 complex and in stabilizing the membrane-interactive end of the trimer of hairpins.
Collapse
Affiliation(s)
- Anna K Bellamy-McIntyre
- Macfarlane Burnet Institute for Medical Research and Public Health, Prahran, Victoria 3004, Australia
| | | | | | | | | | | | | |
Collapse
|
11
|
Moore PL, Crooks ET, Porter L, Zhu P, Cayanan CS, Grise H, Corcoran P, Zwick MB, Franti M, Morris L, Roux KH, Burton DR, Binley JM. Nature of nonfunctional envelope proteins on the surface of human immunodeficiency virus type 1. J Virol 2006; 80:2515-28. [PMID: 16474158 PMCID: PMC1395414 DOI: 10.1128/jvi.80.5.2515-2528.2006] [Citation(s) in RCA: 278] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Human immunodeficiency virus type 1 (HIV-1) neutralizing antibodies are thought be distinguished from nonneutralizing antibodies by their ability to recognize functional gp120/gp41 envelope glycoprotein (Env) trimers. The antibody responses induced by natural HIV-1 infection or by vaccine candidates tested to date consist largely of nonneutralizing antibodies. One might have expected a more vigorous neutralizing response, particularly against virus particles that bear functional trimers. The recent surprising observation that nonneutralizing antibodies can specifically capture HIV-1 may provide a clue relating to this paradox. Specifically, it was suggested that forms of Env, to which nonneutralizing antibodies can bind, exist on virus surfaces. Here, we present evidence that HIV-1 particles bear nonfunctional gp120/gp41 monomers and gp120-depleted gp41 stumps. Using a native electrophoresis band shift assay, we show that antibody-trimer binding predicts neutralization and that the nonfunctional forms of Env may account for virus capture by nonneutralizing antibodies. We hypothesize that these nonfunctional forms of Env on particle surfaces serve to divert the antibody response, helping the virus to evade neutralization.
Collapse
Affiliation(s)
- Penny L Moore
- Torrey Pines Institute for Molecular Studies, San Diego, CA 92121, USA
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
12
|
Davis MR, Jiang J, Zhou J, Freed EO, Aiken C. A mutation in the human immunodeficiency virus type 1 Gag protein destabilizes the interaction of the envelope protein subunits gp120 and gp41. J Virol 2006; 80:2405-17. [PMID: 16474147 PMCID: PMC1395406 DOI: 10.1128/jvi.80.5.2405-2417.2006] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The Gag protein of human immunodeficiency virus type 1 (HIV-1) associates with the envelope protein complex during virus assembly. The available evidence indicates that this interaction involves recognition of the gp41 cytoplasmic tail (CT) by the matrix protein (MA) region of Pr55(Gag). Here we show that substitution of Asp for Leu at position 49 (L49D) in MA results in a specific reduction in particle-associated gp120 without affecting the levels of gp41. Mutant virions were markedly reduced in single-cycle infectivity despite a relatively modest defect in fusion with target cells. Studies with HIV-1 particles containing decreased levels of envelope proteins suggested that the L49D mutation also inhibits a postentry step in infection. Truncation of the gp41 tail, or pseudotyping by vesicular stomatitis virus glycoprotein, restored both the fusion and infectivity of L49D mutant virions to wild-type levels. Truncation of gp41 also resulted in equivalent levels of gp120 on particles with and without the MA mutation and enhanced the replication of the L49D mutant virus in T cells. The impaired fusion and infectivity of L49D mutant particles were also complemented by a single point mutation in the gp41 CT that disrupted the tyrosine-containing endocytic motif. Our results suggest that an altered interaction between the MA domain of Gag and the gp41 cytoplasmic tail leads to dissociation of gp120 from gp41 during HIV-1 particle assembly, thus resulting in impaired fusion and infectivity.
Collapse
Affiliation(s)
- Melody R Davis
- Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232-2363, USA
| | | | | | | | | |
Collapse
|
13
|
Holm GH, Gabuzda D. Distinct mechanisms of CD4+ and CD8+ T-cell activation and bystander apoptosis induced by human immunodeficiency virus type 1 virions. J Virol 2005; 79:6299-311. [PMID: 15858014 PMCID: PMC1091688 DOI: 10.1128/jvi.79.10.6299-6311.2005] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Apoptosis of uninfected bystander T cells contributes to T-cell depletion during human immunodeficiency virus type 1 (HIV-1) infection. HIV-1 envelope/receptor interactions and immune activation have been implicated as contributors to bystander apoptosis. To better understand the relationship between T-cell activation and bystander apoptosis during HIV-1 pathogenesis, we investigated the effects of the highly cytopathic CXCR4-tropic HIV-1 variant ELI6 on primary CD4(+) and CD8(+) T cells. Infection of primary T-cell cultures with ELI6 induced CD4(+) T-cell depletion by direct cell lysis and bystander apoptosis. Exposure of primary CD4(+) and CD8(+) T cells to nonreplicating ELI6 virions induced bystander apoptosis through a Fas-independent mechanism. Bystander apoptosis of CD4(+) T cells required direct contact with virions and Env/CXCR4 binding. In contrast, the apoptosis of CD8(+) T cells was triggered by a soluble factor(s) secreted by CD4(+) T cells. HIV-1 virions activated CD4(+) and CD8(+) T cells to express CD25 and HLA-DR and preferentially induced apoptosis in CD25(+)HLA-DR(+) T cells in a CXCR4-dependent manner. Maximal levels of binding, activation, and apoptosis were induced by virions that incorporated MHC class II and B7-2 into the viral membrane. These results suggest that nonreplicating HIV-1 virions contribute to chronic immune activation and T-cell depletion during HIV-1 pathogenesis by activating CD4(+) and CD8(+) T cells, which then proceed to die via apoptosis. This mechanism may represent a viral immune evasion strategy to increase viral replication by activating target cells while killing immune effector cells that are not productively infected.
Collapse
Affiliation(s)
- Geoffrey H Holm
- Dana-Farber Cancer Institute, JFB 816, 44 Binney St., Boston, MA 02115, USA
| | | |
Collapse
|
14
|
Nakaoke R, Banks WA. In Vitro Methods in the Study of Viral and Prion Permeability Across the Blood–Brain Barrier. Cell Mol Neurobiol 2005; 25:171-80. [PMID: 15966106 DOI: 10.1007/s10571-004-1381-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
(1) Infectious agents capable of entering the central nervous system (CNS) produce some of the most dreaded diseases known to man. The infectious agent within the CNS is often protected by the blood-brain barrier (BBB), shielded from endogenous and exogenous anti-infectious agents. (2) The use of in vitro methods offers many advantages to the study of how infectious agents interact with the BBB. Two such agents which negotiate the BBB early in the course of disease before damage to the BBB are the autoimmune deficiency syndrome virus, or human immunodeficiency virus 1, and scrapie prion. Our laboratories have used in vitro methods to study these agents. (3) Here, we review some of the results form our laboratories and those of others.
Collapse
Affiliation(s)
- Ryota Nakaoke
- Department of Pharmacology 1, Nagasaki University School of Medicine, Nagasaki, Japan
| | | |
Collapse
|
15
|
Holm GH, Zhang C, Gorry PR, Peden K, Schols D, De Clercq E, Gabuzda D. Apoptosis of bystander T cells induced by human immunodeficiency virus type 1 with increased envelope/receptor affinity and coreceptor binding site exposure. J Virol 2004; 78:4541-51. [PMID: 15078935 PMCID: PMC387714 DOI: 10.1128/jvi.78.9.4541-4551.2004] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Apoptosis of uninfected bystander CD4(+) T cells contributes to T-cell depletion during human immunodeficiency virus type 1 (HIV-1) pathogenesis. The viral and host mechanisms that lead to bystander apoptosis are not well understood. To investigate properties of the viral envelope glycoproteins (Env proteins) that influence the ability of HIV-1 to induce bystander apoptosis, we used molecularly cloned viruses that differ only in specific amino acids in Env. The ability of these strains to induce bystander apoptosis was tested in herpesvirus saimiri-immortalized primary CD4(+) T cells (CD4/HVS), which resemble activated primary T cells. Changes in Env that increase affinity for CD4 or CCR5 or increase coreceptor binding site exposure enhanced the capacity of HIV-1 to induce bystander apoptosis following viral infection or exposure to nonreplicating virions. Apoptosis induced by HIV-1 virions was inhibited by CD4, CXCR4, and CCR5 antibodies or by the CXCR4 inhibitor AMD3100, but not the fusion inhibitor T20. HIV-1 virions with mutant Envs that bind CXCR4 but are defective for CD4 binding or membrane fusion induced apoptosis, whereas CXCR4 binding-defective mutants did not. These results demonstrate that HIV-1 virions induce apoptosis through a CXCR4- or CCR5-dependent pathway that does not require Env/CD4 signaling or membrane fusion and suggest that HIV-1 variants with increased envelope/receptor affinity or coreceptor binding site exposure may promote T-cell depletion in vivo by accelerating bystander cell death.
Collapse
Affiliation(s)
- Geoffrey H Holm
- Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | | | | | | | |
Collapse
|
16
|
Pugach P, Kuhmann SE, Taylor J, Marozsan AJ, Snyder A, Ketas T, Wolinsky SM, Korber BT, Moore JP. The prolonged culture of human immunodeficiency virus type 1 in primary lymphocytes increases its sensitivity to neutralization by soluble CD4. Virology 2004; 321:8-22. [PMID: 15033560 DOI: 10.1016/j.virol.2003.12.012] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2003] [Revised: 12/15/2003] [Accepted: 12/15/2003] [Indexed: 10/26/2022]
Abstract
Primary strains of human immunodeficiency virus type 1 (HIV-1) are known to adapt to replication in cell lines in vitro by becoming sensitive to soluble CD4 (sCD4) and neutralizing antibodies (NAb). T-cell lines favor isolation of variants that use CXCR4 as a co-receptor, while primary isolates predominantly use CCR5. We have now studied how a primary R5 isolate, CC1/85, adapts to prolonged replication in primary human peripheral blood mononuclear cells (PBMC). After 19 passages, a variant virus, CCcon.19, had increased sensitivity to both sCD4 and NAb b12 that binds to a CD4-binding site (CD4BS)-associated epitope, but decreased sensitivity to anti-CD4 antibodies. CCcon.19 retains the R5 phenotype, its resistance to other NAbs was unaltered, its sensitivity to various entry inhibitors was unchanged, and its ability to replicate in macrophages was modestly increased. We define CCcon.19 as a primary T-cell adapted (PTCA) variant. Genetic sequence analysis combined with mutagenesis studies on clonal, chimeric viruses derived from CC1/85 and the PTCA variant showed that the most important changes were in the V1/V2 loop structure, one of them involving the loss of an N-linked glycosylation site. Monomeric gp120 proteins expressed from CC1/85 and the PTCA variant did not differ in their affinities for sCD4, suggesting that the structural consequences of the sequence changes were manifested at the level of the native, trimeric Env complex. Overall, the adaptation process probably involves selection for variants with higher CD4 affinity and hence greater fusion efficiency, but this also involves the loss of some resistance to neutralization by agents directed at or near to the CD4BS. The loss of neutralization resistance is of no relevance under in vitro conditions, but NAbs would presumably be a counter-selection pressure against such adaptive changes in vivo, at least when the humoral immune response is intact.
Collapse
Affiliation(s)
- Pavel Pugach
- Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, NY 10021, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
17
|
Affiliation(s)
- Donald J Winzor
- Department of Biochemistry, School of Molecular and Microbial Sciences, University of Queensland, Brisbane, Queensland 4072, Australia.
| |
Collapse
|
18
|
Chertova E, Bess JW, Crise BJ, Sowder II RC, Schaden TM, Hilburn JM, Hoxie JA, Benveniste RE, Lifson JD, Henderson LE, Arthur LO. Envelope glycoprotein incorporation, not shedding of surface envelope glycoprotein (gp120/SU), Is the primary determinant of SU content of purified human immunodeficiency virus type 1 and simian immunodeficiency virus. J Virol 2002; 76:5315-25. [PMID: 11991960 PMCID: PMC137021 DOI: 10.1128/jvi.76.11.5315-5325.2002] [Citation(s) in RCA: 227] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) particles typically contain small amounts of the surface envelope protein (SU), and this is widely believed to be due to shedding of SU from mature virions. We purified proteins from HIV-1 and SIV isolates using procedures which allow quantitative measurements of viral protein content and determination of the ratios of gag- and env-encoded proteins in virions. All of the HIV-1 and most of the SIV isolates examined contained low levels of envelope proteins, with Gag:Env ratios of approximately 60:1. Based on an estimate of 1,200 to 2,500 Gag molecules per virion, this corresponds to an average of between 21 and 42 SU molecules, or between 7 and 14 trimers, per particle. In contrast, some SIV isolates contained levels of SU at least 10-fold greater than SU from HIV-1 isolates. Quantification of relative amounts of SU and transmembrane envelope protein (TM) provides a means to assess the impact of SU shedding on virion SU content, since such shedding would be expected to result in a molar excess of TM over SU on virions that had shed SU. With one exception, viruses with sufficient SU and TM to allow quantification were found to have approximately equivalent molar amounts of SU and TM. The quantity of SU associated with virions and the SU:TM ratios were not significantly changed during multiple freeze-thaw cycles or purification through sucrose gradients. Exposure of purified HIV-1 and SIV to temperatures of 55 degrees C or greater for 1 h resulted in loss of most of the SU from the virus but retention of TM. Incubation of purified virus with soluble CD4 at 37 degrees C resulted in no appreciable loss of SU from either SIV or HIV-1. These results indicate that the association of SU and TM on the purified virions studied is quite stable. These findings suggest that incorporation of SU-TM complexes into the viral membrane may be the primary factor determining the quantity of SU associated with SIV and HIV-1 virions, rather than shedding of SU from mature virions.
Collapse
Affiliation(s)
- Elena Chertova
- AIDS Vaccine Program, SAIC Frederick, Maryland 21702-1201, USA.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
19
|
Affiliation(s)
- M Stevenson
- Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA 01605, USA
| |
Collapse
|
20
|
Arthos J, Cicala C, Steenbeke TD, Chun TW, Dela Cruz C, Hanback DB, Khazanie P, Nam D, Schuck P, Selig SM, Van Ryk D, Chaikin MA, Fauci AS. Biochemical and biological characterization of a dodecameric CD4-Ig fusion protein: implications for therapeutic and vaccine strategies. J Biol Chem 2002; 277:11456-64. [PMID: 11805109 DOI: 10.1074/jbc.m111191200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Drug toxicities associated with HAART lend urgency to the development of new anti-HIV therapies. Inhibition of viral replication at the entry stage of the viral life cycle is an attractive strategy because it prevents de novo infection. Soluble CD4 (sCD4), the first drug in this class, failed to suppress viral replication in vivo. At least three factors contributed to this failure: sCD4 demonstrated poor neutralizing activity against most primary isolates of HIV in vitro; it demonstrated an intrinsic capacity to enhance viral replication at low concentrations; and it exhibited a relatively short half-life in vivo. Many anti-gp120 monoclonal antibodies, including neutralizing monoclonal antibodies also enhance viral replication at suboptimal concentrations. Advances in our understanding of the events leading up to viral entry suggest strategies by which this activity can be diminished. We hypothesized that by constructing a sCD4-based molecule that is large, binds multiple gp120s simultaneously, and is highly avid toward gp120, we could remove its capacity to enhance viral entry. Here we describe the construction of a polymeric CD4-IgG1 fusion protein. The hydrodynamic radius of this molecule is approximately 12 nm. It can bind at least 10 gp120 subunits with binding kinetics that suggest a highly avid interaction toward virion-associated envelope. This protein does not enhance viral replication at suboptimal concentrations. These observations may aid in the design of new therapeutics and vaccines.
Collapse
Affiliation(s)
- James Arthos
- Laboratory of Immunoregulation, NIAID, and the Molecular Interactions Resource Division of Bioengineering and Physical Science, National Institutes of Health, Bethesda, Maryland 20892, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Cortés MJ, Wong-Staal F, Lama J. Cell surface CD4 interferes with the infectivity of HIV-1 particles released from T cells. J Biol Chem 2002; 277:1770-9. [PMID: 11704677 DOI: 10.1074/jbc.m109807200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The CD4 protein is required for the entry of human immunodeficiency virus (HIV) into target cells. Upon expression of the viral genome, three HIV-1 gene products participate in the removal of the primary viral receptor from the cell surface. To investigate the role of surface-CD4 in HIV replication, we have created a set of Jurkat cell lines which constitutively express surface levels of CD4 comparable to those found in peripheral blood lymphocytes and monocytes. Expression of low levels of CD4 on the surface of producer cells exerted an inhibitory effect on the infectivity of HIV-1 particles, whereas no differences in the amount of cell-free p24 antigen were observed. Higher levels of cell surface CD4 exerted a stronger inhibitory effect on infectivity, and also affected the release of free virus in experiments where the viral genomes were delivered by electrotransfection. The CD4-mediated inhibition of HIV-1 infectivity was not observed in experiments where the vesicular stomatitis virus G protein was used to pseudotype viruses, suggesting that an interaction between CD4 and gp120 is required for interference. In contrast, inhibition of particle release by high levels of cell-surface CD4 was not overcome by pseudotyping HIV-1 with foreign envelope proteins. Protein analysis of viral particles released from HIV-infected Jurkat-T cells revealed a CD4-dependent reduction in the incorporation of gp120. These results demonstrate that physiological levels of cell-surface CD4 interfere with HIV-1 replication in T cells by a mechanism that inhibits envelope incorporation into viral membranes, and therefore provide an explanation for the need to down-modulate the viral receptor in infected cells. Our findings have important implications for the spread of HIV in vivo and suggest that the CD4 down-modulation function may be an alternative target for therapeutic intervention.
Collapse
Affiliation(s)
- Maria José Cortés
- Departments of Medicine and Biology, University of California, San Diego, La Jolla, California 92093-0665
| | | | | |
Collapse
|
22
|
Zhang CW, Chishti Y, Hussey RE, Reinherz EL. Expression, purification, and characterization of recombinant HIV gp140. The gp41 ectodomain of HIV or simian immunodeficiency virus is sufficient to maintain the retroviral envelope glycoprotein as a trimer. J Biol Chem 2001; 276:39577-85. [PMID: 11514580 DOI: 10.1074/jbc.m107147200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Efforts to understand the molecular basis of human immunodeficiency virus (HIV) envelope glycoprotein function have been hampered by the inability to generate sufficient quantities of homogeneous material. We now report on the high level expression, purification, and characterization of soluble HIV gp140 ectodomain proteins in Chinese hamster ovary-Lec3.2.8.1 cells. Gel filtration and analytical ultracentrifugation show that the uncleaved ADA strain-derived gp140 proteins are trimeric without further modification required to maintain oligomers. These spike proteins are native as judged by soluble CD4 (sCD4) (K(D) = 1-2 nm) and monoclonal antibody binding studies using surface plasmon resonance. CD4 ligation induces conformational change in the trimer, exposing the chemokine receptor binding site as assessed by 17b monoclonal antibody reactivity. Lack of anti-cooperativity in sCD4-ADA trimer interaction distinct from that observed with sCD4-SIV mac32H implies quaternary structural differences in ground states of their respective spike proteins.
Collapse
Affiliation(s)
- C W Zhang
- Laboratory of Immunobiology, Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115, USA
| | | | | | | |
Collapse
|
23
|
Haddrick M, Brown CR, Plishka R, Buckler-White A, Hirsch VM, Ginsberg H. Biologic studies of chimeras of highly and moderately virulent molecular clones of simian immunodeficiency virus SIVsmPBj suggest a critical role for envelope in acute AIDS virus pathogenesis. J Virol 2001; 75:6645-59. [PMID: 11413332 PMCID: PMC114388 DOI: 10.1128/jvi.75.14.6645-6659.2001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Previous studies identified three molecular clones of the acutely pathogenic SIVsmPBj strain that varied in terms of relative in vivo pathogenicity. One clone, SIVsmPBj6.6, reproducibly induced a rapidly fatal disease in pigtailed macaques. In contrast, a highly related clone (SIVsmPBj6.9) was only minimally pathogenic in macaques. PBj6.6 and PBj6.9 shared a tyrosine substitution at position 17 in the Nef protein that is a major determinant of virulence but differed at one residue in Vpx (C89R), three residues within the envelope (D119G, R871G, G872R), and a single residue in Nef (F252L). SIVsmPBj6.9 was less efficient in inducing proliferation of resting macaque peripheral blood mononuclear cells in vitro than SIVsmPBj6.6 and exhibited a marked reduction in infectivity relative to SIVsmPBj6.6. Chimeric viruses for each of these variable residues were constructed, and their biologic properties were compared to those of the parental strains. Differences in Vpx and Nef did not alter the basic biologic phenotype of the chimeras. However, the D119G substitution in the envelope of SIVsmPBj6.9 was associated with a marked reduction in the infectivity of this virus relative to SIVsmPBj6.6. An associated processing defect in gp160 of SIVsmPBj6.9 and chimeras expressing the D119G substitution suggests that a reduction in virion envelope incorporation is the mechanistic basis for reduced virion infectivity. In vivo studies revealed that substitution of the PBj6.9 amino acid into PBj6.6 (D119) abrogated the pathogenicity of this previously pathogenic virus. Introduction of the PBj6.9 G119, however, did not confer full virulence to the parental PBj6.9 virus, implicating one or all of the other four substitutions in the virulence of SIVsmPBj6.6.
Collapse
Affiliation(s)
- M Haddrick
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Twinbrook II Facility, 12441 Parklawn Dr., Rockville, MD 20852, USA
| | | | | | | | | | | |
Collapse
|
24
|
Owada T, Motomura T, Miyashita-Ogawa Y, Kawada-Homma M, Onishi M, Matondo P, Terunuma H, Numazaki Y, Yamashita S, Yamamoto N. Antibody masking renders HIV-1 resistant to cationic membrane filtration through alteration of its electrostatic characteristics. J Virol Methods 2001; 94:15-24. [PMID: 11337036 DOI: 10.1016/s0166-0934(01)00262-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Previously, it was demonstrated that any human immunodeficiency virus type 1 (HIV-1) strain proliferating in peripheral blood mononuclear cells (PBMCs) in vitro, and resuspended in seronegative plasma, could be captured efficiently (mean > 95%) by a porous polypropylene (PP) membrane modified cationically. We investigated if this cationic membrane could capture HIV-1 obtained from seropositive plasma, and confirmed whether this membrane was effective for the preparation of safe plasma products against HIV-1 transmission. Thirty-six seropositive plasma samples derived from HIV-1 positive cohorts in New York and Lusaka (Republic of Zambia), including 18 cases of acquired immunodeficiency syndrome (AIDS) related complex, AIDS and five terminal cases of AIDS, were filtered through the cationic membrane to determine the reduction of RNA concentration, the gag p24 concentration, and infectious titer. Only a small reduction in RNA concentration (mean < 20%) and almost no decrease in gag concentration (mean < 2%) were obtained, despite the fact that the infectivity was eliminated entirely by the filtration. Due to the possibility that anti-HIV-1 antibodies in patients' plasma combine with HIV-1, laboratory-adapted HIV-1(HTLV-IIIB) was mixed with seropositive plasma to test the effect of antibodies on HIV-1 adsorption, and also to investigate the interfacial electrokinetic potential (zeta-potential) of both intact and plasma-treated HIV-1. The zeta-potential of HIV-1(HTLV-IIIB) in the presence of seropositive plasma was neutral as opposed to negative when stored in seronegative plasma or culture medium. Also the rate of HIV-1 capture by the membrane, as determined by the reduction in RNA concentration, sank from 95% to 20%, the same capture percentage observed when filtering plasma of patients. These findings suggested that in patients' plasma, the antibody-masked HIV-1 comprise most of the viral population, and was not trapped on the cationic membrane because of its electrostatic character. Conversely, the cationic membrane was thought to adsorb antibody-free HIV-1 exclusively. It was suggested that each viral swarm had its own zeta-potential, and this difference in electrostatic character determined the extent of the viral adsorption by the cationic membrane.
Collapse
Affiliation(s)
- T Owada
- Department of New Materials Section, Terumo Research and Development Center, Hadano, 259-0151, Kanagawa, Japan.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
25
|
Banks WA, Freed EO, Wolf KM, Robinson SM, Franko M, Kumar VB. Transport of human immunodeficiency virus type 1 pseudoviruses across the blood-brain barrier: role of envelope proteins and adsorptive endocytosis. J Virol 2001; 75:4681-91. [PMID: 11312339 PMCID: PMC114222 DOI: 10.1128/jvi.75.10.4681-4691.2001] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Blood-borne human immunodeficiency virus type 1 (HIV-1) crosses the blood-brain barrier (BBB) to induce brain dysfunction. How HIV-1 crosses the BBB is unclear. Most work has focused on the ability of infected immune cells to cross the BBB, with less attention devoted to the study of free virus. Since the HIV-1 coat glycoprotein gp120 can cross the BBB, we postulated that gp120 might be key in determining whether free virus can cross the BBB. We used radioactive virions which do (Env+) or do not (Env-) bear the envelope proteins to characterize the ability of HIV-1 to be taken up by the murine BBB. In vivo and in vitro studies showed that the envelope proteins are key to the uptake of free virus and that uptake was enhanced by wheat germ agglutinin, strongly suggesting that the envelope proteins induce viral adsorptive endocytosis and transcytosis in brain endothelia. Capillary depletion showed that Env+ virus completely crossed the vascular BBB to enter the parenchyma of the brain. Virus also entered the cerebrospinal fluid, suggesting passage across the choroid plexus as well. About 0.22% of the intravenously injected dose was taken up per g of brain. In vitro studies showed that postinternalization membrane cohesion (membrane binding not reversed with acid wash or cell lysis) was a regulated event. Intact virus was recovered from the brain endothelial cytosol and was effluxed from the endothelial cells. These results show that free HIV-1 can cross the BBB by an event related to adsorptive endocytosis and mediated by the envelope proteins.
Collapse
Affiliation(s)
- W A Banks
- GRECC, Veterans Affairs Medical Center-St. Louis, and Division of Geriatrics, Department of Internal Medicine, Saint Louis University School of Medicine, St. Louis, Missouri 63106, USA.
| | | | | | | | | | | |
Collapse
|
26
|
Stins MF, Shen Y, Huang SH, Gilles F, Kalra VK, Kim KS. Gp120 activates children's brain endothelial cells via CD4. J Neurovirol 2001; 7:125-34. [PMID: 11517385 DOI: 10.1080/13550280152058780] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Encephalopathy represents a common and serious manifestation of HIV-1 infection in children, but its pathogenesis is unclear. We demonstrated that gp120 activated human brain microvascular endothelial cells (HBMEC) derived from children in up-regulating ICAM-1 and VCAM-1 expression, IL-6 secretion and increased monocyte transmigration across monolayers. Another novel observation was our demonstration of CD4 in isolated HBMEC and on microvessels of children's brain cryosections. Gp120-induced monocyte migration was inhibited by anti-gp120 and anti-CD4 antibodies. This is the first demonstration that gp120 activates HBMEC via CD4, which may contribute to the development of HIV-1 encephalopathy in children.
Collapse
Affiliation(s)
- M F Stins
- Division of Infectious Diseases, Childrens Hospital Los Angeles, California, USA
| | | | | | | | | | | |
Collapse
|
27
|
Kolchinsky P, Kiprilov E, Bartley P, Rubinstein R, Sodroski J. 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. J Virol 2001; 75:3435-43. [PMID: 11238869 PMCID: PMC114136 DOI: 10.1128/jvi.75.7.3435-3443.2001] [Citation(s) in RCA: 147] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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 degrees C than at 37 degrees 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.
Collapse
Affiliation(s)
- P Kolchinsky
- Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, and Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | | | |
Collapse
|
28
|
York J, Follis KE, Trahey M, Nyambi PN, Zolla-Pazner S, Nunberg JH. Antibody binding and neutralization of primary and T-cell line-adapted isolates of human immunodeficiency virus type 1. J Virol 2001; 75:2741-52. [PMID: 11222697 PMCID: PMC115898 DOI: 10.1128/jvi.75.6.2741-2752.2001] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The relative resistance of human immunodeficiency virus type 1 (HIV-1) primary isolates (PIs) to neutralization by a wide range of antibodies remains a theoretical and practical barrier to the development of an effective HIV vaccine. One model to account for the differential neutralization sensitivity between Pls and laboratory (or T-cell line-adapted [TCLA]) strains of HIV suggests that the envelope protein (Env) complex is made more accessible to antibody binding as a consequence of adaptation to growth in established cell lines. Here, we revisit this question using genetically related PI and TCLA viruses and molecularly cloned env genes. By using complementary techniques of flow cytometry and virion binding assays, we show that monoclonal antibodies targeting the V3 loop, CD4-binding site, CD4-induced determinant of gp120, or the ectodomain of gp41 bind equally well to PI and TCLA Env complexes, despite large differences in neutralization outcome. The data suggest that the differential neutralization sensitivity of PI and TCLA viruses may derive not from differences in the initial antibody binding event but rather from differences in the subsequent functioning of the PI and TCLA Envs during virus entry. An understanding of these as yet undefined differences may enhance our ability to generate broadly neutralizing HIV vaccine immunogens.
Collapse
Affiliation(s)
- J York
- Montana Biotechnology Center, The University of Montana, Missoula, Montana 59812, USA
| | | | | | | | | | | |
Collapse
|
29
|
Kolchinsky P, Kiprilov E, Sodroski J. Increased neutralization sensitivity of CD4-independent human immunodeficiency virus variants. J Virol 2001; 75:2041-50. [PMID: 11160708 PMCID: PMC114788 DOI: 10.1128/jvi.75.5.2041-2050.2001] [Citation(s) in RCA: 141] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Naturally occurring human immunodeficiency virus (HIV-1) variants require the presence of CD4 and specific chemokine receptors to enter a cell. In the laboratory, HIV-1 variants that are capable of bypassing CD4 and utilizing only the CCR5 chemokine receptor for virus entry have been generated. Here we report that these CD4-independent viruses are significantly more sensitive to neutralization by soluble CD4 and a variety of antibodies. The same amino acid changes in the HIV-1 gp120 envelope glycoprotein determined CD4 independence and neutralization sensitivity. The CD4-independent envelope glycoproteins exhibited higher affinity for antibodies against CD4-induced gp120 epitopes but not other neutralizing ligands. The CD4-independent envelope glycoproteins did not exhibit increased lability relative to the wild-type envelope glycoproteins. The utilization of two receptors apparently allows HIV-1 to maintain a more neutralization-resistant state prior to engaging CD4 on the target cell, explaining the rarity of CD4 independence in wild-type HIV-1.
Collapse
Affiliation(s)
- P Kolchinsky
- Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | |
Collapse
|
30
|
Peden KW, Farber JM. Coreceptors for human immunodeficiency virus and simian immunodeficiency virus. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2001; 48:409-78. [PMID: 10987098 DOI: 10.1016/s1054-3589(00)48013-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- K W Peden
- Laboratory of Retrovirus Research, Food and Drug Administration, Bethesda, Maryland, USA
| | | |
Collapse
|
31
|
Abstract
The Vif protein of human immunodeficiency virus type 1 (HIV-1) is important for virion infectivity. Previous studies have shown that vif-defective virions exhibit structural abnormalities in the virus core and are defective in the ability to complete proviral DNA synthesis in acutely infected cells. We developed novel assays to assess the relative stability of the core in HIV-1 virions. Using these assays, we examined the role of Vif in the stability of the HIV-1 core. The integrity of the core was examined following virion permeabilization or removal of the lipid envelope and treatment with various triggers, including S100 cytosol, deoxynucleoside triphosphates, detergents, NaCl, and buffers of different pH to mimic aspects of the uncoating and disassembly process which occurs after virus entry but preceding or during reverse transcription. vif mutant cores were more sensitive to disruption by all triggers tested than wild-type cores, as determined by endogenous reverse transcriptase (RT) assays, biochemical analyses, and electron microscopy. RT and the p7 nucleocapsid protein were released more readily from vif mutant virions than from wild-type virions, suggesting that the internal nucleocapsid is less stably packaged in the absence of Vif. Purified cores could be isolated from wild-type but not vif mutant virions by sedimentation through detergent-treated gradients. These results demonstrate that Vif increases the stability of virion cores. This may permit efficient viral DNA synthesis by preventing premature degradation or disassembly of viral nucleoprotein complexes during early events after virus entry.
Collapse
Affiliation(s)
- A Ohagen
- Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | |
Collapse
|
32
|
Adams O, Schaal H, Scheid A. Natural variation in the amino acid sequence around the HIV type 1 glycoprotein 160 cleavage site and its effect on cleavability, subunit association, and membrane fusion. AIDS Res Hum Retroviruses 2000; 16:1235-45. [PMID: 10957721 DOI: 10.1089/08892220050117005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
To assess the natural variation of the structure of the cleavage site as well as the N-terminal region of gp41 for the cytopathogenicity of HIV-1, syncytium-inducing (SI) and non-syncytium-inducing (NSI) virus isolates were obtained from HIV-1-infected patients. In addition, the coreceptor usage of the isolates was determined by infection of primary macrophages and PM-1 cells. DNA sequences encoding the C-terminal 41 amino acid residues of gp120 and the 64 amino acid N-terminal residues of gp41 were amplified by the polymerase chain reaction and inserted into the Env expression vector pNLA1. When transfected into HeLa-T4(+) cells, all the recombinant plasmids, including those with inserts from NSI isolates, led to the formation of processed glycoprotein and to syncytium formation. One construct displayed significant lowered fusion capacity and had an amino acid exchange in the first position of the gp41 N terminus (gp41, 512A-->S) leading to a decreased association of the SU and TM subunits. Four constructs derived from two isolates of the same patient showed an unusual gp41 N terminus (gp41, 514G-->P) and a slightly diminished fusion capacity due to a decreased cleavability. This indicates that the major determinants for the SI and NSI phenotypes are not located around the gp160 cleavage site and that the N terminus of gp41 plays a minor role in the processing and fusion capacity of wild-type HIV-1 isolates.
Collapse
Affiliation(s)
- O Adams
- Institut für Medizinische Mikrobiologie und Virologie, Heinrich-Heine-Universität, Düsseldorf, Germany.
| | | | | |
Collapse
|
33
|
Derdeyn CA, Decker JM, Sfakianos JN, Wu X, O'Brien WA, Ratner L, Kappes JC, Shaw GM, Hunter E. Sensitivity of human immunodeficiency virus type 1 to the fusion inhibitor T-20 is modulated by coreceptor specificity defined by the V3 loop of gp120. J Virol 2000; 74:8358-67. [PMID: 10954535 PMCID: PMC116346 DOI: 10.1128/jvi.74.18.8358-8367.2000] [Citation(s) in RCA: 629] [Impact Index Per Article: 26.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
T-20 is a synthetic peptide that potently inhibits replication of human immunodeficiency virus type 1 by interfering with the transition of the transmembrane protein, gp41, to a fusion active state following interactions of the surface glycoprotein, gp120, with CD4 and coreceptor molecules displayed on the target cell surface. Although T-20 is postulated to interact with an N-terminal heptad repeat within gp41 in a trans-dominant manner, we show here that sensitivity to T-20 is strongly influenced by coreceptor specificity. When 14 T-20-naive primary isolates were analyzed for sensitivity to T-20, the mean 50% inhibitory concentration (IC(50)) for isolates that utilize CCR5 for entry (R5 viruses) was 0.8 log(10) higher than the mean IC(50) for CXCR4 (X4) isolates (P = 0. 0055). Using NL4.3-based envelope chimeras that contain combinations of envelope sequences derived from R5 and X4 viruses, we found that determinants of coreceptor specificity contained within the gp120 V3 loop modulate this sensitivity to T-20. The IC(50) for all chimeric envelope viruses containing R5 V3 sequences was 0.6 to 0.8 log(10) higher than that for viruses containing X4 V3 sequences. In addition, we confirmed that the N-terminal heptad repeat of gp41 determines the baseline sensitivity to T-20 and that the IC(50) for viruses containing GIV at amino acid residues 36 to 38 was 1.0 log(10) lower than the IC(50) for viruses containing a G-to-D substitution. The results of this study show that gp120-coreceptor interactions and the gp41 N-terminal heptad repeat independently contribute to sensitivity to T-20. These results have important implications for the therapeutic uses of T-20 as well as for unraveling the complex mechanisms of virus fusion and entry.
Collapse
Affiliation(s)
- C A Derdeyn
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
34
|
Platt EJ, Kozak SL, Kabat D. Critical role of enhanced CD4 affinity in laboratory adaptation of human immunodeficiency virus type 1. AIDS Res Hum Retroviruses 2000; 16:871-82. [PMID: 10875613 DOI: 10.1089/08892220050042819] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Strains of human immunodeficiency virus type 1 (HIV-1) that use the coreceptor CXCR4 (X4 strains) become laboratory adapted (LA) when selected for ability to replicate in leukemic T cell lines such as H9. Compared with patient X4 viruses, the gp120-gp41 complexes of LA viruses have a constellation of common properties including enhanced affinities for CD4, greater sensitivities to inactivations by diverse antibodies and by soluble CD4, increased shedding of gp120, and improved abilities to infect HeLa-CD4 cell clones that contain only trace quantities of CD4. These common characteristics, which may result from a concerted structural rearrangement of the gp120-gp41 complexes, have made it difficult to identify a specific feature that is critical for laboratory adaptation. To test the hypothesis that replication of patient X4 HIV-1 is limited by the low CD4 concentration in H9 cells (7.0 x 10(3) CD4/cell), we constructed H9 derivatives that express at least 10 times more of this receptor. Interestingly, most patient X4 isolates readily grew in these derivative cells, and the resulting virus preparations retained the characteristics of primary viruses throughout multiple passages. In contrast, selection of the same viruses in the parental H9 cells resulted in outgrowth of LA derivatives. We conclude that a weak interaction of patient X4 HIV-1 isolates with CD4 is the primary factor that limits their replication in leukemic T cell lines.
Collapse
Affiliation(s)
- E J Platt
- Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland 97201, USA
| | | | | |
Collapse
|
35
|
Brand D, Lemiale F, Thibault G, Verrier B, Lebigot S, Roingeard P, Buzelay L, Brunet S, Barin F. Antigenic properties of recombinant envelope glycoproteins derived from T-cell-line-adapted isolates or primary human immunodeficiency virus isolates and their relationship to immunogenicity. Virology 2000; 271:350-62. [PMID: 10860888 DOI: 10.1006/viro.2000.0322] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The native envelope glycoproteins of primary HIV-1 virions have weaker antigenicity than do T-cell laboratory-adapted (TCLA) viruses. These antigenic properties require further evaluation if recombinant envelope glycoproteins are produced as part of a vaccine strategy. In this study, we compared the antigenicity of recombinant envelope glycoproteins derived from three primary isolates (PI) (HIV-1(BX08), HIV-1(CHA), and HIV-1(133)) and two TCLA viruses (HIV-1(HXB2) and HIV-1(MN)) produced using the Semliki Forest virus (SFV) system. This analysis was performed by radioimmunoprecipitation assays and flow cytometry. The results suggest that the SFV produces envelope glycoproteins with features in common with the envelopes found in naturally occurring virions. In particular, the PI envelopes had weak heterogeneous antigenic properties. However, the cytometric analysis also showed that there was less envelope glycoprotein on the cell surface for the PI envelopes than for those of TCLA viruses, suggesting differences in their intracellular trafficking. The immunogenic properties of the various envelope glycoproteins were evaluated in mice using recombinant SFV particles as vaccine vectors. The PI envelopes were less immunogenic than the TCLA envelopes, probably due to both their low antigenicity and cell surface expression level. Thus, it may be difficult to design an effective vaccine based on native recombinant PI envelopes.
Collapse
Affiliation(s)
- D Brand
- Unité de Virologie, Université François Rabelais, Tours, France.
| | | | | | | | | | | | | | | | | |
Collapse
|
36
|
Yang X, Farzan M, Wyatt R, Sodroski J. Characterization of stable, soluble trimers containing complete ectodomains of human immunodeficiency virus type 1 envelope glycoproteins. J Virol 2000; 74:5716-25. [PMID: 10823881 PMCID: PMC112061 DOI: 10.1128/jvi.74.12.5716-5725.2000] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins function as a membrane-anchored trimer of three gp120 exterior glycoproteins and three gp41 transmembrane glycoproteins. Previously, we reported three approaches to stabilize soluble trimers containing parts of the gp41 ectodomains: addition of GCN4 trimeric helices, disruption of the cleavage site between gp120 and gp41, and introduction of cysteines in the gp41 coiled coil to form intersubunit disulfide bonds. Here, we applied similar approaches to stabilize soluble gp140 trimers including the complete gp120 and gp41 ectodomains. A combination of fusion with the GCN4 trimeric sequences and disruption of the gp120-gp41 cleavage site resulted in relatively homogeneous gp140 trimers with exceptional stability. The gp120 epitopes recognized by neutralizing antibodies are intact and exposed on these gp140 trimers. By contrast, the nonneutralizing antibody epitopes on the gp120 subunits of the soluble trimers are relatively occluded compared with those on monomeric gp120 preparations. This antigenic similarity to the functional HIV-1 envelope glycoproteins and the presence of the complete gp41 ectodomain should make the soluble gp140 trimers useful tools for structural and immunologic studies.
Collapse
Affiliation(s)
- X Yang
- Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | |
Collapse
|
37
|
Sei S, Yang QE, O'Neill D, Yoshimura K, Nagashima K, Mitsuya H. Identification of a key target sequence to block human immunodeficiency virus type 1 replication within the gag-pol transframe domain. J Virol 2000; 74:4621-33. [PMID: 10775598 PMCID: PMC111982 DOI: 10.1128/jvi.74.10.4621-4633.2000] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Although the full sequence of the human immunodeficiency virus type 1 (HIV-1) genome has been known for more than a decade, effective genetic antivirals have yet to be developed. Here we show that, of 22 regions examined, one highly conserved sequence (ACTCTTTGGCAACGA) near the 3' end of the HIV-1 gag-pol transframe region, encoding viral protease residues 4 to 8 and a C-terminal Vpr-binding motif of p6(Gag) protein in two different reading frames, can be successfully targeted by an antisense peptide nucleic acid oligomer named PNA(PR2). A disrupted translation of gag-pol mRNA induced at the PNA(PR2)-annealing site resulted in a decreased synthesis of Pr160(Gag-Pol) polyprotein, hence the viral protease, a predominant expression of Pr55(Gag) devoid of a fully functional p6(Gag) protein, and the excessive intracellular cleavage of Gag precursor proteins, hindering the processes of virion assembly. Treatment with PNA(PR2) abolished virion production by up to 99% in chronically HIV-1-infected H9 cells and in peripheral blood mononuclear cells infected with clinical HIV-1 isolates with the multidrug-resistant phenotype. This particular segment of the gag-pol transframe gene appears to offer a distinctive advantage over other regions in invading viral structural genes and restraining HIV-1 replication in infected cells and may potentially be exploited as a novel antiviral genetic target.
Collapse
Affiliation(s)
- S Sei
- HIV Clinical Interface Laboratory, SAIC-Frederick, NCI-Frederick Cancer Research and Development Center, Frederick, Maryland 21702, USA.
| | | | | | | | | | | |
Collapse
|
38
|
Yang X, Florin L, Farzan M, Kolchinsky P, Kwong PD, Sodroski J, Wyatt R. Modifications that stabilize human immunodeficiency virus envelope glycoprotein trimers in solution. J Virol 2000; 74:4746-54. [PMID: 10775613 PMCID: PMC111997 DOI: 10.1128/jvi.74.10.4746-4754.2000] [Citation(s) in RCA: 138] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The functional unit of the human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins is a trimer composed of three gp120 exterior glycoproteins and three gp41 transmembrane glycoproteins. The lability of intersubunit interactions has hindered the production and characterization of soluble, homogeneous envelope glycoprotein trimers. Here we report three modifications that stabilize soluble forms of HIV-1 envelope glycoprotein trimers: disruption of the proteolytic cleavage site between gp120 and gp41, introduction of cysteines that form intersubunit disulfide bonds, and addition of GCN4 trimeric helices. Characterization of these secreted glycoproteins by immunologic and biophysical methods indicates that these stable trimers retain structural integrity. The efficacy of the GCN4 sequences in stabilizing the trimers, the formation of intersubunit disulfide bonds between appropriately placed cysteines, and the ability of the trimers to interact with a helical, C-terminal gp41 peptide (DP178) support a model in which the N-terminal gp41 coiled coil exists in the envelope glycoprotein precursor and contributes to intersubunit interactions within the trimer. The availability of stable, soluble HIV-1 envelope glycoprotein trimers should expedite progress in understanding the structure and function of the virion envelope glycoprotein spikes.
Collapse
Affiliation(s)
- X Yang
- Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Harvard Medical School, Harvard School of Public Health, Boston, Massachusetts 02115, USA
| | | | | | | | | | | | | |
Collapse
|
39
|
Abstract
Infection with human immunodeficiency virus type-1 (HIV-1) requires the presence of a CD4 molecule and chemokine receptors such as CXCR4 or CCR5 on the surface of target cells. However, it is still not clear how the virus enters the cells. Although CD4 was initially identified as the primary receptor for HIV-1, the expression of CD4 or one of the chemokine receptors alone is not sufficient to render susceptibility to infection with the virus. To ascertain whether or not adsorption of the virus needs charge-to-charge interaction between viral envelope and host cell membrane protein(s) and if binding alone promotes penetration of the virus into the cells, we have developed a chemically induced infection system targeting a CD4-negative and CXCR4-positive HeLa cell clone (N7 HeLa) which is usually not susceptible to infection with the LAI strain of HIV-1. Use of a poly-L-lysine (PLL)-coated culture plate to enhance the attachment of the virus to the cells made N7 HeLa cells infectable with HIV-1 at very low efficiency. PLL alone cannot fully substitute for the function of the CD4 molecule. However, trypsin-treated viruses, which have largely lost infectivity to CD4-positive MT-4 cells that are highly susceptible to HIV-1 infection, enhanced infectivity against N7 HeLa cells when the PLL-coated plate was used. These results provide evidence that infection with HIV-1 requires both high binding affinity between viruses and cells, and then needs a modification of the viral envelope such as cleavage of gp120/160 to enhance the infection, probably resulting in exposure of the hydrophobic fusion domain of gp41. HIV-1 infection of N7 HeLa cells was also enhanced by treatment with low pH, 12-O-tetradecanoylphorbol-13-acetate (TPA) and some factor(s) from the MT-4 cell culture supernatant. Not only tight viral adsorption with cleavage of the viral envelope but also some activated status of the cells may be required for sufficient HIV-1 infection in this artificial condition.
Collapse
Affiliation(s)
- S Harada
- Department of Biodefence and Medical Virology, Kumamoto University School of Medicine, Kumamoto, Japan.
| | | |
Collapse
|
40
|
Kolchinsky P, Mirzabekov T, Farzan M, Kiprilov E, Cayabyab M, Mooney LJ, Choe H, Sodroski J. Adaptation of a CCR5-using, primary human immunodeficiency virus type 1 isolate for CD4-independent replication. J Virol 1999; 73:8120-6. [PMID: 10482561 PMCID: PMC112828 DOI: 10.1128/jvi.73.10.8120-8126.1999] [Citation(s) in RCA: 140] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The gp120 envelope glycoprotein of the human immunodeficiency virus type 1 (HIV-1) promotes virus entry by sequentially binding CD4 and chemokine receptors on the target cell. Primary, clinical HIV-1 isolates require interaction with CD4 to allow gp120 to bind the CCR5 chemokine receptor efficiently. We adapted a primary HIV-1 isolate, ADA, to replicate in CD4-negative canine cells expressing human CCR5. The gp120 changes responsible for the adaptation were limited to alteration of glycosylation addition sites in the V2 loop-V1-V2 stem. The gp120 glycoproteins of the adapted viruses bound CCR5 directly, without prior interaction with CD4. Thus, a major function of CD4 binding in the entry of primary HIV-1 isolates can be bypassed by changes in the gp120 V1-V2 elements, which allow the envelope glycoproteins to assume a conformation competent for CCR5 binding.
Collapse
Affiliation(s)
- P Kolchinsky
- Department of Cancer, Dana-Farber Cancer Institute, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | | | | | | | | | |
Collapse
|
41
|
Shibata R, Igarashi T, Haigwood N, Buckler-White A, Ogert R, Ross W, Willey R, Cho MW, Martin MA. Neutralizing antibody directed against the HIV-1 envelope glycoprotein can completely block HIV-1/SIV chimeric virus infections of macaque monkeys. Nat Med 1999; 5:204-10. [PMID: 9930869 DOI: 10.1038/5568] [Citation(s) in RCA: 468] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Virus-specific antibodies protect individuals against a wide variety of viral infections. To assess whether human immunodeficiency virus type 1 (HIV-1) envelope-specific antibodies confer resistance against primate lentivirus infections, we purified immunoglobulin (IgG) from chimpanzees infected with several different HIV-1 isolates, and used this for passive immunization of pig-tailed macaques. These monkeys were subsequently challenged intravenously with a chimeric simian-human immunodeficiency virus (SHIV) bearing an envelope glycoprotein derived form HIV-1DH12, a dual-tropic primary virus isolate. Here we show that anti-SHIV neutralizing activity, determined in vitro using an assay measuring loss of infectivity, is the absolute requirement for antibody-mediated protection in vivo. Using an assay that measures 100% neutralization, the titer in plasma for complete protection of the SHIV-challenged macaques was in the range of 1:5-1:8. The HIV-1-specific neutralizing antibodies studied are able to bind to native gp120 present on infectious virus particles. Administration of non-neutralizing anti-HIV IgG neither inhibited nor enhanced a subsequent SHIV infection.
Collapse
Affiliation(s)
- R Shibata
- Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
42
|
Sullivan N, Sun Y, Binley J, Lee J, Barbas CF, Parren PW, Burton DR, Sodroski J. Determinants of human immunodeficiency virus type 1 envelope glycoprotein activation by soluble CD4 and monoclonal antibodies. J Virol 1998; 72:6332-8. [PMID: 9658072 PMCID: PMC109776 DOI: 10.1128/jvi.72.8.6332-6338.1998] [Citation(s) in RCA: 120] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Infection by some human immunodeficiency virus type 1 (HIV-1) isolates is enhanced by the binding of subneutralizing concentrations of soluble receptor, soluble CD4 (sCD4), or monoclonal antibodies directed against the viral envelope glycoproteins. In this work, we studied the abilities of different antibodies to mediate activation of the envelope glycoproteins of a primary HIV-1 isolate, YU2, and identified the regions of gp120 envelope glycoprotein contributing to activation. Binding of antibodies to a variety of epitopes on gp120, including the CD4 binding site, the third variable (V3) loop, and CD4-induced epitopes, enhanced the entry of viruses containing YU2 envelope glycoproteins. Fab fragments of antibodies directed against either the CD4 binding site or V3 loop also activated YU2 virus infection. The activation phenotype was conferred on the envelope glycoproteins of a laboratory-adapted HIV-1 isolate (HXBc2) by replacing the gp120 V3 loop or V1/V2 and V3 loops with those of the YU2 virus. Infection by the YU2 virus in the presence of activating antibodies remained inhibitable by macrophage inhibitory protein 1beta, indicating dependence on the CCR5 coreceptor on the target cells. Thus, antibody enhancement of YU2 entry involves neither Fc receptor binding nor envelope glycoprotein cross-linking, is determined by the same variable loops that dictate enhancement by sCD4, and probably proceeds by a process fundamentally similar to the receptor-activated virus entry pathway.
Collapse
Affiliation(s)
- N Sullivan
- Division of Human Retrovirology, Dana-Farber Cancer Institute, Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | | | | | | | | | |
Collapse
|
43
|
Sullivan N, Sun Y, Sattentau Q, Thali M, Wu D, Denisova G, Gershoni J, Robinson J, Moore J, Sodroski J. CD4-Induced conformational changes in the human immunodeficiency virus type 1 gp120 glycoprotein: consequences for virus entry and neutralization. J Virol 1998; 72:4694-703. [PMID: 9573233 PMCID: PMC109994 DOI: 10.1128/jvi.72.6.4694-4703.1998] [Citation(s) in RCA: 244] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Human immunodeficiency virus type 1 (HIV-1) entry into target cells involves sequential binding of the gp120 exterior envelope glycoprotein to CD4 and to specific chemokine receptors. Soluble CD4 (sCD4) is thought to mimic membrane-anchored CD4, and its binding alters the conformation of the HIV-1 envelope glycoproteins. Two cross-competing monoclonal antibodies, 17b and CG10, that recognize CD4-inducible gp120 epitopes and that block gp120-chemokine receptor binding were used to investigate the nature and functional significance of gp120 conformational changes initiated by CD4 binding. Envelope glycoproteins derived from both T-cell line-adapted and primary HIV-1 isolates exhibited increased binding of the 17b antibody in the presence of sCD4. CD4-induced exposure of the 17b epitope on the oligomeric envelope glycoprotein complex occurred over a wide range of temperatures and involved movement of the gp120 V1/V2 variable loops. Amino acid changes that reduced the efficiency of 17b epitope exposure following CD4 binding invariably compromised the ability of the HIV-1 envelope glycoproteins to form syncytia or to support virus entry. Comparison of the CD4 dependence and neutralization efficiencies of the 17b and CG10 antibodies suggested that the epitopes for these antibodies are minimally accessible following attachment of gp120 to cell surface CD4. These results underscore the functional importance of these CD4-induced changes in gp120 conformation and illustrate viral strategies for sequestering chemokine receptor-binding regions from the humoral immune response.
Collapse
Affiliation(s)
- N Sullivan
- Division of Human Retrovirology, Dana-Farber Cancer Institute, Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
44
|
Owada T, Miyashita Y, Motomura T, Onishi M, Yamashita S, Yamamoto N. Enhancement of human immunodeficiency virus type 1 (HIV-1) infection via increased membrane fluidity by a cationic polymer. Microbiol Immunol 1998; 42:97-107. [PMID: 9572041 DOI: 10.1111/j.1348-0421.1998.tb02257.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Cationic polymers are known to have potent activity against bacteria, but their effects on viral activity have been little studied. We investigated the effect of one such polymer, polyethyleneimine (PEI), on HIV-1 infection. Although virus-cell binding was significantly inhibited by PEI, HIV-1 infection in human T-cell lines such as MT-4 and MOLT-4 was accelerated conversely when the drug treatment was carried out, after the virus had attached to the cells or PEI was simultaneously added to the virus and cell culture system. This paradoxical effect of PEI on HIV-1 infection was examined using HIV-1 chronically infected cells (MOLT-4/HIV-1). Dissociation of the glycoprotein gp120 (as revealed by exposure of transmembrane protein gp41) from MOLT-4/HIV-1 cells and the resultant fusion of these cells was shown to be induced by the addition of PEI. Accordingly, it was suggested that the binding inhibition of HIV-1 to CD4-positive cells by PEI was due to the shedding of gp120 from HIV-1 particles, and this PEI rather promoted membrane fusion between the virus and cells leading to the enhancement of HIV-1 infection. Similarly, dissociation of gp120 from MOLT-4/HIV-1 was also induced by sCD4. The effect of these reagents on changes in membrane fluidity was evaluated by polarization (p) measurements, and it was observed that the acceleration of membrane fluidity occurred only in the PEI system. Therefore, it is likely that PEI accelerates HIV-1 infection by facilitating virus entry into the host cells through an increase in membrane fluidity.
Collapse
Affiliation(s)
- T Owada
- Department of Microbiology, Tokyo Medical and Dental University School of Medicine, Japan
| | | | | | | | | | | |
Collapse
|
45
|
Trkola A, Ketas T, Kewalramani VN, Endorf F, Binley JM, Katinger H, Robinson J, Littman DR, Moore JP. Neutralization sensitivity of human immunodeficiency virus type 1 primary isolates to antibodies and CD4-based reagents is independent of coreceptor usage. J Virol 1998; 72:1876-85. [PMID: 9499039 PMCID: PMC109478 DOI: 10.1128/jvi.72.3.1876-1885.1998] [Citation(s) in RCA: 133] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/1997] [Accepted: 12/04/1997] [Indexed: 02/06/2023] Open
Abstract
We have investigated whether the identity of the coreceptor (CCR5, CXCR4, or both) used by primary human immunodeficiency virus type 1 (HIV-1) isolates to enter CD4+ cells influences the sensitivity of these isolates to neutralization by monoclonal antibodies and CD4-based agents. Coreceptor usage was not an important determinant of neutralization titer for primary isolates in peripheral blood mononuclear cells. We also studied whether dualtropic primary isolates (able to use both CCR5 and CXCR4) were differentially sensitive to neutralization by the same antibodies when entering U87MG-CD4 cells stably expressing either CCR5 or CXCR4. Again, we found that the coreceptor used by a virus did not greatly affect its neutralization sensitivity. Similar results were obtained for CCR5- or CXCR4-expressing HOS cell lines engineered to express green fluorescent protein as a reporter of HIV-1 entry. Neutralizing antibodies are therefore unlikely to be the major selection pressure which drives the phenotypic evolution (change in coreceptor usage) of HIV-1 that can occur in vivo. In addition, the increase in neutralization sensitivity found when primary isolates adapt to growth in transformed cell lines in vitro has little to do with alterations in coreceptor usage.
Collapse
Affiliation(s)
- A Trkola
- Aaron Diamond AIDS Research Center, The Rockefeller University, New York, New York 10016, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
46
|
Lee S, Peden K, Dimitrov DS, Broder CC, Manischewitz J, Denisova G, Gershoni JM, Golding H. Enhancement of human immunodeficiency virus type 1 envelope-mediated fusion by a CD4-gp120 complex-specific monoclonal antibody. J Virol 1997; 71:6037-43. [PMID: 9223495 PMCID: PMC191861 DOI: 10.1128/jvi.71.8.6037-6043.1997] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The entry of human immunodeficiency virus type 1 (HIV-1) into cells is initiated by binding of the viral glycoprotein gp120-gp41 to its cellular receptor CD4. The gp120-CD4 complex formed at the cell surface undergoes conformational changes that may allow its association with an additional membrane component(s) and the eventual formation of the fusion complex. These conformational rearrangements are accompanied by immunological changes manifested by altered reactivity with monoclonal antibodies specific for the individual components and presentation of new epitopes unique to the postbinding complex. In order to analyze the structure and function of the gp120-CD4 complex, monoclonal antibodies were generated from splenocytes of BALB/c mice immunized with soluble CD4-gp120 (IIIB) molecules (J. M. Gershoni, G. Denisova, D. Raviv, N. I. Smorodinsky, and D. Buyaner, FASEB J. 7:1185-1187 1993). One of those monoclonal antibodies, CG10, was found to be strictly complex specific. Here we demonstrate that this monoclonal antibody can significantly enhance the fusion of CD4+ cells with effector cells expressing multiple HIV-1 envelopes. Both T-cell-line-tropic and macrophage-tropic envelope-mediated cell fusion were enhanced, albeit at different optimal doses. Furthermore, infection of HeLa CD4+ (MAGI) cells by HIV-1 LAI, ELI1, and ELI2 strains was increased two- to fourfold in the presence of CG10 monoclonal antibodies, suggesting an effect on viral entry. These findings indicate the existence of a novel, conserved CD4-gp120 intermediate structure that plays an important role in HIV-1 cell fusion.
Collapse
Affiliation(s)
- S Lee
- Division of Viral Products, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892, USA
| | | | | | | | | | | | | | | |
Collapse
|
47
|
Liao F, Alkhatib G, Peden KW, Sharma G, Berger EA, Farber JM. STRL33, A novel chemokine receptor-like protein, functions as a fusion cofactor for both macrophage-tropic and T cell line-tropic HIV-1. J Exp Med 1997; 185:2015-23. [PMID: 9166430 PMCID: PMC2196334 DOI: 10.1084/jem.185.11.2015] [Citation(s) in RCA: 286] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The chemokine receptors CXCR4, CCR2B, CCR3, and CCR5 have recently been shown to serve along with CD4 as coreceptors for HIV-1. The tropisms of HIV-1 strains for subgroups of CD4(+) cells can be explained, at least partly, by the selective use of G protein-coupled receptors (GPCRs). We have identified a novel human gene, STRL33, located on chromosome 3 that encodes a GPCR with sequence similarity to chemokine receptors and to chemokine receptor-like orphan receptors. STRL33 is expressed in lymphoid tissues and activated T cells, and is induced in activated peripheral blood lymphocytes. When transfected into nonhuman NIH 3T3 cells expressing human CD4, the STRL33 cDNA rendered these cells competent to fuse with cells expressing HIV-1 envelope glycoproteins (Envs). Of greatest interest, STRL33, in contrast with CXCR4 or CCR5, was able to function as a cofactor for fusion mediated by Envs from both T cell line-tropic and macrophage-tropic HIV-1 strains. STRL33-transfected Jurkat cell lines also supported enhanced productive infection with HIV-1 compared with control Jurkat cells. Despite the sequence similarities between STRL33 and chemokine receptors, STRL33-transfected cell lines did not respond to any in a panel of chemokines. Based on the pattern of tissue expression of the STRL33 mRNA, and given the ability of STRL33 to function with Envs of differing tropisms, STRL33 may play a role in the establishment and/or progression of HIV-1 infection.
Collapse
MESH Headings
- Amino Acid Sequence
- Animals
- CD4 Antigens/physiology
- Cell Fusion
- Cell Line
- Chemokines/metabolism
- Chemokines/pharmacology
- Chromosomes, Human, Pair 3
- Cloning, Molecular
- GTP-Binding Proteins/physiology
- HIV-1/physiology
- Humans
- Macrophages/virology
- Mice
- Molecular Sequence Data
- Polymerase Chain Reaction
- Receptors, CXCR6
- Receptors, Chemokine
- Receptors, Cytokine/chemistry
- Receptors, Cytokine/genetics
- Receptors, Cytokine/physiology
- Receptors, G-Protein-Coupled
- Receptors, HIV/physiology
- Receptors, Virus
- Sequence Alignment
- T-Lymphocytes/virology
- Transfection
- Viral Envelope Proteins/metabolism
Collapse
Affiliation(s)
- F Liao
- Laboratory of Clinical Investigation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA
| | | | | | | | | | | |
Collapse
|
48
|
Fouts TR, Binley JM, Trkola A, Robinson JE, Moore JP. Neutralization of the human immunodeficiency virus type 1 primary isolate JR-FL by human monoclonal antibodies correlates with antibody binding to the oligomeric form of the envelope glycoprotein complex. J Virol 1997; 71:2779-85. [PMID: 9060632 PMCID: PMC191401 DOI: 10.1128/jvi.71.4.2779-2785.1997] [Citation(s) in RCA: 203] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
To test whether antibodies that are neutralizing or nonneutralizing for human immunodeficiency virus type 1 (HIV-1) primary isolates can be distinguished by their affinities for the oligomeric envelope glycoproteins, we selected HIV-1(JR-FL) as a model primary virus and a panel of 13 human monoclonal antibodies (MAbs) and evaluated three parameters: (i) half-maximal binding to recombinant monomeric envelope, gp120(JR-FL); (ii) half-maximal binding to oligomeric envelope of HIV-1(JR-FL) expressed on the surface of transfected 293 cells; and (iii) neutralization of HIV-1(JR-FL) in a peripheral blood mononuclear cell-based neutralization assay. Two conclusions can be drawn from these experiments. First, we confirm that antibody interactions with monomeric gp120 do not predict primary virus neutralization. Second, we show that neutralization correlates qualitatively with the relative affinity of an antibody for the oligomeric envelope glycoproteins, at least for HIV-1(JR-FL).
Collapse
Affiliation(s)
- T R Fouts
- Aaron Diamond AIDS Research Center, The Rockefeller University, New York, New York 10016, USA
| | | | | | | | | |
Collapse
|
49
|
Orlik O, Ban J, Hlavaty J, Altaner C, Kettmann R, Portetelle D, Splitter GA. Polyclonal bovine sera but not virus-neutralizing monoclonal antibodies block bovine leukemia virus (BLV) gp51 binding to recombinant BLV receptor BLVRcp1. J Virol 1997; 71:3263-7. [PMID: 9060692 PMCID: PMC191461 DOI: 10.1128/jvi.71.4.3263-3267.1997] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Bovine leukemia virus (BLV), a transactivating lymphotropic retrovirus, is the etiologic agent of enzootic lymphosarcoma or leukemia in cattle. Sera from BLV-infected animals possess high BLV-neutralizing antibody titres. The availability of the recombinant BLV receptor candidate, BLVRcp1, allowed us to determine a mechanism of virus neutralization by polyclonal sera and monoclonal antibodies (MAbs). Bovine sera from animals naturally infected with BLV blocked gp51 binding to recombinant BLVRcp1. In contrast, virus-neutralizing MAbs specific for gp51 F, G, and H epitopes did not prevent gp51-receptor attachment. Furthermore, gp51 neutralization epitopes F, G, and H were accessible to antibodies following gp51 attachment to BLVRcp1. This finding implies that virus neutralization by MAbs to defined BLV gp51 epitopes can occur subsequent to virus engagement of the receptor while polyclonal sera can specifically block virus attachment to the receptor. In conclusion, these data suggest that cell infection by BLV is a multistep process requiring receptor binding (inhibited by polyclonal sera) followed by a second, postbinding event(s) at the cell membrane (inhibited by anti-gp51 MAbs).
Collapse
Affiliation(s)
- O Orlik
- Department of Animal Health and Biomedical Sciences, University of Wisconsin-Madison, 53706, USA
| | | | | | | | | | | | | |
Collapse
|
50
|
Platt EJ, Madani N, Kozak SL, Kabat D. Infectious properties of human immunodeficiency virus type 1 mutants with distinct affinities for the CD4 receptor. J Virol 1997; 71:883-90. [PMID: 8995604 PMCID: PMC191135 DOI: 10.1128/jvi.71.2.883-890.1997] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Recent evidence suggests that primary patient isolates of T-cell-tropic human immunodeficiency virus type 1 (HIV-1 ) have lower affinities for CD4 than their laboratory-adapted derivatives, that this may partly result from tighter gp120-gp41 bonds that constrain the CD4 binding sites of the primary viruses, and that selection for increased CD4 affinity may be the principal factor in laboratory adaptation of HIV-1 (S. L. Kozak, E. J. Platt, N. Madani, F. E. Ferro, Jr., K. Peden, and D. Kabat, J. Virol. 71:873-882, 1997). These conclusions were based on studies with a panel of HeLa-CD4 cell clones that differ in CD4 levels over a broad range, with laboratory-adapted viruses infecting all clones with equal efficiencies and primary T-cell-tropic viruses infecting the clones in proportion to cellular CD4 levels. Additionally, all of the primary and laboratory-adapted T-cell-tropic viruses efficiently used CXCR-4 (fusin) as a coreceptor. To test these conclusions by an independent approach, we studied mutations in the laboratory-adapted virus LAV/IIIB that alter the CD)4 binding region of gp120 and specifically reduce CD4 affinities of free gp 120 by 85 to 98% (U. Olshevsky et al., J. Virol. 64:5701-5707, 1990). These mutations reduced virus titers to widely varying extents that ranged from severalfold to several orders of magnitude and converted infectivities on the HeLa-CD4 panel from CD4 independency to a high degree of CD4 dependency that resembled the behavior of primary patient viruses. The relative infectivities of the mutants correlated closely with their sensitivities to inactivation by soluble CD4 but did not correlate with the relative CD4 affinities of their free gp120s. Most of the mutations did not substantially alter envelope glycoprotein synthesis, processing, expression on cell surfaces, incorporation into virions, or rates of gp120 shedding from virions. However, one mutation (D457R) caused a decrease in gp160 processing by approximately 80%. The fact that several mutations increased rates of spontaneous viral inactivation (especially D368P) suggests that HIV-1 life spans may be determined by structural stabilities of viral envelope glycoproteins. All of the wild-type and mutant viruses were only slowly and inefficiently adsorbed onto cultured CD4-positive cells at 37 degrees C, and the gradual declines in viral titers in the media were caused almost exclusively by spontaneous inactivation rather than by adsorption. The extreme inefficiency with which infectious HIV-1 is able to infect cultured susceptible CD4-positive cells in standard assay conditions casts doubt on previous inferences that the vast majority of retrovirions produced in cultures are noninfectious. Apparent infectivity of T-cell-tropic HIV-1 in culture is limited by productive associations with CD4 and is influenced in an interdependent manner by CD4 affinities of viral gp120-gp41 complexes and quantities of cell surface CD4.
Collapse
Affiliation(s)
- E J Platt
- Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland 97201-3098, USA
| | | | | | | |
Collapse
|