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Swanstrom AE, Del Prete GQ, Deleage C, Elser SE, Lackner AA, Hoxie JA. The SIV Envelope Glycoprotein, Viral Tropism, and Pathogenesis: Novel Insights from Nonhuman Primate Models of AIDS. Curr HIV Res 2019; 16:29-40. [PMID: 29173176 DOI: 10.2174/1570162x15666171124123116] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Revised: 10/12/2017] [Accepted: 10/13/2017] [Indexed: 12/14/2022]
Abstract
BACKGROUND Cellular tropism of human immunodeficiency virus (HIV-1) is closely linked to interactions between the viral envelope glycoprotein (Env) with CD4 and chemokine receptor family members, CCR5 and CXCR4. This interaction plays a key role in determining anatomic sites that are infected in vivo and the cascade of early and late events that result in chronic immune activation, immunosuppression and ultimately, AIDS. CD4+ T cells are critical to adaptive immune responses, and their early and rapid infection in gut lamina propria and secondary lymphoid tissues in susceptible hosts likely contributes to viral persistence and progression to disease. CD4+ macrophages are also infected, although their role in HIV-1 pathogenesis is more controversial. METHODS Pathogenic infection by simian immunodeficiency viruses (SIV) in Asian macaques as models of HIV-1 infection has enabled the impact of cellular tropism on pathogenesis to be directly probed. This review will highlight examples in which experimental interventions during SIV infection or the introduction of viral mutations have altered cellular tropism and, subsequently, pathogenesis. RESULTS Alterations to the interaction of Env and its cellular receptors has been shown to result in changes to CD4 dependence, coreceptor specificity, and viral tropism for gut CD4+ T cells and macrophages. CONCLUSION Collectively, these findings have yielded novel insights into the critical role of the viral Env and tropism as a driver of pathogenesis and host control and have helped to identify new areas for targeted interventions in therapy and prevention of HIV-1 infection.
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Affiliation(s)
- Adrienne E Swanstrom
- AIDS and Cancer Virus Program, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research Inc., Frederick, MD, United States
| | - Gregory Q Del Prete
- AIDS and Cancer Virus Program, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research Inc., Frederick, MD, United States
| | - Claire Deleage
- AIDS and Cancer Virus Program, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research Inc., Frederick, MD, United States
| | - Samra E Elser
- Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, United States
| | - Andrew A Lackner
- Tulane National Primate Research Center, Covington, LA, United States
| | - James A Hoxie
- Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, United States
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Lineage-Specific Differences between the gp120 Inner Domain Layer 3 of Human Immunodeficiency Virus and That of Simian Immunodeficiency Virus. J Virol 2016; 90:10065-10073. [PMID: 27535053 DOI: 10.1128/jvi.01215-16] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Accepted: 08/11/2016] [Indexed: 01/16/2023] Open
Abstract
Binding of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) gp120 exterior envelope glycoprotein to CD4 triggers conformational changes in gp120 that promote its interaction with one of the chemokine receptors, usually CCR5, ultimately leading to gp41-mediated virus-cell membrane fusion and entry. We previously described that topological layers (layer 1, layer 2, and layer 3) in the gp120 inner domain contribute to gp120-trimer association in the unliganded state but also help secure CD4 binding. Relative to layer 1 of HIV-1 gp120, the SIVmac239 gp120 layer 1 plays a more prominent role in maintaining gp120-trimer association but is minimally involved in promoting CD4 binding, which could be explained by the existence of a well-conserved tryptophan at position 375 (Trp 375) in HIV-2/SIVsmm. In this study, we investigated the role of SIV layer 3 in viral entry, cell-to-cell fusion, and CD4 binding. We observed that a network of interactions involving some residues of the β8-α5 region in SIVmac239 layer 3 may contribute to CD4 binding by helping shape the nearby Phe 43 cavity, which directly contacts CD4. In summary, our results suggest that layer 3 in SIV has a greater impact on CD4 binding than in HIV-1. This work defines lineage-specific differences in layer 3 from HIV-1 and that from SIV. IMPORTANCE CD4-induced conformational changes in the gp120 inner domain involve rearrangements between three topological layers. While the role of layers 1 to 3 for HIV-1 and layers 1 and 2 for SIV on gp120 transition to the CD4-bound conformation has been reported, the role of SIV layer 3 remains unknown. Here we report that SIV layer 3 has a greater impact on CD4 binding than does layer 3 in HIV-1 gp120. This work defines lineage-specific differences in layer 3 from HIV-1 and SIV.
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Swanstrom AE, Haggarty B, Jordan APO, Romano J, Leslie GJ, Aye PP, Marx PA, Lackner AA, Del Prete GQ, Robinson JE, Betts MR, Montefiori DC, LaBranche CC, Hoxie JA. Derivation and Characterization of a CD4-Independent, Non-CD4-Tropic Simian Immunodeficiency Virus. J Virol 2016; 90:4966-4980. [PMID: 26937037 PMCID: PMC4859711 DOI: 10.1128/jvi.02851-15] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2015] [Accepted: 02/24/2016] [Indexed: 12/16/2022] Open
Abstract
UNLABELLED CD4 tropism is conserved among all primate lentiviruses and likely contributes to viral pathogenesis by targeting cells that are critical for adaptive antiviral immune responses. Although CD4-independent variants of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) have been described that can utilize the coreceptor CCR5 or CXCR4 in the absence of CD4, these viruses typically retain their CD4 binding sites and still can interact with CD4. We describe the derivation of a novel CD4-independent variant of pathogenic SIVmac239, termed iMac239, that was used to derive an infectious R5-tropic SIV lacking a CD4 binding site. Of the seven mutations that differentiate iMac239 from wild-type SIVmac239, a single change (D178G) in the V1/V2 region was sufficient to confer CD4 independence in cell-cell fusion assays, although other mutations were required for replication competence. Like other CD4-independent viruses, iMac239 was highly neutralization sensitive, although mutations were identified that could confer CD4-independent infection without increasing its neutralization sensitivity. Strikingly, iMac239 retained the ability to replicate in cell lines and primary cells even when its CD4 binding site had been ablated by deletion of a highly conserved aspartic acid at position 385, which, for HIV-1, plays a critical role in CD4 binding. iMac239, with and without the D385 deletion, exhibited an expanded host range in primary rhesus peripheral blood mononuclear cells that included CCR5(+) CD8(+) T cells. As the first non-CD4-tropic SIV, iMac239-ΔD385 will afford the opportunity to directly assess the in vivo role of CD4 targeting on pathogenesis and host immune responses. IMPORTANCE CD4 tropism is an invariant feature of primate lentiviruses and likely plays a key role in pathogenesis by focusing viral infection onto cells that mediate adaptive immune responses and in protecting virions attached to cells from neutralizing antibodies. Although CD4-independent viruses are well described for HIV and SIV, these viruses characteristically retain their CD4 binding site and can engage CD4 if available. We derived a novel CD4-independent, CCR5-tropic variant of the pathogenic molecular clone SIVmac239, termed iMac239. The genetic determinants of iMac239's CD4 independence provide new insights into mechanisms that underlie this phenotype. This virus remained replication competent even after its CD4 binding site had been ablated by mutagenesis. As the first truly non-CD4-tropic SIV, lacking the capacity to interact with CD4, iMac239 will provide the unique opportunity to evaluate SIV pathogenesis and host immune responses in the absence of the immunomodulatory effects of CD4(+) T cell targeting and infection.
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Affiliation(s)
- Adrienne E Swanstrom
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Beth Haggarty
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Andrea P O Jordan
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Josephine Romano
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - George J Leslie
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Pyone P Aye
- Tulane National Primate Research Center, Covington, and Department of Tropical Medicine, Tulane University, New Orleans, Louisiana, USA
| | - Preston A Marx
- Tulane National Primate Research Center, Covington, and Department of Tropical Medicine, Tulane University, New Orleans, Louisiana, USA
| | - Andrew A Lackner
- Tulane National Primate Research Center, Covington, and Department of Tropical Medicine, Tulane University, New Orleans, Louisiana, USA
| | - Gregory Q Del Prete
- AIDS and Cancer Virus Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, Maryland, USA
| | - James E Robinson
- Department of Pediatrics, Tulane University School of Medicine, New Orleans, Louisiana, USA
| | - Michael R Betts
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - David C Montefiori
- Department of Surgery, Duke University Medical Center, Durham, North Carolina, USA
| | - Celia C LaBranche
- Department of Surgery, Duke University Medical Center, Durham, North Carolina, USA
| | - James A Hoxie
- Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Characterization and Implementation of a Diverse Simian Immunodeficiency Virus SIVsm Envelope Panel in the Assessment of Neutralizing Antibody Breadth Elicited in Rhesus Macaques by Multimodal Vaccines Expressing the SIVmac239 Envelope. J Virol 2015; 89:8130-51. [PMID: 26018167 DOI: 10.1128/jvi.01221-14] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 09/03/2014] [Indexed: 02/02/2023] Open
Abstract
UNLABELLED Antibodies that can neutralize diverse viral strains are likely to be an important component of a protective human immunodeficiency virus type 1 (HIV-1) vaccine. To this end, preclinical simian immunodeficiency virus (SIV)-based nonhuman primate immunization regimens have been designed to evaluate and enhance antibody-mediated protection. However, these trials often rely on a limited selection of SIV strains with extreme neutralization phenotypes to assess vaccine-elicited antibody activity. To mirror the viral panels used to assess HIV-1 antibody breadth, we created and characterized a novel panel of 14 genetically and phenotypically diverse SIVsm envelope (Env) glycoproteins. To assess the utility of this panel, we characterized the neutralizing activity elicited by four SIVmac239 envelope-expressing DNA/modified vaccinia virus Ankara vector- and protein-based vaccination regimens that included the immunomodulatory adjuvants granulocyte-macrophage colony-stimulating factor, Toll-like receptor (TLR) ligands, and CD40 ligand. The SIVsm Env panel exhibited a spectrum of neutralization sensitivity to SIV-infected plasma pools and monoclonal antibodies, allowing categorization into three tiers. Pooled sera from 91 rhesus macaques immunized in the four trials consistently neutralized only the highly sensitive tier 1a SIVsm Envs, regardless of the immunization regimen. The inability of vaccine-mediated antibodies to neutralize the moderately resistant tier 1b and tier 2 SIVsm Envs defined here suggests that those antibodies were directed toward epitopes that are not accessible on most SIVsm Envs. To achieve a broader and more effective neutralization profile in preclinical vaccine studies that is relevant to known features of HIV-1 neutralization, more emphasis should be placed on optimizing the Env immunogen, as the neutralization profile achieved by the addition of adjuvants does not appear to supersede the neutralizing antibody profile determined by the immunogen. IMPORTANCE Many in the HIV/AIDS vaccine field believe that the ability to elicit broadly neutralizing antibodies capable of blocking genetically diverse HIV-1 variants is a critical component of a protective vaccine. Various SIV-based nonhuman primate vaccine studies have investigated ways to improve antibody-mediated protection against a heterologous SIV challenge, including administering adjuvants that might stimulate a greater neutralization breadth. Using a novel SIV neutralization panel and samples from four rhesus macaque vaccine trials designed for cross comparison, we show that different regimens expressing the same SIV envelope immunogen consistently elicit antibodies that neutralize only the very sensitive tier 1a SIV variants. The results argue that the neutralizing antibody profile elicited by a vaccine is primarily determined by the envelope immunogen and is not substantially broadened by including adjuvants, resulting in the conclusion that the envelope immunogen itself should be the primary consideration in efforts to elicit antibodies with greater neutralization breadth.
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Mefford ME, Kunstman K, Wolinsky SM, Gabuzda D. Bioinformatic analysis of neurotropic HIV envelope sequences identifies polymorphisms in the gp120 bridging sheet that increase macrophage-tropism through enhanced interactions with CCR5. Virology 2015; 481:210-22. [PMID: 25797607 DOI: 10.1016/j.virol.2015.01.032] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2013] [Revised: 12/17/2013] [Accepted: 01/28/2015] [Indexed: 10/23/2022]
Abstract
Macrophages express low levels of the CD4 receptor compared to T-cells. Macrophage-tropic HIV strains replicating in brain of untreated patients with HIV-associated dementia (HAD) express Envs that are adapted to overcome this restriction through mechanisms that are poorly understood. Here, bioinformatic analysis of env sequence datasets together with functional studies identified polymorphisms in the β3 strand of the HIV gp120 bridging sheet that increase M-tropism. D197, which results in loss of an N-glycan located near the HIV Env trimer apex, was detected in brain in some HAD patients, while position 200 was estimated to be under positive selection. D197 and T/V200 increased fusion and infection of cells expressing low CD4 by enhancing gp120 binding to CCR5. These results identify polymorphisms in the HIV gp120 bridging sheet that overcome the restriction to macrophage infection imposed by low CD4 through enhanced gp120-CCR5 interactions, thereby promoting infection of brain and other macrophage-rich tissues.
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Affiliation(s)
- Megan E Mefford
- Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Boston, MA, USA.
| | - Kevin Kunstman
- Northwestern University Medical School, Chicago, IL, USA.
| | | | - Dana Gabuzda
- Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Boston, MA, USA; Department of Neurology (Microbiology and Immunobiology), Harvard Medical School, Boston, MA, USA.
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Loss of a conserved N-linked glycosylation site in the simian immunodeficiency virus envelope glycoprotein V2 region enhances macrophage tropism by increasing CD4-independent cell-to-cell transmission. J Virol 2014; 88:5014-28. [PMID: 24554659 DOI: 10.1128/jvi.02785-13] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
UNLABELLED Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) strains differ in their capacity to replicate in macrophages, but mechanisms underlying these differences are not fully understood. Here, we identify a highly conserved N-linked glycosylation site (N173 in SIV, corresponding to N160 in HIV) in the V2 region of the SIV envelope glycoprotein (Env) as a novel determinant of macrophage tropism and characterize mechanisms underlying this phenotype. Loss of the N173 glycosylation site in the non-macrophage-tropic SIVmac239 by introducing an N173Q mutation enhanced viral replication and multinucleated giant cell formation upon infection of rhesus macrophages, while the addition of N173 to SIVmac251 had the opposite effect. The removal of N173 in SIVmac239 enhanced CD4-independent cell-to-cell transmission to CCR5-expressing cells. SIVmac239 with N173Q mediated CD4-independent cell-cell fusion but could not infect CD4-negative cells in single-round infections. Thus, CD4-independent phenotypes were detected only in the context of cell-to-cell contact. Similar results were obtained in SIVmac251 with and without N173. N173 decreased the neutralization sensitivity of SIVmac251 but had no effect on the neutralization sensitivity of SIVmac239. The N173Q mutation had no effect on SIVmac239 binding to CD4 in Biacore assays, coimmunoprecipitation assays, and enzyme-linked immunosorbent assays (ELISAs). These findings suggest that the loss of the N173 N-linked glycosylation site increases SIVmac239 replication in macrophages by enhancing CD4-independent cell-to-cell virus transmission through CCR5-mediated fusion. This mechanism may facilitate the escape of macrophage-tropic viruses from neutralizing antibodies while promoting spreading infection by these viruses in vivo. IMPORTANCE In this study, we identify a genetic determinant in the viral envelope (N173) that increases replication and spreading infection of SIV strains in macrophages by enhancing cell-to-cell virus transmission. This effect is explained by a novel mechanism involving increased cell-to-cell fusion in the absence of CD4, the primary receptor that normally mediates virus entry. The same genetic determinant also affects the sensitivity of these viruses to inhibition by neutralizing antibodies. Most macrophage-tropic HIV/SIV strains are known to be neutralization sensitive. Together, these findings suggest that this efficient mode of virus transmission may facilitate the escape of macrophage-tropic viruses from neutralizing antibodies while promoting spreading infection by these viruses to cells expressing little or no CD4 in vivo.
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Iyengar S, Schwartz DH. Acquisition of CD4-dependence by CD4-independent SIV passaged in human peripheral blood mononuclear cells. Retrovirology 2012; 9:61. [PMID: 22830620 PMCID: PMC3418575 DOI: 10.1186/1742-4690-9-61] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Accepted: 07/25/2012] [Indexed: 11/18/2022] Open
Abstract
Background Chemokine receptors (CKRs), the primordial receptors for primate lentiviruses, are sufficient to mediate virus-cell fusion. Several different fusogenic CKRs and related receptors provide a broad potential host cell range, presumably advantageous for viral spread within a given infected individual, and across species. By contrast, the additional constraint of obligatory CD4 binding, just prior to CKR engagement, radically restricts potential host cells within an individual (or lymph node microenvironment), and might also limit xenotransmission, as CD4 sequences vary among primates. In spite of these potential drawbacks, CD4 dependent entry for SIV and HIV is the rule rather than the exception, and is generally thought to have evolved by selection for 1) stabilization of virus–cell surface interactions, and 2) conformational shielding of readily neutralized CKR binding epitopes. CD4 binding residues of SIV and HIV envelope are recessed, (relatively hidden from immune detection) and may exhibit a strong degree of automimicry, thus benefitting from self tolerance. Documented evolution, within individual macaques, of neutralization-resistant CD4-dependent SIV, derived from CD4-independent inocula, supports these ideas, but does not explain CD4’s exclusive role as the penultimate receptor-even more striking, given the wide diversity of CKRs and other surface molecules that can serve as actual fusion receptors for SIV. We, therefore, explored the additional, non-exclusive, hypothesis that surface CD4 on leukocytes is a marker of a more favorable host cell environment, as compared to CD8, NK, or B cell surface markers. Results We demonstrate progressive in vitro evolution of two SIV strains to CD4-dependence (and CXCR4 tropism) in normal human PBMCs (hPBMCs). The two CD4-independent strains of SIV tested developed nearly complete CD4 dependence over several months of serial passage in hPBMCs, correlating with a limited number of non-synonymous env region mutations, some previously reported to be determinants of CD4-dependency. The initial ability of SIV stocks to grow to significant (albeit, relatively low) levels in CD4(−), CD14(−) cells was also lost with long term passage. Rapid emergence and subsequent prominence of G → A and A → G mutations within env regions associated with CD4 dependence was seen. Conclusions Progressive acquisition of strict CD4 tropism, independent of immunoselection, supports the idea that surface CD4 identifies optimal host cells having intracellular environments most favorable to viral replication. The prominence of mutations involving G to A, or A to G, suggests that APOBEC 3 mediated infidelity may facilitate rapid switching of cell surface receptor usage within SIV swarms encountering fluctuating availability of optimal CD4+CKR+ targets. These observations of non-immune selection are compatible with, and may accelerate, simultaneous selection for previously described CD4-dependent neutralization resistance in vivo.
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Affiliation(s)
- Sujatha Iyengar
- Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, USA
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Lineage-specific differences between human and simian immunodeficiency virus regulation of gp120 trimer association and CD4 binding. J Virol 2012; 86:8974-86. [PMID: 22696649 DOI: 10.1128/jvi.01076-12] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Metastable conformations of the gp120 and gp41 envelope glycoproteins of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) must be maintained in the unliganded state of the envelope glycoprotein trimer. Binding of gp120 to the primary receptor, CD4, triggers the transition to an open conformation of the trimer, promoting interaction with the CCR5 chemokine receptor and ultimately leading to gp41-mediated virus-cell membrane fusion and entry. Topological layers in the gp120 inner domain contribute to gp120-trimer association in the unliganded state and to CD4 binding. Here we describe similarities and differences between HIV-1 and SIVmac gp120. In both viruses, the gp120 N/C termini and the inner domain β-sandwich and layer 2 support the noncovalent association of gp120 with the envelope glycoprotein trimer. Layer 1 of the SIVmac gp120 inner domain contributes more to trimer association than the corresponding region of HIV-1 gp120. On the other hand, layer 1 plays an important role in stabilizing the CD4-bound conformation of HIV-1 but not SIVmac gp120 and thus contributes to HIV-1 binding to CD4. In SIVmac, CD4 binding is instead enhanced by tryptophan 375, which fills the Phe 43 cavity of gp120. Activation of SIVmac by soluble CD4 is dependent on tryptophan 375 and on layer 1 residues that determine a tight association of gp120 with the trimer. Distinct biological requirements for CD4 usage have resulted in lineage-specific differences in the HIV-1 and SIV gp120 structures that modulate trimer association and CD4 binding.
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Phenotypic and immunologic comparison of clade B transmitted/founder and chronic HIV-1 envelope glycoproteins. J Virol 2011; 85:8514-27. [PMID: 21715507 DOI: 10.1128/jvi.00736-11] [Citation(s) in RCA: 108] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Sexual transmission of human immunodeficiency virus type 1 (HIV-1) across mucosal barriers is responsible for the vast majority of new infections. This relatively inefficient process results in the transmission of a single transmitted/founder (T/F) virus, from a diverse viral swarm in the donor, in approximately 80% of cases. Here we compared the biological activities of 24 clade B T/F envelopes (Envs) with those from 17 chronic controls to determine whether the genetic bottleneck that occurs during transmission is linked to a particular Env phenotype. To maximize the likelihood of an intact mucosal barrier in the recipients and to enhance the sensitivity of detecting phenotypic differences, only T/F Envs from individuals infected with a single T/F variant were selected. Using pseudotyping to assess Env function in single-round infectivity assays, we compared coreceptor tropism, CCR5 utilization efficiencies, primary CD4(+) T cell subset tropism, dendritic cell trans-infections, fusion kinetics, and neutralization sensitivities. T/F and chronic Envs were phenotypically equivalent in most assays; however, T/F Envs were modestly more sensitive to CD4 binding site antibodies b12 and VRC01, as well as pooled human HIV Ig. This finding was independently validated with a panel of 14 additional chronic HIV-1 Env controls. Moreover, the enhanced neutralization sensitivity was associated with more efficient binding of b12 and VRC01 to T/F Env trimers. These data suggest that there are subtle but significant structural differences between T/F and chronic clade B Envs that may have implications for HIV-1 transmission and the design of effective vaccines.
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Tagliamonte M, Tornesello ML, Buonaguro FM, Buonaguro L. Conformational HIV-1 envelope on particulate structures: a tool for chemokine coreceptor binding studies. J Transl Med 2011; 9 Suppl 1:S1. [PMID: 21284899 PMCID: PMC3105500 DOI: 10.1186/1479-5876-9-s1-s1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) external envelope glycoprotein gp120 presents conserved binding sites for binding to the primary virus receptor CD4 as well as the major HIV chemokine coreceptors, CCR5 and CXCR4. Concerted efforts are underway to understand the specific interactions between gp120 and coreceptors as well as their contribution to the subsequent membrane fusion process. The present review summarizes the current knowledge on this biological aspect, which represents one of the key and essential points of the HIV-host cell interplay and HIV life cycle. The relevance of conformational HIV-1 Envelope proteins presented on Virus-like Particles for appropriate assessment of this molecular interaction, is also discussed.
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Affiliation(s)
- Maria Tagliamonte
- Lab, of Molecular Biology and Viral Oncogenesis & AIDS Reference Center, Istituto Nazionale Tumori Fond, G, Pascale, Naples, Italy
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White TA, Bartesaghi A, Borgnia MJ, Meyerson JR, de la Cruz MJV, Bess JW, Nandwani R, Hoxie JA, Lifson JD, Milne JLS, Subramaniam S. Molecular architectures of trimeric SIV and HIV-1 envelope glycoproteins on intact viruses: strain-dependent variation in quaternary structure. PLoS Pathog 2010; 6:e1001249. [PMID: 21203482 PMCID: PMC3009598 DOI: 10.1371/journal.ppat.1001249] [Citation(s) in RCA: 152] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Accepted: 12/03/2010] [Indexed: 11/19/2022] Open
Abstract
The initial step in target cell infection by human, and the closely related simian immunodeficiency viruses (HIV and SIV, respectively) occurs with the binding of trimeric envelope glycoproteins (Env), composed of heterodimers of the viral transmembrane glycoprotein (gp41) and surface glycoprotein (gp120) to target T-cells. Knowledge of the molecular structure of trimeric Env on intact viruses is important both for understanding the molecular mechanisms underlying virus-cell interactions and for the design of effective immunogen-based vaccines to combat HIV/AIDS. Previous analyses of intact HIV-1 BaL virions have already resulted in structures of trimeric Env in unliganded and CD4-liganded states at ~20 Å resolution. Here, we show that the molecular architectures of trimeric Env from SIVmneE11S, SIVmac239 and HIV-1 R3A strains are closely comparable to that previously determined for HIV-1 BaL, with the V1 and V2 variable loops located at the apex of the spike, close to the contact zone between virus and cell. The location of the V1/V2 loops in trimeric Env was definitively confirmed by structural analysis of HIV-1 R3A virions engineered to express Env with deletion of these loops. Strikingly, in SIV CP-MAC, a CD4-independent strain, trimeric Env is in a constitutively "open" conformation with gp120 trimers splayed out in a conformation similar to that seen for HIV-1 BaL Env when it is complexed with sCD4 and the CD4i antibody 17b. Our findings suggest a structural explanation for the molecular mechanism of CD4-independent viral entry and further establish that cryo-electron tomography can be used to discover distinct, functionally relevant quaternary structures of Env displayed on intact viruses.
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Affiliation(s)
- Tommi A. White
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America
| | - Alberto Bartesaghi
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America
| | - Mario J. Borgnia
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America
| | - Joel R. Meyerson
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America
| | - M. Jason V. de la Cruz
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America
| | - Julian W. Bess
- AIDS and Cancer Virus Program, SAIC-Frederick, Inc., National Cancer Institute-Frederick, Frederick, Maryland, United States of America
| | - Rachna Nandwani
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America
| | - James A. Hoxie
- Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Jeffrey D. Lifson
- AIDS and Cancer Virus Program, SAIC-Frederick, Inc., National Cancer Institute-Frederick, Frederick, Maryland, United States of America
| | - Jacqueline L. S. Milne
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America
| | - Sriram Subramaniam
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland, United States of America
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Faith SA, Wu Y, Kuhrt D, Steckbeck JD, Craigo JK, Clements JE, Cole KS. Induction of antibody-mediated neutralization in SIVmac239 by a naturally acquired V3 mutation. Virology 2010; 400:86-92. [PMID: 20153009 DOI: 10.1016/j.virol.2010.01.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Revised: 01/04/2010] [Accepted: 01/08/2010] [Indexed: 01/14/2023]
Abstract
Achieving humoral immunity against human immunodeficiency virus (HIV) is a major obstacle in AIDS vaccine development. Despite eliciting robust humoral responses to HIV, exposed hosts rarely produce broadly neutralizing antibodies. The present study utilizes simian immunodeficiency virus (SIV) to identify viral epitopes that conferred antibody neutralization to clone SIV/17E-CL, an in vivo variant derived from neutralization resistant SIVmac239. Neutralization assays using rhesus macaque monoclonal antibodies were performed on viruses engineered to express single or multiple amino acid mutations. Results identified a single amino acid mutation, P334R, in the carboxy-terminal half of the V3 loop as a critical residue that induced neutralization while retaining normal glycoprotein expression on the surface of the virus. Furthermore, the R334 residue yielded neutralization sensitivity by antibodies recognizing diverse conformational and linear epitopes of gp120, suggesting that neutralization phenotype was a consequence of global structural changes of the envelope protein rather than a specific site epitope.
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Affiliation(s)
- Seth A Faith
- University of Pittsburgh Center for Vaccine Research, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
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A quantitative affinity-profiling system that reveals distinct CD4/CCR5 usage patterns among human immunodeficiency virus type 1 and simian immunodeficiency virus strains. J Virol 2009; 83:11016-26. [PMID: 19692480 DOI: 10.1128/jvi.01242-09] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The affinity of human immunodeficiency virus (HIV) envelope for CD4 and CCR5 appears to be associated with aspects of R5 virus (virus using the CCR5 coreceptor) pathogenicity. However, entry efficiency results from complex interactions between the viral envelope glycoprotein and both CD4 and CCR5, which limits attempts to correlate viral pathogenicity with surrogate measures of envelope CD4 and CCR5 affinities. Here, we present a system that provides a quantitative and comprehensive characterization of viral entry efficiency as a direct interdependent function of both CD4 and CCR5 levels. This receptor affinity profiling system also revealed heretofore unappreciated complexities underlying CD4/CCR5 usage. We first developed a dually inducible cell line in which CD4 and CCR5 could be simultaneously and independently regulated within a physiologic range of surface expression. Infection by multiple HIV type 1 (HIV-1) and simian immunodeficiency virus isolates could be examined simultaneously for up to 48 different combinations of CD4/CCR5 expression levels, resulting in a distinct usage pattern for each virus. Thus, each virus generated a unique three-dimensional surface plot in which viral infectivity varied as a function of both CD4 and CCR5 expression. From this functional form, we obtained a sensitivity vector along with corresponding metrics that quantified an isolate's overall efficiency of CD4/CCR5 usage. When applied to viral isolates with well-characterized sensitivities to entry/fusion inhibitors, the vector metrics were able to encapsulate their known biological phenotypes. The application of the vector metrics also indicated that envelopes derived from elite suppressors had overall-reduced entry efficiencies compared to those of envelopes derived from chronically infected viremic progressors. Our affinity-profiling system may help to refine studies of R5 virus tropism and pathogenesis.
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Crooks ET, Jiang P, Franti M, Wong S, Zwick MB, Hoxie JA, Robinson JE, Moore PL, Binley JM. Relationship of HIV-1 and SIV envelope glycoprotein trimer occupation and neutralization. Virology 2008; 377:364-78. [PMID: 18539308 DOI: 10.1016/j.virol.2008.04.045] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Revised: 03/21/2008] [Accepted: 04/24/2008] [Indexed: 11/26/2022]
Abstract
Insights into the process of HIV-1 neutralization may assist rational vaccine design. Here, we compared antibody neutralization against the JR-FL primary isolate and trimer binding affinities judged by native PAGE. Monovalent Fab-trimer binding and neutralization showed a direct quantitative relationship, implying that neutralization begins as each trimer is occupied by one antibody. At saturation, three Fab or soluble CD4 molecules engaged each trimer. In contrast, a maximum of one soluble CD4 molecule bound to functional SIV trimers with a truncated a gp41 tail. Remarkably, soluble CD4 was found to trigger dramatic enhancement of this virus. Unlike Fabs, a quantitative correlation between JR-FL trimer binding and neutralization was unclear for some, but not all IgGs, as neutralization was markedly increased, but trimer affinity was largely unchanged. In addition, only one molecule of certain gp41-specific IgGs appeared to be able to bind each trimer. We discuss the implications of these findings in weighing the relative contributions of size, multivalent binding and other possible effects of IgGs to explain their increased potency.
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Affiliation(s)
- Emma T Crooks
- Torrey Pines Institute for Molecular Studies, 3550 General Atomics Court, San Diego, CA 92121, USA
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Lin G, Bertolotti-Ciarlet A, Haggarty B, Romano J, Nolan KM, Leslie GJ, Jordan APO, Huang CC, Kwong PD, Doms RW, Hoxie JA. Replication-competent variants of human immunodeficiency virus type 2 lacking the V3 loop exhibit resistance to chemokine receptor antagonists. J Virol 2007; 81:9956-66. [PMID: 17609282 PMCID: PMC2045409 DOI: 10.1128/jvi.00385-07] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Entry of human immunodeficiency virus type 1 (HIV-1) and HIV-2 requires interactions between the envelope glycoprotein (Env) on the virus and CD4 and a chemokine receptor, either CCR5 or CXCR4, on the cell surface. The V3 loop of the HIV gp120 glycoprotein plays a critical role in this process, determining tropism for CCR5- or CXCR4-expressing cells, but details of how V3 interacts with these receptors have not been defined. Using an iterative process of deletion mutagenesis and in vitro adaptation of infectious viruses, variants of HIV-2 were derived that could replicate without V3, either with or without a deletion of the V1/V2 variable loops. The generation of these functional but markedly minimized Envs required adaptive changes on the gp120 core and gp41 transmembrane glycoprotein. V3-deleted Envs exhibited tropism for both CCR5- and CXCR4-expressing cells, suggesting that domains on the gp120 core were mediating interactions with determinants shared by both coreceptors. Remarkably, HIV-2 Envs with V3 deletions became resistant to small-molecule inhibitors of CCR5 and CXCR4, suggesting that these drugs inhibit wild-type viruses by disrupting a specific V3 interaction with the coreceptor. This study represents a proof of concept that HIV Envs lacking V3 alone or in combination with V1/V2 that retain functional domains required for viral entry can be derived. Such minimized Envs may be useful in understanding Env function, screening for new inhibitors of gp120 core interactions with chemokine receptors, and designing novel immunogens for vaccines.
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Affiliation(s)
- George Lin
- Department of Medicine, University of Pennsylvania, 421 Curie Blvd., Philadelphia, PA 19104, USA
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Chen MF, Westmoreland S, Ryzhova EV, Martín-García J, Soldan SS, Lackner A, González-Scarano F. Simian immunodeficiency virus envelope compartmentalizes in brain regions independent of neuropathology. J Neurovirol 2006; 12:73-89. [PMID: 16798669 DOI: 10.1080/13550280600654565] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Simian immunodeficiency virus (SIV) and human immunodeficiency virus (HIV) gp160s obtained from the brain are often genetically distinct from those isolated from other organs, suggesting the presence of brain-specific selective pressures or founder effects that result in the compartmentalization of viral quasi-species. Whereas HIV has also been found to compartmentalize within different regions of the brain, the extent of brain-regional compartmentalization of SIV in rhesus macaques has not been characterized. Furthermore, much is still unknown about whether phenotypic differences exist in envelopes from different brain regions. To address these questions, env DNA sequences were amplified from four SIVmac239-infected macaques and subjected to phylogenetic and phenetic analysis. The authors demonstrated that sequences from different areas of the brain form distinct clades, and that the long-term progressing macaques demonstrated a greater degree of regional compartmentalization compared to the rapidly progressing macaques. In addition, regional compartmentalization occurred regardless of the presence of giant-cell encephalitis. Nucleotide substitution rates at synonymous and nonsynonymous sites (ds:dn rates) indicated that positive selection varied among envelopes from different brain regions. In one macaque, envelopes from some but not all brain regions acquired changes in a conserved CD4-binding motif GGGDPE at amino acids 382 to 387. Furthermore, gp160s with the mutation G383E were able to mediate cell-to-cell fusion in a CD4-independent manner and were more susceptible to fusion inhibition by pooled plasma from infected macaques. Reversion of this mutation by site-directed mutagenesis resulted in reduction of CD4-independence and resistance to fusion inhibition in cell fusion assays. These studies demonstrate that SIV evolution within the brain results in a heterogeneous viral population with different phenotypes among different regions.
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Affiliation(s)
- Maria F Chen
- Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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Rychert J, Lacour N, Amedee AM. Genetic analysis of simian immunodeficiency virus expressed in milk and selectively transmitted through breastfeeding. J Virol 2006; 80:3721-31. [PMID: 16571789 PMCID: PMC1440429 DOI: 10.1128/jvi.80.8.3721-3731.2006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To develop effective intervention strategies that prevent breast milk transmission of human immunodeficiency virus (HIV), we must understand the specific viral properties and mechanisms responsible for infant infection. We have used lactating rhesus macaques infected with a pathogenic simian immunodeficiency virus (SIV) stock to analyze the viral genotypes expressed in plasma and milk throughout the disease course and to identify those variants ultimately transmitted to infants through breastfeeding. In these studies we observed mother-to-infant transmission of SIV/Delta(B670) by eight females during the chronic phase of disease, and we analyzed by heteroduplex tracking assays and sequence analysis the distribution and fluctuations in viral genotypes expressed. Each female expressed multiple V1 envelope genotypes in milk near the time of transmission, while a single genotype was found in each of the infants. Variants transmitted to infants were not expressed throughout the maternal disease course but were only detected near the time of transmission. The emergence of the transmitted genotype in the dam typically occurred in plasma before milk and was coincident with increased milk viral loads. Transmitted genotypes tended to be longer and more glycosylated and had a less negative charge over the V1 region compared to viral genotypes expressed in milk but not transmitted. These observations demonstrate that specific viral genotypes are selectively transmitted to infants through breastfeeding and support the hypothesis that transmission occurs as genotypes adapt for efficient expression in milk.
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Affiliation(s)
- Jenna Rychert
- Department of Microbiology, Immunology, Parasitology, Louisiana State University Health Sciences Center, 1901 Perdido St., New Orleans, Louisiana 70112, USA
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Demma LJ, Vanderford TH, Logsdon JM, Feinberg MB, Staprans SI. Evolution of the uniquely adaptable lentiviral envelope in a natural reservoir host. Retrovirology 2006; 3:19. [PMID: 16549011 PMCID: PMC1431560 DOI: 10.1186/1742-4690-3-19] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2006] [Accepted: 03/20/2006] [Indexed: 12/02/2022] Open
Abstract
Background The ability of emerging pathogens to infect new species is likely related to the diversity of pathogen variants present in existing reservoirs and their degree of genomic plasticity, which determines their ability to adapt to new environments. Certain simian immunodeficiency viruses (SIVcpz, SIVsm) have demonstrated tremendous success in infecting new species, including humans, resulting in the HIV-1 and HIV-2 epidemics. Although SIV diversification has been studied on a population level, the essential substrates for cross-species transmission, namely SIV sequence diversity and the types and extent of viral diversification present in individual reservoir animals have not been elucidated. To characterize this intra-host SIV diversity, we performed sequence analyses of clonal viral envelope (env) V1V2 and gag p27 variants present in individual SIVsm-infected sooty mangabeys over time. Results SIVsm demonstrated extensive intra-animal V1V2 length variation and amino acid diversity (le38%), and continual variation in V1V2 N-linked glycosylation consensus sequence frequency and location. Positive selection was the predominant evolutionary force. Temporal sequence shifts suggested continual selection, likely due to evolving antibody responses. In contrast, gag p27 was predominantly under purifying selection. SIVsm V1V2 sequence diversification is at least as great as that in HIV-1 infected humans, indicating that extensive viral diversification in and of itself does not inevitably lead to AIDS. Conclusion Positive diversifying selection in this natural reservoir host is the engine that has driven the evolution of the uniquely adaptable SIV/HIV envelope protein. These studies emphasize the importance of retroviral diversification within individual host reservoir animals as a critical substrate in facilitating cross-species transmission.
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Affiliation(s)
- LJ Demma
- Program in Population Biology, Evolution and Ecology, and Emory Vaccine Center, Emory University, Atlanta, GA, USA
- Centers for Disease Control and Prevention, Division of Bacterial and Mycotic Diseases, 1600 Clifton Road, Mailstop D-63, Atlanta, GA 30333, USA
| | - TH Vanderford
- Program in Population Biology, Evolution and Ecology, and Emory Vaccine Center, Emory University, Atlanta, GA, USA
| | - JM Logsdon
- Department of Biology, Emory University, Atlanta, GA. Current address: University of Iowa, Department of Biological Sciences, Roy J. Carver Center for Comparative Genomics, 301 Biology Building, Iowa City, IA 52242, USA
| | - MB Feinberg
- Departments of Medicine and Microbiology and Immunology, and Emory Vaccine Center, Emory University School of Medicine, Atlanta, GA, USA
- Merck Vaccine Division, Merck and Company, Inc., 770 Sumneytown Pike, West Point, PA 19486, USA
| | - SI Staprans
- Departments of Medicine and Microbiology and Immunology, and Emory Vaccine Center, Emory University School of Medicine, Atlanta, GA, USA
- Emory Vaccine Center, 954 Gatewood Rd., Atlanta, GA, 30329, USA
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Bonavia A, Bullock B, Gisselman K, Margulies B, Clements J. A single amino acid change and truncated TM are sufficient for simian immunodeficiency virus to enter cells using CCR5 in a CD4-independent pathway. Virology 2005; 341:12-23. [PMID: 16061266 PMCID: PMC2676328 DOI: 10.1016/j.virol.2005.07.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2005] [Revised: 06/01/2005] [Accepted: 07/01/2005] [Indexed: 10/25/2022]
Abstract
Entry of HIV and SIV into susceptible cells is mediated by CD4 and chemokine receptors, which act as coreceptors. To study cell entry of SIV, we constructed a cell line, xKLuSIV, derived from non-susceptible human K562 cells, that express the firefly luciferase reporter gene under control of a minimal SIV long terminal repeat (LTR). Using these susceptible cells, we studied the entry of a well-characterized molecularly cloned macrophage-tropic SIV. xKLuSIV cells that express rhesus macaque CD4 and/or the rhesus chemokine receptor CCR5 are susceptible to infection with the macrophage-tropic, neurovirulent strain SIV/17E-Fr, but only xKLuSIV cells expressing both CCR5 and CD4 were susceptible to infection by the macrophage-tropic, non-neurovirulent strain SIV/17E-Cl. CCR5-dependent, CD4-independent infection by SIV/17E-Fr was abrogated by pre-incubation of the cells with AOP-RANTES, a ligand for CCR5. In addition to viral entry occurring by a CD4-independent mechanism, neutralization of SIV/17E-Fr with rhesus mAbs from 3 different neutralization groups blocked entry into x KLuSIV cells by both CD4-dependent and -independent mechanisms. Triggering the env glycoprotein of SIV-17 EFr with soluble CD4 had no significant effect in infectivity, but triggering of the same glycoprotein of SIV/17E-Cl allowed it to enter cells in a CD4-independent fashion. Using mutant molecular clones, we studied the determinants for CD4 independence, all of which are confined to the env gene. We report here that truncation of the TM at amino acid 764 and changing a single amino acid (R751G) in the SIV envelope transmembrane protein (TM) conferred the observed CD4-independent phenotype. Our data suggest that the envelope from the neurovirulent SIV/17E-Fr interacts with CCR5 in a CD4-independent manner, and changes in the TM protein of this virus are important components that contribute to neurovirulence in SIV.
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Affiliation(s)
| | | | | | | | - J.E. Clements
- Corresponding author. Fax: +1 410 955 9823., E-mail address: (J.E. Clements)
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Demma LJ, Logsdon JM, Vanderford TH, Feinberg MB, Staprans SI. SIVsm quasispecies adaptation to a new simian host. PLoS Pathog 2005; 1:e3. [PMID: 16201015 PMCID: PMC1238738 DOI: 10.1371/journal.ppat.0010003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2005] [Accepted: 06/20/2005] [Indexed: 11/19/2022] Open
Abstract
Despite the potential for infectious agents harbored by other species to become emerging human pathogens, little is known about why some agents establish successful cross-species transmission, while others do not. The simian immunodeficiency viruses (SIVs), certain variants of which gave rise to the human HIV-1 and HIV-2 epidemics, have demonstrated tremendous success in infecting new host species, both simian and human. SIVsm from sooty mangabeys appears to have infected humans on several occasions, and was readily transmitted to nonnatural Asian macaque species, providing animal models of AIDS. Here we describe the first in-depth analysis of the tremendous SIVsm quasispecies sequence variation harbored by individual sooty mangabeys, and how this diverse quasispecies adapts to two different host species—new nonnatural rhesus macaque hosts and natural sooty mangabey hosts. Viral adaptation to rhesus macaques was associated with the immediate amplification of a phylogenetically related subset of envelope (env) variants. These variants contained a shorter variable region 1 loop and lacked two specific glycosylation sites, which may be selected for during acute infection. In contrast, transfer of SIVsm to its natural host did not subject the quasispecies to any significant selective pressures or bottleneck. After 100 d postinfection, variants more closely representative of the source inoculum reemerged in the macaques. This study describes an approach for elucidating how pathogens adapt to new host species, and highlights the particular importance of SIVsm env diversity in enabling cross-species transmission. The replicative advantage of a subset of SIVsm variants in macaques may be related to features of target cells or receptors that are specific to the new host environment, and may involve CD4-independent engagement of a viral coreceptor conserved among primates. Why do some infectious agents establish successful cross-species transmission while others do not? Despite the clear potential for diseases harbored by animals to become emerging human pathogens, this question remains unanswered. Certain simian immunodeficiency viruses (SIVs) responsible for the human HIV-1 and HIV-2 epidemics have succeeded in infecting new host species, including humans. This study provides clues to how an SIV adapts to a new host in an experimental cross-species transmission. Indeed, many emerging diseases are caused by highly mutation-prone RNA viruses like SIV, which exist not as a single species, but rather as a population of genetic variants within a single infection. The presence of numerous viral variants in an infected animal increases the chance that variants with the ability to enter into or multiply in a new host species are present. This study describes how an SIV population from a natural reservoir host, the sooty mangabey, adapts to a new monkey species, the rhesus macaque. A limited subset of SIV variants containing unique viral surface proteins appears well suited to multiply in the new host. This study documents how viral variation facilitates cross-species transmission, and highlights the particular importance of immunodeficiency virus envelope variants in infecting new hosts.
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Affiliation(s)
- Linda J Demma
- Department of Biology, Emory University, Atlanta, Georgia, United States of America
| | - John M Logsdon
- Department of Biology, Emory University, Atlanta, Georgia, United States of America
| | - Thomas H Vanderford
- Department of Biology, Emory University, Atlanta, Georgia, United States of America
| | - Mark B Feinberg
- Departments of Medicine and Microbiology and Immunology, and Emory Vaccine Center, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Silvija I Staprans
- Departments of Medicine and Microbiology and Immunology, and Emory Vaccine Center, Emory University School of Medicine, Atlanta, Georgia, United States of America
- *To whom correspondence should be addressed. E-mail:
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Chen B, Vogan EM, Gong H, Skehel JJ, Wiley DC, Harrison SC. Structure of an unliganded simian immunodeficiency virus gp120 core. Nature 2005; 433:834-41. [PMID: 15729334 DOI: 10.1038/nature03327] [Citation(s) in RCA: 443] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2004] [Accepted: 12/22/2004] [Indexed: 01/18/2023]
Abstract
Envelope glycoproteins of human and simian immunodeficiency virus (HIV and SIV) undergo a series of conformational changes when they interact with receptor (CD4) and co-receptor on the surface of a potential host cell, leading ultimately to fusion of viral and cellular membranes. Structures of fragments of gp120 and gp41 from the envelope protein are known, in conformations corresponding to their post-attachment and postfusion states, respectively. We report the crystal structure, at 4 A resolution, of a fully glycosylated SIV gp120 core, in a conformation representing its prefusion state, before interaction with CD4. Parts of the protein have a markedly different organization than they do in the CD4-bound state. Comparison of the unliganded and CD4-bound structures leads to a model for events that accompany receptor engagement of an envelope glycoprotein trimer. The two conformations of gp120 also present distinct antigenic surfaces. We identify the binding site for a compound that inhibits viral entry.
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Affiliation(s)
- Bing Chen
- Children's Hospital Laboratory of Molecular Medicine, Harvard Medical School, Boston, Massachusetts 02115, USA
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