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Klaus Strebel - One of the best experts on this subject based on the ideXlab platform.
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Some Human Immunodeficiency Virus Type 1 Vpu Proteins Are Able To Antagonize Macaque BST-2 In Vitro and In Vivo: Vpu-Negative Simian-Human Immunodeficiency Viruses Are Attenuated In Vivo
Journal of virology, 2011Co-Authors: Masashi Shingai, Takeshi Yoshida, Malcolm A. Martin, Klaus StrebelAbstract:Human immunodeficiency virus type 1 (HIV-1) Vpu enhances the release of viral particles from infected cells by targeting BST-2/tetherin, a cellular Protein inhibiting virus release. The widely used HIV-1NL4-3 Vpu functionally inactivates human BST-2 but not murine or monkey BST-2, leading to the notion that Vpu antagonism is species specific. Here we investigated the properties of the CXCR4-tropic simian-human immunodeficiency virus DH12 (SHIVDH12) and the CCR5-tropic SHIVAD8, each of which carries Vpu genes derived from different primary HIV-1 isolates. We found that virion release from infected rhesus peripheral blood mononuclear cells was enhanced to various degrees by the Vpu present in both SHIVs. Transfer of the SHIVDH12 Vpu transmembrane domain to the HIV-1NL4-3 Vpu conferred antagonizing activity against macaque BST-2. Inactivation of the SHIVDH12 and SHIVAD8 Vpu genes impaired virus replication in 6 of 8 inoculated rhesus macaques, resulting in lower plasma viral RNA loads, slower losses of CD4+ T cells, and delayed disease progression. The expanded host range of the SHIVDH12 Vpu was not due to adaptation during passage in macaques but was an intrinsic property of the parental HIV-1DH12 Vpu Protein. These results demonstrate that the species-specific inhibition of BST-2 by HIV-1NL4-3 Vpu is not characteristic of all HIV-1 Vpu Proteins; some HIV-1 isolates encode a Vpu with a broader host range.
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differential effects of human immunodeficiency virus type 1 Vpu on the stability of bst 2 tetherin
Journal of Virology, 2011Co-Authors: Amy J Andrew, Eri Miyagi, Klaus StrebelAbstract:BST-2/CD317/tetherin is a host factor that inhibits the release of HIV-1 and other unrelated viruses. A current model proposes that BST-2 physically tethers virions to the surface of virus-producing cells. The HIV-1-encoded Vpu Protein effectively antagonizes the activity of BST-2. How Vpu accomplishes this task remains unclear; however, it is known that Vpu has the ability to down-modulate BST-2 from the cell surface. Here we analyzed the effects of Vpu on BST-2 by performing a series of kinetic studies with HeLa, 293T, and CEMx174 cells. Our results indicate that the surface downregulation of BST-2 is not due to an accelerated internalization or reduced recycling of internalized BST-2 but instead is caused by interference with the resupply of newly synthesized BST-2 from within the cell. While our data confirm previous reports that the high-level expression of Vpu can cause the endoplasmic reticulum (ER)-associated degradation of BST-2, we found no evidence that Vpu targets endogenous BST-2 in the ER in the course of a viral infection. Instead, we found that Vpu acts in a post-ER compartment and increases the turnover of newly synthesized mature BST-2. Our observation that Vpu does not affect the recycling of BST-2 suggests that Vpu does not act directly at the cell surface but may interfere with the trafficking of newly synthesized BST-2 to the cell surface, resulting in the accelerated targeting of BST-2 to the lysosomal compartment for degradation.
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multilayered mechanism of cd4 downregulation by hiv 1 Vpu involving distinct er retention and erad targeting steps
PLOS Pathogens, 2010Co-Authors: Javier G Magadan, Javier F Perezvictoria, Rachid Sougrat, Klaus Strebel, Yihong Ye, Juan S BonifacinoAbstract:A key function of the Vpu Protein of HIV-1 is the targeting of newly-synthesized CD4 for proteasomal degradation. This function has been proposed to occur by a mechanism that is fundamentally distinct from the cellular ER-associated degradation (ERAD) pathway. However, using a combination of genetic, biochemical and morphological methodologies, we find that CD4 degradation induced by Vpu is dependent on a key component of the ERAD machinery, the VCP-UFD1L-NPL4 complex, as well as on SCFβ-TrCP-dependent ubiquitination of the CD4 cytosolic tail on lysine and serine/threonine residues. When degradation of CD4 is blocked by either inactivation of the VCP-UFD1L-NPL4 complex or prevention of CD4 ubiquitination, Vpu still retains the bulk of CD4 in the ER mainly through transmembrane domain interactions. Addition of a strong ER export signal from the VSV-G Protein overrides this retention. Thus, Vpu exerts two distinct activities in the process of downregulating CD4: ER retention followed by targeting to late stages of ERAD. The multiple levels at which Vpu engages these cellular quality control mechanisms underscore the importance of ensuring profound suppression of CD4 to the life cycle of HIV-1.
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The HIV-1 Vpu Protein: a multifunctional enhancer of viral particle release.
Microbes and infection, 2003Co-Authors: Stephan Bour, Klaus StrebelAbstract:HIV accessory genes are expressed throughout the viral life cycle and regulate wide-ranging aspects of virus replication including viral infectivity (Vif and Nef), viral gene expression (Vpr) and progeny virion production (Vpu). While in many cases the molecular basis of accessory Protein function is not fully understood, a consensus is emerging that these viral products are generally devoid of enzymatic activity and instead act as multifunctional adapters, subverting normal cellular processes to serve the needs of the virus. This review focuses on presenting our current knowledge of the HIV-1-specific Vpu Protein and its essential role in regulating viral particle release, viral load and expression of the CD4 receptor.
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the human immunodeficiency virus type 1 Vpu Protein inhibits nf κb activation by interfering with βtrcp mediated degradation of iκb
Journal of Biological Chemistry, 2001Co-Authors: Stephan Bour, Christele Perrin, Hirofumi Akari, Klaus StrebelAbstract:The human immunodeficiency virus type 1 (HIV-1) Vpu Protein binds to the CD4 receptor and induces its degradation by cytosolic proteasomes. This process involves the recruitment of human betaTrCP (TrCP), a key member of the SkpI-Cdc53-F-box E3 ubiquitin ligase complex that specifically interacts with phosphorylated Vpu molecules. Interestingly, Vpu itself, unlike other TrCP-interacting Proteins, is not targeted for degradation by proteasomes. We now report that, by virtue of its affinity for TrCP and resistance to degradation, Vpu, but not a phosphorylation mutant unable to interact with TrCP, has a dominant negative effect on TrCP function. As a consequence, expression of Vpu in HIV-infected T cells or in HeLa cells inhibited TNF-alpha-induced degradation of IkappaB-alpha. Vpu did not inhibit TNF-alpha-mediated activation of the IkappaB kinase but instead interfered with the subsequent TrCP-dependent degradation of phosphorylated IkappaB-alpha. This resulted in a pronounced reduction of NF-kappaB activity. We also observed that in cells producing Vpu-defective virus, NF-kappaB activity was significantly increased even in the absence of cytokine stimulation. However, in the presence of Vpu, this HIV-mediated NF-kappaB activation was markedly reduced. These results suggest that Vpu modulates both virus- and cytokine-induced activation of NF-kappaB in HIV-1-infected cells.
John C Guatelli - One of the best experts on this subject based on the ideXlab platform.
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upregulation of bst 2 tetherin by hiv infection in vivo
Journal of Virology, 2011Co-Authors: Stefanie Homann, Davey M Smith, Susan J Little, Douglas D Richman, John C GuatelliAbstract:The interferon-inducible antiviral factor BST-2 prevents several enveloped viruses, including HIV, from escaping infected cells. The HIV Protein Vpu antagonizes this host defense. Little is known about the expression of BST-2 during HIV infection in vivo and whether it can be modulated to the host's advantage. We studied the expression of BST-2 on blood cells from HIV-infected patients during the acute and chronic phases of disease as well as after antiretroviral treatment (ART). The expression of BST-2 was increased on mononuclear leukocytes, including CD4-positive T lymphocytes from HIV-positive patients, compared to that on cells of uninfected controls. The expression of BST-2 was highest during acute infection and decreased to levels similar to those of uninfected individuals after ART. Treatment of primary blood mononuclear cells in vitro with alpha interferon or with Toll-like receptor (TLR) agonists increased the expression of BST-2 to levels similar to those found during infection in vivo. The interferon-induced levels were sufficient to overcome the Vpu Protein in vitro, reducing the release of wild-type HIV. These data show that BST-2 is upregulated during HIV infection, consistent with its role as an interferon-stimulated gene. The data further suggest that this upregulation is sufficient to saturate the activity of Vpu and inhibit wild-type HIV.
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hiv 1 Vpu and hiv 2 env counteract bst 2 tetherin by sequestration in a perinuclear compartment
Retrovirology, 2010Co-Authors: Heiko Hauser, John C Guatelli, Su Jung Yang, Lisa A Lopez, Colin M Exline, Jill Oldenburg, Paula M CannonAbstract:In the absence of the Vpu Protein, newly formed HIV-1 particles can remain attached to the surface of human cells due to the action of an interferon-inducible cellular restriction factor, BST-2/tetherin. Tetherin also restricts the release of other enveloped viral particles and is counteracted by a several viral anti-tetherin factors including the HIV-2 Env, SIV Nef and KSHV K5 Proteins. We observed that a fraction of tetherin is located at the surface of restricting cells, and that co-expression of both HIV-1 Vpu and HIV-2 Env reduced this population. In addition, Vpu, but not the HIV-2 Env, reduced total cellular levels of tetherin. An additional effect observed for both Vpu and the HIV-2 Env was to redirect tetherin to an intracellular perinuclear compartment that overlapped with markers for the TGN (trans-Golgi network). Sequestration of tetherin in this compartment was independent of tetherin's normal endocytosis trafficking pathway. Both HIV-1 Vpu and HIV-2 Env redirect tetherin away from the cell surface and sequester the Protein in a perinuclear compartment, which likely blocks the action of this cellular restriction factor. Vpu also promotes the degradation of tetherin, suggesting that it uses more than one mechanism to counteract tetherin restriction.
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direct restriction of virus release and incorporation of the interferon induced Protein bst 2 into hiv 1 particles
PLOS Pathogens, 2010Co-Authors: Kathleen Fitzpatrick, Mark Skasko, Thomas J Deerinck, John Crum, Mark H Ellisman, John C GuatelliAbstract:Investigation of the Vpu Protein of HIV-1 recently uncovered a novel aspect of the mammalian innate response to enveloped viruses: retention of progeny virions on the surface of infected cells by the interferon-induced, transmembrane and GPI-anchored Protein BST-2 (CD317; tetherin). BST-2 inhibits diverse families of enveloped viruses, but how it restricts viral release is unclear. Here, immuno-electron microscopic data indicate that BST-2 is positioned to directly retain nascent HIV virions on the plasma membrane of infected cells and is incorporated into virions. Virion-incorporation was confirmed by capture of infectivity using antibody to the ectodomain of BST-2. Consistent with a direct tethering mechanism, we confirmed that proteolysis releases restricted virions and further show that this removed the ectodomain of BST-2 from the cell surface. Unexpectedly, enzymatic cleavage of GPI anchors did not release restricted virions, weighing against models in which individual BST-2 molecules span the virion and host cell membranes. Although the exact molecular topology of restriction remains unsolved, we suggest that the incorporation of BST-2 into viral envelopes underlies its broad restrictive activity, whereas its relative exclusion from virions and sites of viral assembly by Proteins such as HIV-1 Vpu may provide viral antagonism of restriction.
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the interferon induced Protein bst 2 restricts hiv 1 release and is downregulated from the cell surface by the viral Vpu Protein
Cell Host & Microbe, 2008Co-Authors: Nanette Van Damme, Chris Katsura, Rebecca L Jorgenson, Richard S Mitchell, Edward B Stephens, Marc C. Johnson, Daniel Goff, John C GuatelliAbstract:Summary The HIV-1 accessory Protein Vpu counteracts a host factor that restricts virion release from infected cells. Here we show that the interferon-induced cellular Protein BST-2/HM1.24/CD317 is such a factor. BST-2 is downregulated from the cell surface by Vpu, and BST-2 is specifically expressed in cells that support the Vpu phenotype. Exogenous expression of BST-2 inhibits HIV-1 virion release, while suppression of BST-2 relieves the requirement for Vpu. Downregulation of BST-2 requires both the transmembrane/ion channel domain and conserved serines in the cytoplasmic domain of Vpu. Endogenous BST-2 colocalizes with the HIV-1 structural Protein Gag in endosomes and at the plasma membrane, suggesting that BST-2 traps virions within and on infected cells. The unusual structure of BST-2, which includes a transmembrane domain and a lumenal GPI anchor, may allow it to retain nascent enveloped virions on cellular membranes, providing a mechanism of viral restriction counteracted by a specific viral accessory Protein.
Edward B Stephens - One of the best experts on this subject based on the ideXlab platform.
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hiv 1 Vpu Protein antagonizes innate restriction factor bst 2 via lipid embedded helix helix interactions
Journal of Biological Chemistry, 2012Co-Authors: Mark Skasko, Edward B Stephens, Autumn Ruiz, Yan Wang, Ye Tian, Andrey Tokarev, Jason Munguia, Stanley J OpellaAbstract:Abstract The Vpu Protein of HIV-1 antagonizes BST-2 (tetherin), a broad spectrum effector of the innate immune response to viral infection, by an intermolecular interaction that maps genetically to the α-helical transmembrane domains (TMDs) of each Protein. Here we utilize NMR spectroscopy to describe key features of the helix-helix pairing that underlies this interaction. The antagonism of BST-2 involves a sequence of three alanines and a tryptophan spaced at four residue intervals within the Vpu TMD helix. Responsiveness to Vpu involves bulky hydrophobic residues in the C-terminal region of the BST-2 TMD helix that likely fit between the alanines on the interactive face of Vpu. These aspects of Vpu and BST-2 form an anti-parallel, lipid-embedded helix-helix interface. Changes in human BST-2 that mimic sequences found in nonhuman primate orthologs unresponsive to Vpu change the tilt angle of the TMD in the lipid bilayer without abrogating its intrinsic ability to interact with Vpu. These data explain the mechanism by which HIV-1 evades a key aspect of innate immunity and the species specificity of Vpu using an anti-parallel helix-helix packing model.
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Membrane raft association of the Vpu Protein of human immunodeficiency virus type 1 correlates with enhanced virus release
Virology, 2010Co-Authors: Autumn Ruiz, M. Sarah Hill, Kimberly Schmitt, Edward B StephensAbstract:Abstract The Vpu Protein of human immunodeficiency virus type 1 (HIV-1) is known to enhance virion release from certain cell types. To accomplish this function, Vpu interacts with the restriction factor known as bone marrow stromal cell antigen 2 (BST-2)/tetherin. In this study, we analyzed whether the Vpu Protein is associated with microdomains known as lipid or membrane rafts. Our results indicate that Vpu partially partitions into detergent-resistant membrane (DRM) fractions when expressed alone or in the context of simian–human immunodeficiency virus (SHIV) infection. The ability to be partitioned into rafts was observed with both subtype B and C Vpu Proteins. The use of cholesterol lowering lovastatin/M-β-cyclodextrin and co-patching experiments confirmed that Vpu can be detected in cholesterol rich regions of membranes. Finally, we present data showing that raft association-defective transmembrane mutants of Vpu have impaired enhanced virus release function, but still maintain the ability to down-regulate CD4.
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The Vpu Protein: New concepts in virus release and CD4 down-modulation
Current HIV research, 2010Co-Authors: Autumn Ruiz, Edward B StephensAbstract:Human immunodeficiency virus type 1 (HIV-1) and several simian immunodeficiency viruses (SIV) encode for a transmembrane Protein known as Vpu (viral Protein U). While one of the smallest of the HIV-1 Proteins, it has two important functions within virus-infected cells. The first of these functions is the down-regulation of the CD4 receptor to prevent its interaction with the HIV-1 envelope glycoProtein. Vpu interacts with the CD4 receptor in the rough endoplasmic reticulum (RER), resulting in its re-translocation across the RER and subsequent degradation via the proteasomal pathway. The second major function of the Vpu Protein is to facilitate release of virus from infected cells. Previous studies have shown that virus release is cell type specific, suggesting that certain cells may express a restriction factor that inhibits virus release in the absence of Vpu. Recently, bone marrow stromal antigen 2 (BST-2/HM1.24/CD317/tetherin) has been identified as this factor. This review will focus on new findings within the last four years on the role of Vpu in CD4 down-regulation and the restriction of virus release from cells. We will relate these findings to virus pathogenesis and propose questions regarding BST-2 as a restriction factor.
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Requirements of the membrane proximal tyrosine and dileucine-based sorting signals for efficient transport of the subtype C Vpu Protein to the plasma membrane and in virus release
Virology, 2008Co-Authors: Autumn Ruiz, M. Sarah Hill, Kimberly Schmitt, Edward B StephensAbstract:Abstract Previously, we showed that the Vpu Protein from HIV-1 subtype C is more efficiently transported to the cell surface than the well studied subtype B Vpu (Pacyniak et al., 2005) and that a SHIV expressing the subtype C Vpu exhibited a decreased rate of CD4 + T cell loss following inoculation in macaques ( Hill et al., 2008 ). In this study, we examined the role of overlapping tyrosine-based (YXXΦ) and dileucine-based ([D/E]XXXL[L/I]) motifs in the membrane proximal region of the subtype C Vpu (EYRKLL) in Vpu intracellular transport, CD4 surface expression and virus release from the cell surface. We constructed three site-directed mutants of the subtype C Vpu and fused these genes to the gene for enhanced green fluorescent Protein (EGFP). The first mutation made altered the tyrosine (E A RKLL; Vpu SC EGFPY35A), the second altered the dileucine motif (EYRKL G ; Vpu SC EGFPL39G), and the third contained both amino acid substitutions ( E ARKL G ; Vpu SC EGFPYL35,39AG) in this region of the Vpu Protein. The Vpu SC EGFPY35A Protein was transported to the cell surface similar to the unmodified Vpu SC EGFP1 while Vpu SC EGFPL39G was expressed at the cell surface at significantly reduced levels. The Vpu SC EGFPYL35,39AG was found to have an intermediate level of cell surface expression. All three mutant Vpu Proteins were analyzed for the ability to prevent cell surface expression of CD4. We found that both single mutants did not significantly effect CD4 surface expression while the double mutant (Vpu SC EGFPYL35,39AG) was significantly less efficient at preventing cell surface CD4 expression. Chimeric simian human immunodeficiency viruses were constructed with these mutations in Vpu (SHIV SCVpuY35A , SHIV SCVpuL39G and SHIV SCVpuYL35,39AG ). Our results indicate that SHIV SCVpuL39G replicated much more efficiently and was much more cytopathic than SHIV SCVpu. In contrast, SHIV SCVpuY35A and SHIV SCVpuYL35,39AG replicated less efficiently when compared to the parental SHIV SCVpu . Taken together, these results show for the first time that the membrane proximal tyrosine-based sorting motif in the cytoplasmic domain of Vpu is essential for efficient virus release. These results also indicate that the dileucine-based sorting motif affects the intracellular trafficking of subtype C Vpu Proteins, virus replication, and release.
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the interferon induced Protein bst 2 restricts hiv 1 release and is downregulated from the cell surface by the viral Vpu Protein
Cell Host & Microbe, 2008Co-Authors: Nanette Van Damme, Chris Katsura, Rebecca L Jorgenson, Richard S Mitchell, Edward B Stephens, Marc C. Johnson, Daniel Goff, John C GuatelliAbstract:Summary The HIV-1 accessory Protein Vpu counteracts a host factor that restricts virion release from infected cells. Here we show that the interferon-induced cellular Protein BST-2/HM1.24/CD317 is such a factor. BST-2 is downregulated from the cell surface by Vpu, and BST-2 is specifically expressed in cells that support the Vpu phenotype. Exogenous expression of BST-2 inhibits HIV-1 virion release, while suppression of BST-2 relieves the requirement for Vpu. Downregulation of BST-2 requires both the transmembrane/ion channel domain and conserved serines in the cytoplasmic domain of Vpu. Endogenous BST-2 colocalizes with the HIV-1 structural Protein Gag in endosomes and at the plasma membrane, suggesting that BST-2 traps virions within and on infected cells. The unusual structure of BST-2, which includes a transmembrane domain and a lumenal GPI anchor, may allow it to retain nascent enveloped virions on cellular membranes, providing a mechanism of viral restriction counteracted by a specific viral accessory Protein.
Frank Kirchhoff - One of the best experts on this subject based on the ideXlab platform.
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Vpu-Mediated Counteraction of Tetherin Is a Major Determinant of HIV-1 Interferon Resistance
mBio, 2016Co-Authors: Dorota Kmiec, Shilpa S Iyer, Daniel Sauter, Christina M. Stürzel, Frank KirchhoffAbstract:ABSTRACT Human immunodeficiency virus type 1 (HIV-1) groups M, N, O, and P are the result of independent zoonotic transmissions of simian immunodeficiency viruses (SIVs) infecting great apes in Africa. Among these, only Vpu Proteins of pandemic HIV-1 group M strains evolved potent activity against the restriction factor tetherin, which inhibits virus release from infected cells. Thus, effective Vpu-mediated tetherin antagonism may have been a prerequisite for the global spread of HIV-1. To determine whether this particular function enhances primary HIV-1 replication and interferon resistance, we introduced mutations into the Vpu genes of HIV-1 group M and N strains to specifically disrupt their ability to antagonize tetherin, but not other Vpu functions, such as degradation of CD4, down-modulation of CD1d and NTB-A, and suppression of NF-κB activity. Lack of particular human-specific adaptations reduced the ability of HIV-1 group M Vpu Proteins to enhance virus production and release from primary CD4 + T cells at high levels of type I interferon (IFN) from about 5-fold to 2-fold. Interestingly, transmitted founder HIV-1 strains exhibited higher virion release capacity than chronic control HIV-1 strains irrespective of Vpu function, and group M viruses produced higher levels of cell-free virions than an N group HIV-1 strain. Thus, efficient virus release from infected cells seems to play an important role in the spread of HIV-1 in the human population and requires a fully functional Vpu Protein that counteracts human tetherin. IMPORTANCE Understanding which human-specific adaptations allowed HIV-1 to cause the AIDS pandemic is of great importance. One feature that distinguishes pandemic HIV-1 group M strains from nonpandemic or rare group O, N, and P viruses is the acquisition of mutations in the accessory Vpu Protein that confer potent activity against human tetherin. Adaptation was required because human tetherin has a deletion that renders it resistant to the Nef Protein used by the SIV precursor of HIV-1 to antagonize this antiviral factor. It has been suggested that these adaptations in Vpu were critical for the effective spread of HIV-1 M strains, but direct evidence has been lacking. Here, we show that these changes in Vpu significantly enhance virus replication and release in human CD4 + T cells, particularly in the presence of IFN, thus supporting an important role in the spread of pandemic HIV-1.
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Vpu-Mediated Counteraction of Tetherin Is a Major Determinant of HIV-1 Interferon Resistance
American Society for Microbiology, 2016Co-Authors: Dorota Kmiec, Shilpa S Iyer, Daniel Sauter, Christina M. Stürzel, Beatrice H. Hahn, Frank KirchhoffAbstract:Human immunodeficiency virus type 1 (HIV-1) groups M, N, O, and P are the result of independent zoonotic transmissions of simian immunodeficiency viruses (SIVs) infecting great apes in Africa. Among these, only Vpu Proteins of pandemic HIV-1 group M strains evolved potent activity against the restriction factor tetherin, which inhibits virus release from infected cells. Thus, effective Vpu-mediated tetherin antagonism may have been a prerequisite for the global spread of HIV-1. To determine whether this particular function enhances primary HIV-1 replication and interferon resistance, we introduced mutations into the Vpu genes of HIV-1 group M and N strains to specifically disrupt their ability to antagonize tetherin, but not other Vpu functions, such as degradation of CD4, down-modulation of CD1d and NTB-A, and suppression of NF-κB activity. Lack of particular human-specific adaptations reduced the ability of HIV-1 group M Vpu Proteins to enhance virus production and release from primary CD4+ T cells at high levels of type I interferon (IFN) from about 5-fold to 2-fold. Interestingly, transmitted founder HIV-1 strains exhibited higher virion release capacity than chronic control HIV-1 strains irrespective of Vpu function, and group M viruses produced higher levels of cell-free virions than an N group HIV-1 strain. Thus, efficient virus release from infected cells seems to play an important role in the spread of HIV-1 in the human population and requires a fully functional Vpu Protein that counteracts human tetherin
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Emerging role of the host restriction factor tetherin in viral immune sensing.
Journal of molecular biology, 2013Co-Authors: Dominik Hotter, Daniel Sauter, Frank KirchhoffAbstract:Tetherin (BST-2, CD317) is an interferon-inducible cellular factor that inhibits the release of diverse enveloped viruses by tethering them to the cell surface. Its importance in antiviral immunity is underscored by the observation that various viruses have evolved antagonists against this restriction factor. Accumulating evidence suggests that this is not only due to its ability to inhibit virus release but that tetherin also acts as an innate immune sensor of viral infections that activates NF-κB to induce an inflammatory response. Furthermore, tetherin modulates immune activation through interactions with the immunoglobulin-like transcript 7 (ILT7, LILRA4). This surface receptor is specifically expressed on plasmacytoid dendritic cells, which are the main producers of type I interferons in response to viral infections. Here, we summarize some of our current knowledge about the role of tetherin as a viral immune sensor and discuss how the accessory HIV-1 (human immunodeficiency virus type 1) Vpu Protein counteracts this effect.
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Vpu serine 52 dependent counteraction of tetherin is required for HIV-1 replication in macrophages, but not in ex vivo human lymphoid tissue
Retrovirology, 2010Co-Authors: Michael Schindler, Daniel Sauter, Devi Rajan, Carina Banning, Peter Wimmer, Herwig Koppensteiner, Alicja Iwanski, Anke Specht, Thomas Dobner, Frank KirchhoffAbstract:Background The human immunodeficiency virus type 1 (HIV-1) Vpu Protein degrades CD4 and counteracts a restriction factor termed tetherin (CD317; Bst-2) to enhance virion release. It has been suggested that both functions can be genetically separated by mutation of a serine residue at position 52. However, recent data suggest that the S52 phosphorylation site is also important for the ability of Vpu to counteract tetherin. To clarify this issue, we performed a comprehensive analysis of HIV-1 with a mutated casein kinase-II phosphorylation site in Vpu in various cell lines, primary blood lymphocytes (PBL), monocyte-derived macrophages (MDM) and ex vivo human lymphoid tissue (HLT). Results We show that mutation of serine 52 to alanine (S52A) entirely disrupts Vpu-mediated degradation of CD4 and strongly impairs its ability to antagonize tetherin. Furthermore, casein-kinase II inhibitors blocked the ability of Vpu to degrade tetherin. Overall, Vpu S52A could only overcome low levels of tetherin, and its activity decreased in a manner dependent on the amount of transiently or endogenously expressed tetherin. As a consequence, the S52A Vpu mutant virus was unable to replicate in macrophages, which express high levels of this restriction factor. In contrast, HIV-1 Vpu S52A caused CD4+ T-cell depletion and spread efficiently in ex vivo human lymphoid tissue and PBL, most likely because these cells express comparably low levels of tetherin. Conclusion Our data explain why the effect of the S52A mutation in Vpu on virus release is cell-type dependent and suggest that a reduced ability of Vpu to counteract tetherin impairs HIV-1 replication in macrophages, but not in tissue CD4+ T cells.
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nef Proteins from simian immunodeficiency viruses are tetherin antagonists
Cell Host & Microbe, 2009Co-Authors: Marc C. Johnson, Fengwen Zhang, Sam J Wilson, Wilmina N Landford, Beatriz Virgen, Devon A Gregory, Jan Munch, Frank KirchhoffAbstract:The tetherin/BST2/CD317 Protein blocks the release of HIV-1 and other enveloped viruses by inducing tethering of nascent particles to infected cell surfaces. The HIV-1 Vpu Protein antagonizes the antiviral activity of human but not monkey tetherins and many simian immunodeficiency viruses (SIVs) do not encode Vpu. Here, we show that the apparently “missing” antitetherin activity in SIVs has been acquired by several SIV Nef Proteins. Specifically, SIVMAC/SIVSMM, SIVAGM, and SIVBLU Nef Proteins can suppress tetherin activity. Notably, tetherin antagonism by SIV Nef Proteins is species specific, is genetically separable from other Nef activities, and is most evident with simian rather than human tetherin Proteins. Accordingly, a critical determinant of sensitivity to SIVMAC Nef in the tetherin cytoplasmic tail is variable in nonhuman primate tetherins and deleted in human tetherin, likely due to selective pressures imposed by viral antagonists, perhaps including Nef Proteins.
Daniel Sauter - One of the best experts on this subject based on the ideXlab platform.
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Vpu-Mediated Counteraction of Tetherin Is a Major Determinant of HIV-1 Interferon Resistance
mBio, 2016Co-Authors: Dorota Kmiec, Shilpa S Iyer, Daniel Sauter, Christina M. Stürzel, Frank KirchhoffAbstract:ABSTRACT Human immunodeficiency virus type 1 (HIV-1) groups M, N, O, and P are the result of independent zoonotic transmissions of simian immunodeficiency viruses (SIVs) infecting great apes in Africa. Among these, only Vpu Proteins of pandemic HIV-1 group M strains evolved potent activity against the restriction factor tetherin, which inhibits virus release from infected cells. Thus, effective Vpu-mediated tetherin antagonism may have been a prerequisite for the global spread of HIV-1. To determine whether this particular function enhances primary HIV-1 replication and interferon resistance, we introduced mutations into the Vpu genes of HIV-1 group M and N strains to specifically disrupt their ability to antagonize tetherin, but not other Vpu functions, such as degradation of CD4, down-modulation of CD1d and NTB-A, and suppression of NF-κB activity. Lack of particular human-specific adaptations reduced the ability of HIV-1 group M Vpu Proteins to enhance virus production and release from primary CD4 + T cells at high levels of type I interferon (IFN) from about 5-fold to 2-fold. Interestingly, transmitted founder HIV-1 strains exhibited higher virion release capacity than chronic control HIV-1 strains irrespective of Vpu function, and group M viruses produced higher levels of cell-free virions than an N group HIV-1 strain. Thus, efficient virus release from infected cells seems to play an important role in the spread of HIV-1 in the human population and requires a fully functional Vpu Protein that counteracts human tetherin. IMPORTANCE Understanding which human-specific adaptations allowed HIV-1 to cause the AIDS pandemic is of great importance. One feature that distinguishes pandemic HIV-1 group M strains from nonpandemic or rare group O, N, and P viruses is the acquisition of mutations in the accessory Vpu Protein that confer potent activity against human tetherin. Adaptation was required because human tetherin has a deletion that renders it resistant to the Nef Protein used by the SIV precursor of HIV-1 to antagonize this antiviral factor. It has been suggested that these adaptations in Vpu were critical for the effective spread of HIV-1 M strains, but direct evidence has been lacking. Here, we show that these changes in Vpu significantly enhance virus replication and release in human CD4 + T cells, particularly in the presence of IFN, thus supporting an important role in the spread of pandemic HIV-1.
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Vpu-Mediated Counteraction of Tetherin Is a Major Determinant of HIV-1 Interferon Resistance
American Society for Microbiology, 2016Co-Authors: Dorota Kmiec, Shilpa S Iyer, Daniel Sauter, Christina M. Stürzel, Beatrice H. Hahn, Frank KirchhoffAbstract:Human immunodeficiency virus type 1 (HIV-1) groups M, N, O, and P are the result of independent zoonotic transmissions of simian immunodeficiency viruses (SIVs) infecting great apes in Africa. Among these, only Vpu Proteins of pandemic HIV-1 group M strains evolved potent activity against the restriction factor tetherin, which inhibits virus release from infected cells. Thus, effective Vpu-mediated tetherin antagonism may have been a prerequisite for the global spread of HIV-1. To determine whether this particular function enhances primary HIV-1 replication and interferon resistance, we introduced mutations into the Vpu genes of HIV-1 group M and N strains to specifically disrupt their ability to antagonize tetherin, but not other Vpu functions, such as degradation of CD4, down-modulation of CD1d and NTB-A, and suppression of NF-κB activity. Lack of particular human-specific adaptations reduced the ability of HIV-1 group M Vpu Proteins to enhance virus production and release from primary CD4+ T cells at high levels of type I interferon (IFN) from about 5-fold to 2-fold. Interestingly, transmitted founder HIV-1 strains exhibited higher virion release capacity than chronic control HIV-1 strains irrespective of Vpu function, and group M viruses produced higher levels of cell-free virions than an N group HIV-1 strain. Thus, efficient virus release from infected cells seems to play an important role in the spread of HIV-1 in the human population and requires a fully functional Vpu Protein that counteracts human tetherin
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a naturally occurring rev1 Vpu fusion gene does not confer a fitness advantage to hiv 1
PLOS ONE, 2015Co-Authors: Simon Langer, Kristina Hopfensperger, Shilpa S Iyer, Edward F Kreider, Gerald H Learn, Daniel SauterAbstract:Background Pandemic strains of HIV-1 (group M) encode a total of nine structural (gag, pol, env), regulatory (rev, tat) and accessory (vif, vpr, Vpu, nef) genes. However, some subtype A and C viruses exhibit an unusual gene arrangement in which the first exon of rev (rev1) and the Vpu gene are placed in the same open reading frame. Although this rev1-Vpu gene fusion is present in a considerable fraction of HIV-1 strains, its functional significance is unknown. Results Examining infectious molecular clones (IMCs) of HIV-1 that encode the rev1-Vpu polymorphism, we show that a fusion Protein is expressed in infected cells. Due to the splicing pattern of viral mRNA, however, these same IMCs also express a regular Vpu Protein, which is produced at much higher levels. To investigate the function of the fusion gene, we characterized isogenic IMC pairs differing only in their ability to express a Rev1-Vpu Protein. Analysis in transfected HEK293T and infected CD4+ T cells showed that all of these viruses were equally active in known Vpu functions, such as down-modulation of CD4 or counteraction of tetherin. Furthermore, the polymorphism did not affect Vpu-mediated inhibition of NF-кB activation or Rev-dependent nuclear export of incompletely spliced viral mRNAs. There was also no evidence for enhanced replication of Rev1-Vpu expressing viruses in primary PBMCs or ex vivo infected human lymphoid tissues. Finally, the frequency of HIV-1 quasispecies members that encoded a rev1-Vpu fusion gene did not change in HIV-1 infected individuals over time. Conclusions Expression of a rev1-Vpu fusion gene does not affect regular Rev and Vpu functions or alter HIV-1 replication in primary target cells. Since there is no evidence for increased replication fitness of rev1-Vpu encoding viruses, this polymorphism likely emerged in the context of other mutations within and/or outside the rev1-Vpu intergenic region, and may have a neutral phenotype.
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Emerging role of the host restriction factor tetherin in viral immune sensing.
Journal of molecular biology, 2013Co-Authors: Dominik Hotter, Daniel Sauter, Frank KirchhoffAbstract:Tetherin (BST-2, CD317) is an interferon-inducible cellular factor that inhibits the release of diverse enveloped viruses by tethering them to the cell surface. Its importance in antiviral immunity is underscored by the observation that various viruses have evolved antagonists against this restriction factor. Accumulating evidence suggests that this is not only due to its ability to inhibit virus release but that tetherin also acts as an innate immune sensor of viral infections that activates NF-κB to induce an inflammatory response. Furthermore, tetherin modulates immune activation through interactions with the immunoglobulin-like transcript 7 (ILT7, LILRA4). This surface receptor is specifically expressed on plasmacytoid dendritic cells, which are the main producers of type I interferons in response to viral infections. Here, we summarize some of our current knowledge about the role of tetherin as a viral immune sensor and discuss how the accessory HIV-1 (human immunodeficiency virus type 1) Vpu Protein counteracts this effect.
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human tetherin exerts strong selection pressure on the hiv 1 group n Vpu Protein
PLOS Pathogens, 2012Co-Authors: Daniel Sauter, Edward D. Barker, Daniel Unterweger, Michael Vogl, Shariq M Usmani, Anke Heigele, Silvia F Kluge, Elisabeth Hermkes, Markus Moll, Martine PeetersAbstract:HIV-1 groups M and N emerged within the last century following two independent cross-species transmissions of SIVcpz from chimpanzees to humans. In contrast to pandemic group M strains, HIV-1 group N viruses are exceedingly rare, with only about a dozen infections identified, all but one in individuals from Cameroon. Poor adaptation to the human host may be responsible for this limited spread of HIV-1 group N in the human population. Here, we analyzed the function of Vpu Proteins from seven group N strains from Cameroon, the place where this zoonosis originally emerged. We found that these N-Vpus acquired four amino acid substitutions (E15A, V19A and IV25/26LL) in their transmembrane domain (TMD) that allow efficient interaction with human tetherin. However, despite these adaptive changes, most N-Vpus still antagonize human tetherin only poorly and fail to down-modulate CD4, the natural killer (NK) cell ligand NTB-A as well as the lipid-antigen presenting Protein CD1d. These functional deficiencies were mapped to amino acid changes in the cytoplasmic domain that disrupt putative adaptor Protein binding sites and an otherwise highly conserved sTrCP-binding DSGxxS motif. As a consequence, N-Vpus exhibited aberrant intracellular localization and/or failed to recruit the ubiquitin-ligase complex to induce tetherin degradation. The only exception was the Vpu of a group N strain recently discovered in France, but originally acquired in Togo, which contained intact cytoplasmic motifs and counteracted tetherin as effectively as the Vpus of pandemic HIV-1 M strains. These results indicate that HIV-1 group N Vpu is under strong host-specific selection pressure and that the acquisition of effective tetherin antagonism may lead to the emergence of viral variants with increased transmission fitness.
