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Identification of calcium-modulating cyclophilin ligand as a human host restriction to HIV-1 release overcome by Vpu.

ABSTRACT: The HIV-1 Vpu protein is required for efficient viral release from human cells. For HIV-2, the envelope (Env) protein replaces the role of Vpu. Both Vpu and HIV-2 Env enhance virus release by counteracting an innate host-cell block within human cells that is absent in African green monkey (AGM) cells. Here we identify calcium-modulating cyclophilin ligand (CAML) as a Vpu-interacting host factor that restricts HIV-1 release. Expression of human CAML (encoded by CAMLG) in AGM cells conferred a strong restriction of virus release that was reversed by Vpu and HIV-2 Env, suggesting that CAML is the mechanistic link between these two viral regulators. Depletion of CAML in human cells eliminated the need for Vpu in enhancing HIV-1 and murine leukemia virus release. These results point to CAML as a Vpu-sensitive host restriction factor that inhibits HIV release from human cells. The ability of CAML to inhibit virus release should illuminate new therapeutic strategies against HIV.

SUBMITTER: Varthakavi V

PROVIDER: S-EPMC2652483 | biostudies-literature | 2008 Jun

REPOSITORIES: biostudies-literature

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Identification of calcium-modulating cyclophilin ligand as a human host restriction to HIV-1 release overcome by Vpu.

Varthakavi Vasundhara V Heimann-Nichols Ellen E Smith Rita M RM Sun Yuehui Y Bram Richard J RJ Ali Showkat S Rose Jeremy J Ding Lingmei L Spearman Paul P

Nature medicine 20080525 6

The HIV-1 Vpu protein is required for efficient viral release from human cells. For HIV-2, the envelope (Env) protein replaces the role of Vpu. Both Vpu and HIV-2 Env enhance virus release by counteracting an innate host-cell block within human cells that is absent in African green monkey (AGM) cells. Here we identify calcium-modulating cyclophilin ligand (CAML) as a Vpu-interacting host factor that restricts HIV-1 release. Expression of human CAML (encoded by CAMLG) in AGM cells conferred a str ...[more]

PMID: 18500349

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Project description:UnlabelledThe intrinsic immunity factor CD317 (BST-2/HM1.24/tetherin) imposes a barrier to HIV-1 release at the cell surface that can be overcome by the viral protein Vpu. Expression of Vpu results in a reduction of CD317 surface levels; however, the mechanism of this Vpu activity and its contribution to the virological antagonism are incompletely understood. Here, we characterized the influence of Vpu on major CD317 trafficking pathways using quantitative antibody-based endocytosis and recycling assays as well as a microinjection/microscopy-based kinetic de novo expression approach. We report that HIV-1 Vpu inhibited both the anterograde transport of newly synthesized CD317 and the recycling of CD317 to the cell surface, while the kinetics of CD317 endocytosis remained unaffected. Vpu trapped trafficking CD317 molecules at the trans-Golgi network, where the two molecules colocalized. The subversion of both CD317 transport pathways was dependent on the highly conserved diserine S52/S56 motif of Vpu; however, it did not require recruitment of the diserine motif interactor and substrate adaptor of the SCF-E3 ubiquitin ligase complex, ?-TrCP. Treatment of cells with the malaria drug primaquine resulted in a CD317 trafficking defect that mirrored that induced by Vpu. Importantly, primaquine could functionally replace Vpu as a CD317 antagonist and rescue HIV-1 particle release.ImportanceHIV efficiently replicates in the human host and induces the life-threatening immunodeficiency AIDS. Mammalian genomes encode proteins such as CD317 that can inhibit viral replication at the cellular level. As a countermeasure, HIV has evolved genes like vpu that can antagonize these intrinsic immunity factors. Investigating the mechanism by which Vpu overcomes the virion release restriction imposed by CD317, we find that Vpu subverts recycling and anterograde trafficking pathways of CD317, resulting in surface levels of the restriction factor insufficient to block HIV-1 spread. This describes a novel mechanism of immune evasion by HIV.

Project description:The Vpu accessory protein promotes HIV-1 release by counteracting Tetherin/BST-2, an interferon-regulated restriction factor, which retains virions at the cell-surface. Recent reports proposed beta-TrCP-dependent proteasomal and/or endo-lysosomal degradation of Tetherin as potential mechanisms by which Vpu could down-regulate Tetherin cell-surface expression and antagonize this restriction. In all of these studies, Tetherin degradation did not, however, entirely account for Vpu anti-Tetherin activity. Here, we show that Vpu can promote HIV-1 release without detectably affecting Tetherin steady-state levels or turnover, suggesting that Tetherin degradation may not be necessary and/or sufficient for Vpu anti-Tetherin activity. Even though Vpu did not enhance Tetherin internalization from the plasma membrane (PM), it did significantly slow-down the overall transport of the protein towards the cell-surface. Accordingly, Vpu expression caused a specific removal of cell-surface Tetherin and a re-localization of the residual pool of Tetherin in a perinuclear compartment that co-stained with the TGN marker TGN46 and Vpu itself. This re-localization of Tetherin was also observed with a Vpu mutant unable to recruit beta-TrCP, suggesting that this activity is taking place independently from beta-TrCP-mediated trafficking and/or degradation processes. We also show that Vpu co-immunoprecipitates with Tetherin and that this interaction involves the transmembrane domains of the two proteins. Importantly, this association was found to be critical for reducing cell-surface Tetherin expression, re-localizing the restriction factor in the TGN and promoting HIV-1 release. Overall, our results suggest that association of Vpu to Tetherin affects the outward trafficking and/or recycling of the restriction factor from the TGN and as a result promotes its sequestration away from the PM where productive HIV-1 assembly takes place. This mechanism of antagonism that results in TGN trapping is likely to be augmented by beta-TrCP-dependent degradation, underlining the need for complementary and perhaps synergistic strategies to effectively counteract the powerful restrictive effects of human Tetherin.

Dataset Information

Identification of calcium-modulating cyclophilin ligand as a human host restriction to HIV-1 release overcome by Vpu.

Publications

Identification of calcium-modulating cyclophilin ligand as a human host restriction to HIV-1 release overcome by Vpu.

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