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HIV-2 Depletes CD4 T Cells through Pyroptosis despite Vpx-Dependent Degradation of SAMHD1.

ABSTRACT: Human immunodeficiency virus type 2 (HIV-2) infection results in a milder course of disease and slower progression to AIDS than does HIV-1. We hypothesized that this difference may be due to degradation of the sterile alpha motif and HD domain 1 (SAMHD1) host restriction factor by the HIV-2 Vpx gene product, thereby diminishing abortive infection and pyroptotic cell death within bystander CD4 T cells. We have compared CD4 T cell death in tonsil-derived human lymphoid aggregate cultures (HLACs) infected with wild-type HIV-2, HIV-2 ?Vpx, or HIV-1. In contrast to our hypothesis, HIV-2, HIV-2 ?Vpx, and HIV-1 induced similar levels of bystander CD4 T cell death. In all cases, cell death was blocked by AMD3100, a CXCR4 entry inhibitor, but not by raltegravir, an integrase, indicating that only early life cycle events were required. Cell death was also blocked by a caspase-1 inhibitor, a key enzyme promoting pyroptosis, but not by a caspase-3 inhibitor, an important enzyme in apoptosis. HIV-1-induced abortive infection and pyroptotic cell death were also not reduced by forced encapsidation of HIV-2 Vpx into HIV-1 virions. Together, these findings indicate that HIV-2 and HIV-1 support similar levels of CD4 T cell depletion in vitro despite HIV-2 Vpx-mediated degradation of the SAMHD1 transcription factor. The milder disease course observed with HIV-2 infection likely stems from factors other than abortive infection and caspase-1-dependent pyroptosis in bystander CD4 T cells.IMPORTANCE CD4 T cell depletion during HIV-1 infection involves the demise of bystander CD4 T cells due to abortive infection, viral DNA sensing, inflammasome assembly, and death by caspase-1-dependent pyroptosis. HIV-2 infection is associated with milder disease and lower rates of CD4 T cell loss. We hypothesized that HIV-2 infection produces lower levels of pyroptosis due to the action of its Vpx gene product. Vpx degrades the SAMHD1 restriction factor, potentially reducing abortive forms of infection. However, in tonsil cell cultures, HIV-2, HIV-2 ?Vpx, and HIV-1 induced indistinguishable levels of pyroptosis. Forced encapsidation of Vpx into HIV-1 virions also did not reduce pyroptosis. Thus, SAMHD1 does not appear to play a key role in the induction of bystander cell pyroptosis. Additionally, the milder clinical course of HIV-2-induced disease is apparently not explained by a decrease in this inflammatory form of programmed cell death.

SUBMITTER: Luo X

PROVIDER: S-EPMC6880156 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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HIV-2 Depletes CD4 T Cells through Pyroptosis despite Vpx-Dependent Degradation of SAMHD1.

Luo Xiaoyu X Herzig Eytan E Doitsh Gilad G Grimmett Zachary W ZW Muñoz-Arias Isa I Greene Warner C WC

Journal of virology 20191126 24

Human immunodeficiency virus type 2 (HIV-2) infection results in a milder course of disease and slower progression to AIDS than does HIV-1. We hypothesized that this difference may be due to degradation of the sterile alpha motif and HD domain 1 (SAMHD1) host restriction factor by the HIV-2 Vpx gene product, thereby diminishing abortive infection and pyroptotic cell death within bystander CD4 T cells. We have compared CD4 T cell death in tonsil-derived human lymphoid aggregate cultures (HLACs) i ...[more]

PMID: 31578293

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Project description:Human Immunodeficiency viruses type 1 and 2 (HIV-1 and HIV-2) succeed to evade host immune defenses by using their viral auxiliary proteins to antagonize host restriction factors. HIV-2/SIVsmm Vpx is known for degrading SAMHD1, a factor impeding the reverse transcription. More recently, Vpx was also shown to counteract HUSH, a complex constituted of TASOR, MPP8 and periphilin, which blocks viral expression from the integrated viral DNA. In a classical ubiquitin ligase hijacking model, Vpx bridges the DCAF1 ubiquitin ligase substrate adaptor to SAMHD1, for subsequent ubiquitination and degradation. Here, we investigated whether the same mechanism is at stake for Vpx-mediated HUSH degradation. While we confirm that Vpx bridges SAMHD1 to DCAF1, we show that TASOR can interact with DCAF1 in the absence of Vpx. Nonetheless, this association was stabilized in the presence of Vpx, suggesting the existence of a ternary complex. The N-terminal PARP-like domain of TASOR is involved in DCAF1 binding, but not in Vpx binding. We also characterized a series of HIV-2 Vpx point mutants impaired in TASOR degradation, while still degrading SAMHD1. Vpx mutants ability to degrade TASOR correlated with their capacity to enhance HIV-1 minigenome expression as expected. Strikingly, several Vpx mutants impaired for TASOR degradation, but not for SAMHD1 degradation, had a reduced binding affinity for DCAF1, but not for TASOR. In macrophages, Vpx R34A-R42A and Vpx R42A-Q47A-V48A, strongly impaired in DCAF1, but not in TASOR binding, could not degrade TASOR, while being efficient in degrading SAMHD1. Altogether, our results highlight the central role of a robust Vpx-DCAF1 association to trigger TASOR degradation. We then propose a model in which Vpx interacts with both TASOR and DCAF1 to stabilize a TASOR-DCAF1 complex. Furthermore, our work identifies Vpx mutants enabling the study of HUSH restriction independently from SAMHD1 restriction in primary myeloid cells. Author summary Human Immunodeficiency Virus (HIV) is still a major public health issue. The understanding of the molecular battle occurring during viral infection, between HIV components and cellular antiviral factors, the so-called restriction factors, is a key determinant for new treatment development. Namely, HIV auxiliary proteins are powerful to induce the downregulation of cellular restriction factors by hijacking the Ubiquitin/proteasome pathway, in order to facilitate the completion of a well-processed HIV replication cycle. For instance, HIV-2 Vpx eases reverse transcription in myeloid cells by counteracting the SAMDH1 restriction factor. More recently, we discovered the ability of Vpx to induce the degradation of the HUSH epigenetic repressor complex to favor in turn, the expression of the provirus. In this study, we uncovered the mechanisms by which Vpx antagonizes TASOR, the core subunit of the HUSH complex. We highlighted key differences between Vpx-induced TASOR and SAMHD1 degradation. These findings will help to propose strategies to study or to target either HUSH or SAMHD1, especially in myeloid cells where SAMHD1 restriction operates.

Project description:Virus-host interactions play vital roles in viral replication and virus-induced pathogenesis. Viruses rely entirely upon host cells to reproduce progeny viruses; however, host factors positively or negatively regulate virus replication by interacting with viral proteins. The elucidation of virus-host protein interaction not only provides a better understanding of the molecular mechanisms by which host cells combat viral infections, but also facilitates the development of new anti-viral therapeutics. Identification of relevant host factors requires techniques that enable comprehensive characterization of virus-host protein interactions. In this study, we developed a proteomic approach to systematically identify human protein kinases that interact potently with viral proteins. For this purpose, we synthesized 412 full-length human protein kinases using the wheat germ cell-free protein synthesis system, and screened them for their association with a virus protein using the amplified luminescent proximity homogenous assay (AlphaScreen). Using this system, we attempted to discover a robust anti-viral host restriction mechanism targeting virus protein X (Vpx) of HIV-2. The screen identified H11/HSPB8 as a Vpx-binding protein that negatively regulates the stability and function of Vpx. Indeed, overexpression of H11/HSPB8 promoted the degradation of Vpx via the ubiquitin-proteasome pathway and inhibited its interaction with SAMHD1, a host restriction factor responsible for blocking replication of HIV. Conversely, targeted knockdown of H11/HSPB8 in human trophoblast cells, which ordinarily express high levels of this protein, restored the expression and function of Vpx, making the cells highly susceptible to viral replication. These results demonstrate that our proteomic approach represents a powerful tool for revealing virus-host interaction not yet identified by conventional methods. Furthermore, we showed that H11/HSPB8 could be a potential host regulatory factor that may prevent placental infection of HIV-2 during pregnancy.

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HIV-2 Depletes CD4 T Cells through Pyroptosis despite Vpx-Dependent Degradation of SAMHD1.

Publications

HIV-2 Depletes CD4 T Cells through Pyroptosis despite Vpx-Dependent Degradation of SAMHD1.

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