Vpu Exploits the Cross-Talk between BST2 and the ILT7 Receptor to Suppress Anti-HIV-1 Responses by Plasmacytoid Dendritic Cells

RESEARCH ARTICLE Vpu Exploits the Cross-Talk between BST2 and the ILT7 Receptor to Suppress Anti-HIV-1 Responses by Plasmacytoid Dendritic Cells Mariana G. Bego1, Édouard Côté1, Nick Aschman2, Johanne Mercier1, Winfried Weissenhorn2, Éric A. Cohen1,3* 1 Institut de Recherches Cliniques de Montréal (IRCM), Montreal, Quebec, Canada, 2 Université Grenoble Alpes, Unit of Virus Host Cell Interactions (UVHCI), CNRS, UVHCI, Grenoble, France, 3 Department of Microbiology, Infectiology and Immunology, Université de Montréal, Montreal, Quebec, Canada * Abstract OPEN ACCESS Citation: Bego MG, Côté É, Aschman N, Mercier J, Weissenhorn W, Cohen ÉA (2015) Vpu Exploits the Cross-Talk between BST2 and the ILT7 Receptor to Suppress Anti-HIV-1 Responses by Plasmacytoid Dendritic Cells. PLoS Pathog 11(7): e1005024. doi:10.1371/journal.ppat.1005024 Editor: Susan R Ross, University of Pennsylvania School of Medicine, UNITED STATES Received: March 16, 2015 Accepted: June 16, 2015 Published: July 14, 2015 Copyright: © 2015 Bego et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper. Funding: This work was supported by a Canadian Institutes of Health Research (CIHR) grant MOP111226 and by the Canadian HIV Cure Enterprise Grant HIG-133050 from the CIHR partnership with CANFAR and IAS to EAC as well as by a pilot grant from the Fonds de Recherche du Québec-Santé AIDS network to MGB and EAC. WW acknowledges support from the ANRS, and the Grenoble Partnership for Structural Biology platforms (ISBG; UMS 3518 CNRS-CEA-UJF-EMBL) funded by Plasmacytoid dendritic cells (pDCs) constitute a major source of type-I interferon (IFN-I) production during acute HIV infection. Their activation results primarily from TLR7-mediated sensing of HIV-infected cells. However, the interactions between HIV-infected T cells and pDCs that modulate this sensing process remain poorly understood. BST2/Tetherin is a restriction factor that inhibits HIV release by cross-linking virions onto infected cell surface. BST2 was also shown to engage the ILT7 pDC-specific inhibitory receptor and repress TLR7/9-mediated IFN-I production by activated pDCs. Here, we show that Vpu, the HIV-1 antagonist of BST2, suppresses TLR7-mediated IFN-I production by pDC through a mechanism that relies on the interaction of BST2 on HIV-producing cells with ILT7. Even though Vpu downregulates surface BST2 as a mean to counteract the restriction on HIV-1 release, we also find that the viral protein re-locates remaining BST2 molecules outside viral assembly sites where they are free to bind and activate ILT7 upon cell-to-cell contact. This study shows that through a targeted regulation of surface BST2, Vpu promotes HIV-1 release and limits pDC antiviral responses upon sensing of infected cells. This mechanism of innate immune evasion is likely to be important for an efficient early viral dissemination during acute infection. Author Summary Plasmacytoid dendritic cells (pDCs) produce large quantities of type I interferon (IFN-I) upon stimulation by many viruses, including HIV. Their activation is very effective following cell contacts with HIV-1-infected CD4+ T cells. We investigated whether HIV-1 could regulate the antiviral responses of pDCs triggered upon sensing of infected cells. We show that HIV-1 suppresses the levels of IFN-I produced by pDCs through a process that requires expression of the Vpu accessory protein in virus-producing cells. A well-described role of Vpu is to promote efficient HIV-1 production by counteracting BST2, a host factor that entraps nascent viral particle at the cell surface. Apart from its antiviral activity, BST2 PLOS Pathogens | DOI:10.1371/journal.ppat.1005024 July 14, 2015 1 / 32 Vpu Inhibits the Anti-HIV Response of pDCs FRISBI (ANR-10-INSB-05-02) and GRAL (ANR-10LABX-49-01). EAC is a recipient of the Canada Research Chair in Human Retrovirology and EC received a studentship from the Gabriel-Marquis Foundation. NA was supported by a PhD fellowship from the Fond National de la Recherche Luxembourg. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. was reported to inhibit IFN-I production by pDCs through binding and activation of the ILT7 pDC-specific inhibitory receptor. Our results reveal that through a highly sophisticated targeted regulation of BST2 levels at the surface of infected cells, Vpu promotes HIV-1 release and limits IFN-I production by pDCs via the negative signaling exerted by the BST2-ILT7 pair. Overall, this study sheds light on a novel Vpu-BST2 interaction that allows HIV-1 to escape pDC antiviral responses. This modulation of pDC antiviral response by HIV Vpu may facilitate the initial viral expansion during acute infection. Competing Interests: The authors have declared that no competing interests exist. Introduction Plasmacytoid dendritic cells (pDCs) are a distinct subset of DCs that exhibit a unique ability to secrete high amounts of interferons and other cytokines in response to viruses. Even though they constitute less than 1% of the total cell content of peripheral blood in humans, they are considered a primary source of type-I IFN (IFN-I) for antiviral responses. Hence, pDCs represent the first line of defense against viral infections, and as such, serve as a vital link between innate and adaptive immunity. Detection of virus infection by pDCs is mediated through recognition of viral nucleic acids, including single-stranded RNA (ssRNA) and double-stranded DNA containing unmethylated CpG motifs by the Toll-like receptor 7 (TLR7) and 9 (TLR9) endosomal sensors. Activation of TLR7/9 induces signaling events that ultimately lead to the stimulation of IFN genes through IRF7 and pro-inflammatory cytokines genes via NF-κB [1]. The role of pDCs during HIV infection appears to be complex [2]. pDCs are activated in HIV and SIV infection and are rapidly depleted from blood, coinciding with their redistribution to lymph nodes and mucosal tissues [3] where they are largely responsible for the IFN-I being produced during acute infection [4]. In addition, pDCs may be chronically stimulated during HIV infection and a continuing source of IFN-I, a feature that seems central to the immune activation and the CD4+ T cell loss during pathogenic infection [2,5]. pDCs express the primary HIV receptor, CD4, as well as the main co-receptors, CXCR4 and CCR5, and as such support entry of X4 and R5 strains of HIV [6]. Upon sensing HIV-1, pDCs produce IFN-I and other cytokines, and undergo phenotypic activation [7–9]. Although high concentrations of purified HIV virions are capable of inducing IFN-I from pDCs, HIV-infected CD4+ T cells are much more effective at stimulating these (...truncated)