To evade host immune defences, human immunodeficiency viruses 1 and 2 (HIV-1 and HIV-2) have evolved auxiliary proteins that target cell restriction factors. Viral protein X (Vpx) from the HIV-2/SIVsmm lineage enhances viral infection by antagonizing SAMHD1 (refs 1,2), but this antagonism is not sufficient to explain all Vpx phenotypes. Here, through a proteomic screen, we identified another Vpx target—HUSH (TASOR, MPP8 and periphilin)—a complex involved in position-effect variegation3. HUSH downregulation by Vpx is observed in primary cells and HIV-2-infected cells. Vpx binds HUSH and induces its proteasomal degradation through the recruitment of the DCAF1 ubiquitin ligase adaptor, independently from SAMHD1 antagonism. As a consequence, Vpx is able to reactivate HIV latent proviruses, unlike Vpx mutants, which are unable to induce HUSH degradation. Although antagonism of human HUSH is not conserved among all lentiviral lineages including HIV-1, it is a feature of viral protein R (Vpr) from simian immunodeficiency viruses (SIVs) of African green monkeys and from the divergent SIV of l’Hoest's monkey, arguing in favour of an ancient lentiviral species-specific vpx/vpr gene function. Altogether, our results suggest the HUSH complex as a restriction factor, active in primary CD4+ T cells and counteracted by Vpx, therefore providing a molecular link between intrinsic immunity and epigenetic control.
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The authors thank C. Pique and her group and M. Mangeney for discussions, S. Emiliani and A. Abdouni for their advice and protocols for conducting the ChIP experiment, L. Guéguen and L. Picard for the Bio++ analyses and their input on evolutionary analyses, S. Jacquet for her comments on the manuscript, and A. Cimarelli, head of the ‘Host–Pathogen Interaction during Lentiviral Infection’ team at CIRI Lyon. The authors also thank M. Mangeney, G. Lê-Bury and F. Niedergang for their frequent gifts of primary cells, E. Verdin for J-Lat clones, A. Adachi and N. Manel for HIV-2 constructs, N. Landau for SIV packaging constructs and A. Cimarelli for HIV-1- and SIV-based transfer vectors, M.-L. Blondot for her contribution to the SILAC screen and E. Le Rouzic for raising some Vpx mutants. The authors acknowledge the Cytometry and Immunobiology Facility of the Cochin Institute and the 3P5 proteomic facility of Paris Descartes University. The authors also thank all the contributors of publically available genome sequences. This work was supported by grants from the Agence Nationale de la Recherche sur le SIDA et les hépatites virales (ANRS), SIDACTION, Fondation de France and Fondation pour la Recherche Médicale (FRM, grant no. DEQ20140329528 to F.M.-G.). G.C. acknowedges a fellowship from the French government, S.M.-M. received a fellowship from the Fondation pour la Recherche Médicale (FRM, grant no. DEQ20140329528 to F.M.-G.) and H.L. from SIDACTION. L.E. is supported by the CNRS and by grants from the amfAR (Mathilde Krim Phase II Fellowship no. 109140-58-RKHF), the Fondation pour la Recherche Médicale (FRM ‘Projet Innovant’ no. ING20160435028), the FINOVI (‘Recently Settled Scientist’ grant), the ANRS (no. ECTZ19143) and the ANR LABEX ECOFECT (ANR-11-LABX-0048 of Université de Lyon, within the programme ‘Investissements d’Avenir’ (ANR-11-IDEX-0007) operated by the French National Research Agency).