Centrosomal pre-integration latency of HIV-1 in quiescent cells

Human immunodeficiency virus type 1 (HIV-1) efficiently replicates in dividing and non-dividing cells. However, HIV-1 infection is blocked at an early post-entry step in quiescent CD4+ T cells in vitro. The molecular basis of this restriction is still poorly understood. Here, we show that in quiescent cells, incoming HIV-1 sub-viral complexes concentrate and stably reside at the centrosome for several weeks. Upon cell activation, viral replication resumes leading to viral gene expression. Thus, HIV-1 can persist in quiescent cells as a stable, centrosome-associated, pre-integration intermediate

The invariant arginine within the chromatin-binding motif regulates both nucleolar localization and chromatin binding of Foamy virus Gag

Abstract Background Nuclear localization of Gag is a property shared by many retroviruses and retrotransposons. The importance of this stage for retroviral replication is still unknown, but studies on the Rous Sarcoma virus indicate that Gag might select the viral RNA genome for packaging in the nucleus. In the case of Foamy viruses, genome encapsidation is mediated by Gag C-terminal domain (CTD), which harbors three clusters of glycine and arginine residues named GR boxes (GRI-III). In this study we investigated how PFV Gag subnuclear distribution might be regulated. Results We show that the isolated GRI and GRIII boxes act as nucleolar localization signals. In contrast, both the entire Gag CTD and the isolated GRII box, which contains the chromatin-binding motif, target the nucleolus exclusively upon mutation of the evolutionary conserved arginine residue at position 540 (R540), which is a key determinant of FV Gag chromatin tethering. We also provide evidence that Gag localizes in the nucleolus during FV replication and uncovered that the viral protein interacts with and is methylated by Protein Arginine Methyltransferase 1 (PRMT1) in a manner that depends on the R540 residue. Finally, we show that PRMT1 depletion by RNA interference induces the concentration of Gag C-terminus in nucleoli. Conclusion Altogether, our findings suggest that methylation by PRMT1 might finely tune the subnuclear distribution of Gag depending on the stage of the FV replication cycle. The role of this step for viral replication remains an open question

MOESM1 of The invariant arginine within the chromatin-binding motif regulates both nucleolar localization and chromatin binding of Foamy virus Gag

Additional file 1: Figure S1. Nucleolar targeting is a conserved feature of EFV GRI and GRIII boxes and is antagonized by R472 within GRII. A) Amino acid sequences of the GR boxes of PFV and EFV and the NoLS of HIV-1 Rev protein (aa 35–51). B) Electron microscopy images of HeLa cells expressing GFP, GFP-GRI or GFP-RevNoLS and stained with an anti-GFP antibody (ab6556, Abcam, 1:200) and a secondary antibody coupled to 15 nm gold particles (goat anti-rabbit 15 nm Gold, BBI International, 1: 60). C) PFV GRI fused to DsRed and PFV GRIII, EFV GRI (aa 395–427) or GRIII (aa 492–524) fused to GFP were expressed in HeLa cells. Their localization was analyzed 24 h later as described in Fig. 1b. Nuclei are stained with DAPI. D) The C-terminal region (GRs) of EFV Gag fused to GFP and bearing the R472A mutation or not, was expressed in HeLa cells, and its localization was studied as described in Fig. 1b. Nuclei are stained with DAPI. Scale bar represents 10 µm

SUMOylation of SAMHD1 at Lysine 595 is required for HIV-1 restriction in non-cycling cells

International audienceSAMHD1 is a cellular triphosphohydrolase (dNTPase) proposed to inhibit HIV-1 reverse transcription in non-cycling immune cells by limiting the supply of the dNTP substrates. Yet, phosphorylation of T592 downregulates SAMHD1 antiviral activity, but not its dNTPase function, implying that additional mechanisms contribute to viral restriction. Here, we show that SAMHD1 is SUMOylated on residue K595, a modification that relies on the presence of a proximal SUMO-interacting motif (SIM). Loss of K595 SUMOylation suppresses the restriction activity of SAMHD1, even in the context of the constitutively active phospho-ablative T592A mutant but has no impact on dNTP depletion. Conversely, the artificial fusion of SUMO2 to a non-SUMOylatable inactive SAMHD1 variant restores its antiviral function, a phenotype that is reversed by the phosphomimetic T 592 E mutation. Collectively, our observations clearly establish that lack of T592 phosphorylation cannot fully account for the restriction activity of SAMHD1. We find that SUMOylation of K595 is required to stimulate a dNTPase-independent antiviral activity in non-cycling immune cells, an effect that is antagonized by cyclin/CDK-dependent phosphorylation of T592 in cycling cells