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Resting CD4 + T cells are resistant to HIV-1 infection, but the underlying reasons for this lack of permissiveness have not been clear. Oliver Fackler and colleagues now report that SAMHD1, the deoxynucleoside triphosphate triphosphohydrolase responsible for restriction of HIV-1 infection in myeloid cells, also restricts infection of resting CD4 + T cells. The findings shed new light on the mechanisms of cellular and molecular regulation of HIV-1 infection. Unlike activated CD4 + T cells, resting CD4 + T cells are highly resistant to productive HIV-1 infection 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . Early after HIV-1 entry, a major block limits reverse transcription of incoming viral genomes. Here we show that the deoxynucleoside triphosphate triphosphohydrolase SAMHD1 prevents reverse transcription of HIV-1 RNA in resting CD4 + T cells. SAMHD1 is abundantly expressed in resting CD4 + T cells circulating in peripheral blood and residing in lymphoid organs. The early restriction to infection in unstimulated CD4 + T cells is overcome by HIV-1 or HIV-2 virions into which viral Vpx is artificially or naturally packaged, respectively, or by addition of exogenous deoxynucleosides. Vpx-mediated proteasomal degradation of SAMHD1 and elevation of intracellular deoxynucleotide pools precede successful infection by Vpx-carrying HIV. Resting CD4 + T cells from healthy donors following SAMHD1 silencing or from a patient with Aicardi-Goutières syndrome homozygous for a nonsense mutation in SAMHD1 were permissive for HIV-1 infection. Thus, SAMHD1 imposes an effective restriction to HIV-1 infection in the large pool of noncycling CD4 + T cells in vivo . Bypassing SAMHD1 was insufficient for the release of viral progeny, implicating other barriers at later stages of HIV replication. Together, these findings may unveil new ways to interfere with the immune evasion and T cell immunopathology of pandemic HIV-1.

Viral protein X (Vpx) is a unique accessory protein encoded by the genome of the human immunodeficiency virus type 2 (HIV-2) and lineages of the simian immunodeficiency virus of sooty mangabeys. So far, counteracting the cellular restriction factor SAMHD1 and mediating the efficient translocation of viral pre-integration complex have been recognized as key functions of Vpx; however, a thorough exploration of its effects on the cellular transcriptome and cytokine milieu has not yet been undertaken. In this study, we carried out the transcriptomic analysis of THP-1 cells and determined differential gene expressions induced by HIV-2 Vpx, utilizing vectors coding for the wild-type and K68-R70 functionally restricted proteins. Significantly altered genes were then validated and quantified through real-time quantitative PCR (qPCR); additionally, replication-competent virions were also used to confirm the findings. Moreover, we analyzed the effect of Vpx expression on the secretion of key cytokines in the medium of transfected cells. Our findings revealed that wild-type HIV-2 Vpx can significantly alter the expression of genes coding for helicases, zinc finger proteins, chaperons, transcription factors and proteins involved in DNA methylation. Differentially altered genes were involved in negative regulation of viral processes, the type I interferon-signaling pathway, DNA-template transcription, elongation, the positive regulation of interferon beta production and the negative regulation of innate immune response. Importantly, Vpx was also found to decrease the expression of HIV-1 Tat, possibly through the downregulation of a crucial splicing factor, required for the maturation of Tat. Additionally, studies on cellular cytokine milieu showed that this accessory protein induced key proinflammatory cytokines. Our study provides important information about the complex role played by HIV-2 Vpx in priming and taming the cellular environment to allow for the establishment of the infection.

CCR5 and CXCR4 both act as HIV co-receptors, though CXCR4 is less explored. CXCR4 binds the chemokine CXCL12 to regulate cellular processes and mediate HIV entry, a process that CXCL12 inhibits. Using cryo-EM, we investigate HIV-2 envelope (Env) spike recognition by CXCR4 and how CXCL12 inhibit this interaction. We discover that CXCR4 unexpected forms a tetramer, both alone and in complex. It binds CXCL12 with 4:8 and 8:8 stoichiometries, with the CXCL12 N-terminus inserting into the CXCR4 pocket. Structures of CXCR4-gp120 HIV-2 complex show one or two gp120 molecules per CXCR4 tetramer, with the V3 loop occupying the major sub-pocket of CXCR4 through deep embedment of its GFKF motif. The CXCL12 N-terminus chashes with gp120 HIV-2 V3 loops, explain its inhibitory effect. Docking analyses of other HIV antagonists further clarify their mechanisms. The CXCR4-gp120 HIV-1 model illustrate how V3 loop residues define co-receptor specificity, offering insights into co-receptor switching and therapeutic design. CXCR4 is a less-studied co-receptor for HIV entry that also serves as the receptor for the chemokine CXCL12. In this study, the authors reveal how HIV-2 engages CXCR4 and how CXCL12 inhibits this interaction, uncovering structural features that underlie viral specificity and inhibition

The Human Silencing Hub (HUSH) complex constituted of TASOR, MPP8 and Periphilin recruits the histone methyl-transferase SETDB1 to spread H3K9me3 repressive marks across genes and transgenes in an integration site-dependent manner. The deposition of these repressive marks leads to heterochromatin formation and inhibits gene expression, but the underlying mechanism is not fully understood. Here, we show that TASOR silencing or HIV-2 Vpx expression, which induces TASOR degradation, increases the accumulation of transcripts derived from the HIV-1 LTR promoter at a post-transcriptional level. Furthermore, using a yeast 2-hybrid screen, we identify new TASOR partners involved in RNA metabolism including the RNA deadenylase CCR4-NOT complex scaffold CNOT1. TASOR and CNOT1 synergistically repress HIV expression from its LTR. Similar to the RNA-induced transcriptional silencing complex found in fission yeast, we show that TASOR interacts with the RNA exosome and RNA Polymerase II, predominantly under its elongating state. Finally, we show that TASOR facilitates the association of RNA degradation proteins with RNA polymerase II and is detected at transcriptional centers. Altogether, we propose that HUSH operates at the transcriptional and post-transcriptional levels to repress HIV proviral expression. The human silencing hub (HUSH) complex, which includes TASOR, deposits repressive marks on HIV proviruses, resulting in gene repression. Here, Matkovic et al. show that TASOR interacts with RNA Polymerase II, predominantly under its elongating state, and RNA degradation proteins to repress HIV provirus expression.

During the progression of HIV-1 infection, macrophage tropic HIV-1 that use the CCR5 co-receptor undergoes a change in co-receptor use to CXCR4 that is predominately T cell tropic. This change in co-receptor preference makes the virus able to infect T cells. HIV-2 is known to infect MDMs and T cells and is dual tropic. The aim of this study was to elucidate the differential expression profiles of host miRNAs and their role in cells infected with HIV-1/HIV-2. To achieve this goal, a comparative global miRNA expression profile was determined in human PBMCs and MDMs infected with HIV-1/HIV-2. Differentially expressed miRNAs were identified in HIV-1/HIV-2 infected PBMCs and MDMs using the next-generation sequencing (NGS) technique. A comparative global miRNA expression profile in infected MDMs and PBMCs with HIV-1 and HIV-2 identified differential expression of several host miRNAs. These differentially expressed miRNAs are likely to be involved in many signaling pathways, like the p53 signaling pathway, PI3K-Akt signaling pathways, MAPK signaling pathways, FoxO signaling pathway, and viral carcinogenesis. Thus, a comparative study of the differential expression of host miRNAs in MDMs and T cell in response to HIV-1 and HIV-2 infection will help us to identify unique biomarkers that can differentiate HIV-1 and HIV-2 infection.

APOBEC3G is a member of the human cytidine deaminase family that restricts Vif-deficient viruses by being packaged with progeny virions and inducing the G to A mutation during the synthesis of HIV-1 viral DNA when the progeny virus infects new cells. HIV-1 Vif protein resists the activity of A3G by mediating A3G degradation. Phorbol esters are plant-derived organic compounds belonging to the tigliane family of diterpenes and could activate the PKC pathway. In this study, we identified an inhibitor 12-O-tricosanoylphorbol-20-acetate (hop-8), a novel ester of phorbol which was isolated from Ostodes katharinae of the family Euphorbiaceae, that inhibited the replication of wild-type HIV-1 and HIV-2 strains and drug-resistant strains broadly both in C8166 cells and PBMCs with low cytotoxicity and the EC50 values ranged from 0.106 μM to 7.987 μM. One of the main mechanisms of hop-8 is to stimulate A3G expressing in HIV-1 producing cells and upregulate the A3G level in progeny virions, which results in reducing the infectivity of the progeny virus. This novel mechanism of hop-8 inhibition of HIV replication might represents a promising approach for developing new therapeutics for HIV infection.

HIV-2 viral protein X (Vpx) plays a pivotal role in antagonizing the host restriction factors, including SAMHD1 and components of the HUSH complex, to facilitate viral replication. However, the regulatory mechanisms controlling Vpx stability remain unclear. In this study, we identify the von Hippel–Lindau (VHL) tumor suppressor as a novel E3 ubiquitin ligase that specifically targets Vpx for proteasomal degradation. Mechanistically, we demonstrate that VHL-mediated degradation depends on the oxygen-dependent hydroxylation of Vpx at proline residue 41 (Pro41), a modification catalyzed by prolyl hydroxylase domain-containing protein 3 (PHD3). Using an integrated approach combining crosslinking mass spectrometry and molecular modeling analyses, we elucidate the structural architecture of the PHD3-Vpx complex, revealing the spatial orientation of the catalytic domain of PHD3 required for Pro41 hydroxylation. Furthermore, we establish the physiological significance of this pathway in human macrophages, where pharmacological inhibition or genetic ablation of VHL or PHD3 enhances HIV-2 infection by facilitating Vpx-mediated SAMHD1 degradation. Collectively, our findings unveil a previously unrecognized oxygen-sensitive regulatory mechanism influencing HIV-2 infection and suggest novel therapeutic strategies targeting Vpx stability through modulation of its prolyl hydroxylation status.

SAMHD1 is a host restriction factor that blocks the ability of lentiviruses such as HIV-1 to undergo reverse transcription in myeloid cells and resting T-cells. This restriction is alleviated by expression of the lentiviral accessory proteins Vpx and Vpr (Vpx/Vpr), which target SAMHD1 for proteasome-mediated degradation. However, the precise determinants within SAMHD1 for recognition by Vpx/Vpr remain unclear. Here we show that evolution of Vpx/Vpr in primate lentiviruses has caused the interface between SAMHD1 and Vpx/Vpr to alter during primate lentiviral evolution. Using multiple HIV-2 and SIV Vpx proteins, we show that Vpx from the HIV-2 and SIVmac lineage, but not Vpx from the SIVmnd2 and SIVrcm lineage, require the C-terminus of SAMHD1 for interaction, ubiquitylation, and degradation. On the other hand, the N-terminus of SAMHD1 governs interactions with Vpx from SIVmnd2 and SIVrcm, but has little effect on Vpx from HIV-2 and SIVmac. Furthermore, we show here that this difference in SAMHD1 recognition is evolutionarily dynamic, with the importance of the N- and C-terminus for interaction of SAMHD1 with Vpx and Vpr toggling during lentiviral evolution. We present a model to explain how the head-to-tail conformation of SAMHD1 proteins favors toggling of the interaction sites by Vpx/Vpr during this virus-host arms race. Such drastic functional divergence within a lentiviral protein highlights a novel plasticity in the evolutionary dynamics of viral antagonists for restriction factors during lentiviral adaptation to its hosts.

Target cell entry of HIV-1 is dependent on the binding of gp120, the outer component of the viral envelope glycoprotein complex (Env), to CD4 and a coreceptor, preferentially CCR5 or CXCR4. Still, other interactions may also contribute to the infectivity of the virus. One such interaction is between the highly glycosylated gp120 and carbohydrate-binding proteins, such as galectins. Here, we studied the interaction between HIV-1 Env and a panel of galectins and found that galectin-8 (Gal-8), bound with highest affinity (K D < 1µM) and also interacted with soluble CD4. Detailed analysis using probes for different parts of Gal-8 revealed that it was primarily the N-terminal carbohydrate recognition domain that interacted with HIV-1 Env expressing sialylated galactosides and both N- and O-linked glycans. Importantly, in cell cultures Gal-8 enhanced the infectivity of HIV-1, including strains with different coreceptor use and subtype origin, as well as HIV-2. This Gal-8 infectivity enhancement was particularly strong (up to 100-fold) at low virus inoculum doses. Next, we compared Gal-8 infectivity enhancement of primary HIV-1 isolates from people living with HIV at different stages of the infection. Of note, the infectivity of HIV-1 isolates obtained during the chronic, relatively immunocompetent phase, was significantly more enhanced by Gal-8 than isolates obtained at late-stage disease during severe immunodeficiency. Taken together, this study reveals novel carbohydrate dependent interactions between Gal-8 and HIV-1 Env, resulting in enhanced infectivity of HIV-1, with particularly strong effects at low dose exposure of strains circulating during the chronic infection phase. These results suggest that Gal-8 is a cell attachment protein that HIV-1 utilizes for optimized infectivity, which may guide the development of novel intervention strategies targeting this interaction.

The AIDS pandemic is still of importance. HIV-1 and HIV-2 are the causative agents of this pandemic, and in the absence of a viable vaccine, drugs are continually required to provide quality of life for infected patients. The HIV capsid (CA) protein performs critical functions in the life cycle of HIV-1 and HIV-2, is broadly conserved across major strains and subtypes, and is underexploited. Therefore, it has become a therapeutic target of interest. Here, we report a novel series of 2-pyridone-bearing phenylalanine derivatives as HIV capsid modulators. Compound FTC-2 is the most potent anti-HIV-1 compound in the new series of compounds, with acceptable cytotoxicity in MT-4 cells (selectivity index HIV-1 > 49.57; HIV-2 > 17.08). However, compound TD-1a has the lowest EC50 in the anti-HIV-2 assays (EC50 = 4.86 ± 1.71 μM; CC50= 86.54 ± 29.24 μM). A water solubility test found that TD-1a showed a moderately increased water solubility compared with PF74, while the water solubility of FTC-2 was improved hundreds of times. Furthermore, we use molecular simulation studies to provide insight into the molecular contacts between the new compounds and HIV CA. We also computationally predict drug-like properties and metabolic stability for FTC-2 and TD-1a. Based on this analysis, TD-1a is predicted to have improved drug-like properties and metabolic stability over PF74. This study increases the repertoire of CA modulators and has important implications for developing anti-HIV agents with novel mechanisms, especially those that inhibit the often overlooked HIV-2.