HIV-1 cDNA Research Articles

Cytosolic sensing of HIV by cGAS (INM2P.350)

Abstract HIV infection abrogates adaptive immunity by the depletion of CD4 T cells. However, innate immune defense mechanisms against HIV is largely unknown. Here we show that pseudotyped HIV can infect human and mouse cell lines, leading to the production of interferons and other antiviral cytokines. Activation of innate immunity by HIV requires viral cDNA synthesis but not cDNA integration. We show that retrotranscribed HIV cDNA is sensed by the cytosolic DNA sensor cGAS, which then produces the second messenger 2'3'cGAMP to activate the adaptor STING. Importantly, wild type HIV also triggers cGAMP production in human primary macrophages, underscoring the key role of cGAS in HIV sensing. Furthermore, cytosolic sensing of other retroviruses such as murine leukemia virus and simian immunodeficiency virus also depends on cGAS. These results further our understanding of immune detection of HIV and can be potentially applied in HIV vaccine and adjuvant designs.

Dynamics of HIV DNA and Residual Viremia in Patients Treated With a Raltegravir-Containing Regimen

Dynamics of HIV DNA and Residual Viremia in Patients Treated With a Raltegravir-Containing Regimen

Combined Antiviral Therapy Using Designed Molecular Scaffolds Targeting Two Distinct Viral Functions, HIV-1 Genome Integration and Capsid Assembly.

Designed molecular scaffolds have been proposed as alternative therapeutic agents against HIV-1. The ankyrin repeat protein (AnkGAG1D4) and the zinc finger protein (2LTRZFP) have recently been characterized as intracellular antivirals, but these molecules, used individually, do not completely block HIV-1 replication and propagation. The capsid-binder AnkGAG1D4, which inhibits HIV-1 assembly, does not prevent the genome integration of newly incoming viruses. 2LTRZFP, designed to target the 2-LTR-circle junction of HIV-1 cDNA and block HIV-1 integration, would have no antiviral effect on HIV-1-infected cells. However, simultaneous expression of these two molecules should combine the advantage of preventive and curative treatments. To test this hypothesis, the genes encoding the N-myristoylated Myr(+)AnkGAG1D4 protein and the 2LTRZFP were introduced into human T-cells, using a third-generation lentiviral vector. SupT1 cells stably expressing 2LTRZFP alone or with Myr(+)AnkGAG1D4 showed a complete resistance to HIV-1 in viral challenge. Administration of the Myr(+)AnkGAG1D4 vector to HIV-1-preinfected SupT1 cells resulted in a significant antiviral effect. Resistance to viral infection was also observed in primary human CD4+ T-cells stably expressing Myr(+)AnkGAG1D4, and challenged with HIV-1, SIVmac, or SHIV. Our data suggest that our two anti-HIV-1 molecular scaffold prototypes are promising antiviral agents for anti-HIV-1 gene therapy.

Impact of raltegravir on HIV-1 RNA and DNA forms following initiation of antiretroviral therapy in treatment-naive patients.

The rapid early-phase decay of plasma HIV-1 RNA during integrase inhibitor-based therapy is not fully understood. The accumulation of biologically active episomal HIV-1 cDNAs, following aborted integration, could contribute to antiviral potency in vivo. This prospective, controlled clinical observation study explored raltegravir's impact on the dynamics of HIV-1 RNA in plasma, and concentrations of total HIV-1 cDNA, episomal 2-long terminal repeat (LTR) circles and HIV-1 integrants in peripheral blood mononuclear cells (PBMC). Individuals starting therapy with two nucleoside reverse transcriptase inhibitors plus either raltegravir (raltegravir group; n = 10 patients) or boosted protease inhibitor/non-nucleoside reverse transcriptase inhibitor (control group; n = 10 patients) were followed for 48 weeks. Suppression of HIV-1 RNA (<50 copies/mL) was reached earlier (5/10 versus 0/10 at week 4; 8/10 versus 4/10 at week 12) on raltegravir. Significant total HIV-1 cDNA reductions in PBMC were reached by day 99 and persisted until day 330, with median factors of decrease of 7.2 and 8.9, respectively. Broad inter-individual variations, yet no treatment-associated differences, were noted for HIV-1 cDNA concentrations. Despite reductions in HIV-1 RNA (∼3 log) and total HIV-1 cDNA (∼1 log), concentrations of integrants and 2-LTR circles remained largely unchanged. These results extend the previously reported early benefit of raltegravir on the decline of plasma viraemia to treatment-naive patients. The modest treatment-associated, yet group-independent, decline in total HIV-1 cDNA load and the lack of significant changes in integrated and episomal HIV-1 cDNA suggest that most integrated DNA is archival and targeting of HIV reservoirs other than PBMC may underlie beneficial effects of raltegravir.

Impairment of HIV-1 cDNA Synthesis by DBR1 Knockdown

Previous studies showed that short hairpin RNA (shRNA) knockdown of the RNA lariat debranching enzyme (DBR1) led to a decrease in the production of HIV-1 cDNA. To further characterize this effect, DBR1 shRNA was introduced into GHOST-R5X4 cells, followed by infection at a multiplicity near unity with HIV-1 or an HIV-1-derived vector. DNA and RNA were isolated from whole cells and from cytoplasmic and nuclear fractions at different times postinfection. Inhibition of DBR1 had little or no effect on the formation of minus-strand strong-stop cDNA but caused a significant reduction in the formation of intermediate and full-length cDNA. Moreover, minus-strand strong-stop DNA rapidly accumulated in the cytoplasm in the first 2 h of infection but shifted to the nuclear fraction by 6 h postinfection. Regardless of DBR1 inhibition, greater than 95% of intermediate-length and full-length HIV-1 cDNA was found in the nuclear fraction at all time points. Thus, under these experimental conditions, HIV-1 cDNA synthesis was initiated in the cytoplasm and completed in the nucleus or perinuclear region of the infected cell. When nuclear import of the HIV-1 reverse transcription complex was blocked by expressing a truncated form of the mRNA cleavage and polyadenylation factor CPSF6, the completion of HIV-1 vector cDNA synthesis was detected in the cytoplasm, where it was not inhibited by DBR1 knockdown. Refinement of the cell fractionation procedure indicated that the completion of reverse transcription occurred both within nuclei and in the perinuclear region. Taken together the results indicate that in infections at a multiplicity near 1, HIV-1 reverse transcription is completed in the nucleus or perinuclear region of the infected cell, where it is dependent on DBR1. When nuclear transport is inhibited, reverse transcription is completed in the cytoplasm in a DBR1-independent manner. Thus, there are at least two mechanisms of HIV-1 reverse transcription that require different factors and occur in different intracellular locations. This study shows that HIV-1 reverse transcription starts in the cytoplasm but is completed in or on the surface of the nucleus. Moreover, we show that nuclear reverse transcription is dependent on the activity of the human RNA lariat debranchng enzyme (DBR1), while cytoplasmic reverse transcription is not. These findings may provide new avenues for inhibiting HIV-1 replication and therefore may lead to new medicines for treating HIV-1-infected individuals.

Vpx rescue of HIV-1 from the antiviral state in mature dendritic cells is independent of the intracellular deoxynucleotide concentration

BackgroundSIVMAC/HIV-2 Vpx recruits the CUL4A-DCAF1 E3 ubiquitin ligase complex to degrade the deoxynucleotide hydrolase SAMHD1. This increases the concentration of deoxynucleotides available for reverse transcription in myeloid cells and resting T cells. Accordingly, transduction of these cells by SIVMAC requires Vpx. Virus-like particles containing SIVMAC Vpx (Vpx-VLPs) also increase the efficiency of HIV-1 transduction in these cells, and rescue transduction by HIV-1, but not SIVMAC, in mature monocyte-derived dendritic cells (MDDCs). Differences in Vpx mechanism noted at that time, along with recent data suggesting that SAMHD1 gains additional restriction capabilities in the presence of type I IFN prompted further examination of the role of Vpx and SAMHD1 in HIV-1 transduction of mature MDDCs.ResultsWhen challenged with Vpx-VLPs, SAMHD1 was degraded in MDDCs even after cells had been matured with LPS, though there was no increase in deoxynucleotide levels. Steady-state levels of HIV-1 late reverse transcription products in mature MDDCs were increased to the same extent by either Vpx-VLPs or exogenous nucleosides. In contrast, only Vpx-VLPs increased the levels of 2-LTR circles and proviral DNA in myeloid cells. These results demonstrate that exogenous nucleosides and Vpx-VLPs both increase the levels of HIV-1 cDNA in myeloid cells, but only Vpx-VLPs rescue 2-LTR circles and proviral DNA in myeloid cells with a previously established antiviral state. Finally, since trans-acting Vpx-VLPs provide long-lasting rescue of HIV-1 vector transduction in the face of the antiviral state, and exogenous nucleosides do not, exogenous nucleosides were used to achieve efficient transduction of MDDCs by vectors that stably encode Vprs and Vpxs from a collection of primate lentiviruses. Vpr from SIVDEB or SIVMUS, Vpx from SIVMAC251 or HIV-2, but not SIVRCM, degraded endogenous SAMHD1, increased steady-state levels of HIV-1 cDNA, and rescued HIV-1 from the antiviral state in MDDCs.ConclusionInhibition of deoxynucleotide hydrolysis by promoting SAMHD1 degradation is not the only mechanism by which Vpx rescues HIV-1 in MDDCs from the antiviral state. Vpx has an additional effect on HIV-1 transduction of these cells that occurs after completion of reverse transcription and acts independently of deoxynucleotide levels.

Dynamics of CD8 T-Cell Activation After Discontinuation of HIV Treatment Intensification

Detection of episomal HIV cDNA has been associated with greater levels of CD8 and CD4 T-cell activation in HIV-1-infected highly active antiretroviral therapy (HAART)-suppressed individuals. However, HAART intensification exclusively reduced CD8 T-cell activation. We evaluated activation markers 12 weeks after raltegravir withdrawal in a previously described 48-week raltegravir intensification study. The subjects (n = 34) were subgrouped into 2-LTR(+) (n = 12) or 2-LTR(-) (n = 22) subgroups according to delectability of 2-LTR episomes during the intensification period. The initial differences in CD8 T-cell activation between subgroups were lost after intensification. Linear mixed models revealed significant reductions in CD8 T-cell activation in both 2-LTR(-) and 2-LTR(+) subgroups, suggesting that raltegravir impacts subjects irrespective of 2-LTR detection. Remarkably, a partial rebound in CD8 activation markers after raltegravir discontinuation was observed in the 2-LTR(+) subgroup. This restored the differences between subgroups observed at study entry, particularly in terms of CD38 expression within CD8 memory T-cells. Conversely, CD4 T-cell activation remained unchanged in both subgroups during the study period, although an early and transient CD45RA(-) CD4 T-cell redistribution from tissues was apparent. CD8 T-cell activation undergoes reversible changes during raltegravir intensification and discontinuation in patients showing detectable 2-LTR circles. The general decrease in CD8 T-cell activation and a transient CD45RA(-) CD4 T-cell redistribution in intensified individuals may reflect residual viral replication during apparently suppressive HAART.

A Carboxy-Terminally Truncated Human CPSF6 Lacking Residues Encoded by Exon 6 Inhibits HIV-1 cDNA Synthesis and Promotes Capsid Disassembly

Since HIV-1 replication is modulated at multiple stages by host cell factors, identification and characterization of those host cell factors are expected to contribute to the development of novel anti-HIV therapeutics. Previous studies showed that a C-terminally truncated cytosolic form of cleavage and polyadenylation-specific factor 6 (CPSF6-358) inhibits HIV-1 infection through interference with HIV-1 trafficking to the nucleus. Here we identified and characterized a different configuration of C-terminally truncated human CPSF6 (hCPSF6-375) through cDNA expression cloning coupled with ganciclovir-mediated lethal selection. Notably, hCPSF6-375, but not mouse CPSF6-358 (mCPSF6-358) as previously reported, remarkably interfered with viral cDNA synthesis after HIV-1 infection. Moreover, we found that hCPSF6-375 aberrantly accelerated the disassembly of the viral capsid in target cells, while CPSF6-358 did not. Sequence comparison of CPSF6-375 and CPSF6-358 cDNAs showed a lack of exon 6 and additional coding sequence for 54 amino acid residues in the C terminus of hCPSF6-375. Mutational analyses revealed that the residues encoded by exon 6, but not the C-terminal 54 residues in hCPSF6-375, is responsible for impaired viral cDNA synthesis by hCPSF6-375. This is the first report demonstrating a novel mode of HIV-1 inhibition by truncated forms of CPSF6 that involves rapid capsid disassembly and inhibition of viral cDNA synthesis. These findings could facilitate an increased understanding of viral cDNA synthesis in light of the viral capsid disassembly.

Structural and Functional Role of INI1 and LEDGF in the HIV-1 Preintegration Complex

Integration of the HIV-1 cDNA into the human genome is catalyzed by the viral integrase (IN) protein. Several studies have shown the importance of cellular cofactors that interact with integrase and affect viral integration and infectivity. In this study, we produced a stable complex between HIV-1 integrase, viral U5 DNA, the cellular cofactor LEDGF/p75 and the integrase binding domain of INI1 (INI1-IBD), a subunit of the SWI/SNF chromatin remodeling factor. The stoichiometry of the IN/LEDGF/INI1-IBD/DNA complex components was found to be 4/2/2/2 by mass spectrometry and Fluorescence Correlation Spectroscopy. Functional assays showed that INI1-IBD inhibits the 3′ processing reaction but does not interfere with specific viral DNA binding. Integration assays demonstrate that INI1-IBD decreases the amount of integration events but inhibits by-product formation such as donor/donor or linear full site integration molecules. Cryo-electron microscopy locates INI1-IBD within the cellular DNA binding site of the IN/LEDGF complex, constraining the highly flexible integrase in a stable conformation. Taken together, our results suggest that INI1 could stabilize the PIC in the host cell, by maintaining integrase in a stable constrained conformation which prevents non-specific interactions and auto integration on the route to its integration site within nucleosomes, while LEDGF organizes and stabilizes an active integrase tetramer suitable for specific vDNA integration. Moreover, our results provide the basis for a novel type of integrase inhibitor (conformational inhibitor) representing a potential new strategy for use in human therapy.

TNPO3 protects HIV-1 replication from CPSF6-mediated capsid stabilization in the host cell cytoplasm

BackgroundDespite intensive investigation the mechanism by which HIV-1 reaches the host cell nucleus is unknown. TNPO3, a karyopherin mediating nuclear entry of SR-proteins, was shown to be required for HIV-1 infectivity. Some investigators have reported that TNPO3 promotes HIV-1 nuclear import, as would be expected for a karyopherin. Yet, an equal number of investigators have failed to obtain evidence that supports this model. Here, a series of experiments were performed to better elucidate the mechanism by which TNPO3 promotes HIV-1 infectivity.ResultsTo examine the role of TNPO3 in HIV-1 replication, the 2-LTR circles that are commonly used as a marker for HIV-1 nuclear entry were cloned after infection of TNPO3 knockdown cells. Potential explanation for the discrepancy in the literature concerning the effect of TNPO3 was provided by sequencing hundreds of these clones: a significant fraction resulted from autointegration into sites near the LTRs and therefore were not bona fide 2-LTR circles. In response to this finding, new techniques were developed to monitor HIV-1 cDNA, including qPCR reactions that distinguish 2-LTR circles from autointegrants, as well as massive parallel sequencing of HIV-1 cDNA. With these assays, TNPO3 knockdown was found to reduce the levels of 2-LTR circles. This finding was puzzling, though, since previous work has shown that the HIV-1 determinant for TNPO3-dependence is capsid (CA), an HIV-1 protein that forms a mega-dalton protein lattice in the cytoplasm. TNPO3 imports cellular splicing factors via their SR-domain. Attention was therefore directed towards CPSF6, an SR-protein that binds HIV-1 CA and inhibits HIV-1 nuclear import when the C-terminal SR-domain is deleted. The effect of 27 HIV-1 capsid mutants on sensitivity to TNPO3 knockdown was then found to correlate strongly with sensitivity to inhibition by a C-terminal deletion mutant of CPSF6 (R2 = 0.883, p < 0.0001). TNPO3 knockdown was then shown to cause CPSF6 to accumulate in the cytoplasm. Mislocalization of CPSF6 to the cytoplasm, whether by TNPO3 knockdown, deletion of the CPSF6 nuclear localization signal, or by fusion of CPSF6 to a nuclear export signal, resulted in inhibition of HIV-1 replication. Additionally, targeting CPSF6 to the nucleus by fusion to a heterologous nuclear localization signal rescued HIV-1 from the inhibitory effects of TNPO3 knockdown. Finally, mislocalization of CPSF6 to the cytoplasm was associated with abnormal stabilization of the HIV-1 CA core.ConclusionTNPO3 promotes HIV-1 infectivity indirectly, by shifting the CA-binding protein CPSF6 to the nucleus, thus preventing the excessive HIV-1 CA stability that would otherwise result from cytoplasmic accumulation of CPSF6.

Uracil DNA glycosylase initiates degradation of HIV-1 cDNA containing misincorporated dUTP and prevents viral integration

HIV-1 reverse transcriptase discriminates poorly between dUTP and dTTP, and accordingly, viral DNA products become heavily uracilated when viruses infect host cells that contain high ratios of dUTP:dTTP. Uracilation of invading retroviral DNA is thought to be an innate immunity barrier to retroviral infection, but the mechanistic features of this immune pathway and the cellular fate of uracilated retroviral DNA products is not known. Here we developed a model system in which the cellular dUTP:dTTP ratio can be pharmacologically increased to favor dUTP incorporation, allowing dissection of this innate immunity pathway. When the virus-infected cells contained elevated dUTP levels, reverse transcription was found to proceed unperturbed, but integration and viral protein expression were largely blocked. Furthermore, successfully integrated proviruses lacked detectable uracil, suggesting that only nonuracilated viral DNA products were integration competent. Integration of the uracilated proviruses was restored using an isogenic cell line that had no detectable human uracil DNA glycosylase (hUNG2) activity, establishing that hUNG2 is a host restriction factor in cells that contain high dUTP. Biochemical studies in primary cells established that this immune pathway is not operative in CD4+ T cells, because these cells have high dUTPase activity (low dUTP), and only modest levels of hUNG activity. Although monocyte-derived macrophages have high dUTP levels, these cells have low hUNG activity, which may diminish the effectiveness of this restriction pathway. These findings establish the essential elements of this pathway and reconcile diverse observations in the literature.

Monitoring the HIV-1 integrase enzymatic activity using atomic force microscopy in a 2LTR system

Integration of the HIV cDNA into the host chromosome is a key event in the viral replication cycle. It is mediated by the viral integrase (IN) enzyme, which is an attractive anti-HIV drug target. Here we present the first AFM imaging of IN-mediated DNA integration products in a two-LTR system.

In Vitro HIV-1 LTR Integration into T-Cell Activation Gene CD27 Segment and the Decoy Effect of Modified-Sequence DNA

Integration into the host genome is an essential step in the HIV-1 life cycle. However, the host genome sequence that is favored by HIV-1 during integration has never been documented. Here, we report that CD27, a T cell activation gene, includes a sequence that is a target for in vitro HIV-1 cDNA integration. This sequence has a high affinity for integrase, and the target nucleotides responsible for this higher affinity were identified using a crystal microbalance assay. In experiments involving a segment of the CD27 gene, integration converged in the target nucleotides and flanking sequence DNA, indicating that integration is probably dependent upon the secondary structure of the substrate DNA. Notably, decoy modified CD27 sequence DNAs in which the target nucleotides were replaced suppressed integration when accompanying the original CD27 sequence DNA. Our identified CD27 sequence DNA is useful for investigating the biochemistry of integrase and for in vitro assessment of integrase-binding inhibitors.

GCN2 Has Inhibitory Effect on Human Immunodeficiency Virus-1 Protein Synthesis and Is Cleaved upon Viral Infection

The reversible phosphorylation of the alpha-subunit of eukaryotic translation initiation factor 2 (eIF2alpha) is a well-characterized mechanism of translational control in response to a wide variety of cellular stresses, including viral infection. Beside PKR, the eIF2alpha kinase GCN2 participates in the cellular response against viral infection by RNA viruses with central nervous system tropism. PKR has also been involved in the antiviral response against HIV-1, although this antiviral effect is very limited due to the distinct mechanisms evolved by the virus to counteract PKR action. Here we report that infection of human cells with HIV-1 conveys the proteolytic cleavage of GCN2 and that purified HIV-1 and HIV-2 proteases produce direct proteolysis of GCN2 in vitro, abrogating the activation of GCN2 by HIV-1 RNA. Transfection of distinct cell lines with a plasmid encoding an HIV-1 cDNA clone competent for a single round of replication resulted in the activation of GCN2 and the subsequent eIF2alpha phosphorylation. Moreover, transfection of GCN2 knockout cells or cells with low levels of phosphorylated eIF2alpha with the same HIV-1 cDNA clone resulted in a marked increase of HIV-1 protein synthesis. Also, the over-expression of GCN2 in cells led to a diminished viral protein synthesis. These findings suggest that viral RNA produced during HIV-1 infection activates GCN2 leading to inhibition of viral RNA translation, and that HIV-1 protease cleaves GCN2 to overcome its antiviral effect.

Fangchinoline Inhibits Human Immunodeficiency Virus Type 1 Replication by Interfering with gp160 Proteolytic Processing

The introduction of highly active antiretroviral therapy has led to a significant reduction in the morbidity and mortality of acquired immunodeficiency syndrome patients. However, the emergence of drug resistance has resulted in the failure of treatments in large numbers of patients and thus necessitates the development of new classes of anti-HIV drugs. In this study, more than 200 plant-derived small-molecule compounds were evaluated in a cell-based HIV-1 antiviral screen, resulting in the identification of a novel HIV-1 inhibitor (fangchinoline). Fangchinoline, a bisbenzylisoquinoline alkaloid isolated from Radix Stephaniae tetrandrae, exhibited antiviral activity against HIV-1 laboratory strains NL4-3, LAI and BaL in MT-4 and PM1 cells with a 50% effective concentration ranging from 0.8 to 1.7 µM. Mechanism-of-action studies showed that fangchinoline did not exhibit measurable antiviral activity in TZM-b1 cells but did inhibit the production of infectious virions in HIV-1 cDNA transfected 293T cells, which suggests that the compound targets a late event in infection cycle. Furthermore, the antiviral effect of fangchinoline seems to be HIV-1 enve1ope-dependent, as the production of infectious HIV-1 particles packaged with a heterologous envelope, the vesicular stomatitis virus G glycoprotein, was unaffected by fangchinoline. Western blot analysis of HIV envelope proteins expressed in transfected 293T cells and in isolated virions showed that fangchinoline inhibited HIV-1 gp160 processing, resulting in reduced envelope glycoprotein incorporation into nascent virions. Collectively, our results demonstrate that fangchinoline inhibits HIV-1 replication by interfering with gp160 proteolytic processing. Fangchinoline may serve as a starting point for developing a new HIV-1 therapeutic approach.

A Novel VSV/HIV Pseudotype Approach for the Study of HIV Microbicides Without Requirement for level 3 Biocontainment

Studies of potential HIV mucosal microbicides are difficult to undertake due to the requirement for a suitable animal model and the use of biosafety level 3 containment, which are not always available to researchers. Here we show the use of a mouse model of vaginal and rectal transmission of an HIV chimeric virus that does not require level 3 biosafety containment, to test the ex vivo efficacy of soluble Gb3 analogs for the prevention of mucosal HIV infection. The model uses a pseudoenvelope-typed vesicular stomatitis virus (VSV)/HIV recombinant virus that can infect all murine cell types. We demonstrate that the envelope glycoproteins VSV-G of VSV and gp-120 of HIV both bind Gb3. We show that soluble Gb3 analogs inhibit in vitro infection of cervical and vaginal-derived cell lines by both intact HIV and the VSV/HIV recombinant virus. Soluble Gb3 analogs incorporated into gel or used alone and applied directly to the vaginal and rectal mucosal tissue of mice were able to resist viral infection as monitored by PCR and quantitative real-time PCR copy number of HIV cDNA extracted from mouse tissue. Only a trend towards significant efficacy for prevention of mucosal transmission through lower copy number in the treatment groups was evident from these studies; however, this finding warrants further evaluation. In addition, we illustrate a methodology to evaluate inflammatory responses in either vagina or rectum after administration of soluble microbicidal compounds. These studies provide a potential new ex vivo methodology suitable for animal facilities in general, to screen microbicide drug candidates, including drug candidates that target viral proteins, for efficacy and safety, in order to accelerate development and discovery of prophylactic and therapeutic agents for HIV/AIDS.

Target Cell-Mediated Editing of HIV-1 cDNA by APOBEC3 Proteins in Human Macrophages

Apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3 (APOBEC3) proteins are encapsidated by assembling HIV-1 virions and edit viral cDNA in the next round of infection. Using alpha interferon (IFN-α)-treated monocyte-derived macrophages, we show that infrequent editing of HIV-1 reverse transcripts can also be mediated by APOBEC3 proteins supplied by the targets of infection. Based on the local sequence contexts of these mutations and the established characteristics of APOBEC3 protein expression in myeloid cells, we speculate that APOBEC3A may be responsible for a substantial proportion of this activity.

Vpx rescues HIV-1 transduction of dendritic cells from the antiviral state established by type 1 interferon

BackgroundVpx is a virion-associated protein encoded by SIVSM, a lentivirus endemic to the West African sooty mangabey (Cercocebus atys). HIV-2 and SIVMAC, zoonoses resulting from SIVSM transmission to humans or Asian rhesus macaques (Macaca mulatta), also encode Vpx. In myeloid cells, Vpx promotes reverse transcription and transduction by these viruses. This activity correlates with Vpx binding to DCAF1 (VPRBP) and association with the DDB1/RBX1/CUL4A E3 ubiquitin ligase complex. When delivered experimentally to myeloid cells using VSV G-pseudotyped virus-like particles (VLPs), Vpx promotes reverse transcription of retroviruses that do not normally encode Vpx.ResultsHere we show that Vpx has the extraordinary ability to completely rescue HIV-1 transduction of human monocyte-derived dendritic cells (MDDCs) from the potent antiviral state established by prior treatment with exogenous type 1 interferon (IFN). The magnitude of rescue was up to 1,000-fold, depending on the blood donor, and was also observed after induction of endogenous IFN and IFN-stimulated genes (ISGs) by LPS, poly(I:C), or poly(dA:dT). The effect was relatively specific in that Vpx-associated suppression of soluble IFN-β production, of mRNA levels for ISGs, or of cell surface markers for MDDC differentiation, was not detected. Vpx did not rescue HIV-2 or SIVMAC transduction from the antiviral state, even in the presence of SIVMAC or HIV-2 VLPs bearing additional Vpx, or in the presence of HIV-1 VLPs bearing all accessory genes. In contrast to the effect of Vpx on transduction of untreated MDDCs, HIV-1 rescue from the antiviral state was not dependent upon Vpx interaction with DCAF1 or on the presence of DCAF1 within the MDDC target cells. Additionally, although Vpx increased the level of HIV-1 reverse transcripts in MDDCs to the same extent whether or not MDDCs were treated with IFN or LPS, Vpx rescued a block specific to the antiviral state that occurred after HIV-1 cDNA penetrated the nucleus.ConclusionVpx provides a tool for the characterization of a potent, new HIV-1 restriction activity, which acts in the nucleus of type 1 IFN-treated dendritic cells.

A Functional Role for ADAM10 in Human Immunodeficiency Virus Type-1 Replication

BackgroundGene trap insertional mutagenesis was used as a high-throughput approach to discover cellular genes participating in viral infection by screening libraries of cells selected for survival from lytic infection with a variety of viruses. Cells harboring a disrupted ADAM10 (A Disintegrin and Metalloprotease 10) allele survived reovirus infection, and subsequently ADAM10 was shown by RNA interference to be important for replication of HIV-1.ResultsSilencing ADAM10 expression with small interfering RNA (siRNA) 48 hours before infection significantly inhibited HIV-1 replication in primary human monocyte-derived macrophages and in CD4+ cell lines. In agreement, ADAM10 over-expression significantly increased HIV-1 replication. ADAM10 down-regulation did not inhibit viral reverse transcription, indicating that viral entry and uncoating are also independent of ADAM10 expression. Integration of HIV-1 cDNA was reduced in ADAM10 down-regulated cells; however, concomitant 2-LTR circle formation was not detected, suggesting that HIV-1 does not enter the nucleus. Further, ADAM10 silencing inhibited downstream reporter gene expression and viral protein translation. Interestingly, we found that while the metalloprotease domain of ADAM10 is not required for HIV-1 replication, ADAM15 and γ-secretase (which proteolytically release the extracellular and intracellular domains of ADAM10 from the plasma membrane, respectively) do support productive infection.ConclusionsWe propose that ADAM10 facilitates replication at the level of nuclear trafficking. Collectively, our data support a model whereby ADAM10 is cleaved by ADAM15 and γ-secretase and that the ADAM10 intracellular domain directly facilitates HIV-1 nuclear trafficking. Thus, ADAM10 represents a novel cellular target class for development of antiretroviral drugs.

Intensity of Deoxycytidine Deamination of HIV-1 Proviral DNA by the Retroviral Restriction Factor APOBEC3G Is Mediated by the Noncatalytic Domain

APOBEC3G is a single-stranded (ss) DNA deaminase that restricts replication of HIV-1 by inducing viral genome mutagenesis through deamination of cytosine to uracil on HIV-1 cDNA. APOBEC3G has polydisperse oligomeric states and deaminates ssDNA processively through jumping and sliding. APOBEC3G has a catalytically inactive N-terminal CD1 domain that mediates processivity and an active C-terminal CD2 domain that catalyzes deaminations. Here, we assess the determinants of APOBEC3G deamination efficiency mediated by the CD1 domain by comparing native APOBEC3G and two CD1 mutants, a monomeric mutant (F126A/W127A) and a clinical mutant associated with high viral loads (H186R). Biochemical assays on ssDNA or partially dsDNA and with a reconstituted HIV replication system demonstrate that both mutants of Apo3G have altered DNA scanning properties in either jumping (F126A/W127A) or sliding (H186R), which results in decreased abilities to induce mutagenesis during reverse transcription. The data reveal a functionality for Apo3G oligomers in deamination and provide the first biochemical characterization of the clinical mutant H186R. The data demonstrate that the balance between the jumping and sliding of Apo3G is needed for efficient mutational inactivation of HIV-1.