Fate of the human immunodeficiency virus type 1 provirus in infected cells: a role for vpr

Exploring viral neuropathic pain: Molecular mechanisms and therapeutic implications

As the Coronavirus Disease 2019 (COVID-19) pandemic continues, there is a growing concern regarding the relationship between viral infections and neuropathic pain. Chronic neuropathic pain resulting from virus-induced neural dysfunction has emerged as a significant issue currently faced. However, the molecular mechanisms underlying this phenomenon remain unclear, and clinical treatment outcomes are often suboptimal. Therefore, delving into the relationship between viral infections and neuropathic pain, exploring the pathophysiological characteristics and molecular mechanisms of different viral pain models, can contribute to the discovery of potential therapeutic targets and methods, thereby enhancing pain relief and improving the quality of life for patients. This review focuses on HIV-related neuropathic pain (HNP), postherpetic neuralgia (PHN), and neuropathic pain caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infections, examining rodent models and relevant cellular molecular pathways. Through elucidating the connection between viral infections and neuropathic pain, it aims to delineate the current limitations and challenges faced by treatments, thereby providing insights and directions for future clinical practice and research.

In vivo Serial Passaging of Human-Simian Immunodeficiency Virus Clones Identifies Characteristics for Persistent Viral Replication

We previously reported that a human immunodeficiency virus type 1 with a simian immunodeficiency virus vif substitution (HSIV-vif_NL4-3) could replicate in pigtailed macaques (PTMs), demonstrating that Vif is a species-specific tropism factor of primate lentiviruses. However, infections did not result in high-peak viremia or setpoint plasma viral loads, as observed during simian immunodeficiency virus (SIV) infection of PTMs. Here, we characterized variants isolated from one of the original infected animals with CD4 depletion after nearly 4years of infection to identify determinants of increased replication fitness. In our studies, we found that the HSIV-vif clones did not express the HIV-1 Vpr protein due to interference from the vpx open reading frame (ORF) in singly spliced vpr mRNA. To examine whether these viral genes contribute to persistent viral replication, we generated infectious HSIV-vif clones expressing either the HIV-1 Vpr or SIV Vpx protein. And then to determine viral fitness determinants of HSIV-vif, we conducted three rounds of serial in vivo passaging in PTMs, starting with an initial inoculum containing a mixture of CXCR4-tropic [Vpr-HSIV-vif_NL4-3 isolated at 196 (C/196) and 200 (C/200) weeks post-infection from a PTM with depressed CD4 counts] and CCR5-tropic HSIV (Vpr⁺ HSIV-vif derivatives based NL-AD8 and Bru-Yu2 and a Vpx expressing HSIV-vif_Yu2). Interestingly, all infected PTMs showed peak plasma viremia close to or above 10⁵ copies/ml and persistent viral replication for more than 20weeks. Infectious molecular clones (IMCs) recovered from the passage 3 PTM (HSIV-P3 IMCs) included mutations required for HIV-1 Vpr expression and those mutations encoded by the CXCR4-tropic HSIV-vif_NL4-3 isolate C/196. The data indicate that the viruses selected during long-term infection acquired HIV-1 Vpr expression, suggesting the importance of Vpr for in vivo pathogenesis. Further passaging of HSIV-P3 IMCs in vivo may generate pathogenic variants with higher replication capacity, which will be a valuable resource as challenge virus in vaccine and cure studies.

Neutralization assay with SARS-CoV-1 and SARS-CoV-2 spike pseudotyped murine leukemia virions

BACKGROUND

Virus neutralization by antibodies is an important prognostic factor in many viral diseases. To easily and rapidly measure titers of neutralizing antibodies in serum or plasma, we developed pseudovirion particles composed of the spike glycoprotein of SARS-CoV-2 incorporated onto murine leukemia virus capsids and a modified minimal murine leukemia virus genome encoding firefly luciferase. This assay design is intended for use in laboratories with biocontainment level 2 and therefore circumvents the need for the biocontainment level 3 that would be required for replication-competent SARS-CoV-2 virus. To validate the pseudovirion assay, we set up comparisons with other available antibody tests including those from Abbott, Euroimmun and Siemens, using archived, known samples.

RESULTS

11 out of 12 SARS-CoV-2-infected patient serum samples showed neutralizing activity against SARS-CoV-2-spike pseudotyped MLV viruses, with neutralizing titers-50 (NT50) that ranged from 1:25 to 1:1,417. Five historical samples from patients hospitalized for severe influenza infection in 2016 tested negative in the neutralization assay (NT50 < 25). Three serum samples with high neutralizing activity against SARS-CoV-2/MLV pseudoviruses showed no detectable neutralizing activity (NT50 < 25) against SARS-CoV-1/MLV pseudovirions. We also compared the semiquantitative Siemens SARS-CoV-2 IgG test, which measures binding of IgG to recombinantly expressed receptor binding domain of SARS-CoV-2 spike glycoprotein with the neutralization titers obtained in the pseudovirion assay and the results show high concordance between the two tests (R2 = 0.9344).

CONCLUSIONS

SARS-CoV-2 spike/MLV pseudovirions provide a practical means of assessing neutralizing activity of antibodies in serum or plasma from infected patients under laboratory conditions consistent with biocontainment level 2. This assay offers promise also in evaluating immunogenicity of spike glycoprotein-based candidate vaccines in the near future.

Neutralization Assay with SARS-CoV-1 and SARS-CoV-2 Spike Pseudotyped Murine Leukemia Virions

Antibody neutralization is an important prognostic factor in many viral diseases. To easily and rapidly measure titers of neutralizing antibodies in serum or plasma, we developed pseudovirion particles composed of the spike glycoprotein of SARS-CoV-2 incorporated onto murine leukemia virus capsids and a modified minimal MLV genome encoding firefly luciferase. These pseudovirions provide a practical means of assessing immune responses under laboratory conditions consistent with biocontainment level 2.

Resistance to the Tat Inhibitor Didehydro-Cortistatin A Is Mediated by Heightened Basal HIV-1 Transcription

Human immunodeficiency virus type 1 (HIV-1) Tat binds the viral RNA structure transactivation-responsive element (TAR) and recruits transcriptional cofactors, amplifying viral mRNA expression. The Tat inhibitor didehydro-cortistatin A (dCA) promotes a state of persistent latency, refractory to viral reactivation. Here we investigated mechanisms of HIV-1 resistance to dCA in vitro Mutations in Tat and TAR were not identified, consistent with the high level of conservation of these elements. Instead, viruses resistant to dCA developed higher Tat-independent basal transcription. We identified a combination of mutations in the HIV-1 promoter that increased basal transcriptional activity and modifications in viral Nef and Vpr proteins that increased NF-κB activity. Importantly, these variants are unlikely to enter latency due to accrued transcriptional fitness and loss of sensitivity to Tat feedback loop regulation. Furthermore, cells infected with these variants become more susceptible to cytopathic effects and immune-mediated clearance. This is the first report of viral escape to a Tat inhibitor resulting in heightened Tat-independent activity, all while maintaining wild-type Tat and TAR.IMPORTANCE HIV-1 Tat enhances viral RNA transcription by binding to TAR and recruiting activating factors. Tat enhances its own transcription via a positive-feedback loop. Didehydro-cortistatin A (dCA) is a potent Tat inhibitor, reducing HIV-1 transcription and preventing viral rebound. dCA activity demonstrates the potential of the "block-and-lock" functional cure approaches. We investigated the viral genetic barrier to dCA resistance in vitro While mutations in Tat and TAR were not identified, mutations in the promoter and in the Nef and Vpr proteins promoted high Tat-independent activity. Promoter mutations increased the basal transcription, while Nef and Vpr mutations increased NF-κB nuclear translocation. This heightened transcriptional activity renders CD4⁺ T cells infected with these viruses more susceptible to cytotoxic T cell-mediated killing and to cell death by cytopathic effects. Results provide insights on drug resistance to a novel class of antiretrovirals and reveal novel aspects of viral transcriptional regulation.

Cell and Gene Therapy for HIV Cure

As the HIV pandemic rapidly spread worldwide in the 1980s and 1990s, a new approach to treat cancer, genetic diseases, and infectious diseases was also emerging. Cell and gene therapy strategies are connected with human pathologies at a fundamental level, by delivering DNA and RNA molecules that could correct and/or ameliorate the underlying genetic factors of any illness. The history of HIV gene therapy is especially intriguing, in that the virus that was targeted was soon co-opted to become part of the targeting strategy. Today, HIV-based lentiviral vectors, along with many other gene delivery strategies, have been used to evaluate HIV cure approaches in cell culture, small and large animal models, and in patients. Here, we trace HIV cell and gene therapy from the earliest clinical trials, using genetically unmodified cell products from the patient or from matched donors, through current state-of-the-art strategies. These include engineering HIV-specific immunity in T-cells, gene editing approaches to render all blood cells in the body HIV-resistant, and most importantly, combination therapies that draw from both of these respective "offensive" and "defensive" approaches. It is widely agreed upon that combinatorial approaches are the most promising route to functional cure/remission of HIV infection. This chapter outlines cell and gene therapy strategies that are poised to play an essential role in eradicating HIV-infected cells in vivo.

HIV-1 Escape from Small-Molecule Antagonism of Vif

Although antiretroviral therapy can suppress HIV-1 replication effectively, virus reservoirs persist in infected individuals and virus replication rapidly rebounds if therapy is interrupted. Currently, there is a need for therapeutic approaches that eliminate, reduce, or control persistent viral reservoirs if a cure is to be realized. This work focuses on the preclinical development of novel, small-molecule inhibitors of the HIV-1 Vif protein. Vif inhibitors represent a new class of antiretroviral drugs that may expand treatment options to more effectively suppress virus replication or to drive HIV-1 reservoirs to a nonfunctional state by harnessing the activity of the DNA-editing cytidine deaminase A3G, a potent, intrinsic restriction factor expressed in macrophage and CD4⁺ T cells. In this study, we derived inhibitor escape variants to characterize the mechanism by which these novel agents inhibit virus replication and to provide evidence for target validation.

The HIV-1 accessory protein Vif, which counteracts the antiviral action of the DNA-editing cytidine deaminase APOBEC3G (A3G), is an attractive and yet unexploited therapeutic target. Vif reduces the virion incorporation of A3G by targeting the restriction factor for proteasomal degradation in the virus-producing cell. Compounds that inhibit Vif-mediated degradation of A3G in cells targeted by HIV-1 would represent a novel antiviral therapeutic. We previously described small molecules with activity consistent with Vif antagonism. In this study, we derived inhibitor escape HIV-1 variants to characterize the mechanism by which these novel agents inhibit virus replication. Here we show that resistance to these agents is dependent on an amino acid substitution in Vif (V142I) and on a point mutation that likely upregulates transcription by modifying the lymphocyte enhancing factor 1 (LEF-1) binding site. Molecular modeling demonstrated a docking site in the Vif-Elongin C complex that is disrupted by these inhibitors. This docking site is lost when Vif acquires the V142I mutation that leads to inhibitor resistance. Competitive fitness experiments indicated that the V142I Vif and LEF-1 binding site mutations created a virus that is better adapted to growing in the presence of A3G than the wild-type virus.

HIV-1 infection renders brain vascular pericytes susceptible to the extracellular glutamate

Reduced pericytes' coverage of endothelium in the brain is one of the structural changes leading to breach of the blood-brain barrier during HIV infection. We previously showed in central memory T (T_CM) cells that HIV latency increases cellular susceptibility to DNA damage. In this study, we investigated susceptibility of primary brain pericytes infected with HIV-1 to DNA damage in response to glutamate and TNF-α, both known to induce neuronal death during chronic inflammatory conditions. To infect pericytes, we used a single-cycle HIV-1 pseudotyped with VSV-G envelope glycoprotein and maintained the cultures until latency was established. Our data indicate that pericytes silence HIV-1 expression at similar rate compared to primary T_CM cells. TNF-α and IL-1β caused partial reactivation of the virus suggesting that progression of disease and neuroinflammation might facilitate virus reactivation from latency. Significant increases in the level of γH2AX, which reflect DNA damage, were observed in infected cultures exposed to TNF-α and glutamate at day 2 post-infection. Glutamate, an excitatory neurologic stimuli, also caused increases in the γH2AX level in latently infected pericytes, whereas PARP and DNA-PK inhibitors caused reductions in cell population suggesting that HIV-1 latency affects repairs of single- and double-strand DNA breaks. For comparison, we also analyzed latently infected astrocytes and determined that DNA damage response in astrocytes is less affected by HIV-1. In conclusion, our results indicate that productive infection and HIV-1 latency in pericytes interfere with DNA damage response, rendering them vulnerable to the agents that are characteristic of chronic neuroinflammatory disease conditions.

eIF4A2 is a host factor required for efficient HIV-1 replication

Host factors are required for efficient HIV-1 replication. To identify these factors, genome-wide RNA interference screening was performed using a human T cell line. In the present study, we assessed whether eukaryotic translation initiation factor 4A isoform 2 (eIF4A2), a DEAD-box protein identified in our screen, is necessary for efficient HIV-1 replication. Exploiting MT4C5 cells depleted of eIF4A2 by stable expression of eIF4A2-specific short-hairpin RNA (shRNA) using a lentiviral system, we found that depletion of eIF4A2 markedly inhibited the infection of a replication-competent reporter HIV-1. eIF4A2 depletion reduced the efficiency of viral cDNA synthesis with virion entry into target cells being unaffected. Depletion of eIF4A2 also inhibited HIV-1 spreading infection in a knockdown level-dependent manner. These results suggest that HIV-1 requires eIF4A2 for optimal replication in human T cells.

N-terminally truncated POM121C inhibits HIV-1 replication

Recent studies have identified host cell factors that regulate early stages of HIV-1 infection including viral cDNA synthesis and orientation of the HIV-1 capsid (CA) core toward the nuclear envelope, but it remains unclear how viral DNA is imported through the nuclear pore and guided to the host chromosomal DNA. Here, we demonstrate that N-terminally truncated POM121C, a component of the nuclear pore complex, blocks HIV-1 infection. This truncated protein is predominantly localized in the cytoplasm, does not bind to CA, does not affect viral cDNA synthesis, reduces the formation of 2-LTR and diminished the amount of integrated proviral DNA. Studies with an HIV-1-murine leukemia virus (MLV) chimeric virus carrying the MLV-derived Gag revealed that Gag is a determinant of this inhibition. Intriguingly, mutational studies have revealed that the blockade by N-terminally-truncated POM121C is closely linked to its binding to importin-β/karyopherin subunit beta 1 (KPNB1). These results indicate that N-terminally-truncated POM121C inhibits HIV-1 infection after completion of reverse transcription and before integration, and suggest an important role for KPNB1 in HIV-1 replication.

Sensing of HIV-1 Infection in Tzm-bl Cells with Reconstituted Expression of STING

Production of proinflammatory cytokines indicative of potent recognition by the host innate immune system has long been recognized as a hallmark of the acute phase of HIV-1 infection. The first components of the machinery by which primary HIV target cells sense infection have recently been described; however, the mechanistic dissection of innate immune recognition and viral evasion would be facilitated by an easily accessible cell line model. Here we describe that reconstituted expression of the innate signaling adaptor STING enhanced the ability of the well-established HIV reporter cell line Tzm-bl to sense HIV infection and to convert this information into nuclear translocation of IRF3 as well as expression of cytokine mRNA. STING-dependent immune sensing of HIV-1 required virus entry and reverse transcription but not genome integration. Particularly efficient recognition was observed for an HIV-1 variant lacking expression of the accessory protein Vpr, suggesting a role of the viral protein in circumventing STING-mediated immune signaling. Vpr as well as STING significantly impacted the magnitude and breadth of the cytokine mRNA expression profile induced upon HIV-1 infection. However, cytoplasmic DNA sensing did not result in detectable cytokine secretion in this cell system, and innate immune recognition did not affect infection rates. Despite these deficits in eliciting antiviral effector functions, these results establish Tzm-bl STING and Tzm-bl STING IRF3.GFP cells as useful tools for studies aimed at dissecting mechanisms and regulation of early innate immune recognition of HIV infection.

IMPORTANCE

Cell-autonomous immune recognition of HIV infection was recently established as an important aspect by which the host immune system attempts to fend off HIV-1 infection. Mechanistic studies on host cell recognition and viral evasion are hampered by the resistance of many primary HIV target cells to detailed experimental manipulation. We describe here that expression of the signaling adaptor STING renders the well-established HIV reporter cell line Tzm-bl competent for innate recognition of HIV infection. Key characteristics reflected in this cell model include nuclear translocation of IRF3, expression of a broad range of cytokine mRNAs, and an antagonistic activity of the HIV-1 protein Vpr. These results establish Tzm-bl STING and Tzm-bl STING IRF3.GFP cells as a useful tool for studies of innate recognition of HIV infection.

Generation of a stable packaging cell line producing high-titer PPT-deleted integration-deficient lentiviral vectors

The risk of insertional mutagenesis inherent to all integrating exogenous expression cassettes was the impetus for the development of various integration-defective lentiviral vector (IDLV) systems. These systems were successfully employed in a plethora of preclinical applications, underscoring their clinical potential. However, current production of IDLVs by transient plasmid transfection is not optimal for large-scale production of clinical grade vectors. Here, we describe the development of the first tetracycline-inducible stable IDLV packaging cell line comprising the D64E integrase mutant and the VSV-G envelope protein. A conditional self-inactivating (cSIN) vector and a novel polypurine tract (PPT)-deleted vector were incorporated into the newly developed stable packaging cell line by transduction and stable transfection, respectively. High-titer (~10(7) infectious units (IU)/ml) cSIN vectors were routinely generated. Furthermore, screening of single-cell clones stably transfected with PPT-deleted vector DNA resulted in the identification of highly efficient producer cell lines generating IDLV titers higher than 10(8) IU/mL, which upon concentration increased to 10(10) IU/ml. IDLVs generated by stable producer lines efficiently transduce CNS tissues of rodents. Overall, the availability of high-titer IDLV lentivirus packaging cell line described here will significantly facilitate IDLV-based basic science research, as well as preclinical and clinical applications.

Vpr Promotes Macrophage-Dependent HIV-1 Infection of CD4+ T Lymphocytes

Vpr is a conserved primate lentiviral protein that promotes infection of T lymphocytes in vivo by an unknown mechanism. Here we demonstrate that Vpr and its cellular co-factor, DCAF1, are necessary for efficient cell-to-cell spread of HIV-1 from macrophages to CD4+ T lymphocytes when there is inadequate cell-free virus to support direct T lymphocyte infection. Remarkably, Vpr functioned to counteract a macrophage-specific intrinsic antiviral pathway that targeted Env-containing virions to LAMP1+ lysosomal compartments. This restriction of Env also impaired virological synapses formed through interactions between HIV-1 Env on infected macrophages and CD4 on T lymphocytes. Treatment of infected macrophages with exogenous interferon-alpha induced virion degradation and blocked synapse formation, overcoming the effects of Vpr. These results provide a mechanism that helps explain the in vivo requirement for Vpr and suggests that a macrophage-dependent stage of HIV-1 infection drives the evolutionary conservation of Vpr.

Ectopic expression of anti-HIV-1 shRNAs protects CD8(+) T cells modified with CD4ζ CAR from HIV-1 infection and alleviates impairment of cell proliferation

Chimeric antigen receptors (CARs) are artificially engineered receptors that confer a desired specificity to immune effector T cells. As an HIV-1-specific CAR, CD4ζ CAR has been extensively tested in vitro as well as in clinical trials. T cells modified with this CAR mediated highly potent anti-HIV-1 activities in vitro and were well-tolerated in vivo, but exerted limited effects on viral load and reservoir size due to poor survival and/or functionality of the transduced cells in patients. We hypothesize that ectopic expression of CD4ζ on CD8(+) T cells renders them susceptible to HIV-1 infection, resulting in poor survival of those cells. To test this possibility, highly purified CD8(+) T cells were genetically modified with a CD4ζ-encoding lentiviral vector and infected with HIV-1. CD8(+) T cells were vulnerable to HIV-1 infection upon expression of CD4ζ as evidenced by elevated levels of p24(Gag) in cells and culture supernatants. Concurrently, the number of CD4ζ-modified CD8(+) T cells was reduced relative to control cells upon HIV-1 infection. To protect these cells from HIV-1 infection, we co-expressed two anti-HIV-1 shRNAs previously developed by our group together with CD4ζ. This combination vector was able to suppress HIV-1 infection without impairing HIV-1-dependent effector activities of CD4ζ. In addition, the number of CD4ζ-modified CD8(+) T cells maintained similar levels to that of the control even under HIV-1 infection. These results suggest that protecting CD4ζ-modified CD8(+) T cells from HIV-1 infection is required for prolonged HIV-1-specific immune surveillance.

Procyanidin trimer C1 derived from Theobroma cacao reactivates latent human immunodeficiency virus type 1 provirus

Despite remarkable advances in combination antiretroviral therapy (cART), human immunodeficiency virus type 1 (HIV-1) infection remains incurable due to the incomplete elimination of the replication-competent virus, which persists in latent reservoirs. Strategies for targeting HIV reservoirs for eradication that involves reactivation of latent proviruses while protecting uninfected cells by cART are urgently needed for cure of HIV infection. We screened medicinal plant extracts for compounds that could reactivate the latent HIV-1 provirus and identified a procyanidin trimer C1 derived from Theobroma cacao as a potent activator of the provirus in human T cells latently infected with HIV-1. This reactivation largely depends on the NF-κB and MAPK signaling pathways because either overexpression of a super-repressor form of IκBα or pretreatment with a MEK inhibitor U0126 diminished provirus reactivation by C1. A pan-PKC inhibitor significantly blocked the phorbol ester-induced but not the C1-induced HIV-1 reactivation. Although C1-induced viral gene expression persisted for as long as 48 h post-stimulation, NF-κB-dependent transcription peaked at 12 h post-stimulation and then quickly declined, suggesting Tat-mediated self-sustainment of HIV-1 expression. These results suggest that procyanidin C1 trimer is a potential compound for reactivation of latent HIV-1 reservoirs.

How SLX4 cuts through the mystery of HIV-1 Vpr-mediated cell cycle arrest

Vpr is one of the most enigmatic viral auxiliary proteins of HIV. During the past twenty years, several activities have been ascribed to this viral protein, but one, its ability to mediate cell cycle arrest at the G2 to M transition has been the most extensively studied. Nonetheless, the genuine role of Vpr and its pathophysiological relevance in the viral life cycle have remained mysterious. Recent work by Laguette et al. (Cell 156:134-145, 2014) provides important insight into the molecular mechanism of Vpr-mediated G2 arrest. This study highlights for the first time how Vpr recruits the SLX4 endonuclease complex and how Vpr-induced inappropriate activation of this complex leads to G2 arrest. Here, we will discuss these findings in the light of previous work to show how they change the view of Vpr’s mechanism of action. We will also discuss how these findings open new questions towards the understanding of the biological function of Vpr regarding innate immune sensing.

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.

Inhibition of HIV-1 replication by RNA with a microRNA-like function

Human immunodeficiency virus type 1 (HIV-1) replication is suppressed by a small guide RNA (sgRNA) that targets the packaging signal of HIV-1 RNA. We unintentionally produced a plasmid with the reverse sequence of the sgRNA and its terminator (pR-Ψ-sgRNA-ter). Both sgRNA and R-Ψ-sgRNA suppress HIV-1, but the mechanism by which R-Ψ-sgRNA suppresses HIV is not clear. To evaluate whether the suppressive effect is caused by an RNA interference or microRNA (miRNA)-like mechanism, R-Ψ-sgRNA was synthesized in vitro and treated with the Dicer enzyme, an important enzyme for RNA interference and miRNA. The RNA was cleaved into fragments of approximately 24 nucleotides (nt). We analyzed the sequence of the RNA fragments and predicted the RNA secondary structure of R-Ψ-sgRNA to determine the region recognized by the Dicer enzyme. The lengths of the R-Ψ-sgRNA fragments ranged from 48 to 140 nt, and were predicted to form double strands, including mismatches, in this region. An HIV-1 p24 assay indicated that the R-Ψ-sgRNA fragments suppressed HIV-1 replication. These findings suggest that R-Ψ-sgRNA acts as a miRNA to inhibit HIV-1.

Inhibition of HIV Replication by Cyclic and Hairpin PNAs Targeting the HIV-1 TAR RNA Loop

Human immunodeficiency virus-1 (HIV-1) replication and gene expression entails specific interaction of the viral protein Tat with its transactivation responsive element (TAR), to form a highly stable stem-bulge-loop structure. Previously, we described triphenylphosphonium (TPP) cation-based vectors that efficiently deliver nucleotide analogs (PNAs) into the cytoplasm of cells. In particular, we showed that the TPP conjugate of a linear 16-mer PNA targeting the apical stem-loop region of TAR impedes Tat-mediated transactivation of the HIV-1 LTR in vitro and also in cell culture systems. In this communication, we conjugated TPP to cyclic and hairpin PNAs targeting the loop region of HIV-1 TAR and evaluated their antiviral efficacy in a cell culture system. We found that TPP-cyclic PNAs containing only 8 residues, showed higher antiviral potency compared to hairpin PNAs of 12 or 16 residues. We further noted that the TPP-conjugates of the 8-mer cyclic PNA as well as the 16-mer linear PNA displayed similar antiviral efficacy. However, cyclic PNAs were shown to be highly specific to their target sequences. This communication emphasizes on the importance of small constrained cyclic PNAs over both linear and hairpin structures for targeting biologically relevant RNA hairpins.

ZBRK1 represses HIV-1 LTR-mediated transcription

The identification of cellular proteins that interact with the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) provides a basic understanding of HIV-1 gene expression, which is the major determinant regulating virus replication. We show that ZBRK1 negatively regulates the HIV-1 LTR. Ectopic expression of ZBRK1 represses transcriptional activity of the HIV-1 LTR, whereas the depletion of endogenous ZBRK1 leads to activation of the HIV-1 LTR. The repressor activity of ZBRK1 is required for TRIM28 binding. Furthermore, ZBRK1 is bound to the HIV-1 LTR in vivo. These results indicate that ZBRK1 could be involved in a potent intrinsic antiretroviral defense.

Differential effects of Vpr on single-cycle and spreading HIV-1 infections in CD4+ T-cells and dendritic cells

The Vpr protein of human immunodeficiency virus type 1 (HIV-1) contributes to viral replication in non-dividing cells, specifically those of the myeloid lineage. However, the effects of Vpr in enhancing HIV-1 infection in dendritic cells have not been extensively investigated. Here, we evaluated the role of Vpr during infection of highly permissive peripheral blood mononuclear cells (PBMCs) and CD4(+) T-cells and compared it to that of monocyte-derived dendritic cells (MDDCs), which are less susceptible to HIV-1 infection. Infections of dividing PBMCs and non-dividing MDDCs were carried out with single-cycle and replication-competent HIV-1 encoding intact Vpr or Vpr-defective mutants. In contrast to previous findings, we observed that single-cycle HIV-1 infection of both PBMCs and MDDCs was significantly enhanced in the presence of Vpr when the viral stocks were carefully characterized and titrated. HIV-1 DNA quantification revealed that Vpr only enhanced the reverse transcription and nuclear import processes in single-cycle HIV-1 infected MDDCs, but not in CD4(+) T-cells. However, a significant enhancement in HIV-1 gag mRNA expression was observed in both CD4(+) T-cells and MDDCs in the presence of Vpr. Furthermore, Vpr complementation into HIV-1 virions did not affect single-cycle viral infection of MDDCs, suggesting that newly synthesized Vpr plays a significant role to facilitate single-cycle HIV-1 infection. Over the course of a spreading infection, Vpr significantly enhanced replication-competent HIV-1 infection in MDDCs, while it modestly promoted viral infection in activated PBMCs. Quantification of viral DNA in replication-competent HIV-1 infected PBMCs and MDDCs revealed similar levels of reverse transcription products, but increased nuclear import in the presence of Vpr independent of the cell types. Taken together, our results suggest that Vpr has differential effects on single-cycle and spreading HIV-1 infections, which are dependent on the permissiveness of the target cell.

Construction and testing of orfA +/- FIV reporter viruses

Single cycle reporter viruses that preserve the majority of the HIV-1 genome, long terminal repeat-promoted transcription and Rev-dependent structural protein expression are useful for investigating the viral life cycle. Reporter viruses that encode the viral proteins in cis in this way have been lacking for feline immunodeficiency virus (FIV), where the field has used genetically minimized transfer vectors with viral proteins supplied in trans. Here we report construction and use of a panel of single cycle FIV reporter viruses that express fluorescent protein markers. The viruses can be produced to high titer using human cell transfection and can transduce diverse target cells. To illustrate utility, we tested versions that are (+) and (-) for OrfA, an FIV accessory protein required for replication in primary lymphocytes and previously implicated in down-regulation of the primary FIV entry receptor CD134. We observed CD134 down-regulation after infection with or without OrfA, and equivalent virion production as well. These results suggest a role for FIV proteins besides Env or OrfA in CD134 down-regulation.

Human immunodeficiency virus-1 Nef suppresses Hsp70-mediated Tat activation

The human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) contains binding sites for several host transcription factors that contribute to HIV-1 gene expression. Although previous reports have indicated that HIV-1 Nef positively or negatively regulates HIV-1 gene expression, the precise molecular mechanisms by which this occurs remain largely unknown. In this study, we report that Nef suppressed LTR-driven transcription only in the presence of HIV-1 Tat, which was localized to the cytoplasm and degraded by the proteasome. However, the depletion of Hsp70 was found to reduce the suppressive effect of Nef on HIV-1 gene expression. These results suggest that Nef suppresses Hsp70-mediated HIV-1 Tat activation.

RD114 envelope proteins provide an effective and versatile approach to pseudotype lentiviral vectors

Lentiviral vectors derived from the HIV-1 genome offer great promise for gene therapy due to their ability to transduce non-dividing cells and sustain long-term expression of transgenes. The majority of current lentiviral vectors are pseudotyped with the vesicular stomatitis viral envelope (VSV-G). VSV-G equips lentiviral vectors with a broad host cell tropism and increased stability. Increased particle stability enables viral supernatants to be concentrated by high-speed centrifugation to enhance their infectivity. Despite its efficacy, VSV-G is cytotoxic - a feature that prohibits the development of stable cell lines that constitutively express this envelope. Therefore, non-toxic envelope proteins are being investigated. RD114 is an attractive alternative because it also provides increased particle stability and its receptor is widely expressed on hematopoietic stem cells (HSCs). In this study, the packaging efficiency of three envelope proteins, RD114, RDpro and VSV-G, were evaluated with two lentiviral vectors (TRIP GFP and HPV-402). RDpro is an RD114-HIV chimera designed to pseudotype lentiviral vectors more efficiently. In transient systems, VSV-G generated titers of 10(8) and 10(7) viral particles/mL for TRIP GFP and HPV-402. RDpro possessed titers of 10(7) and 10(6), while RD114 titers were one log lower for each vector. Despite having relatively lower titers, RD114 proteins are less toxic; this was demonstrated in the extension of transient transfection reactions from 48 to 96 h. VSV-G transfections are generally limited to 48 h. In regard to gene therapy applications, we show that RDpro supernatants efficiently transduce peripheral blood HSCs. The versatility of RD114 envelopes was again demonstrated by using a 'mixed' expression system; composed of stably expressed RD114 envelope proteins to pseudotype lentiviral vectors generated in trans (titer range 10(3)-10(5)). Our data show that RD114 envelope proteins are effective and versatile constructs that could prove to be essential components of therapeutic lentiviral gene transfer systems.

Limelight on two HIV/SIV accessory proteins in macrophage infection: is Vpx overshadowing Vpr?

HIV viruses encode a set of accessory proteins, which are important determinants of virulence due to their ability to manipulate the host cell physiology for the benefit of the virus. Although these viral proteins are dispensable for viral growth in many in vitro cell culture systems, they influence the efficiency of viral replication in certain cell types. Macrophages are early targets of HIV infection which play a major role in viral dissemination and persistence in the organism. This review focuses on two HIV accessory proteins whose functions might be more specifically related to macrophage infection: Vpr, which is conserved across primate lentiviruses including HIV-1 and HIV-2, and Vpx, a protein genetically related to Vpr, which is unique to HIV-2 and a subset of simian lentiviruses. Recent studies suggest that both Vpr and Vpx exploit the host ubiquitination machinery in order to inactivate specific cellular proteins. We review here why it remains difficult to decipher the role of Vpr in macrophage infection by HIV-1 and how recent data underscore the ability of Vpx to antagonize a restriction factor which counteracts synthesis of viral DNA in monocytic cells.

HIV-1 Vpr triggers natural killer cell-mediated lysis of infected cells through activation of the ATR-mediated DNA damage response

Natural killer (NK) cells are stimulated by ligands on virus-infected cells. We have recently demonstrated that NK cells respond to human immunodeficiency virus type-1 (HIV-1)-infected autologous T-cells, in part, through the recognition of ligands for the NK cell activating receptor NKG2D on the surface of the infected cells. Uninfected primary CD4^pos T-cell blasts express little, if any, NKG2D ligands. In the present study we determined the mechanism through which ligands for NKG2D are induced on HIV-1-infected cells. Our studies reveal that expression of vpr is necessary and sufficient to elicit the expression of NKG2D ligands in the context of HIV-1 infection. Vpr specifically induces surface expression of the unique-long 16 binding proteins (ULBP)-1 and ULBP-2, but not ULBP-3, MHC class I-related chain molecules (MIC)-A or MIC-B. In these studies we also demonstrated that Vpr increases the level of ULBP-1 and ULBP-2 mRNA in primary CD4^pos T-cell blasts. The presence of ULBP-1 and ULBP-2 on HIV-1 infected cells is dependent on the ability of Vpr to associate with a protein complex know as Cullin 4a (Cul4a)/damaged DNA binding protein 1 (DDB1) and Cul4a-associated factor-1(DCAF-1) E3 ubiquitin ligase (Cul4a^DCAF-1). ULBP-1 and -2 expression by Vpr is also dependent on activation of the DNA damage sensor, ataxia telangiectasia and rad-3-related kinase (ATR). When T-cell blasts are infected with a vpr-deficient HIV-1, NK cells are impaired in killing the infected cells. Thus, HIV-1 Vpr actively triggers the expression of the ligands to the NK cell activation receptor.

Natural killer (NK) cells are part of the innate immune response against virus infection and cancer. Recently we demonstrated that ligands for the NK cell activation receptor, NKG2D, trigger NK cell-mediated response to infected cells. These ligands are expressed on HIV-1-infected cells and not on uninfected cells. Despite the observation that NKG2D ligands are expressed on infected cells, it is unclear how HIV-1 induces their expression. In the present study, we demonstrate that HIV induces the ligands of the NKG2D receptor through the viral gene product Vpr. Vpr triggers a DNA damage response in infected cells, which in turn, increases virus production. We also demonstrate that by blocking the activity of ATR, a major component in the DNA damage response, we were able to prevent NKG2D ligand expression. When Vpr was removed from the virus genome, NK cells lost their ability to lyse the HIV-infected cells. Thus, HIV-1 actively triggers NK cells through the activity of its viral gene product, Vpr.

An efficient biodelivery system for antisense polyamide nucleic acid (PNA)

With the aim of developing a general and straightforward procedure for the intracellular delivery of naked peptide nucleic acids (PNAs), we designed an intracellularly biodegradable triphenylphosphonium (TPP) cation based transporter system. In this system, TPP is linked, via a biolabile disulfide bridge, to an activated mercaptoethoxycarbonyl moiety, allowing its direct coupling to the N-terminal extremity of a free PNA through a carbamate bond. We found that such TPP-PNA-carbamate conjugates were highly stable in a cell culture medium containing fetal calf serum. In a glutathione-containing medium mimicking the cytosol, the conjugates were rapidly degraded into an unstable intermediate, which spontaneously decomposed, releasing the free PNA. Using a fluorescence-labeled PNA-TPP conjugate, we demonstrated that conjugates were taken up by cells. Efficient cellular uptake and release of the PNA into the cytosol was further confirmed by the anti-HIV activity measured for the TPP-conjugate of a 16-mer PNA targeting the TAR region of the HIV-1 genome. This conjugate exhibited an IC(50) value of 1 microM, while the free 16-mer PNA did not inhibit replication of HIV in the same cellular test.

Modulation of human immunodeficiency virus type 1 infectivity through incorporation of tetraspanin proteins

Accumulating evidence indicates that human immunodeficiency virus type 1 (HIV-1) acquires various cellular membrane proteins in the lipid bilayer of the viral envelope membrane. Although some virion-incorporated cellular membrane proteins are known to potently affect HIV-1 infectivity, the virological functions of most virion-incorporated membrane proteins remain unclear. Among these host proteins, we found that CD63 was eliminated from the plasma membranes of HIV-1-producing T cells after activation, followed by a decrease in the amount of virion-incorporated CD63, and in contrast, an increase in the infectivity of the released virions. On the other hand, we found that CD63 at the cell surface was preferentially embedded on the membrane of released virions in an HIV-1 envelope protein (Env)-independent manner and that virion-incorporated CD63 had the potential to inhibit HIV-1 Env-mediated infection in a strain-specific manner at the postattachment entry step(s). In addition, these behaviors were commonly observed in other tetraspanin proteins, such as CD9, CD81, CD82, and CD231. However, L6 protein, whose topology is similar to that of tetraspanins but which does not belong to the tetraspanin superfamily, did not have the potential to prevent HIV-1 infection, despite its successful incorporation into the released particles. Taken together, these results suggest that tetraspanin proteins have the unique potential to modulate HIV-1 infectivity through incorporation into released HIV-1 particles, and our findings may provide a clue to undiscovered aspects of HIV-1 entry.

Anti HIV-1 virucidal activity of polyamide nucleic acid-membrane transducing peptide conjugates targeted to primer binding site of HIV-1 genome

We have shown that polyamide nucleic acids (PNAs) targeted to the PBS (PNA(PBS)) and A-loop (PNA(A-loop)) sequences, when transfected into cells, inhibit HIV-1 replication by blocking the initiation of reverse transcription via destabilizing tRNA(3)(Lys) primer from the viral genome. Here we demonstrate that both PNA(PBS) and PNA(A-loop) conjugated with the membrane-transducing peptide (MTD) vectors penetratin and Tat are rapidly taken up by cells and inhibit HIV-1 replication. Moreover, MTD peptide conjugates of PNA(PBS) and PNA(A-loop) displayed potent virucidal activity against HIV-1. Brief exposure of HIV-1 virions to these conjugates rendered them noninfectious. The IC(50) values for virucidal activity were in the range of approximately 50 nM; IC(50) values for inhibition of HIV-1 replication/infection were 0.5 microM-0.7 microM. The virucidal property of these conjugates suggests that a cocktail of anti-HIV-1 PNA-MTD peptide conjugates targeting critical regions of the HIV-1 genome could serve as a prophylactic agent for inactivating HIV-1 virions after exposure to HIV-1.

Immediate activation fails to rescue efficient human immunodeficiency virus replication in quiescent CD4+ T cells

Unlike activated T cells, quiescent CD4+ T cells have shown resistance to human immunodeficiency virus (HIV) infection due to a block in the early events of the viral life cycle. To further investigate the nature of this block, we infected quiescent CD4+ T cells with HIV-1(NL4-3) and immediately stimulated them. Compared to activated (prestimulated) cells, these poststimulated cells showed slightly decreased viral entry and delays in the completion of reverse transcription. However, the relative efficiency of integration was similar to that of prestimulated cells. Together, this resulted in decreased expression of tat/rev mRNA and synthesis of viral protein. Furthermore, based on cell cycle staining and BrdU incorporation, poststimulated cells expressing viral protein failed to initiate a second round of their cell cycle, independently of Vpr-mediated arrest. Together, these data demonstrate that the early stages of the HIV life cycle are inefficient in these poststimulated cells and that efficient replication cannot be induced by subsequent activation.

Activation of the ATR pathway by human immunodeficiency virus type 1 Vpr involves its direct binding to chromatin in vivo

The human immunodeficiency virus type 1 (HIV-1) protein Vpr (viral protein R) arrests cells in the G2 phase of the cell cycle, a process that requires activation of the ATR (ataxia-telangiectasia and Rad3-related) pathway. In this study we demonstrate that the expression of Vpr does not cause DNA double-strand breaks but rather induces ATR activation, as indicated by induction of Chk1 phosphorylation and the formation of gamma-H2AX and 53BP1 nuclear foci. We define a C-terminal domain containing repeated H(F/S)RIG sequences required for Vpr-induced activation of ATR. Further investigation of the mechanism by which Vpr activates the ATR pathway reveals an increase in chromatin binding of replication protein A (RPA) upon Vpr expression. Immunostaining shows that RPA localizes to nuclear foci in Vpr-expressing cells. Furthermore, we demonstrate direct binding of Vpr to chromatin in vivo, whereas Vpr C-terminal domain mutants lose this chromatin-binding activity. These data support a mechanism whereby HIV-1 Vpr induces ATR activation by targeting the host cell DNA and probably interfering with normal DNA replication.

The cell cycle independence of HIV infections is not determined by known karyophilic viral elements

Human immunodeficiency virus and other lentiviruses infect cells independent of cell cycle progression, but gammaretroviruses, such as the murine leukemia virus (MLV) require passage of cells through mitosis. This property is thought to be important for the ability of HIV to infect resting CD4+ T cells and terminally differentiated macrophages. Multiple and independent redundant nuclear localization signals encoded by HIV have been hypothesized to facilitate migration of viral genomes into the nucleus. The integrase (IN) protein of HIV is one of the HIV elements that targets to the nucleus; however, its role in nuclear entry of virus genomes has been difficult to describe because mutations in IN are pleiotropic. To investigate the importance of the HIV IN protein for infection of non-dividing cells, and to investigate whether or not IN was redundant with other viral signals for cell cycle-independent nuclear entry, we constructed an HIV-based chimeric virus in which the entire IN protein of HIV was replaced by that of MLV. This chimeric virus with a heterologous IN was infectious at a low level, and was able to integrate in an IN-dependent manner. Furthermore, this virus infected non-dividing cells as well as it infected dividing cells. Moreover, we used the chimeric HIV with MLV IN to further eliminate all of the other described nuclear localization signals from an HIV genome—matrix, IN, Viral Protein R, and the central polypurine tract—and show that no combination of the virally encoded NLS is essential for the ability of HIV to infect non-dividing cells.

Human immunodeficiency virus can infect many cells irrespective of whether or not they are dividing, whereas some other retroviruses, such as the murine leukemia virus can only infect cells that are proliferating. This property is important for the ability of HIV to establish infections in critical cell types in infected people. Multiple and redundant signals encoded by HIV have been hypothesized to facilitate migration of viral genomes into the nucleus. However, here the authors eliminated all four described nuclear localizing signals from an HIV genome and show that no combination of these virally encoded signals is essential for the ability of HIV to infect non-dividing cells. They suggest that another step of the virus lifecycle, other than nuclear import, is the rate-limiting step that determines the cell cycle dependence/independence of retroviral infections.

Anti-HIV-1 activity of anti-TAR polyamide nucleic acid conjugated with various membrane transducing peptides

The transactivator responsive region (TAR) present in the 5′-NTR of the HIV-1 genome represents a potential target for antiretroviral intervention and a model system for the development of specific inhibitors of RNA–protein interaction. Earlier, we have shown that an anti-TAR polyamide nucleotide analog (PNA_TAR) conjugated to a membrane transducing (MTD) peptide, transportan, is efficiently taken up by the cells and displays potent antiviral and virucidal activity [B. Chaubey, S. Tripathi, S. Ganguly, D. Harris, R. A. Casale and V. N. Pandey (2005) Virology, 331, 418–428]. In the present communication, we have conjugated five different MTD peptides, penetratin, tat peptide, transportan-27, and two of its truncated derivatives, transportan-21 and transportan-22, to a 16mer PNA targeted to the TAR region of the HIV-1 genome. The individual conjugates were examined for their uptake efficiency as judged by FACScan analysis, uptake kinetics using radiolabeled conjugate, virucidal activity and antiviral efficacy assessed by inhibition of HIV-1 infection/replication. While FACScan analysis revealed concentration-dependent cellular uptake of all the PNA_TAR–peptide conjugates where uptake of the PNA_TAR–penetratin conjugate was most efficient as >90% MTD was observed within 1 min at a concentration of 200 nM. The conjugates with penetratin, transportan-21 and tat-peptides were most effective as an anti-HIV virucidal agents with IC₅₀ values in the range of 28–37 nM while IC₅₀ for inhibition of HIV-1 replication was lowest with PNA_TAR–transportan-27 (0.4 μM) followed by PNA_TAR–tat (0.72 μM) and PNA_TAR–penetratin (0.8 μM). These results indicate that anti-HIV-1 PNA conjugated with MTD peptides are not only inhibitory to HIV-1 replication in vitro but are also potent virucidal agents which render HIV-1 virions non-infectious upon brief exposure.

The ataxia telangiectasia-mutated and Rad3-related protein is dispensable for retroviral integration

Integration into the host cell DNA is an essential part of the retroviral life cycle and is required for the productive replication of a retrovirus. Retroviral integration involves cleavage of the host DNA and insertion of the viral DNA, forming an integration intermediate that contains two gaps, each with a viral 5' flap. The flaps are then removed, and the gap is filled by as yet unidentified nuclease and polymerase activities. It is thought that repair of these gaps flanking the site of retroviral integration is achieved by host DNA repair machinery. The ATM and Rad3-related protein (ATR) is a member of the phosphatidylinositol 3 kinase-related family of protein kinases that play a major role in sensing and triggering repair of DNA lesions in mammalian cells. In an effort to examine the role of ATR in retroviral integration, we used RNA interference to selectively downregulate ATR and measured integration efficiency. In addition, we examined the possible role that Vpr may play in enhancing integration and, in particular, whether activation of ATR by Vpr (Roshal et al., J. Biol. Chem. 278:25879-25886, 2003) will favor human immunodeficiency virus type 1 integration. We conclude that cells in which ATR has been depleted are competent for retroviral integration. We also conclude that the presence of Vpr as a virion-bound protein does not enhance integration of a lentivirus vector in dividing cells.

Identification of a preferred region for recombination and mutation in HIV-1 gag

We designed a cell culture-based system to test the hypothesis that recombination events during HIV-1 replication would be more frequent near the dimerization initiation sequence (DIS). A 459-bp region spanning the DIS through the 5'-end of gag was sequenced and analyzed to determine the frequency and distribution of crossover sites. We found a strong preference for recombination events occurring within a 112-nt-long region encompassing the gag AUG (64% of crossovers occurred in this region, compared to 10-14% in surrounding regions with similar lengths). Surprisingly, the region immediately surrounding the DIS was not a preferred site of recombination. Analysis of recombination events using RNA templates transcribed in vitro revealed a preference for crossover sites at the start of the gag coding region, similar to that observed in cell culture. This recombinogenic region was unusually G-rich and promoted extensive pausing by RT in vitro. Template features that induce RT pausing very likely contribute to the observed template switching events in gag during minus-strand synthesis. The region in gag that was a preferred site for recombination also had an approximately 2-fold higher mutation frequency compared to the rest of the region sequenced, but mutations were no more common in recombinant compared to non-recombinant clones, suggesting that recombination events were not mutagenic.

Focal glomerulosclerosis in proviral and c-fms transgenic mice links Vpr expression to HIV-associated nephropathy

Clinical and morphologic features of human immunodeficiency virus (HIV)-associated nephropathy (HIVAN), such as proteinuria, sclerosing glomerulopathy, tubular degeneration, and interstitial disease, have been modeled in mice bearing an HIV proviral transgene rendered noninfectious through a deletion in gag/pol. Exploring the genetic basis of HIVAN, HIV transgenic mice bearing mutations in either or both of the accessory genes nef and vpr were created. Proteinuria and focal glomerulosclerosis (FGS) only developed in mice with an intact vpr gene. Transgenic mice bearing a simplified proviral DNA (encoding only Tat and Vpr) developed renal disease characterized by FGS in which Vpr protein was localized to glomerular and tubular epithelia by immunohistochemistry. The dual transgenic progeny of HIV[Tat/Vpr] mice bred to HIV[DeltaVpr] proviral transgenic mice displayed a more severe nephropathy with no apparent increase in Vpr expression, implying that multiple viral genes contribute to HIVAN. However, the unique contribution of macrophage-specific Vpr expression in the development of glomerular disease was underscored by the induction of FGS in multiple murine lines bearing a c-fms/vpr transgene.

Effects of HIV-1 Vpr on Neuroinvasion and Neuropathogenesis

Human immunodeficiency virus type I (HIV-1) infection leads to penetration of the central nervous system (CNS) in virtually all infected individuals and HIV-1-induced encephalopathy in a significant number of untreated patients. The molecular mechanisms by which HIV-1 enters the CNS and yields CNS dysfunction are still unclear. Our laboratories and others have begun to explore the direct effects of prioritized HIV-1-specific proteins on diverse human CNS cell types. One of these proteins, the accessory HIV-1 protein Vpr, is a critical moiety in these studies, and will be discussed in this article.

Cell cycle arrest induction by an adenoviral vector expressing HIV-1 Vpr in bovine and feline cells

An accessory protein, Vpr, of human immunodeficiency virus type 1 (HIV-1) induces the cell cycle G(2)/M arrest in primate cells, but not in rodent cells, suggesting that a species-specific factor might be involved in the phenomenon. To study whether Vpr can cause G(2)/M arrest in non-primate cells, a novel adenoviral vector, Ad-VIG, co-expressing HIV-1 Vpr and green fluorescent protein (GFP) was constructed and infected on cell lines derived from various mammalian species. With its ability to express GFP, Ad-VIG enabled flow cytometric evaluation of transduction efficiency in the infected cells, and Western blot analysis showed successful expression of Vpr in the vector-transduced cells. Upon Ad-VIG infection, human HeLa, African green monkey Vero, feline CRFK, and bovine MDBK cells manifested cell cycle G(2)/M arrest. This is the first study showing that non-primate feline and bovine cells are susceptible to Vpr-induced cell cycle arrest.

Quantitative analysis of human immunodeficiency virus type 1 DNA dynamics by real-time PCR: integration efficiency in stimulated and unstimulated peripheral blood mononuclear cells

We established a set of real-time PCR assay to accurately quantify human immunodeficiency virus type 1 (HIV-1) DNA in infected cells. Using this assay we were able to measure the strong-stop, full-length/ 1-LTR circle, 2-LTR circle, and integrated forms of viral DNA, and the data provided was quite consistent with the characteristics of mutant viruses in early phase of infection. Since our assay is particularly applicable to quantify the integrated DNA in small scale of samples, we measured the level of integrated DNA in wild-type virus (WT)- or Vpr-defective virus (deltaVpr)-infected peripheral blood mononuclear cells (PBMC), and examined whether quiescent condition of the PBMC influences integration step of HIV-1. Under stimulating condition approximately 25% of total viral DNA was in integrated form in either WT- or DeltaVpr-infected cells. In contrast, under unstimulated condition the level of integration efficiency was not significantly reduced in WT-infected cells, while this efficiency was severely impaired in the absence of vpr gene. This result clearly demonstrated a crucial role of the Vpr for nuclear localization and subsequent integration of viral DNA in nondividing cells. Therefore, our assay is useful for analyzing the events in early phase of HIV-1 infection under various conditions.

PNA targeting the PBS and A-loop sequences of HIV-1 genome destabilizes packaged tRNA3(Lys) in the virions and inhibits HIV-1 replication

During assembly of the HIV-1 virions, cellular tRNA(Lys)(3) is packaged into the virion particles and is utilized as a primer for the initiation of reverse transcription. The 3'-terminal 18 nucleotides of the cellular tRNA(Lys)(3) are complementary to nucleotides 183-201 of the viral RNA genome, referred to as the primer binding sequence (PBS). Additional sequences (A-Loop) upstream of the PBS are essential for tRNA primer selection. We report here that a PNA targeted to PBS and A-Loop sequence (PNA(PBS)) exhibits high specificity for its target sequence and prevents tRNA(Lys)(3) priming on the viral genome. We also demonstrate that PNA(PBS) is able to invade the duplex region of the tRNA(Lys)(3)-viral RNA complex and destabilize the priming process, thereby inhibiting the in vitro initiation of reverse transcription. The endogenously packaged tRNA(Lys)(3) bound to the PBS region of the viral RNA genome in the HIV-1 virion is efficiently competed out by PNA(PBS), resulting in near complete inhibition of initiation of endogenous reverse transcription. Examination of the effect of PNA(PBS) on HIV-1 production in CEM cells infected with pseudotyped HIV-1 virions carrying luciferase reporter exhibited dramatic reduction of HIV-1 replication by nearly 99%. Analysis of the mechanism of PNA(PBS)-mediated inhibition indicated that PNA(PBS) interferes at the step of reverse transcription. These findings suggest the antiviral efficacy of PNA(PBS) in blocking the process of HIV-1 replication.

Inhibition of HIV-1 replication by anti-trans-activation responsive polyamide nucleotide analog

Efficient replication and gene expression of human immunodeficiency virus-1 (HIV-1) involves specific interaction of the viral protein Tat, with its trans-activation responsive element (TAR) which forms a highly stable stem-loop structure. We have earlier shown that a 15-mer polyamide nucleotide analog (PNA) targeted to the loop and bulge region of TAR blocks Tat-mediated transactivation of the HIV-1 LTR both in vitro and in cell culture (Mayhood et al., Biochemistry 39 (2000) 11532). In this communication, we have designed four anti-TAR PNAs of different length such that they either complement the entire loop and bulge region (PNA(TAR-16) and PNA(TAR-15)) or are short of few sequences in the loop (PNA(TAR-13)) or in both the loop and bulge (PNA(TAR-12)), and examined their functional efficacy in vitro as well as in HIV-1 infected cell cultures. All four anti-TAR PNAs showed strong affinity for TAR RNA, while their ability to block in vitro reverse transcription was influenced by their length. In marked contrast to PNA(TAR-12) and PNA(TAR-13), the two longer PNA(TARs) were able to efficiently sequester the targeted site on TAR RNA, thereby substantially inhibiting Tat-mediated transactivation of the HIV-1 LTR. Further, a substantial inhibition of virus production was noted with all the four anti-TAR PNA, with PNA(TAR-16) exhibiting a dramatic reduction of HIV-1 production by nearly 99%. These results point to PNA(TAR-16) as a potential anti-HIV agent.

Insights into the biology of HIV-1 viral protein R

HIV-1 viral protein R (Vpr) is a small, highly conserved accessory protein encoded by the HIV genome that serves many functions in the viral life cycle. Vpr induces G2 cell cycle arrest, which is thought to indirectly enhance viral replication by increasing transcription from the LTR. Vpr has also been implicated in facilitating infection of nondividing cells, most notably macrophages. Because Vpr is a nucleo-cytoplasmic shuttling protein, its role in enhancing viral replication in macrophages may be mediated through enhanced entry of the HIV preintegration complex through the limiting nuclear pore. Free Vpr is detectable in the serum of patients, and in vitro studies implicate extracellular forms of Vpr as an effector of cellular responses mediated through its ability to transduce through intact cytoplasmic membranes. We review the biologic properties of Vpr, focusing on its mechanism of action, role in HIV replication, and significance for host pathogenesis.

Engraftment of NOD/SCID mice with human CD34(+) cells transduced by concentrated oncoretroviral vector particles pseudotyped with the feline endogenous retrovirus (RD114) envelope protein

Oncoretrovirus vectors pseudotyped with the feline endogenous retrovirus (RD114) envelope protein produced by the FLYRD18 packaging cell line have previously been shown to transduce human hematopoietic progenitor cells with a greater efficiency than similar amphotropic envelope-pseudotyped vectors. In this report, we describe the production and efficient concentration of RD114-pseudotyped murine leukemia virus (MLV)-based vectors. Following a single round of centrifugation, vector supernatants were concentrated approximately 200-fold with a 50 to 70% yield. Concentrated vector stocks transduced prestimulated human CD34(+) (hCD34(+)) cells with approximately 69% efficiency (n = 7, standard deviation = 4.4%) using a single addition of vector at a low multiplicity of infection (MOI = 5). Introduction of transduced hCD34(+) cells into irradiated NOD/SCID recipients resulted in multilineage engraftment with long-term transgene expression. These data demonstrate that RD114-pseudotyped MLV-based vectors can be efficiently concentrated to high titers and that hCD34(+) cells transduced with concentrated vector stocks retain in vivo repopulating potential. These results highlight the potential of RD114-pseudotyped oncoretrovirus vectors for future clinical implementation in hematopoietic stem cell gene transfer.

Palmitoylation-dependent control of degradation, life span, and membrane expression of the CCR5 receptor

We have shown that the chemokine and HIV receptor CCR5 is palmitoylated on a cluster of cysteine residues located at the boundary between the seventh transmembrane region and the cytoplasmic tail. Single or combined substitutions of the three cysteines (Cys-321, Cys-323, and Cys-324) or incubation of wild-type CCR5-transfected cells with the palmitic acid analog 2-bromopalmitate prevented palmitoylation of the receptor. Moreover, failure of CCR5 to be palmitoylated resulted in both accumulation in intracellular stores and a profound decrease of membrane expression of the receptor. Upon metabolic labeling, kinetic experiments showed that the half-life of palmitoylation-deficient CCR5 is profoundly decreased. Bafilomycin A1, but not a specific proteasome inhibitor, prevented early degradation of palmitoylation-deficient CCR5 and promoted its accumulation in lysosomal compartments. Although membrane expression of the CCR5 mutant was diminished, the molecules reaching the membrane were still able to interact efficiently with the chemokine ligand MIP1 beta and remained able to function as HIV co-receptors. Thus we conclude that palmitoylation controls CCR5 expression through regulation of the life span of this receptor.

Comparison of cell cycle arrest, transactivation, and apoptosis induced by the simian immunodeficiency virus SIVagm and human immunodeficiency virus type 1 vpr genes

All primate lentiviruses known to date contain one or two open reading frames with homology to the human immunodeficiency virus type 1 (HIV-1) vpr gene. HIV-1 vpr encodes a 96-amino-acid protein with multiple functions in the viral life cycle. These functions include modulation of the viral replication kinetics, transactivation of the long terminal repeat, participation in the nuclear import of preintegration complexes, induction of G2 arrest, and induction of apoptosis. The simian immunodeficiency virus (SIV) that infects African green monkeys (SIVagm) contains a vpr homologue, which encodes a 118-amino-acid protein. SIVagm vpr is structurally and functionally related to HIV-1 vpr. The present study focuses on how three specific functions (transactivation, induction of G2 arrest, and induction of apoptosis) are related to one another at a functional level, for HIV-1 and SIVagm vpr. While our study supports previous reports demonstrating a causal relationship between induction of G2 arrest and transactivation for HIV-1 vpr, we demonstrate that the same is not true for SIVagm vpr. Transactivation by SIVagm vpr is independent of cell cycle perturbation. In addition, we show that induction of G2 arrest is necessary for the induction of apoptosis by HIV-1 vpr but that the induction of apoptosis by SIVagm vpr is cell cycle independent. Finally, while SIVagm vpr retains its transactivation function in human cells, it is unable to induce G2 arrest or apoptosis in such cells, suggesting that the cytopathic effects of SIVagm vpr are species specific. Taken together, our results suggest that while the multiple functions of vpr are conserved between HIV-1 and SIVagm, the mechanisms leading to the execution of such functions are divergent.

Establishment of latent HIV-1 infection of resting CD4(+) T lymphocytes does not require inactivation of Vpr

The introduction of highly active antiretroviral therapy (HAART) for the treatment of HIV-1 infection has allowed dramatic reductions in plasma virus levels to below the limit of detection in many patients. However, latently infected CD4(+) memory T lymphocytes persist as an important reservoir for the virus in the presence of this aggressive therapy and represent a major barrier to HIV-1 eradication with HAART. The mechanism through which the latent compartment is formed has not yet been established. It may involve actively proliferating CD4(+) T-cell intermediates that are infected with HIV-1 and revert back to a resting state, carrying integrated provirus at some low frequency. The HIV-1 accessory protein Vpr, which mediates G(2) cell cycle arrest in host cells, may interfere with the formation of the latently infected T cells by preventing them from exiting the cell cycle to return to a resting state. To investigate the role of the Vpr in the formation of latently infected memory T cells, we cloned and characterized vpr genes from viruses in the latent reservoir. Both sequence analysis and functional assays demonstrated that the vpr gene products of the viruses isolated from the latent pool did not differ significantly from those of a functional Vpr (NL4-3). These results indicate that the generation of resting G(0) memory T lymphocytes that carry latent HIV-1 provirus occurs despite the G(2) arrest function of the vpr gene product.