HIV-1 Rev protein specifies the viral RNA export pathway by suppressing TAP/NXF1 recruitment

Interferon-Regulated Expression of Cellular Splicing Factors Modulates Multiple Levels of HIV-1 Gene Expression and Replication

Type I interferons (IFN-Is) are pivotal in innate immunity against human immunodeficiency virus I (HIV-1) by eliciting the expression of IFN-stimulated genes (ISGs), which encompass potent host restriction factors. While ISGs restrict the viral replication within the host cell by targeting various stages of the viral life cycle, the lesser-known IFN-repressed genes (IRepGs), including RNA-binding proteins (RBPs), affect the viral replication by altering the expression of the host dependency factors that are essential for efficient HIV-1 gene expression. Both the host restriction and dependency factors determine the viral replication efficiency; however, the understanding of the IRepGs implicated in HIV-1 infection remains greatly limited at present. This review provides a comprehensive overview of the current understanding regarding the impact of the RNA-binding protein families, specifically the two families of splicing-associated proteins SRSF and hnRNP, on HIV-1 gene expression and viral replication. Since the recent findings show specifically that SRSF1 and hnRNP A0 are regulated by IFN-I in various cell lines and primary cells, including intestinal lamina propria mononuclear cells (LPMCs) and peripheral blood mononuclear cells (PBMCs), we particularly discuss their role in the context of the innate immunity affecting HIV-1 replication.

Limited nucleotide changes of HIV-1 subtype B Rev response element in China affect overall Rev-RRE activity and viral replication

The HIV-1 Rev response element (RRE) is a cis-acting RNA element that facilitates the nuclear export of mRNA-containing introns by binding specifically to the Rev protein, enabling a critical step in the viral replication cycle. This study aims to determine the subtype-specific loci of HIV-1 subtype B RRE circulating in China and to analyze their effects on Rev-RRE function and HIV-1 replication. We amplified 71 HIV-1 subtype B RRE full-length sequences from the HIV patients' blood samples collected in China, analyzed the subtype-specific loci on them by comparing them with subtype B in the United States, and predicted their RNA secondary structures. Rev-RRE activity assay was used to test the binding activity of Rev and different RREs. Infectious clones were mutated to test the effect of the subtype-specific loci on replication capacity. In this study, two sites were determined to be the subtype-specific loci of HIV-1 subtype B RRE circulating in China. Both site 186 and site 56-57insAAC can significantly increase the viral mRNA transcription and Rev-RRE activity, but only the site 186 can significantly improve viral replication ability. Collectively, the subtype-specific loci of subtype B RRE circulating in China have a significant effect on the Rev-RRE activity and viral replication. This study investigates the subtype-specific loci of RRE, which are unique to retroviruses and essential for viral replication, and will help to explore the reasons why subtype B circulating in China is more widespread and persistent than American subtype B in China at the genetic level, and will provide theoretical support for the development of more inclusive detection and treatment methods for subtype B circulating in China. At the same time, it will also provide insight into the impact of different subtype HIV-1 genetic characteristics on viral replication.

Tuning Rex rules HTLV-1 pathogenesis

HTLV-1 is an oncovirus causing ATL and other inflammatory diseases such as HAM/TSP and HU in about 5% of infected individuals. It is also known that HTLV-1-infected cells maintain a disease-free, immortalized, latent state throughout the lifetimes of about 95% of infected individuals. We believe that the stable maintenance of disease-free infected cells in the carrier is an intrinsic characteristic of HTLV-1 that has been acquired during its evolution in the human life cycle. We speculate that the pathogenesis of the virus is ruled by the orchestrated functions of viral proteins. In particular, the regulation of Rex, the conductor of viral replication rate, is expected to be closely related to the viral program in the early active viral replication followed by the stable latency in HTLV-1 infected T cells. HTLV-1 and HIV-1 belong to the family Retroviridae and share the same tropism, e.g., human CD4⁺ T cells. These viruses show significant similarities in the viral genomic structure and the molecular mechanism of the replication cycle. However, HTLV-1 and HIV-1 infected T cells show different phenotypes, especially in the level of virion production. We speculate that how the activity of HTLV-1 Rex and its counterpart HIV-1 Rev are regulated may be closely related to the properties of respective infected T cells. In this review, we compare various pathological aspects of HTLV-1 and HIV-1. In particular, we investigated the presence or absence of a virally encoded “regulatory valve” for HTLV-1 Rex or HIV-1 Rev to explore its importance in the regulation of viral particle production in infected T cells. Finally, wereaffirm Rex as the key conductor for viral replication and viral pathogenesis based on our recent study on the novel functional aspects of Rex. Since the activity of Rex is closely related to the viral replication rate, we hypothesize that the “regulatory valve” on the Rex activity may have been selectively evolved to achieve the “scenario” with early viral particle production and the subsequent long, stable deep latency in HTLV-1 infected cells.

DEAD-ly Affairs: The Roles of DEAD-Box Proteins on HIV-1 Viral RNA Metabolism

In order to ensure viral gene expression, Human Immunodeficiency virus type-1 (HIV-1) recruits numerous host proteins that promote optimal RNA metabolism of the HIV-1 viral RNAs (vRNAs), such as the proteins of the DEAD-box family. The DEAD-box family of RNA helicases regulates multiple steps of RNA metabolism and processing, including transcription, splicing, nucleocytoplasmic export, trafficking, translation and turnover, mediated by their ATP-dependent RNA unwinding ability. In this review, we provide an overview of the functions and role of all DEAD-box family protein members thus far described to influence various aspects of HIV-1 vRNA metabolism. We describe the molecular mechanisms by which HIV-1 hijacks these host proteins to promote its gene expression and we discuss the implications of these interactions during viral infection, their possible roles in the maintenance of viral latency and in inducing cell death. We also speculate on the emerging potential of pharmacological inhibitors of DEAD-box proteins as novel therapeutics to control the HIV-1 pandemic.

Let It Go: HIV-1 cis-Acting Repressive Sequences

After human immunodeficiency virus type 1 (HIV-1) was identified in the early 1980s, intensive work began to understand the molecular basis of HIV-1 gene expression. Subgenomic HIV-1 RNA regions, spread throughout the viral genome, were described to have a negative impact on the nuclear export of some viral transcripts. Those studies revealed an intrinsic RNA code as a new form of nuclear export regulation. Since such regulatory regions were later also identified in other viruses, as well as in cellular genes, it can be assumed that, during evolution, viruses took advantage of them to achieve more sophisticated replication mechanisms. Here, we review HIV-1 cis-acting repressive sequences that have been identified, and we discuss their possible underlying mechanisms and importance. Additionally, we show how current bioinformatic tools might allow more predictive approaches to identify and investigate them.

How SARS-CoV-2 and Other Viruses Build an Invasion Route to Hijack the Host Nucleocytoplasmic Trafficking System

The host nucleocytoplasmic trafficking system is often hijacked by viruses to accomplish their replication and to suppress the host immune response. Viruses encode many factors that interact with the host nuclear transport receptors (NTRs) and the nucleoporins of the nuclear pore complex (NPC) to access the host nucleus. In this review, we discuss the viral factors and the host factors involved in the nuclear import and export of viral components. As nucleocytoplasmic shuttling is vital for the replication of many viruses, we also review several drugs that target the host nuclear transport machinery and discuss their feasibility for use in antiviral treatment.

CRNKL1 Is a Highly Selective Regulator of Intron-Retaining HIV-1 and Cellular mRNAs

The HIV-1 Rev protein is a nuclear export factor for unspliced and incompletely spliced HIV-1 RNAs. Without Rev, these intron-retaining RNAs are trapped in the nucleus. A genome-wide screen identified nine proteins of the spliceosome, which all enhanced expression from the HIV-1 unspliced RNA after CRISPR/Cas knockdown. Depletion of DHX38, WDR70, and four proteins of the Prp19-associated complex (ISY1, BUD31, XAB2, and CRNKL1) resulted in a more than 20-fold enhancement of unspliced HIV-1 RNA levels in the cytoplasm. Targeting of CRNKL1, DHX38, and BUD31 affected nuclear export efficiencies of the HIV-1 unspliced RNA to a much larger extent than splicing. Transcriptomic analyses further revealed that CRNKL1 also suppresses cytoplasmic levels of a subset of cellular mRNAs, including some with selectively retained introns. Thus, CRNKL1-dependent nuclear retention is a novel cellular mechanism for the regulation of cytoplasmic levels of intron-retaining HIV-1 mRNAs, which HIV-1 may have harnessed to direct its complex splicing pattern.IMPORTANCE To regulate its complex splicing pattern, HIV-1 uses the adaptor protein Rev to shuttle unspliced or partially spliced mRNA from the nucleus to the cytoplasm. In the absence of Rev, these RNAs are retained in the nucleus, but it is unclear why. Here we identify cellular proteins whose depletion enhances cytoplasmic levels of the HIV-1 unspliced RNA. Depletion of one of them, CRNKL1, also increases cytoplasmic levels of a subset of intron-retaining cellular mRNA, suggesting that CRNKL1-dependent nuclear retention may be a basic cellular mechanism exploited by HIV-1.

HIV Rev-isited

The human immunodeficiency virus type 1 (HIV-1) proteome is expressed from alternatively spliced and unspliced genomic RNAs. However, HIV-1 RNAs that are not fully spliced are perceived by the host machinery as defective and are retained in the nucleus. During late infection, HIV-1 bypasses this regulatory mechanism by expression of the Rev protein from a fully spliced mRNA. Once imported into the nucleus, Rev mediates the export of unprocessed HIV-1 RNAs to the cytoplasm, leading to the production of the viral progeny. While regarded as a canonical RNA export factor, Rev has also been linked to HIV-1 RNA translation, stabilization, splicing and packaging. However, Rev's functions beyond RNA export have remained poorly understood. Here, we revisit this paradigmatic protein, reviewing recent data investigating its structure and function. We conclude by asking: what remains unknown about this enigmatic viral protein?

HIV-1 Gag Forms Ribonucleoprotein Complexes with Unspliced Viral RNA at Transcription Sites

The ability of the retroviral Gag protein of Rous sarcoma virus (RSV) to transiently traffic through the nucleus is well-established and has been implicated in genomic RNA (gRNA) packaging Although other retroviral Gag proteins (human immunodeficiency virus type 1, HIV-1; feline immunodeficiency virus, FIV; Mason-Pfizer monkey virus, MPMV; mouse mammary tumor virus, MMTV; murine leukemia virus, MLV; and prototype foamy virus, PFV) have also been observed in the nucleus, little is known about what, if any, role nuclear trafficking plays in those viruses. In the case of HIV-1, the Gag protein interacts in nucleoli with the regulatory protein Rev, which facilitates nuclear export of gRNA. Based on the knowledge that RSV Gag forms viral ribonucleoprotein (RNPs) complexes with unspliced viral RNA (USvRNA) in the nucleus, we hypothesized that the interaction of HIV-1 Gag with Rev could be mediated through vRNA to form HIV-1 RNPs. Using inducible HIV-1 proviral constructs, we visualized HIV-1 Gag and USvRNA in discrete foci in the nuclei of HeLa cells by confocal microscopy. Two-dimensional co-localization and RNA-immunoprecipitation of fractionated cells revealed that interaction of nuclear HIV-1 Gag with USvRNA was specific. Interestingly, treatment of cells with transcription inhibitors reduced the number of HIV-1 Gag and USvRNA nuclear foci, yet resulted in an increase in the degree of Gag co-localization with USvRNA, suggesting that Gag accumulates on newly synthesized viral transcripts. Three-dimensional imaging analysis revealed that HIV-1 Gag localized to the perichromatin space and associated with USvRNA and Rev in a tripartite RNP complex. To examine a more biologically relevant cell, latently infected CD4+ T cells were treated with prostratin to stimulate NF-κB mediated transcription, demonstrating striking localization of full-length Gag at HIV-1 transcriptional burst site, which was labelled with USvRNA-specific riboprobes. In addition, smaller HIV-1 RNPs were observed in the nuclei of these cells. These data suggest that HIV-1 Gag binds to unspliced viral transcripts produced at the proviral integration site, forming vRNPs in the nucleus.

Comparative transcriptome analysis of the human endocervix and ectocervix during the proliferative and secretory phases of the menstrual cycle

Despite extensive studies suggesting increased susceptibility to HIV during the secretory phase of the menstrual cycle, the molecular mechanisms involved remain unclear. Our goal was to analyze transcriptomes of the endocervix and ectocervix during the proliferative and secretory phases using RNA sequencing to explore potential molecular signatures of susceptibility to HIV. We identified 202 differentially expressed genes (DEGs) between the proliferative and secretory phases of the cycle in the endocervix (adjusted p < 0.05). The biofunctions and pathways analysis of DEGs revealed that cellular assembly and epithelial barrier function in the proliferative phase and inflammatory response/cellular movement in the secretory phase were among the top biofunctions and pathways. The gene set enrichment analysis of ranked DEGs (score = log fold change/p value) in the endocervix and ectocervix revealed that (i) unstimulated/not activated immune cells gene sets positively correlated with the proliferative phase and negatively correlated with the secretory phase in both tissues, (ii) IFNγ and IFNα response gene sets positively correlated with the proliferative phase in the ectocervix, (iii) HIV restrictive Wnt/β-catenin signaling pathway negatively correlated with the secretory phase in the endocervix. Our data show menstrual cycle phase-associated changes in both endocervix and ectocervix, which may modulate susceptibility to HIV.

A Rev-CBP80-eIF4AI complex drives Gag synthesis from the HIV-1 unspliced mRNA

Gag synthesis from the full-length unspliced mRNA is critical for the production of the viral progeny during human immunodeficiency virus type-1 (HIV-1) replication. While most spliced mRNAs follow the canonical gene expression pathway in which the recruitment of the nuclear cap-binding complex (CBC) and the exon junction complex (EJC) largely stimulates the rates of nuclear export and translation, the unspliced mRNA relies on the viral protein Rev to reach the cytoplasm and recruit the host translational machinery. Here, we confirm that Rev ensures high levels of Gag synthesis by driving nuclear export and translation of the unspliced mRNA. These functions of Rev are supported by the CBC subunit CBP80, which binds Rev and the unspliced mRNA in the nucleus and the cytoplasm. We also demonstrate that Rev interacts with the DEAD-box RNA helicase eIF4AI, which translocates to the nucleus and cooperates with the viral protein to promote Gag synthesis. Finally, we show that the Rev/RRE axis is important for the assembly of a CBP80-eIF4AI complex onto the unspliced mRNA. Together, our results provide further evidence towards the understanding of the molecular mechanisms by which Rev drives Gag synthesis from the unspliced mRNA during HIV-1 replication.

A small-molecule inhibitor of HIV-1 Rev function detected by a diversity screen based on RRE-Rev interference

The Rev protein of HIV-1 binds to the Rev Recognition Element (RRE) in the virus RNA to promote nuclear export of unspliced and partially spliced transcripts, an essential step in the virus transmission cycle. Here, we describe the screening of a library of chemically diverse compounds with an assay based on monitoring the interaction between the RNA-binding α-helix of Rev and its high-affinity binding site in the RRE. This screen allowed the identification of a benzofluorenone compound that inhibited the formation of the full-length RRE-Rev ribonucleoprotein by associating to the RRE, and blocked HIV-1 transcription and Rev action in cells. This molecule, previously studied as a cytostatic agent, had substantial antiretroviral activity. Together with other screening hits, it provides a new chemical scaffold for the development of antiretroviral agents based on blockage of HIV-1 RNA biogenesis.

Multiple nuclear-replicating viruses require the stress-induced protein ZC3H11A for efficient growth

There is a strong need for the development of new antiviral therapies, and this study sheds light on a host–virus interaction that is significant for a number of medically important human viruses. The study also suggests that the RNA-binding zinc finger CCCH-type containing 11A (ZC3H11A) protein takes part in a mechanism that facilitates nuclear export of mRNA, particularly under cellular stress, a mechanism that has been “hijacked” by several nuclear-replicating viruses to promote their replication. ZC3H11A is therefore a potential target for development of an antiviral therapy.

The zinc finger CCCH-type containing 11A (ZC3H11A) gene encodes a well-conserved zinc finger protein that may function in mRNA export as it has been shown to associate with the transcription export (TREX) complex in proteomic screens. Here, we report that ZC3H11A is a stress-induced nuclear protein with RNA-binding capacity that localizes to nuclear splicing speckles. During an adenovirus infection, the ZC3H11A protein and splicing factor SRSF2 relocalize to nuclear regions where viral DNA replication and transcription take place. Knockout (KO) of ZC3H11A in HeLa cells demonstrated that several nuclear-replicating viruses are dependent on ZC3H11A for efficient growth (HIV, influenza virus, herpes simplex virus, and adenovirus), whereas cytoplasmic replicating viruses are not (vaccinia virus and Semliki Forest virus). High-throughput sequencing of ZC3H11A–cross-linked RNA showed that ZC3H11A binds to short purine-rich ribonucleotide stretches in cellular and adenoviral transcripts. We show that the RNA-binding property of ZC3H11A is crucial for its function and localization. In ZC3H11A KO cells, the adenovirus fiber mRNA accumulates in the cell nucleus. Our results suggest that ZC3H11A is important for maintaining nuclear export of mRNAs during stress and that several nuclear-replicating viruses take advantage of this mechanism to facilitate their replication.

Immunoinformatics approaches to design a novel multi-epitope subunit vaccine against HIV infection

The end goal of HIV vaccine designing requires novel strategies to elicit a strong humoral and cell-mediated immune response. The emergence of drug resistance and the requirement of next line treatment necessitate the finding of the potential and immunogenic vaccine candidate. This study employed a novel immunoinformatics approach to design multi-epitope subunit vaccine against HIV infection. Here, we designed the subunit vaccine by the combination of CTL, HTL and BCL epitopes along with suitable adjuvant and linkers. Physiochemical characterization of subunit vaccine was assessed to ensure its thermostability, theoretical PI, and amphipathic behavior. In further assessment, subunit vaccine was found to be immunogenic with the capability to generate humoral and cell-mediated immune response. Further, homology modeling and refinement was performed and the refined modeled structure was used for molecular docking with the immune receptor (TLR-3) present on lymphocyte cells. Consequently, molecular dynamics simulation ensured the molecular interaction between TLR-3 and subunit vaccine candidate. Disulfide engineering was performed by placing the cysteine residues in the region of high mobility to enhance the vaccine stability. At last, in silico cloning was performed to warrant the translational efficiency and microbial expression of the designed vaccine.

Pharmacokinetics and tolerability of ABX464, a novel first-in-class compound to treat HIV infection, in healthy HIV-uninfected subjects

Background

An anti-HIV compound (ABX464) has been developed with a novel mechanism of activity in that it blocks viral gene expression in cells that are already infected.

Objectives

A first-in-man study was conducted to determine the pharmacokinetic and safety profiles of ABX464. This was carried out as an open label, parallel group, single ascending dose, exploratory study.

Methods

Twenty-four male subjects in good health without HIV infection, aged from 18 to 55 years old, with BMIs of 18-27 kg/m 2 were included. A single oral dose of ABX464 (50, 100, 150 or 200 mg) was administered on the morning of day 0 after overnight fasting, with follow-up for 45 days. Safety assessments consisted of vital signs, electrocardiogram, physical examination, laboratory tests and urinalysis. Pharmacokinetic parameters were calculated for ABX464 and its main metabolite ABX-464- N -glucuronide (ABX464-NGlc). The study was registered at https://www.clinicaltrials (trial number NCT02792686).

Results

ABX464 was well tolerated; the most frequent related treatment-emergent adverse events were headaches, nausea and vomiting; they were not considered as treatment-limiting effects. ABX464's C max was observed approximately 2 h after administration in all groups. ABX464 was rapidly and substantially metabolized into ABX464-NGlc. The C max of ABX464-NGlc was observed approximately 4 h post-dose and was about 160-fold higher than that of the parent with a much longer t 1/2 (90-110 h). The ratio of metabolite to parent drug was consistent across the complete dose range.

Conclusions

These studies confirmed that ABX464 is well tolerated and rapidly and substantially metabolized into ABX464-NGlc in human subjects.

Safety, Pharmacokinetics, and Antiviral Activity of a Novel HIV Antiviral, ABX464, in Treatment-Naive HIV-Infected Subjects in a Phase 2 Randomized, Controlled Study

We investigated the safety and antiviral effects of an anti-HIV compound (ABX464) with a unique mechanism of viral replication inhibition. This was a randomized, double-blind, placebo-controlled, dose-ranging study in treatment-naive HIV-infected patients. Participants were assigned to eight groups; each group included eight subjects receiving either the study compound, ABX464 (n = 6), or the corresponding placebo (n = 2), according to a randomization code. The first dose administered was 25 mg, given once or 3 times a day over a 2- to 3-week period. Ascending doses of up to 150 mg were delivered after review of the safety data. The primary objective of the study was to assess the safety and tolerability of ABX464 after repeated oral administrations in subjects infected by HIV. Sixty-six subjects were enrolled and were randomized. Sixty-three subjects completed the study according to the study protocol. Twenty-one adverse events (AEs) were reported by 7 subjects out of 16 (44%) who received placebo, and 158 AEs were reported by 39 subjects out of 50 (78%) who received the study drug. In the ABX464 treatment group, all of these adverse events were mild to moderate. No subjects discontinued treatment due to drug-related AEs. Administration of ABX464 at up to 150 mg once a day was safe and well tolerated in HIV-infected subjects. An efficacy signal with respect to a reduction of the viral load by ABX464 was detected, mainly in subjects treated at the highest dose. Further studies will be required to demonstrate antiviral effects in HIV-infected subjects in combination with other antiretroviral therapies. (This study is registered on the ClinicalTrials.gov website under registration no. NCT02452242.)

Randomized Trial of Food Effect on Pharmacokinetic Parameters of ABX464 Administered Orally to Healthy Male Subjects

ABX464 is an antiviral that provides a novel approach to the reduction and control of HIV infection. Investigation of food influence is important in the optimization of treatment. An open-label, food effect, randomized study which included 2 groups of 24 subjects each was carried out to assess the bioavailability and safety of single (group 1) and repeated (group 2) oral doses of ABX464 (50 mg) under fed or fasted conditions. The maximum concentration (Cmax) and the area under the concentration-time curve from time zero to infinity (AUC0-∞) of ABX464 were demonstrated to increase with food after a single dose of ABX464 (219% and 188%, respectively). The apparent terminal elimination half-lives (t1/2s) under fed and fasted conditions were comparable, at about 0.80 h. The median time to maximum concentration (Tmax) was delayed from 1.5 to 2.8 h, and the ratio of the AUC0-∞ obtained under fed conditions to the AUC0-∞ obtained under fasted conditions (Frel) was 2.69. Comparable results were obtained on day 1 and day 10 in group 2. The increases in Cmax and AUC0-∞ of the metabolite ABX464-N-glucuronide (ABX464-NGlc) were, however, much more limited when ABX464 was given with food. The t1/2s were also comparable under the two conditions (around 100 h). Between day 1 and day 10, the Cmax increased by 5% under the fasted condition and by 25% under the fed condition. The most common related treatment-emergent adverse events were headaches, vomiting, and nausea. It was concluded that food has a significant impact on the levels of ABX464 in plasma with a delay in absorption and increased relative bioavailability, with a lesser impact on its biotransformation into ABX464-NGlc. ABX464 was well tolerated under both fasted and fed conditions. (This study has been registered at ClinicalTrials.gov under registration no. NCT02731885.).

Viral interactions with components of the splicing machinery

Eukaryotic genes are often interrupted by stretches of sequence with no protein coding potential or obvious function. After transcription, these interrupting sequences must be removed to give rise to the mature messenger RNA. This fundamental process is called RNA splicing and is achieved by complicated machinery made of protein and RNA that assembles around the RNA to be edited. Viruses also use RNA splicing to maximize their coding potential and economize on genetic space, and use clever strategies to manipulate the splicing machinery to their advantage. This article gives an overview of the splicing process and provides examples of viral strategies that make use of various components of the splicing system to promote their replicative cycle. Representative virus families have been selected to illustrate the interaction with various regulatory proteins and ribonucleoproteins. The unifying theme is fine regulation through protein-protein and protein-RNA interactions with the spliceosome components and associated factors to promote or prevent spliceosome assembly on given splice sites, in addition to a strong influence from cis-regulatory sequences on viral transcripts. Because there is an intimate coupling of splicing with the processes that direct mRNA biogenesis, a description of how these viruses couple the regulation of splicing with the retention or stability of mRNAs is also included. It seems that a unique balance of suppression and activation of splicing and nuclear export works optimally for each family of viruses.

Rescue of dnapol-null Autographa californica multiple nucleopolyhedrovirus with DNA polymerase (DNApol) of Spodoptera litura nucleopolyhedrovirus (SpltNPV) and identification of a nuclear localization signal in SpltNPV DNApol

DNA polymerase (DNApol) is highly conserved in all baculoviruses and plays an essential role in viral DNA replication. It determines the fidelity of baculovirus DNA replication by inserting the correct nucleotides into the primer terminus and proofreading any mispaired nucleotides. DNApols of groups I and II of the genus Alphabaculovirus in the family Baculoviridae share many common structural features. However, it is not clear whether a group I Autographa californica multiple nucleopolyhedrovirus (AcMNPV) DNApol can be substituted by a group II NPV DNApol. Here we report the successful generation of AcMNPV dnapol-null virus being rescued by a group II Spodoptera litura NPV (SpltNPV) dnapol (Bac-AcΔPol : Slpol). Viral growth curves and quantitative real-time PCR showed that the dnapol replacement reduced the level of viral production and DNA replication of Bac-AcΔPol : SlPol compared with WTrep, a native dnapol insertion in an AcMNPV dnapol-null virus. Light microscopy showed that production of occlusion bodies for Bac-AcΔPol : Slpol was reduced. We also identified a nuclear localization signal (NLS) for the SpltNPV DNApol C terminus at residues 827-838 by mutational analysis and confocal microscopy. Multiple point substitution of SpltNPV DNApol NLS abrogated virus production and viral DNA replication. Overall, these data suggested that the NLS plays an important role in SpltNPV DNApol nuclear localization and that SpltNPV DNApol cannot efficiently substitute the AcMNPV DNApol in AcMNPV.

Translational Control of the HIV Unspliced Genomic RNA

Post-transcriptional control in both HIV-1 and HIV-2 is a highly regulated process that commences in the nucleus of the host infected cell and finishes by the expression of viral proteins in the cytoplasm. Expression of the unspliced genomic RNA is particularly controlled at the level of RNA splicing, export, and translation. It appears increasingly obvious that all these steps are interconnected and they result in the building of a viral ribonucleoprotein complex (RNP) that must be efficiently translated in the cytosolic compartment. This review summarizes our knowledge about the genesis, localization, and expression of this viral RNP.

ABX464: a good drug candidate instead of a magic bullet

Despite the significant number of antiviral drugs that are currently available in the clinics of developed countries, none of these affect the production stage of HIV-1 replication, more specifically the process of viral gene expression. For instance, several early attempts failed to generate inhibitors of the viral Tat protein, the small activator of viral transcription from the long terminal repeat (LTR) promoter. A recent study published in Retrovirology by Campos et al. presents a new small molecule inhibitor, ABX464, that targets the other small viral protein essential for viral gene expression, the Rev protein (Retrovirology 12:30, 2015). Targeting of multiple virus replication steps and silencing the generation of new progeny may be of particular value for current attempts to develop novel therapeutic strategies that provide a cure or functional cure for HIV-1 infection (Nat Rev Immunol 12: 607–614, 2012). We will briefly review some of the unique antiviral properties of ABX464, with the focus on its surprising ability to exhibit a sustained antiviral effect in a humanized mouse model. Although ABX464 may remain an important new addition to the anti-HIV arsenal, we do present a sobering alternative explanation for the long-lasting reduction in viral load after treatment cessation.

Long lasting control of viral rebound with a new drug ABX464 targeting Rev - mediated viral RNA biogenesis

BACKGROUND

Current therapies have succeeded in controlling AIDS pandemic. However, there is a continuing need for new drugs, in particular those acting through new and as yet unexplored mechanisms of action to achieve HIV infection cure. We took advantage of the unique feature of proviral genome to require both activation and inhibition of splicing of viral transcripts to develop molecules capable of achieving long lasting effect on viral replication in humanized mouse models through inhibition of Rev-mediated viral RNA biogenesis.

RESULTS

Current HIV therapies reduce viral load during treatment but titers rebound after treatment is discontinued. We devised a new drug that has a long lasting effect after viral load reduction. We demonstrate here that ABX464 compromises HIV replication of clinical isolates of different subtypes without selecting for drug resistance in PBMCs or macrophages. ABX464 alone, also efficiently compromised viral proliferation in two humanized mouse models infected with HIV that require a combination of 3TC, Raltegravir and Tenofovir (HAART) to achieve viral inhibition in current protocols. Crucially, while viral load increased dramatically just one week after stopping HAART treatment, only slight rebound was observed following treatment cessation with ABX464 and the magnitude of the rebound was maintained below to that of HAART for two months after stopping the treatment. Using a system to visualize single HIV RNA molecules in living cells, we show that ABX464 inhibits viral replication by preventing Rev-mediated export of unspliced HIV-1 transcripts to the cytoplasm and by interacting with the Cap Binding Complex (CBC). Deep sequencing of viral RNA from treated cells established that retained viral RNA is massively spliced but importantly, normal cellular splicing is unaffected by the drug. Consistently ABX464 is non-toxic in humans and therefore represents a promising complement to current HIV therapies.

CONCLUSIONS

ABX464 represents a novel class of anti-HIV molecules with unique properties. ABX464 has a long lasting effect in humanized mice and neutralizes the expression of HIV-1 proviral genome of infected immune cells including reservoirs and it is therefore a promising drug toward a functional cure of HIV.

RNA Export through the NPC in Eukaryotes

In eukaryotic cells, RNAs are transcribed in the nucleus and exported to the cytoplasm through the nuclear pore complex. The RNA molecules that are exported from the nucleus into the cytoplasm include messenger RNAs (mRNAs), ribosomal RNAs (rRNAs), transfer RNAs (tRNAs), small nuclear RNAs (snRNAs), micro RNAs (miRNAs), and viral mRNAs. Each RNA is transported by a specific nuclear export receptor. It is believed that most of the mRNAs are exported by Nxf1 (Mex67 in yeast), whereas rRNAs, snRNAs, and a certain subset of mRNAs are exported in a Crm1/Xpo1-dependent manner. tRNAs and miRNAs are exported by Xpot and Xpo5. However, multiple export receptors are involved in the export of some RNAs, such as 60S ribosomal subunit. In addition to these export receptors, some adapter proteins are required to export RNAs. The RNA export system of eukaryotic cells is also used by several types of RNA virus that depend on the machineries of the host cell in the nucleus for replication of their genome, therefore this review describes the RNA export system of two representative viruses. We also discuss the NPC anchoring-dependent mRNA export factors that directly recruit specific genes to the NPC.