HibeRNAtion: HIV-1 RNA Metabolism and Viral Latency

HIV-1 infection remains non-curative due to the latent reservoir, primarily a small pool of resting memory CD4+ T cells bearing replication-competent provirus. Pharmacological reversal of HIV-1 latency followed by intrinsic or extrinsic cell killing has been proposed as a promising strategy to target and eliminate HIV-1 viral reservoirs. Latency reversing agents have been extensively studied for their role in reactivating HIV-1 transcription in vivo, although no permanent reduction of the viral reservoir has been observed thus far. This is partly due to the complex nature of latency, which involves strict intrinsic regulation at multiple levels at transcription and RNA processing. Still, the molecular mechanisms that control HIV-1 latency establishment and maintenance have been almost exclusively studied in the context of chromatin remodeling, transcription initiation and elongation and most known LRAs target LTR-driven transcription by manipulating these. RNA metabolism is a largely understudies but critical mechanistic step in HIV-1 gene expression and latency. In this review we provide an update on current knowledge on the role of RNA processing mechanisms in viral gene expression and latency and speculate on the possible manipulation of these pathways as a therapeutic target for future cure studies.

An insight on promising strategies hoping to cure HIV-1 infection by targeting Rev protein-short review

Human immunodeficiency virus-1 (HIV-1) infection remains to be one of the major threats throughout the world. Many researchers are working in this area to find a cure for HIV-1. The group of the FDA approved drugs which are currently used against HIV-1 in the clinical practice include nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), integrase inhibitors (InIs), and protease inhibitors (PIs). Fixed dose combinations (FDCs) of these drugs are available and are used as per the anti-retroviral therapy (ART) guidelines. Despite these, unfortunately, there is no cure for HIV1 infection to date. The present review is focused upon describing the importance of a post-transcriptional regulatory protein "Rev", responsible for latent HIV-1 infection as a possible, and promising therapeutic target against HIV-1.

Interaction of prion protein mRNA with CBP35 and other cellular proteins Possible implications for prion replication and age-dependent changes

A study of the intracellular distribution of prion protein (PrP) in N2a neuroblastoma cells which had been infected with prions (ScN2a cells) revealed that most PrP is present in the cytoplasm. However, a significant amount of PrP is also present in the nucleus (predominantly in the nucleoli) of these cells, as analyzed by confocal laser scanning microscopy. By contrast, no PrP could be detected in the nucleus of uninfected N2a cells. The steady-state level of PrP mRNA did not markedly differ between the two cell strains. Likewise, no changes were found in the rate of transcription and in the half-life of PrP mRNA. A number of cellular proteins, among them the nuclear lectin CBP35, was identified that bound to the predicted RNA stem-loop structure of PrP RNA. CBP35 could also be detected in purified infections prions, suggesting a possible role in prion replication. Age-dependent studies revealed that the content of normal cellular PrP (PrPC) in brain extracts of rats did not change significantly during ageing, while the level of certain proteins that associate with PrPC mRNA decreases with age. In addition, we show that rat cortical cells when challenged with infectious PrP (PrPSc) undergo cell death (apoptosis) in vitro. This deleterious effect was prevented by memantine (1-amino-3,5-dimethyladamantane) and other blockers of N-methyl-D-aspartate (NMDA) receptor channels.

Construction of a cell-based high-flux assay for the rev protein of HIV-1

The Rev of HIV-1 is essential for the replication of the viruses and is therefore a very attractive target for the development of antiviral drugs. To establish a cell-based high-flux assay system for random screening of Rev inhibitors, cells carrying both the Rev-expressing gene and a Rev-inducible SeAP gene were generated by permanent transfection. SeAP produced by these cells was 5-10-fold higher than that synthesized by cells not carrying the Rev gene. Northern blot analysis demonstrated that the increase in SeAP was due mainly to an increase in SeAP transcripts, indicating the effect of Rev proteins synthesized by the transfected cells. The assay system reported in this study should be useful for screening novel Rev inhibitors.

Niruriside, a new HIV REV/RRE binding inhibitor from Phyllanthus niruri

During the screening of natural products for their ability to inhibit the binding of HIV-REV protein to [33P]-labeled RRE RNA, one novel compound, niruriside (1), was isolated from the MeOH extract of the dried leaf of Phyllanthus niruri L. by bioassay-guided fractionation. The structure of niruriside was determined by spectroscopic methods. Niruriside showed specific inhibitory activity against the binding of REV protein to RRE RNA with an IC50 value of 3.3 microM; however, niruriside did not protect CEM-SS cells from acute HIV infection at concentrations up to 260 microM using an XTT dye reduction assay.

Progress in anti-HIV structure-based drug design

The course of drug development for the treatment of HIV-1 infection and AIDS is being revolutionized by high-resolution structures of essential viral proteins. We survey the impact on drug design of the recently elucidated structural knowledge of two essential enzymes, reverse transcriptase and protease, and three new targets, the viral integrase and the gene regulatory protein-RNA interactions, Tat-TAR and Rev-RRE.