The authors acknowledge Dr. Barbara K. Felber and Dr. George N. Pavlakis for the HLfB adherent culture provided by the National Institutes of Health (NIH) AIDS Research and Reference Reagent Program, Division of AIDS, National Institute of Allergy and Infectious Diseases (NIAID), NIH. The authors also acknowledge financial sources provided by the NIH, Grants AI042552 and AI029329.

<ol>
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The authors have nothing to disclose.

Mass spectrometric analyses comparing Rev-NoLS mutations and WT Rev in the presence of HIV-1 were assessed to understand nucleolar factors involved in the viral replication cycle. This would identify nucleolar components required for viral infectivity. Nucleolar B23 has a high affinity to Rev-NoLS and functions in the nucleolar localization of Rev3 and nucleocytoplasmic transport of Rev-bound HIV mRNAs22. The affinity of B23 with Rev-NoLS mutations, which contained single o...

The nucleolus is postulated as the interaction ground of various cellular host and viral factors required for viral replication. The nucleolus is a complex structure subdivided into three different compartments: the fibrillar compartment, the dense fibrillar compartment, and the granular compartment. The HIV-1 Rev protein localizes specifically within granular compartments; however, the reason for this localization pattern is unknown. In the presence of single-point mutations within the NoLS sequence (Rev mutations 4, 5, and 6), Rev maintains a nucleolar pattern and has previously been shown to rescue HIV-1HXB2 replication, however, with reduced efficiency compared to WT Rev1. All single-point mutations are unable to sustain the HIV-1NL4-3 infectious cycle. In the presence of multiple single-point mutations within the NoLS sequence (Rev-NoLS mutations 2 and 9), Rev has been observed to disperse throughout the nucleus and cytoplasm and has not been able to rescue HIV-1HXB2 replication1. The goal of this proteomics study is to decipher nucleolar as well as nonnucleolar cellular factors involved in the Rev-mediated HIV-1 infectious pathway. Rev immunoprecipitation conditions are optimized through interaction with the nucleolar B23 phosphoprotein, which has previously been shown to lose interaction with Rev in the presence of nucleolar mutations.
Rev cellular factors have been extensively studied in the past; however, this has been done in the absence of viral pathogenesis. One protein, in particular, that is characterized in this study through Rev interaction during HIV-1 replication is the nucleolar phosphoprotein B23 - also called nucleophosmin (NPM), numatrin, or NO38 in amphibians2,3,4. B23 is expressed as three isoforms (NPM1, NPM2, and NPM3) - all members of the nucleophosmin/nucleoplasmin nuclear chaperone family5,6. The NPM1 molecular chaperone functions in the proper assembly of nucleosomes, in the formation of protein/nucleic acid complexes involved in chromatin higher-order structures7,8, and in the prevention of aggregation and misfolding of target proteins through an N-terminal core domain (residues 1-120)9. NPM1 functionality extends to ribosome genesis through the transport of preribosomal particles between the nucleus and cytoplasm10,11, the processing of preribosomal RNA in the internal transcribed spacer sequence12,13, and arresting the nucleolar aggregation of proteins during ribosomal assembly14,15. NPM1 is implicated in the inhibition of apoptosis16 and in the stabilization of tumor suppressors ARF17,18 and p5319, revealing its dual role as an oncogenic factor and tumor suppressor. NPM1 participates in the cellular activities of genome stability, centrosome replication, and transcription. NPM1 is found in nucleoli during cell cycle interphase, along the chromosomal periphery during mitosis, and in prenucleolar bodies (PNB) at the conclusion of mitosis. NPM2 and NPM3 are not as well-studied as NPM1, which undergoes altered expression levels during malignancy20.
NPM1 is documented in the nucleocytoplasmic shuttling of various nuclear/nucleolar proteins through an internal NES and NLS9,21 and was previously reported to drive the nuclear import of HIV-1 Tat and Rev proteins. In the presence of B23-binding-domain-&#946;-galactosidase fusion proteins, Tat mislocalizes within the cytoplasm and loses transactivation activity; this demonstrates a strong affinity of Tat for B232. Another study established a Rev/B23 stable complex in the absence of RRE-containing mRNAs. In the presence of RRE mRNA, Rev dissociates from B23 and binds preferably to the HIV RRE, leading to the displacement of B2322. It is unknown where, at the subnuclear level, Tat transactivation and the Rev exchange process of B23 for HIV mRNA take place. Both proteins are postulated to enter the nucleolus simultaneously through B23 interaction. The involvement of other host cellular proteins in the HIV nucleolar pathway is expected. The methods described in this proteomics investigation will help elucidate the interplay of the nucleolus with host cellular factors involved during HIV-1 pathogenesis.
The proteomics investigation was initiated through the expression of Rev NoLS single-point mutations (M4, M5, and M6) and multiple arginine substitutions (M2 and M9) for HIV-1HXB2 production. In this model, a HeLa cell line stably expressing Rev-deficient HIV-1HXB2 (HLfB) is transfected with WT Rev and Rev nucleolar mutations containing a flag tag at the 3&#39; end. The presence of WT Rev will allow viral replication to occur in HLfB culture, in comparison to Rev-NoLS mutations that do not rescue Rev deficiency (M2 and M9), or allow viral replication to occur but not as efficiently as WT Rev (M4, M5, and M6)1. The cell lysate is collected 48 h later after viral proliferation in the presence of Rev expression and subjected to immunoprecipitation with a lysis buffer optimized for Rev/B23 interaction. Lysis buffer optimization using varying salt concentrations is described, and protein elution methods for HIV-1 Rev are compared and analyzed in silver-stained or Coomassie-stained SDS-PAGE gels. The first proteomics approach involves the direct analysis of an eluted sample from expressed WT Rev, M2, M6, and M9 by tandem mass spectrometry. A second approach by which the eluates of WT Rev, M4, M5, and M6 underwent a gel extraction process is compared to the first approach. Peptide affinity to Rev-NoLS mutations in comparison to WT Rev is analyzed and the protein identification probability displayed. These approaches reveal potential factors (nucleolar and nonnucleolar) that participate in HIV-1 mRNA transport and splicing with Rev during HIV-1 replication. Overall, the cell lysis, IP, and elution conditions described are applicable to viral proteins of interest for the understanding of host cellular factors that activate and regulate infectious pathways. This is also applicable to the study of cellular host factors required for the persistence of various disease models. In this proteomics model, HIV-1 Rev IP is optimized for B23 interaction to elucidate nucleolar factors involved in nucleocytoplasmic shuttling activity and HIV-1 mRNA binding. Additionally, cell lines stably expressing infectious disease models that are deficient for key proteins of interest can be developed, similar to the HLfB cell line, to study infectious pathways of interest.

<table><tbody><tr><td>Acetic acid</td><td>Fisher Chemical</td><td>A38S-212</td><td></td></tr><tr><td>Acetonitrile</td><td>Fisher Chemical</td><td>A955-500</td><td></td></tr><tr><td>Acrylamide:Bisacrylamide</td><td>BioRad</td><td>1610158</td><td></td></tr><tr><td>Ammonium bicarbonate</td><td>Fisher Chemical</td><td>A643-500</td><td></td></tr><tr><td>Ammonium persulfate</td><td>Sigma-Aldrich</td><td>7727-54-0</td><td></td></tr><tr><td>ANTI-Flag M2 affinity gel</td><td>Sigma-Aldrich</td><td>A2220</td><td></td></tr><tr><td>anti-Flag M2 mouse monoclonal IgG</td><td>Sigma-Aldrich</td><td>F3165</td><td></td></tr><tr><td>BioMax MS film</td><td>Carestream</td><td>8294985</td><td></td></tr><tr><td>Bio-Rad Protein Assay Dye Reagent Concentrate, 450 mL</td><td>Bio-Rad</td><td>5000006</td><td></td></tr><tr><td>B23 mouse monoclonal IgG</td><td>Santa Cruz Biotechnologies</td><td>sc-47725</td><td></td></tr><tr><td>Bromophenol blue</td><td>Sigma-Aldrich</td><td>B0126</td><td></td></tr><tr><td>Carnation non-fat powdered milk</td><td>Nestle</td><td>N/A</td><td></td></tr><tr><td>Cell scraper</td><td>ThermoFisher Scientific</td><td>179693PK</td><td></td></tr><tr><td>C18IonKey nanoTile column</td><td>Waters</td><td>186003763</td><td></td></tr><tr><td>Corning 100-mm TC-treated culture dishes</td><td>Fisher Scientific</td><td>08-772-22</td><td></td></tr><tr><td>Dithiothreitol</td><td>Thermo Scientific</td><td>J1539714</td><td></td></tr><tr><td>1 x DPBS</td><td>Corning</td><td>21-030-CVRS</td><td></td></tr><tr><td>ECL Estern blotting substrate</td><td>Pierce</td><td>32106</td><td></td></tr><tr><td>Ethanol, 200 proof</td><td>Fisher Chemical</td><td>A409-4</td><td></td></tr><tr><td>FBS</td><td>Gibco</td><td>16000044</td><td></td></tr><tr><td>Formic Acid</td><td>Fisher Chemical</td><td>A117-50</td><td></td></tr><tr><td>GelCode blue stain reagent</td><td>ThermoFisher</td><td>24590</td><td></td></tr><tr><td>Glycerol</td><td>Fisher Chemical</td><td>56-81-5</td><td></td></tr><tr><td>goat-anti-mouse IgG-HRP</td><td>Santa Cruz Biotechnologies</td><td>sc-2005</td><td></td></tr><tr><td>Iodoacetamide</td><td>ACROS Organics</td><td>122270050</td><td></td></tr><tr><td>KimWipe delicate task wiper</td><td>Kimberly Clark Professional</td><td>34120</td><td></td></tr><tr><td>L-glutamine</td><td>Gibco</td><td>25030081</td><td></td></tr><tr><td>Methanol</td><td>Fisher Chemical</td><td>67-56-1</td><td></td></tr><tr><td>NanoAcuity UPLC</td><td>Waters</td><td>N/A</td><td></td></tr><tr><td>Pierce Silver Stain Kit</td><td>Thermo Scientific</td><td>24600df</td><td></td></tr><tr><td>15-mL Polypropylene conical tube</td><td>Falcon</td><td>352097</td><td></td></tr><tr><td>Prestained Protein Ladder, 10 to 180 kDa</td><td>Thermo Scientific</td><td>26616</td><td></td></tr><tr><td>Protease inhibitor cocktail</td><td>Roche</td><td>4693132001</td><td></td></tr><tr><td>Purified BSA</td><td>New England Biolabs</td><td>B9001</td><td></td></tr><tr><td>PVDF&amp;nbsp; Western blotting membrane</td><td>Roche</td><td>3010040001</td><td></td></tr><tr><td>Sodium Pyruvate</td><td>Gibco</td><td>11360070</td><td></td></tr><tr><td>10 x TBS</td><td>Fisher Bioreagents</td><td>BP2471500</td><td></td></tr><tr><td>TEMED</td><td>BioRad</td><td>1610880edu</td><td></td></tr><tr><td>Triton X-100 detergent solution</td><td>BioRad</td><td>1610407</td><td></td></tr><tr><td>Trizaic source</td><td>Waters</td><td>N/A</td><td></td></tr><tr><td>trypsin-EDTA</td><td>Corning</td><td>25-051-CIS</td><td></td></tr><tr><td>Tween 20</td><td>BioRad</td><td>1706531</td><td></td></tr><tr><td>Synapt G2 mass spectrometer</td><td>Waters</td><td>N/A</td><td></td></tr><tr><td>Whatman filter paper</td><td>Tisch Scientific</td><td>10427813</td><td></td></tr></tbody></table>

identification of nucleolar factors during hiv-1 replication through rev immunoprecipitation and mass spectrometry

The HIV-1 infectious cycle requires viral protein interactions with host factors to facilitate viral replication, packaging, and release. The infectious cycle further requires the formation of viral/host protein complexes with HIV-1 RNA to regulate the splicing and enable nucleocytoplasmic transport. The HIV-1 Rev protein accomplishes the nuclear export of HIV-1 mRNAs through multimerization with intronic cis-acting targets - the Rev response element (RRE). A nucleolar localization signal (NoLS) exists within the COOH-terminus of the Rev arginine-rich motif (ARM), allowing the accumulation of Rev/RRE complexes in the nucleolus. Nucleolar factors are speculated to support the HIV-1 infectious cycle through various other functions in addition to mediating mRNA-independent nuclear export and splicing. We describe an immunoprecipitation method of wild-type (WT) Rev in comparison to Rev nucleolar mutations (deletion and single-point Rev-NoLS mutations) in the presence of HIV-1 replication for mass spectrometry. Nucleolar factors implicated in the nucleocytoplasmic transport (nucleophosmin B23 and nucleolin C23), as well as cellular splicing factors, lose interaction with Rev in the presence of Rev-NoLS mutations. Various other nucleolar factors, such as snoRNA C/D box 58, are identified to lose interaction with Rev mutations, yet their function in the HIV-1 replication cycle remain unknown. The results presented here demonstrate the use of this approach for the identification of viral/host nucleolar factors that maintain the HIV-1 infectious cycle. The concepts used in this approach are applicable to other viral and disease models requiring the characterization of understudied pathways.

Rev-NoLS single- and multiple-point arginine mutations, corresponding to a variety of subcellular localization patterns, were examined in their ability to interact with cellular host factors in comparison to WT Rev. WT Rev-3&#39;flag and pcDNA-flag vector were expressed in HLfB culture. Protein complexes were processed from total cell lysate and stained with silver stain reagent. Rev-NoLS-3&#39;flag is detectable (approximately 18 kDa) in three different lysis buffer conditions containing various concentrations ...

Watch this Scientific Journal Video about Identification of Nucleolar Factors During HIV-1 Replication Through Rev Immunoprecipitation and Mass Spectrometry at JoVE.com

Identification of Nucleolar Factors During HIV-1 Replication Through Rev Immunoprecipitation and Mass Spectrometry

Here we describe Rev immunoprecipitation in the presence of HIV-1 replication for mass spectrometry. The methods described can be used for the identification of nucleolar factors involved in the HIV-1 infectious cycle and are applicable to other disease models for the characterization of understudied pathways.

The HIV-1 infectious cycle requires viral protein interactions with host factors to facilitate viral replication, packaging, and release. The infectious ...

identification-nucleolar-factors-during-hiv-1-replication-through-rev

Research

JoVE Journal

Immunology and Infection

8.0K Views.  Beckman Research Institute at the City of Hope. Ons protocol biedt alternatieve methoden voor de identificatie en karakterisering van virale, nucleolar, en niet-nucleolar host factoren die de HIV-1 infectieuze cyclus te handhaven. De concepten die in deze benadering worden gebruikt, zijn van toepassing op andere virale en ziektemodellen die de karakterisering van onderbestudeerde trajecten vereisen. Probleemoplossingstechnieken worden beschreven voor wijziging van andere eiwitmodellen.Het aantonen van de procedure zal worden Haitang...

Video: Identification of Nucleolar Factors During HIV-1 Replication Through Rev Immunoprecipitation and Mass Spectrometry

In vitro Uncoating of HIV-1 Cores

The genome of the retroviruses is encased in a capsid surrounded by a lipid envelope. For lentiviruses, such as HIV-1, the conical capsid shell is composed of CA protein arranged as a lattice of hexagon. The capsid is closed by 7 pentamers at the broad end and 5 at the narrow end of the cone1, 2. Encased in this capsid shell is the viral ribonucleoprotein complex, and together they comprise the core.
Following fusion of the viral membrane with the target cell membrane, the HIV-1 is released into the cytoplasm. The capsid then disassembles releasing free CA in the soluble form3 in a process referred to as uncoating. The intracellular location and timing of HIV-1 uncoating are poorly understood. Single amino-acid substitutions in CA that alter the stability of the capsid also impair the ability of HIV-1 to infect cells4. This indicates that the stability of the capsid is critical for HIV-1 infection.
HIV-1 uncoating has been difficult to study due to lack of availability of sensitive and reliable assays for this process. Here we describe a quantitative method for studying uncoating in vitro using cores isolated from infectious HIV-1 particles. The approach involves isolation of cores by sedimentation of concentrated virions through a layer of detergent and into a linear sucrose gradient, in the cold. To quantify uncoating, the isolated cores are incubated at 37&deg;C for various timed intervals and subsequently pelleted by ultracentrifugation. The extent of uncoating is analyzed by quantifying the fraction of CA in the supernatant. This approach has been employed to analyze effects of viral mutations on HIV-1 capsid stability4, 5, 6. It should also be useful for studying the role of cellular factors in HIV-1 uncoating.

In vitro Uncoating of HIV-1 Cores

Uncoating is an essential step in the early phase of the HIV-1 life cycle and is defined as the disassembly of the capsid shell and the release of the viral ribonucleoprotein complex (vRNP). Here, we demonstrate techniques for isolating intact cores from HIV-1 virions and for quantifying their uncoating in vitro.

The genome of the retroviruses is encased in a capsid surrounded by a lipid envelope. For lentiviruses, such as HIV-1, the conical capsid shell is ...

Amplification of Near Full-length HIV-1 Proviruses for Next-Generation Sequencing

The Full-Length Individual Proviral Sequencing (FLIPS) assay is an efficient and high-throughput method designed to amplify and sequence single, near full-length (intact and defective), HIV-1 proviruses. FLIPS allows determination of the genetic composition of integrated HIV-1 within a cell population. Through identifying defects within HIV-1 proviral sequences that arise during reverse transcription, such as large internal deletions, deleterious stop codons/hypermutation, frameshift mutations, and mutations/deletions in cis acting elements required for virion maturation, FLIPS can identify integrated proviruses incapable of replication. The FLIPS assay can be utilized to identify HIV-1 proviruses that lack these defects and are&#160;therefore potentially replication-competent. The FLIPS protocol involves: lysis of HIV-1 infected cells, nested PCR of near full-length HIV-1 proviruses (using primers targeted to the HIV-1 5&#39; and 3&#39; LTR), DNA purification and quantification, library preparation for Next-generation Sequencing (NGS), NGS, de novo assembly of proviral contigs, and a simple process of elimination for identifying replication-competent proviruses. FLIPS provides advantages over traditional methods designed to sequence integrated HIV-1 proviruses, such as single-proviral sequencing. FLIPS amplifies and sequences near full-length proviruses enabling replication competency to be determined, and also uses fewer amplification primers, preventing the consequences of primer mismatches. FLIPS is a useful tool for understanding the genetic landscape of integrated HIV-1 proviruses, especially within the latent reservoir, however, its utilization can extend to any application in which the genetic composition of integrated HIV-1 is required.

Full-length individual proviral sequencing (FLIPS) provides an efficient and high-throughput method for the amplification and sequencing of single, near full-length (intact and defective) HIV-1 proviruses and allows for determination of their potential replication-competency. FLIPS overcomes limitations of previous assays designed to sequence the latent HIV-1 reservoir.

The Full-Length Individual Proviral Sequencing (FLIPS) assay is an efficient and high-throughput method designed to amplify and sequence single, near ...

Genetics

Determining 3'-Termini and Sequences of Nascent Single-Stranded Viral DNA Molecules during HIV-1 Reverse Transcription in Infected Cells

Monitoring of nucleic acid intermediates during virus replication provides insights into the effects and mechanisms of action of antiviral compounds and host cell proteins on viral DNA synthesis. Here we address the lack of a cell-based, high-coverage, and high-resolution assay that is capable of defining retroviral reverse transcription intermediates within the physiological context of virus infection. The described method captures the 3'-termini of nascent complementary DNA (cDNA) molecules within HIV-1 infected cells at single nucleotide resolution. The protocol involves harvesting of whole cell DNA, targeted enrichment of viral DNA via hybrid capture, adaptor ligation, size fractionation by gel purification, PCR amplification, deep sequencing, and data analysis. A key step is the efficient and unbiased ligation of adaptor molecules to open 3'-DNA termini. Application of the described method determines the abundance of reverse transcripts of each particular length in a given sample. It also provides information about the (internal) sequence variation in reverse transcripts and thereby any potential mutations. In general, the assay is suitable for any questions relating to DNA 3'-extension, provided that the template sequence is known.

Here we present a deep sequencing approach that provides an unbiased determination of nascent 3&#39;-termini as well as mutational profiles of single-stranded DNA molecules. The main application is the characterization of nascent retroviral complementary DNAs (cDNAs), the intermediates generated during the process of retroviral reverse transcription.

Monitoring of nucleic acid intermediates during virus replication provides insights into the effects and mechanisms of action of antiviral compounds and ...

2D Gel Electrophoresis for Analyzing DNA Replication and Fork Stalling Events

Electrophoretic Analysis of Replication Through Structure-Prone DNA Repeats Within the SV40-Based Human Episome

Two-dimensional neutral/neutral gel-electrophoresis (2DGE) emerged as a benchmark technique to analyze DNA replication through natural impediments. This protocol describes how to analyze replication fork progression through structure-prone, expandable DNA repeats within the simian virus 40 (SV40)-based episome in human cells. In brief, upon plasmid transfection into human cells, replication intermediates are isolated by the modified Hirt protocol and treated with the DpnI restriction enzyme to remove non-replicated DNA. Intermediates are then digested by appropriate restriction enzymes to place the repeat of interest within the origin-distal half of a 3-5 kb-long DNA fragment. The replication intermediates are separated into two perpendicular dimensions, first by size and then by shape. Following Southern blot hybridization, this approach allows researchers to observe fork stalling at various structure-forming repeats on the descending half of the replication Y-arc. Furthermore, this positioning of the stall site allows the visualization of various outcomes of repeat-mediated fork stalling, such as fork reversal, the advent of a converging fork, and recombinational fork restart.

Author Spotlight: Characterizing DNA Replication of Pathogenic Repeats to Uncover Mechanisms of Replication Fork Stalling and Expansion

Here, we outline the procedure for analyzing replication progression through pathogenic, structure-prone repeats using 2-dimensional gel electrophoresis.

Two-dimensional neutral/neutral gel-electrophoresis (2DGE) emerged as a benchmark technique to analyze DNA replication through natural impediments. This ...

Nucleocapsid Annealing-Mediated Electrophoresis (NAME) Assay Allows the Rapid Identification of HIV-1 Nucleocapsid Inhibitors

RNA or DNA folded in stable tridimensional folding are interesting targets in the development of antitumor or antiviral drugs. In the case of HIV-1, viral proteins involved in the regulation of the virus activity recognize several nucleic acids. The nucleocapsid protein NCp7 (NC) is a key protein regulating several processes during virus replication. NC is in fact a chaperone destabilizing the secondary structures of RNA and DNA and facilitating their annealing. The inactivation of NC is a new approach and an interesting target for anti-HIV therapy. The Nucleocapsid Annealing-Mediated Electrophoresis (NAME) assay was developed to identify molecules able to inhibit the melting and annealing of RNA and DNA folded in thermodynamically stable tridimensional conformations, such as hairpin structures of TAR and cTAR elements of HIV, by the nucleocapsid protein of HIV-1. The new assay employs either the recombinant or the synthetic protein, and oligonucleotides without the need of their previous labeling. The analysis of the results is achieved by standard polyacrylamide gel electrophoresis (PAGE) followed by conventional nucleic acid staining. The protocol reported in this work describes how to perform the NAME assay with the full-length protein or its truncated version lacking the basic N-terminal domain, both competent as nucleic acids chaperones, and how to assess the inhibition of NC chaperone activity by a threading intercalator. Moreover, NAME can be performed in two different modes, useful to obtain indications on the putative mechanism of action of the identified NC inhibitors.

Nucleocapsid Annealing-Mediated Electrophoresis NAME Assay Allows the Rapid Identification of HIV-1 Nucleocapsid Inhibitors

This protocol describes NAME, an assay that allows the rapid identification of molecules able to inhibit in vitro the chaperone activities of HIV-1 nucleocapsid protein.

RNA or DNA folded in stable tridimensional folding are interesting targets in the development of antitumor or antiviral drugs. In the case of HIV-1, viral ...

Pairwise Growth Competition Assay for Determining the Replication Fitness of Human Immunodeficiency Viruses

In vitro fitness assays are essential tools for determining viral replication fitness for viruses such as HIV-1. Various measurements have been used to extrapolate viral replication fitness, ranging from the number of viral particles per infectious unit, growth rate in cell culture, and relative fitness derived from multiple-cycle growth competition assays. Growth competition assays provide a particularly sensitive measurement of fitness since the viruses are competing for cellular targets under identical growth conditions. There are several experimental factors to consider when conducting growth competition assays, including the multiplicity of infection (MOI), sampling times, and viral detection and fitness calculation methods. Each factor can affect the end result and hence must be considered carefully during the experimental design. The protocol presented here includes steps from constructing a new recombinant HIV-1 clone to performing growth competition assays and analyzing the experimental results. This protocol utilizes experimental parameter values previously shown to yield consistent and robust results. Alternatives are discussed, as some parameters need to be adjusted according to the cell type and viruses being studied. The protocol contains two alternative viral detection methods to provide flexibility as the availability of instruments, reagents and expertise varies between laboratories.

Growth competition between nearly isogenic viruses provides a sensitive measurement for determining relative replication fitness. The protocols described here include the construction of recombinant HIV-1 clones, virus propagation and growth competition and analysis methods optimized to yield sensitive and consistent results.

In vitro fitness assays are essential tools for determining viral replication fitness for viruses such as HIV-1. Various measurements have been used to ...

Purification of Viral DNA for the Identification of Associated Viral and Cellular Proteins

The goal of this protocol is to isolate herpes simplex virus type 1 (HSV-1) DNA from infected cells for the identification of associated viral and cellular proteins by mass spectrometry. Although proteins that interact with viral genomes play major roles in determining the outcome of infection, a comprehensive analysis of viral genome associated proteins was not previously feasible. Here we demonstrate a method that enables the direct purification of HSV-1 genomes from infected cells. Replicating viral DNA is selectively labeled with modified nucleotides that contain an alkyne functional group. Labeled DNA is then specifically and irreversibly tagged via the covalent attachment of biotin azide via a copper(I)-catalyzed azide-alkyne cycloaddition or click reaction. Biotin-tagged DNA is purified on streptavidin-coated beads and associated proteins are eluted and identified by mass spectrometry. This method enables the selective targeting and isolation of HSV-1 replication forks or whole genomes from complex biological environments. Furthermore, adaptation of this approach will allow for the investigation of various aspects of herpesviral infection, as well as the examination of the genomes of other DNA viruses.

The goal of this protocol is to specifically tag and selectively isolate viral DNA from infected cells for the characterization of viral genome associated proteins.

The goal of this protocol is to isolate herpes simplex virus type 1 (HSV-1) DNA from infected cells for the identification of associated viral and ...

High Throughput In Vitro Assessment of Latency Reversing Agents on HIV Transcription and Splicing

HIV remains incurable due to the existence of a reservoir of cells that harbors stable and latent form of the virus, which stays invisible to the immune system and is not targeted by the current antiretroviral therapy (cART). Transcription and splicing have been shown to reinforce HIV-1 latency in resting CD4+ T cells. Reversal of latency by the use of latency reversal agents (LRAs) in the &#34;shock and kill&#34; approach has been studied extensively in an attempt to purge this reservoir but has thus far not shown any success in clinical trials due to the lack of development of adequate small molecules that can efficiently perturb this reservoir. The protocol presented here provides a method for reliably and efficiently assessing latency reversal agents (LRAs) on HIV transcription and splicing. This approach is based on the use of an LTR-driven dual color reporter that can simultaneously measure the effect of an LRA on transcription and splicing by flow cytometry. The protocol described here is adequate for adherent cells as well as the cells in suspension. It is useful for testing a large number of drugs in a high throughput system. The method is technically simple to implement and cost-effective. In addition, the use of flow cytometry allows the assessment of cell viability and thus drug toxicity at the same time.

A high throughput protocol for functional assessment of HIV efficient reactivation and clearance of latent proviruses is described and applied by testing the impact of interventions on HIV transcription and splicing. Representative results of the effect of latency reversing agents on LTR-driven transcription and splicing are provided.

HIV remains incurable due to the existence of a reservoir of cells that harbors stable and latent form of the virus, which stays invisible to the immune ...

Detection of Viral RNA by Fluorescence in situ Hybridization (FISH)

Viruses that infect cells elicit specific changes to normal cell functions which serve to divert energy and resources for viral replication. Many aspects of host cell function are commandeered by viruses, usually by the expression of viral gene products that recruit host cell proteins and machineries. Moreover, viruses engineer specific membrane organelles or tag on to mobile vesicles and motor proteins to target regions of the cell (during de novo infection, viruses co-opt molecular motor proteins to target the nucleus; later, during virus assembly, they will hijack cellular machineries that will help in the assembly of viruses). Less is understood on how viruses, in particular those with RNA genomes, coordinate the intracellular trafficking of both protein and RNA components and how they achieve assembly of infectious particles at specific loci in the cell. The study of RNA localization began in earlier work. Developing lower eukaryotic embryos and neuronal cells provided important biological information, and also underscored the importance of RNA localization in the programming of gene expression cascades. The study in other organisms and cell systems has yielded similar important information. Viruses are obligate parasites and must utilise their host cells to replicate. Thus, it is critical to understand how RNA viruses direct their RNA genomes from the nucleus, through the nuclear pore, through the cytoplasm and on to one of its final destinations, into progeny virus particles 1.
FISH serves as a useful tool to identify changes in steady-state localization of viral RNA. When combined with immunofluorescence (IF) analysis 22, FISH/IF co-analyses will provide information on the co-localization of proteins with the viral RNA3. This analysis therefore provides a good starting point to test for RNA-protein interactions by other biochemical or biophysical tests 4,5, since co-localization by itself is not enough evidence to be certain of an interaction. In studying viral RNA localization using a method like this, abundant information has been gained on both viral and cellular RNA trafficking events 6. For instance, HIV-1 produces RNA in the nucleus of infected cells but the RNA is only translated in the cytoplasm. When one key viral protein is missing (Rev) 7, FISH of the viral RNA has revealed that the block to viral replication is due to the retention of the HIV-1 genomic RNA in the nucleus 8. 
Here, we present the method for visual analysis of viral genomic RNA in situ. The method makes use of a labelled RNA probe. This probe is designed to be complementary to the viral genomic RNA. During the in vitro synthesis of the antisense RNA probe, the ribonucleotide that is modified with digoxigenin (DIG) is included in an in vitro transcription reaction. Once the probe has hybridized to the target mRNA in cells, subsequent antibody labelling steps (Figure 1) will reveal the localization of the mRNA as well as proteins of interest when performing FISH/IF.

Detection of Viral RNA by Fluorescence in situ Hybridization FISH

A fluorescence in situ hybridization (FISH) method was developed to visually detect viral genomic RNA using fluorescence microscopy. A probe is made with specificity to the viral RNA that can then be identified using a combination of hybridization and immunofluorescence techniques. This technique offers the advantage of identifying the localization of the viral RNA or DNA at steady-state, providing information on the control of intracellular virus trafficking events.

Viruses  that infect cells elicit specific changes to normal cell functions which serve  to divert energy and resources for viral replication. Many ...

Biology

Studying ER Stress and UPR Activation During HIV-1 Infection in T-Cells

Measuring Endoplasmic Reticulum Stress and Unfolded Protein Response in HIV-1 Infected T-Cells and Analyzing its Role in HIV-1 Replication

Viral infections can cause Endoplasmic Reticulum (ER) stress due to abnormal protein accumulation, leading to Unfolded Protein Response (UPR). Viruses have developed strategies to manipulate the host UPR, but there is a lack of detailed understanding of UPR modulation and its functional significance during HIV-1 infection in the literature. In this context, the current article describes the protocols used in our laboratory to measure ER stress levels and UPR during HIV-1 infection in T-cells and the effect of UPR on viral replication and infectivity. 
Thioflavin T (ThT) staining is a relatively new method used to detect ER stress in the cells by detecting protein aggregates. Here, we have illustrated the protocol for ThT staining in HIV-1 infected cells to detect and quantify ER stress. Moreover, ER stress was also detected indirectly by measuring the levels of UPR markers such as BiP, phosphorylated IRE1, PERK, and eIF2&#945;, splicing of XBP1, cleavage of ATF6, ATF4, CHOP, and GADD34 in HIV-1 infected cells, using conventional immunoblotting and quantitative reverse transcription polymerase chain reaction (RT-PCR). We have found that the ThT-fluorescence correlates with the indicators of UPR activation. This article also demonstrates the protocols to analyze the impact of ER stress and UPR modulation on HIV-1 replication by knockdown experiments as well as the use of pharmacological molecules. The effect of UPR on HIV-1 gene expression/replication and virus production was analyzed by Luciferase reporter assays and p24 antigen capture ELISA, respectively, whereas the effect on virion infectivity was analyzed by staining of infected reporter cells. Collectively, this set of methods provides a comprehensive understanding of the Unfolded Protein Response pathways during HIV-1 infection, revealing its intricate dynamics.

Author Spotlight: Exploring the Role of Unfolded Protein Response in HIV-1 Replication and Infectivity

Here, we describe some established methods to determine endoplasmic reticulum (ER) stress and unfolded protein response (UPR) activation, with particular emphasis on HIV-1 infection. This article also describes a set of protocols to investigate the effect of ER stress/UPR on HIV-1 replication and virion infectivity.

Viral infections can cause Endoplasmic Reticulum (ER) stress due to abnormal protein accumulation, leading to Unfolded Protein Response (UPR). Viruses ...

Identification of Nucleolar Factors During HIV-1 Replication Through Rev Immunoprecipitation and Mass Spectrometry

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