Name: using click chemistry to measure the effect of viral infection on host-cell rna synthesis
Uploaded: 2013-08-09T13:00:00
Description: Watch this Scientific Journal Video about Using Click Chemistry to Measure the Effect of Viral Infection on Host-Cell RNA Synthesis at JoVE.com

We thank R.B. Tesh for providing the mouse polyclonal anti-RVFV antiserum and M. Griffin of the UTMB Flow Cytometry Core Facility for help with flow cytometry. This work was supported by 5 U54 AI057156 through the Western Regional Center of Excellence, NIH grant R01 AI08764301, and funding from the Sealy Center for Vaccine Development at UTMB.B.K. was supported by the James W. McLaughlin Fellowship Fund at UTMB.O.L. was supported by a Maurice R. Hilleman Early-Stage Career Investigator Award.

Analysis of transcription by fluorescence microscopy
1. Infect Cells with MP-12 and Label Nascent RNA with EU
<ol>
	<li>Place 12-mm round coverslips into 12-well tissue culture plate, one coverslip per well.</li>
</ol>
Note: If cells have trouble adhering to coverslips, coat with poly-L-lysine (MW &ge; 70,000) before placing in wells. To this aim, submerge coverslips in a sterile 0.1 mg/ml solution in H2O of poly-L-lysine for 5 min. Rinse cove...

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The provided protocol describes a method to measure the effect of viral infection on host cell transcription via incorporation of the uridine analog EU into nascent RNA. This method has several advantages over previous methods: it is fast, sensitive, and it does not rely on the use of radioactive isotopes. Furthermore, the method can be adapted to yield qualitative data through fluorescence microscopy or quantitative data via flow cytometry using essentially the same reagents. When combined with immunofluorescence staini...

Traditionally, transcriptional activity has been measured through incorporation of either radioactive (3H-uridine)1 or halogenated (BrU)2 nucleosides into nascent RNA. These uridine analogs are taken up by cells, converted into uridine-triphosphate (UTP) through the nucleoside salvage pathway, and subsequently incorporated into newly synthesized RNA. 3H-uridine can be detected by autoradiography, which can be time-consuming, or scintillation counting, which requires specialized equipment. Furthermore, the use of radioactive isotopes may not be practical in a number of laboratory settings, including high containment biosafety laboratories. BrU can be detected through immunostaining with anti-BrU antibodies, which may require harsh permeabilization to ensure access of the antibody to the nucleus or partial denaturation of RNA, as RNA secondary structure might be a steric hindrance for antibody binding.
The protocol described here utilizes the recently developed click chemistry3 to measure transcriptional activity in cells infected with the RVFV strain MP-12. Click chemistry relies on a highly selective and efficient copper(I)-catalyzed cycloaddition reaction between an alkyne and an azide moiety4,5. In this protocol, nascent RNA in infected cells is first labeled through incorporation of the uridine analog EU. In a second step, the incorporated EU is detected through reaction with a fluorescent azide. The main advantages of this method are (1) that it does not require the use of radioactive isotopes and (2) that it does not require harsh permeabilization or denaturation of RNA. With a molecular weight of less than 50 Da, access of the fluorescent azide is not impeded by insufficient permeabilization or RNA secondary structure. Furthermore, researchers are not limited in their choice of primary antibodies when combining the detection of RNA with a classical immunostaining for viral proteins.
Two different methods are described in this protocol: one for visualizing transcription via fluorescence microscopy (steps 1-4), and one for quantifying transcription through flow cytometry (steps 5-8). Both of these methods combine labeling of nascent RNA with an intracellular immunostaining for viral proteins, which allows for a correlation between transcriptional activity and viral infection on a cell-by-cell basis.
The authors have successfully used the protocol described here to determine transcriptional activity in cells infected with the RVFV strain MP-126, cells infected with different MP-12 mutants7,8, 9, and cells infected with Toscana virus (TOSV)10. The protocol described here can be easily adapted for use with different viruses and has the potential to be modified to include immunofluorescence staining of specific viral or cellular proteins.

<table border="1">
	<tbody>
		<tr>
			<td>Name of Reagent/Material</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>5-ethynyl-uridine</td>
			<td>Berry &amp; Associates</td>
			<td>PY 7563</td>
			<td>dissolve in DMSO for 100 mM stock</td>
		</tr>
		<tr>
			<td>12-mm round coverslips</td>
			<td>Fisherbrand</td>
			<td>12-545-82</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>5 ml polystyrene tubes</td>
			<td>BD Biosciences</td>
			<td>352058</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Actinomycin D (ActD)</td>
			<td>Sigma</td>
			<td>9415</td>
			<td>dissolve in DMSO for 10 mM stock</td>
		</tr>
		<tr>
			<td>Alexa Fluor 488 goat anti-mouse IgG</td>
			<td>Invitrogen</td>
			<td>A-11029</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin (BSA)</td>
			<td>Santa Cruz</td>
			<td>sc-2323</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>CuSO4</td>
			<td>Sigma</td>
			<td>C-8027</td>
			<td>dissolve in H2O for 100 mM stock</td>
		</tr>
		<tr>
			<td>DAPI</td>
			<td>Sigma</td>
			<td>D-9542</td>
			<td>dissolve in H2O for 5 mg/ml stock</td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Invitrogen</td>
			<td>11965092</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Invitrogen</td>
			<td>16000044</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>fluorescent azide (Alexa Fluor 594-coupled)</td>
			<td>Invitrogen</td>
			<td>A10270</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>fluorescent azide (Alexa Fluor 657-coupled)</td>
			<td>Invitrogen</td>
			<td>A10277</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Fluoromount-G</td>
			<td>Southern Biotech</td>
			<td>0100-01</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>L-ascorbic acid</td>
			<td>Sigma</td>
			<td>A-5960</td>
			<td>dissolve in H2O for 500 mM</td>
		</tr>
		<tr>
			<td>paper filter</td>
			<td>VWRbrand</td>
			<td>28333-087</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>paraformaldehyde</td>
			<td>Sigma</td>
			<td>158127</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin</td>
			<td>Invitrogen</td>
			<td>15140122</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>poly-L-lysine (MW &ge; 70000)</td>
			<td>Sigma</td>
			<td>P1274</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma</td>
			<td>T-8787</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Trizma base</td>
			<td>Sigma</td>
			<td>T-1503</td>
			<td>dissolve in H2O for 1.5 M stock, pH 8.5</td>
		</tr>
		<tr>
			<td>Trypsin-EDTA</td>
			<td>Invitrogen</td>
			<td>25200056</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Fluorescence Microscope</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>e.g. Olympus IX71</td>
		</tr>
		<tr>
			<td>Flow Cytometer</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>e.g. BD Biosciences LSRII Fortessa</td>
		</tr>
	</tbody>
</table>

using click chemistry to measure the effect of viral infection on host-cell rna synthesis

Many RNA viruses have evolved the ability to inhibit host cell transcription as a means to circumvent cellular defenses. For the study of these viruses, it is therefore important to have a quick and reliable way of measuring transcriptional activity in infected cells. Traditionally, transcription has been measured either by incorporation of radioactive nucleosides such as 3H-uridine followed by detection via autoradiography or scintillation counting, or incorporation of halogenated uridine analogs such as 5-bromouridine (BrU) followed by detection via immunostaining. The use of radioactive isotopes, however, requires specialized equipment and is not feasible in a number of laboratory settings, while the detection of BrU can be cumbersome and may suffer from low sensitivity.
The recently developed click chemistry, which involves a copper-catalyzed triazole formation from an azide and an alkyne, now provides a rapid and highly sensitive alternative to these two methods. Click chemistry is a two step process in which nascent RNA is first labeled by incorporation of the uridine analog 5-ethynyluridine (EU), followed by detection of the label with a fluorescent azide. These azides are available as several different fluorophores, allowing for a wide range of options for visualization.
This protocol describes a method to measure transcriptional suppression in cells infected with the Rift Valley fever virus (RVFV) strain MP-12 using click chemistry. Concurrently, expression of viral proteins in these cells is determined by classical intracellular immunostaining. Steps 1 through 4 detail a method to visualize transcriptional suppression via fluorescence microscopy, while steps 5 through 8 detail a method to quantify transcriptional suppression via flow cytometry. This protocol is easily adaptable for use with other viruses.

The NSs protein of RVFV (family Bunyaviridae, genus Phlebovirus) 11 inhibits host cell general transcription through two distinct mechanisms: (i) by sequestering the p44 subunit of the basal transcription factor TFIIH11 and (ii) by promoting the proteasomal degradation of the p62 subunit of TFIIH 6. The RVFV MP-12 vaccine strain 13 has been used for the experiments described in this protocol since MP-12 strain can be handled in a biosafety level 2 laboratory a...

Watch this Scientific Journal Video about Using Click Chemistry to Measure the Effect of Viral Infection on Host-Cell RNA Synthesis at JoVE.com

Using Click Chemistry to Measure the Effect of Viral Infection on Host-Cell RNA Synthesis

This method describes the use of click chemistry to measure changes in host cell transcription after infection with the Rift Valley fever virus (RVFV) strain MP-12. Results can be visualized qualitatively via fluorescence microscopy or obtained quantitatively through flow cytometry. This method is adaptable for use with other viruses.

Many RNA viruses have evolved the ability to inhibit host cell transcription as a means to circumvent cellular defenses. For the study of these viruses, ...

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