Name: electroporation of functional bacterial effectors into mammalian cells
Uploaded: 2015-01-19T13:00:00
Description: Watch this Scientific Journal Video about Electroporation of Functional Bacterial Effectors into Mammalian Cells at JoVE.com

This work was supported by NIGMS, National Institutes of Health (GM094623). Significant portions of this work were performed in the Environmental Molecular Sciences Laboratory, a DOE/BER national scientific user facility located at the Pacific Northwest National Laboratory (PNNL). PNNL is operated for the DOE by Battelle under Contract DE-AC05-76RLO1830.

1. Prepare in Advance
<ol>
	<li>Warm sterile phosphate buffered saline (PBS) to 37 &#176;C.</li>
	<li>Warm Dulbecco&#8217;s Modification of Eagle&#8217;s Medium (DMEM) and Minimal Essential Medium (MEM) supplemented with 10% fetal bovine serum (FBS), 100 I.U./ml penicillin, and 100 &#181;g/ml streptomycin to 37 &#176;C. Note: These represent Normal Growth Media (NGM) for RAW and HeLa cells respectively.</li>
</ol>
2. Preparation of Cells
<ol>
	<li>Grow RAW 264.7 cells to 70-90% confluency in N...

<ol>
	<li>Mota, L. J., Cornelis, G. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+bacterial+injection+kit:+type+III+secretion+systems.">The bacterial injection kit: type III secretion systems.</a> Annals of Medicine. 37, 234-249 (2005).</li><li>Galan, J. E., Collmer, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Type+III+secretion+machines:+bacterial+devices+for+protein+delivery+into+host+cells.">Type III secretion machines: bacterial devices for protein delivery into host cells.</a> Science. 284, 1322-1328 (1999).</li><li>Hueck, C. 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Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Type+III+protein+secretion+systems+in+plant+and+animal+pathogenic+bacteria.">Type III protein secretion systems in plant and animal pathogenic bacteria.</a> Annual Review of Phytopathology. 36, 363-392 (1998).</li><li>Dean, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+domains+and+motifs+of+bacterial+type+III+effector+proteins+and+their+roles+in+infection.">Functional domains and motifs of bacterial type III effector proteins and their roles in infection.</a> FEMS Microbiology Reviews. 35, 1100-1125 (2011).</li><li>Espinosa, A., Alfano, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disabling+surveillance:+bacterial+type+III+secretion+system+effectors+that+suppress+innate+immunity.">Disabling surveillance: bacterial type III secretion system effectors that suppress innate immunity.</a> Cellular Microbiology. 6, 1027-1040 (2004).</li><li>Orchard, R. C., Alto, N. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mimicking+GEFs:+a+common+theme+for+bacterial+pathogens.">Mimicking GEFs: a common theme for bacterial pathogens.</a> Cellular Microbiology. 14, 10-18 (2012).</li><li>Galan, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Common+themes+in+the+design+and+function+of+bacterial+effectors.">Common themes in the design and function of bacterial effectors.</a> Cell Host Microbe. 5, 571-579 (2009).</li><li>Ellis, B. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+survey+of+ex+vivo/in+vitro+transduction+efficiency+of+mammalian+primary+cells+and+cell+lines+with+Nine+natural+adeno-associated+virus+(AAV1-9)+and+one+engineered+adeno-associated+virus+serotype.">A survey of ex vivo/in vitro transduction efficiency of mammalian primary cells and cell lines with Nine natural adeno-associated virus (AAV1-9) and one engineered adeno-associated virus serotype.</a> Virology Journal. 10, 74 (2013).</li><li>Sreelatha, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vibrio+effector+protein,+VopQ,+forms+a+lysosomal+gated+channel+that+disrupts+host+ion+homeostasis+and+autophagic+flux.">Vibrio effector protein, VopQ, forms a lysosomal gated channel that disrupts host ion homeostasis and autophagic flux.</a> Proceedings of the National Academy of Sciences of the United States of America. 110, 11559-11564 (2013).</li><li>McNeil, P. L., Murphy, R. F., Lanni, F., Taylor, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+method+for+incorporating+macromolecules+into+adherent+cells.">A method for incorporating macromolecules into adherent cells.</a> The Journal of Cell Biology. 98, 1556-1564 (1984).</li><li>Lafon, M., Lafage, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antiviral+activity+of+monoclonal+antibodies+specific+for+the+internal+proteins+N+and+NS+of+rabies+virus.">Antiviral activity of monoclonal antibodies specific for the internal proteins N and NS of rabies virus.</a> The Journal of General Virology. 68 (Pt. 12), 3113-3123 (1987).</li><li>Kriegler, M. P., Livingston, D. 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E., Schuster, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transfer+of+monoclonal+antibodies+into+mammalian+cells+by+electroporation.">Transfer of monoclonal antibodies into mammalian cells by electroporation.</a> The Journal of Biological Chemistry. 264, 15494-15500 (1989).</li><li>Graziadei, L., Burfeind, P., Bar-Sagi, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Introduction+of+unlabeled+proteins+into+living+cells+by+electroporation+and+isolation+of+viable+protein-loaded+cells+using+dextran-fluorescein+isothiocyanate+as+a+marker+for+protein+uptake.">Introduction of unlabeled proteins into living cells by electroporation and isolation of viable protein-loaded cells using dextran-fluorescein isothiocyanate as a marker for protein uptake.</a> Analytical Biochemistry. 194, 198-203 (1991).</li><li>Wilson, A. K., Horwitz, J., De Lanerolle, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+the+electroinjection+method+for+introducing+proteins+into+living+cells.">Evaluation of the electroinjection method for introducing proteins into living cells.</a> The American Journal of Physiology. 260, C355-C363 (1991).</li><li>Prasanna, G. L., Panda, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electroporation:+Basic+principles,+practical+considerations+and+applications+in+molecular+biology.">Electroporation: Basic principles, practical considerations and applications in molecular biology.</a> Bioprocess Engineering. 16, 261-264 (1997).</li><li>Weaver, J. C., Chizmadzhev, Y. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theory+of+electroporation:+A+review.">Theory of electroporation: A review.</a> Bioelectrochemistry and Bioenergetics. 41, 135-160 (1996).</li><li>Weaver, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electroporation+theory.+Concepts+and+mechanisms.">Electroporation theory. Concepts and mechanisms.</a> Methods in Molecular Biology. 55, 3-28 (1995).</li><li>McAteer, J. A., Douglas, W. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Monolayer+culture+techniques.">Monolayer culture techniques.</a> Methods in Enzymology. 58, 132-140 (1979).</li><li>Ho, T. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+GtgE,+a+novel+virulence+factor+encoded+on+the+Gifsy-2+bacteriophage+of+Salmonella+enterica+serovar+Typhimurium.">Identification of GtgE, a novel virulence factor encoded on the Gifsy-2 bacteriophage of Salmonella enterica serovar Typhimurium.</a> Journal of Bacteriology. 184, 5234-5239 (2002).</li><li>Niemann, G. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Discovery+of+novel+secreted+virulence+factors+from+Salmonella+enterica+serovar+Typhimurium+by+proteomic+analysis+of+culture+supernatants.">Discovery of novel secreted virulence factors from Salmonella enterica serovar Typhimurium by proteomic analysis of culture supernatants.</a> Infection and Immunity. 79, 33-43 (2011).</li><li>Spano, S., Liu, X., Galan, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proteolytic+targeting+of+Rab29+by+an+effector+protein+distinguishes+the+intracellular+compartments+of+human-adapted+and+broad-host+Salmonella.">Proteolytic targeting of Rab29 by an effector protein distinguishes the intracellular compartments of human-adapted and broad-host Salmonella.</a> Proceedings of the National Academy of Sciences of the United States of America. 108, 18418-18423 (2011).</li><li>Haraga, A., Miller, S. 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Secreted effectors from pathogenic bacteria have evolved to function within the host cell environment and thus it is helpful to study them in situ within the host. Introduction of specific effectors of interest into host cells allows the relevant pathogen-host interactions to be studied in isolation without interference from other bacterial proteins. The goal was to explore electroporation as a means to introduce bacterial effector proteins into eukaryotic host cells, thereby avoiding some of the challenges asso...

Many Gram-negative bacteria employ specialized secretion systems to inject virulence-related proteins (referred to as effectors) directly into host cells 1-5. These effectors have a wide range of biological functions including: suppression of host immunity, cytoskeletal changes, modification of intracellular trafficking and signaling, transcriptional changes, and host proteasome alterations 6-9. The functions of some effectors are known, however the host targets and biochemical action(s) of many others remains to be determined. While comparing wild-type and recombinant bacterial infections is a valid approach to study intracellular effector virulence mechanisms, it is often advantageous to introduce an individual effector into the host cell. Thus, simple methods for introducing and characterizing bacterial effector proteins in the context of host cells is highly desirable.
Simplifying the experimental analysis with a single effector is critical as other effectors may have opposing or redundant functions. To accomplish this simplification, researchers have previously introduced macromolecules into cells by many different methods, including viral transduction 10, microinjection 11, scrape loading 12,13, cell fusion with chemically induced microinjection 14, proprietary protein &#8220;transfection&#8221; reagents 15, calcium phosphate precipitations 16, and electroporation 17-20. The introduced molecules range from nucleic acids including DNA, RNA, &#38; RNAi species to proteins, cell-impermeable dyes, and antibodies for intracellular targets 21,22. Some methods have limitations including the type of macromolecule that can be introduced, and particular downstream analyses may be limited due to high cellular toxicity, damaging mechanisms of action, low efficacy, or introduction efficiency. Transfection, an often-used method for expressing bacterial genes in mammalian cells, also suffers the limitation that some relevant host cell types, such as macrophages and primary cells, are particularly resistant towards transfection. Beyond this, it is difficult to control the levels of bacterial protein produced upon introduction of foreign DNA.
Much work has established electroporation of nucleic acids into both bacterial and mammalian cells as a common laboratory technique; however, there is ongoing research into the best methods for delivering proteins into cells under physiological conditions. Reports on protein transfection are promising, but require expensive reagents and optimization. The desire to introduce potentially toxic bacterial effectors into a wide variety of cell targets with minimal cost led us to consider electroporation as a method for studying these proteins in vivo. 
Protein electroporation 23-25 is a method to introduce proteins into living cells via electropermeabilization, also known as electro-transfection or electro-injection 26. This technique uses high-intensity electrical pulses to create pores in cell membranes. These reversible pores allow macromolecules that are normally excluded from intracellular space to enter the cell. Upon removal of the external electric field, the membrane can reseal, allowing the cell to retain molecules that passed through the pores 27,28.
A standard electroporator was used in this study to consistently introduce bacterial effectors into both mouse macrophage-like cells and human epithelial cells. The method is quick, efficient, and inexpensive, with no appreciable decrease in cellular viability. The introduced proteins can be visualized via immunofluorescence microscopy or used for functional assays. This has been demonstrated using green fluorescent protein (GFP) as a non-toxic standard, as well as two Salmonella effector proteins, SspH1 and GtgE. We propose protein electroporation as an additional tool in the repertoire for the study of bacterial virulence proteins and their functions in eukaryotic host cells.

<table border="0" cellpadding="0" cellspacing="0" width="1132">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:532px;">Material or Equipment</td>
			<td style="width:177px;">Company</td>
			<td style="width:108px;">Catalog Number</td>
			<td style="width:315px;">Comments</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">0.25% Trypsin-EDTA Solution</td>
			<td>Cellgro</td>
			<td>25-050-Cl</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">0.4cm Gap-disposable electroporation cuvettes</td>
			<td>Bio-Rad</td>
			<td>165-2088</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">100% Methanol</td>
			<td>Any</td>
			<td>N/A</td>
			<td>Flammable, Toxic</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Bovine Serum Albumin (BSA)</td>
			<td>Sigma-Aldrich</td>
			<td>A4919</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Cell Counting Apparatus - Hemocytometer or Coulter Counter</td>
			<td>Beckman Coulter</td>
			<td>Model Z1</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Cell Culture Incubator</td>
			<td>Any</td>
			<td>N/A</td>
			<td>Humidified 95% air/5% CO2 atmosphere at 37 &#176;C&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Cell Culture Plastic</td>
			<td>Any</td>
			<td>N/A</td>
			<td>Cell culture flasks/plates, pipets, tubes, rubber policeman</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dulbecco&#39;s Modification of Eagle&#8217;s Medium (DMEM)</td>
			<td>Cellgro</td>
			<td>10-013</td>
			<td>Warm to 37 &#176;C&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Electroporator</td>
			<td>Bio-Rad</td>
			<td>E. coli Pulser</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Fetal Bovine Serum (FBS)</td>
			<td>Cellgro</td>
			<td>35-016-CV</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Fluorescent confocal microscope&#160;</td>
			<td>Ziess</td>
			<td>Model&#160; LSM 710&#160;</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Glass Bottom Dishes for Microscopy</td>
			<td>Wilco Wells</td>
			<td>HBSt-3522</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HALT Protease Inhibitor Cocktail</td>
			<td>Pierce</td>
			<td align="right">78430</td>
			<td>Corrosive, Toxic</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HeLa Cell Line</td>
			<td>ATCC</td>
			<td>ATCC CCL-2</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">LDS 4X Loading Buffer</td>
			<td>Invitrogen</td>
			<td>NP0007</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Minimal Essential Medium (MEM)&#160;</td>
			<td>Cellgro</td>
			<td>10-010</td>
			<td>Warm to 37 &#176;C&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Other fluorescent stains (WGA, DAPI) in conjunction with anti-fade reagent</td>
			<td>Any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Penicillin/Streptomycin</td>
			<td>Cellgro</td>
			<td>30-002-Cl</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">RAW 264.7 Cell line</td>
			<td>ATCC</td>
			<td>TIB-71</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Primary Antibody Against Target of Interest</td>
			<td>Any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Secondary Antibody Conjugated to Fluorophore</td>
			<td>Any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Phosphate Buffered Saline</td>
			<td>Any</td>
			<td>N/A</td>
			<td>Chill to 4 &#176;C&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sterile Phosphate Buffered Saline</td>
			<td>Any</td>
			<td>N/A</td>
			<td>Warm to 37 &#176;C&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Streptavidin Agarose Resin Suspension&#160;</td>
			<td>Pierce</td>
			<td align="right">20353</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Table Top Centrifuge Capable of Accepting Conical Tubes (swinging bucket preferred)</td>
			<td>Any</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">TCEP</td>
			<td>Sigma-Aldrich</td>
			<td align="right">646547</td>
			<td>Corrosive, Toxic</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>T8585</td>
			<td>Irritant, Toxic</td>
		</tr>
	</tbody>
</table>

electroporation of functional bacterial effectors into mammalian cells

The study of protein interactions in the context of living cells can generate critical information about localization, dynamics, and interacting partners. This information is particularly valuable in the context of host-pathogen interactions. Many pathogen proteins function within host cells in a variety of way such as, enabling evasion of the host immune system and survival within the intracellular environment. To study these pathogen-protein host-cell interactions, several approaches are commonly used, including: in vivo infection with a strain expressing a tagged or mutant protein, or introduction of pathogen genes via transfection or transduction. Each of these approaches has advantages and disadvantages. We sought a means to directly introduce exogenous proteins into cells. Electroporation is commonly used to introduce nucleic acids into cells, but has been more rarely applied to proteins although the biophysical basis is exactly the same. A standard electroporator was used to introduce affinity-tagged bacterial effectors into mammalian cells. Human epithelial and mouse macrophage cells were cultured by traditional methods, detached, and placed in 0.4 cm gap electroporation cuvettes with an exogenous bacterial pathogen protein of interest (e.g. Salmonella Typhimurium GtgE). After electroporation (0.3 kV) and a short (4 hr) recovery period, intracellular protein was verified by fluorescently labeling the protein via its affinity tag and examining spatial and temporal distribution by confocal microscopy. The electroporated protein was also shown to be functional inside the cell and capable of correct subcellular trafficking and protein-protein interaction. While the exogenous proteins tended to accumulate on the surface of the cells, the electroporated samples had large increases in intracellular effector concentration relative to incubation alone. The protocol is simple and fast enough to be done in a parallel fashion, allowing for high-throughput characterization of pathogen proteins in host cells including subcellular targeting and function of virulence proteins.

As an initial proof of concept, purified green fluorescent protein was successfully introduced into mammalian cells using electroporation. GFP, an approximate 27 kD a molecular weight protein is commonly introduced into mammalian cells (normally expressed from plasmid DNA) as a molecular biology tool without significant cellular toxicity. HeLa cells were incubated (Figure 1A) or electroporated (Figure 1B) with 25 &#181;g/ml GFP, followed by immunofluorescence confocal microscopy to check...

Watch this Scientific Journal Video about Electroporation of Functional Bacterial Effectors into Mammalian Cells at JoVE.com

Electroporation of Functional Bacterial Effectors into Mammalian Cells

Electroporation was used to insert purified bacterial virulence effector proteins directly into living eukaryotic cells. Protein localization was monitored by confocal immunofluorescence microscopy. This method allows for studies on trafficking, function, and protein-protein interactions using active exogenous proteins, avoiding the need for heterologous expression in eukaryotic cells.

The study of protein interactions in the context of living cells can generate critical information about localization, dynamics, and interacting partners. ...

Research

JoVE Journal

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