Name: conditional knockdown of gene expression in cancer cell lines to study the recruitment of monocytes/macrophages to the tumor microenvironment
Uploaded: 2017-11-23T14:00:00
Description: Watch this Scientific Journal Video about Conditional Knockdown of Gene Expression in Cancer Cell Lines to Study the Recruitment of Monocytes/Macrophages to the Tumor Microenvironment at JoVE.com

The authors would like to acknowledge Jacqueline Rosenberg for proofreading the manuscript. This work was supported by the US Department of Health and Human Services/National Institutes of Health with a grant to YA DeClerck (grant 5R01 CA 129377) and the TJ Martell Foundation. MH Kubala is the recipient of a Research Career Development Fellowship award of The Saban Research Institute at Children's Hospital Los Angeles.

The protocol section that uses human monocytes obtained from healthy volunteers follows the guidelines of the Children&#39;s Hospital Los Angeles Human Research Ethics Committee and has been approved by the Institutional Review Board under the Human Material Protocol number: CCI 08-00208.
1. Preparation of Cancer Cell Lines with Tetracycline-regulated shRNA Expression
<ol>
	<li>Cloning of shRNA PAI-1 into Tet-pLKO-puro vector8,<sup class="x...

<ol>
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R., Gustavsson, B., Masback, A., Casslen, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dedifferentiation+of+serous+ovarian+cancer+from+cystic+to+solid+tumors+is+associated+with+increased+expression+of+mRNA+for+urokinase+plasminogen+activator+(uPA),+its+receptor+(uPAR)+and+its+inhibitor+(PAI-1).">Dedifferentiation of serous ovarian cancer from cystic to solid tumors is associated with increased expression of mRNA for urokinase plasminogen activator (uPA), its receptor (uPAR) and its inhibitor (PAI-1).</a> Int J Cancer. 92 (4), 497-502 (2001).</li><li>Devy, 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=The+pro-+or+antiangiogenic+effect+of+plasminogen+activator+inhibitor+1+is+dose+dependent.">The pro- or antiangiogenic effect of plasminogen activator inhibitor 1 is dose dependent.</a> FASEB J. 16 (2), 147-154 (2002).</li><li>Bajou, K., 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=Plasminogen+activator+inhibitor-1+protects+endothelial+cells+from+FasL-mediated+apoptosis.">Plasminogen activator inhibitor-1 protects endothelial cells from FasL-mediated apoptosis.</a> Cancer Cell. 14 (4), 324-334 (2008).</li><li>Xu, X., Wang, H., Wang, Z., Xiao, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasminogen+activator+inhibitor-1+promotes+inflammatory+process+induced+by+cigarette+smoke+extraction+or+lipopolysaccharides+in+alveolar+epithelial+cells.">Plasminogen activator inhibitor-1 promotes inflammatory process induced by cigarette smoke extraction or lipopolysaccharides in alveolar epithelial cells.</a> Exp Lung Res. 35 (9), 795-805 (2009).</li><li>Ji, Y., 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=Pharmacological+Targeting+of+Plasminogen+Activator+Inhibitor-1+Decreases+Vascular+Smooth+Muscle+Cell+Migration+and+Neointima+Formation.">Pharmacological Targeting of Plasminogen Activator Inhibitor-1 Decreases Vascular Smooth Muscle Cell Migration and Neointima Formation.</a> Arterioscler Thromb Vasc Biol. 36 (11), 2167-2175 (2016).</li><li>Carmeliet, P., 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=Inhibitory+role+of+plasminogen+activator+inhibitor-1+in+arterial+wound+healing+and+neointima+formation:+a+gene+targeting+and+gene+transfer+study+in+mice.">Inhibitory role of plasminogen activator inhibitor-1 in arterial wound healing and neointima formation: a gene targeting and gene transfer study in mice.</a> Circulation. 96 (9), 3180-3191 (1997).</li><li>Cao, C., 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=Endocytic+receptor+LRP+together+with+tPA+and+PAI-1+coordinates+Mac-1-dependent+macrophage+migration.">Endocytic receptor LRP together with tPA and PAI-1 coordinates Mac-1-dependent macrophage migration.</a> EMBO J. 25 (9), 1860-1870 (2006).</li><li>Thapa, B., Koo, B. 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Composed of a variety of cell types, the TME is crucial for the development of cancer. To ascertain optimal growth conditions, cancer cells attract monocytes through secretion of chemotactic factors. Here we present a protocol for studying the mechanism of monocyte recruitment by tumor cells in vitro. For this purpose, a combination of inducible gene expression system, purification of primary human monocytes, and as an example of a migration assay, the Boyden chamber assay, is used.
T...

Tumor associated macrophages (TAMs) contribute to tumor development by promoting tumor growth, metastasis, and regulating the immune response2. Cancer cells recruit inflammatory monocytes, which infiltrate tumor and differentiate into pro-tumorigenic TAMs3. Infiltration of the tumor with TAMs correlates with poor clinical outcome and has been linked to the immunosuppressive role of macrophages4,5. However, the mechanisms of the recruitment of macrophages to the tumor are not well explored and a better understanding of the involved pathways is crucial for further advancement of the field and promising therapies. One of the challenges in studying interactions between tumor cells and normal cells in the tumor microenvironment (TME) is the complexity of the mechanisms and cells involved, requiring in vitro approaches that allow dissection of the crosstalk. Here we present a versatile methodology that can be applied to study the paracrine effect of a cancer cell-derived, secreted protein on migration of other cell types like macrophages, in vitro. Using a system where the expression of the shRNA against a cancer cell-derived protein involved in the recruitment of monocytes is under the control of the tetracycline inducible promoter, the paracrine effect of the secreted protein on monocytes is quantitated. In this protocol, cloning of shRNA sequences into the tetracycline regulated vector is presented followed by generation of stable cancer cell lines. Further, the purification of primary human monocytes and a Boyden chamber assay are used to analyze the paracrine effect of a cancer-cell derived protein on migration of monocytes.
Downregulation of protein coding genes is commonly applied with siRNA and shRNA techniques, though not without limitations in its use. The long-term knock-down (KD) of genes may elicit secondary adaptive responses of cells that interfere with experimental results. Lack of temporal control over gene expression makes it challenging to study the dynamic role of a protein over time or the role of a protein crucial for cell survival. This issue is especially important in in vivo settings, where the role of a protein in tumor development and progression might require downregulation of the expression of the protein of interest only after tumor is established. Conditional KD has the advantage of preventing a too early lethal effect of the KD on cells, and to enable analysis of the role of the protein within different stages of tumor growth, while unconditional KD could result in lack of tumor development.
A number of conditional KD systems have been developed to address the limitations of stable KD. The conditional gene expression systems include Ecdysone-inducible overexpression systems, the Cytochrome P-450 induction system1, and tetracycline regulated gene expression systems. The tetracycline-regulated gene expression systems allow control over expression of the shRNA upon addition of the antibiotic tetracycline (or its more stable analogue - doxycycline). In Tet-ON systems, the expression of shRNA is induced in the presence of tetracycline/doxycycline resulting in a gene expression KD, while in Tet-OFF systems, the expression of shRNA is suppressed in the presence of tetracycline resulting in gene expression. A drawback of tetracycline-inducible system is previously reported low levels of expression of shRNA in the absence of doxycycline - so-called leakiness6,7. In the Tet-ON system described here, upon administration of tetracycline, the binding of constitutively expressed tetracycline repressor (TetR) protein to the Tet-responsive element (TRE) sequence within the H1 promoter region of the shRNA of interest is suppressed. This results in expression of shRNA and inhibition of translation of the protein of interest in a tetracycline-dependent manner8,9.
Other available Tet-ON systems include simultaneous knock-in of the TetO sequence between TATA box and proximal sequence element (PSE) and between TATA box and transcription start site developed by Chan et al.10 This system requires less than toxic doses of tetracycline to regulate shRNA expression, however, under a non-induced state, low levels of shRNA are expressed. The Kr&#252;ppel-associated box (KRAB) based Tet-ON system11 includes KRAB, a zinc finger protein, which subjects genes located within a 3 kb range of the KRAB binding site to transcriptional suppression. The chimeric protein tTRKRAB can bind to TetO, and due to the large-range of DNA controllable capacity, TetO do not need to be limited between the transcription start site and the promoter and have low impact on the activity of the promoter. Under the non-induced state, this controllable RNA interference system was reported to show a lower level of leaked expression of shRNA11,12; however, it requires a sequential, two-vector cloning approach. In comparison to previously developed conditional KD systems such as the Ecdysone-inducible overexpression system or Cytochrome P-450 induction system, the tetracycline-regulated system has the advantage of its robustness and reversibility, and therefore is the most routinely used system13. The system used in this protocol has the advantage over the dual TetO knock-in system and KRAB Tet-ON system as it requires straight forward, single vector cloning, allowing quick generation of multiple clones, and it exhibits very low levels of leakiness in the absence of doxycycline.
TME is critical for the development of cancer. To facilitate tumor growth, cancer cells recruit inflammatory monocytes by secreting chemotactic proteins. Recruited monocytes infiltrate the tumor and differentiate into pro-tumorigenic TAMs that contribute to tumor growth and metastasis. In vitro studies of the immune cell recruitment utilize migration assays, with Boyden chamber assay being widely used14,15,16,17. In this assay, the chemoattractant protein source, for example, cancer cells, or a purified protein, is placed in the bottom chamber. Immune cells are placed in the upper chamber separated with porous membrane from the bottom compartment. Cells migrating toward the increasing gradient of chemoattractant, and those found on the lower side of the membrane are stained and counted under the microscope. Here we test the chemoattractant function of Plasminogen Activator Inhibitor 1 (PAI-1) on monocytes by generating stable, inducible cancer cell lines where expression of PAI-1 is regulated by doxycycline addition. We use human primary monocytes in the Boyden chamber migration assay to assess the role of PAI-1 in monocyte migration. Differences between human primary monocytes and widely used monocytic cell lines like THP1 have been reported and include different cytokine expression patterns18; for example, 5 - 10 fold increase in TNF-&#945; expression levels by THP1 cells compared to human monocytes19. THP1 cells are derived from human leukemia monocytic cells, are easy to maintain, and proliferate with an average doubling time of 19 - 50 h20. On the contrary, human monocytes are characterized by a short lifespan in the absence of growth factors. Since monocytes are purified from blood of donors, a fair amount of variability occurs among the individuals and depending on the purification method, contamination with other cell types may occur. Nevertheless, primary monocytes are relevant and it has been recommended to use or confirm the results obtained with the monocytic cell lines using primary monocytes in biological research19. Here we describe a protocol for purification of human primary monocytes from peripheral blood. Alternative methods of monocyte purification include density gradient and adhesion protocols and two step procedure with single gradients of Ficoll-Hypaque followed by a Percoll gradient21. The purity of the monocyte population obtained by those methods ranges between 70 - 90%. The method described here uses a density gradient followed by a negative immune selection22 and enables the purification of human monocytes without direct contact with antibodies, thereby avoiding their accidental activation and resulting in a &#62;95% pure population of monocytes.
The protocol presented here is used for setting up a functional Tet-ON system for gene expression KD in human cancer cell lines to study the chemoattractant effect of the cancer-derived secreted protein PAI-1 on monocytes. PAI-1 is overexpressed by a variety of tumors and its expression paradoxically correlates with poor clinical outcome23,24. The pro-tumorigenic role of PAI-1 is a result of its pro-angiogenic and anti-apoptotic functions25,26. PAI-1 has been shown to contribute to inflammation by promoting the recruitment of macrophages to the site of inflammation27. PAI-1 was shown to promote smooth muscle cellmigration28,29 and to participate in the Mac-1 dependent macrophage migration30. PAI-1 overexpression has been also shown to significantly enhance the recruitment of Raw 264.7 macrophages into B16F10 melanoma tumors31. However, the role of PAI-1 in TAM migration has not been investigated in detail. We use the described protocol to answer the question of whether PAI-1 attracts monocytes to cancer cells. This methodology allows dissection of the crosstalk between tumor and TME by silencing the secreted protein in cancer cells and analyzing the components of the TME.

<table border="0" cellpadding="0" cellspacing="0" width="868">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Tet-pLKO-puro lentiviral vector</td>
			<td style="width:177px;">Addgene</td>
			<td style="width:119px;">21915</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">FBS (Tetracycline-free)</td>
			<td style="width:177px;">Omega Scientific</td>
			<td style="width:119px;">FB-15</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Histopaque</td>
			<td style="width:177px;">Sigma</td>
			<td>10771-500ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">EasySep Human Monocyte Enrichment Kit</td>
			<td style="width:177px;">StemCell</td>
			<td>19059</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">EasySep Magnet</td>
			<td style="width:177px;">StemCell</td>
			<td>18002</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">EcoRI HF</td>
			<td style="width:177px;">NEB</td>
			<td>R3101S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">AgeI HF</td>
			<td style="width:177px;">NEB</td>
			<td>R3552S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cut Smart buffer</td>
			<td style="width:177px;">NEB</td>
			<td>B7200S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">EndoFree Plasmid Maxi Kit</td>
			<td style="width:177px;">Qiagen</td>
			<td>12362</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PROMEGA Wizard SV Gel and PCR Cleanup System</td>
			<td style="width:177px;">PROMEGA</td>
			<td>A9281</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">psPAX vector</td>
			<td style="width:177px;">Addgene</td>
			<td style="width:119px;">12260</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">pMD2.G vector</td>
			<td style="width:177px;">Addgene</td>
			<td style="width:119px;">12259</td>
			<td></td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:405px;">One Shot Stbl3 Chemically Competent&#160;E. coli</td>
			<td style="width:177px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">C737303</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hema 3 stain set for Wright-Giemsa stain</td>
			<td style="width:177px;">Protocol</td>
			<td style="width:119px;">123-869</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HEK293 cells</td>
			<td style="width:177px;">ATCC</td>
			<td style="width:119px;">CRL-1573</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PBS</td>
			<td style="width:177px;">Corning</td>
			<td style="width:119px;">21-031-CV</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">XhoI restriction enzyme</td>
			<td style="width:177px;">NEB</td>
			<td>R0146S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ligase</td>
			<td style="width:177px;">NEB</td>
			<td>M0202S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ligase buffer</td>
			<td style="width:177px;">NEB</td>
			<td>M0202S</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">EDTA 0.5 M solution</td>
			<td style="width:177px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">R1021</td>
			<td></td>
		</tr>
		<tr height="21">
			<td>Lipofectamine 2000</td>
			<td style="width:177px;">Invitrogen</td>
			<td>11668019</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">The Big Easy&#34; EasySep Magnet</td>
			<td style="width:177px;">Stem Cell</td>
			<td style="width:119px;">18001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">0.1% Poly-L-Lysine solution</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">P8920</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium Acetate</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">S7670</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium butyrate</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">B5887</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">0.45 &#956;M syringe filters</td>
			<td style="width:177px;">VWR International</td>
			<td>28145-479</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NaOH</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">S5881-500g</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tris(hydroxymethyl)aminomethane (Tris)</td>
			<td style="width:177px;">Invitrogen</td>
			<td style="width:119px;">15504-020</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium Chloride(NaCl)</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">S7653-5 kg</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Magnesium Chloride (MgCl2)</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">M8266-100g</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">dithioerythritol (DTE)</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">B8255-5g</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ethanol (EtOH)</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">792780</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">tryptone</td>
			<td style="width:177px;">Amresco</td>
			<td style="width:119px;">J859-500g</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">yeast extract</td>
			<td style="width:177px;">Fluka</td>
			<td style="width:119px;">70161-500g</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bacto agar</td>
			<td style="width:177px;">BD</td>
			<td style="width:119px;">214010</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ampicillin</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">A9393-5g</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dulbecco&#8217;s Modified Eagle&#8217;s Medium (DMEM)</td>
			<td style="width:177px;">Corning</td>
			<td style="width:119px;">10-013-CV</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">phosphate-buffered saline (PBS)</td>
			<td style="width:177px;">Corning</td>
			<td style="width:119px;">21-031-CV</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">H3375</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">puromycin</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">P9620</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Doxycycline hyclate</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">D9891-25g</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Roswell Park Memorial Institute (RPMI)</td>
			<td style="width:177px;">Corning</td>
			<td style="width:119px;">10-040-CV</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">0.5 M EDTA pH 8.0</td>
			<td style="width:177px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">R1021</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:405px;">Falcon Permeable Support for 24 Well Plate with 8.0&#956;m Transparent PET Membrane</td>
			<td style="width:177px;">Becton Dickinson</td>
			<td style="width:119px;">353097</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Bovine Serum Albumin</td>
			<td style="width:177px;">Sigma-Aldrich</td>
			<td style="width:119px;">A7906</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cotton-Tipped Applicator&#160;</td>
			<td style="width:177px;">Medline</td>
			<td style="width:119px;">MDS202000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Protocol Hema 3 STAT pack&#160;</td>
			<td style="width:177px;">Fisher Scientific Company</td>
			<td style="width:119px;">123-869</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Resolve Immersion Oil, High Viscosity</td>
			<td style="width:177px;">Richard Allan Scientific</td>
			<td style="width:119px;">M4004</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Penicillin Streptomycin</td>
			<td style="width:177px;">Gibco</td>
			<td style="width:119px;">15140122</td>
			<td></td>
		</tr>
	</tbody>
</table>

conditional knockdown of gene expression in cancer cell lines to study the recruitment of monocytes/macrophages to the tumor microenvironment

siRNA and shRNA-mediated knock down (KD) methods of regulating gene expression are invaluable tools for understanding gene and protein function. However, in the case that the KD of the protein of interest has a lethal effect on cells or the anticipated effect of the KD is time-dependent, unconditional KD methods are not appropriate. Conditional systems are more suitable in these cases and have been the subject of much interest. These include Ecdysone-inducible overexpression systems, Cytochrome P-450 induction system1, and the tetracycline regulated gene expression systems. 
The tetracycline regulated gene expression system enables reversible control over protein expression by induction of shRNA expression in the presence of tetracycline. In this protocol, we present an experimental design using functional Tet-ON system in human cancer cell lines for conditional regulation of gene expression. We then demonstrate the use of this system in the study of tumor cell-monocyte interaction.

Three shRNA sequences were tested for the most efficient KD of PAI-1. For this, shRNA sequences against PAI-1 and scrambled (Table 1) were cloned into Tet-pLKO-puro expression vector following the protocol described above. The HT-1080 fibrosarcoma cell line was stably transfected with generated constructs and the cells were treated with doxycycline for 3 days. The expression of PAI-1 was verified by Western blotting (Figure 2A</strong...

Watch this Scientific Journal Video about Conditional Knockdown of Gene Expression in Cancer Cell Lines to Study the Recruitment of Monocytes/Macrophages to the Tumor Microenvironment at JoVE.com

Conditional Knockdown of Gene Expression in Cancer Cell Lines to Study the Recruitment of Monocytes/Macrophages to the Tumor Microenvironment

This protocol serves as a scheme for setting up a functional Tet-ON system in cancer cell lines and its subsequent use, in particular for studying the role of tumor cell-derived proteins in recruitment of monocytes/macrophages to the tumor microenvironment.

siRNA and shRNA-mediated knock down (KD) methods of regulating gene expression are invaluable tools for understanding gene and protein function. However, ...

The overall of this protocol is to utilize conditional knockdown of gene expression in cancer cells to study the recruitment of monocytes and macrophages to the tumor microenvironment in vitro. This method can help answer key questions in the tumor microenvironment field regarding the nature of the cross stock between the cancer cells and the cells of the immune system. The main advantage of this technique is that the system used here requires single vector cloning, allows quick generation of multiple clones, and exhibits very low levels of thickness.Also demonstrated is a method for purification of human monocytes without direct contact with antibodies which avoids accidental activation while resulting in more than 95%pure population of human monocytes. To produce viral particles, transfect 70%confluent 150 millimeter dishes of HEK-293 cells with 25 micrograms of pLKO-tet-on shRNA, 25 micrograms of the psPAX packaging plasmid, and five micrograms of the envelope-expressing plasmid pMD2. G using transfection reagent as per standard protocols.Add mix to the 150 millimeter dishes. The next day, induce Lentiviral production in the cells by changing the medium to DMEM supplemented with 10 millimolar sodium butyrate and 20 millimolar HEPES. Culture for eight hours at 37 degrees Celsius and 5%carbon dioxide.After eight hours, wash the cells with PBS and add 25 milliliters of fresh DMEM medium with 20 millimolar HEPES and without sodium butyrate. After incubation for 48 hours, carefully collect the virus-containing medium with a pipette. To generate stable cell lines, start by seeding HCT-116 colon cancer cells and MDA-MB-231 breast cancer cells into a 12-well plate and 50, 000 cells per well.Incubate at 37 degrees Celsius and 5%carbon dioxide. When the cells are 60-70%confluent, wash the cells with PBS and add one milliliter of virus-containing medium to each well. The next day, carefully remove the virus-containing medium by aspiration.Then after washing the cells with PBS, add medium containing tetracycline-free FBS. After 72 hours, wash the cells as before and add medium supplemented with one microgram per milliliter puromycin for the selection of virus-transfected cells. Select virus-transduced cells by culturing cells in the presence of puromycin for three to 14 days.Observe partial killing of the wells by puromycin in the cells with virus-transduced cells. Non-transduced cells will not grow in the presence of puromycin. When these control cells have died, continue culture of the conditionally regulated cell lines for two weeks in the presence of antibiotics to create the conditionally regulated cell lines.Verify the efficiency of the conditional knockdown in the puromycin-resistant HCT-116 colon cancer and MDA-MB-231 breast cancer cells by adding medium with different concentrations of doxycycline and culturing the cells for 72 hours. After preparing cell lysate, verify the level of knockdown by western blot analysis. Levels of PAI-1 are shown here.To isolate peripheral blood monocytes, first prepare three 50 milliliter tubes containing 15 milliliters of density gradient solution. Then use a pipette controller set on gravitational flow to slowly layer 30 milliliters of diluted blood over the density gradient solution. Centrifuge in a swing rotor at 400 g at room temperature without breaks for 25 minutes.Following the centrifugation, dispose of the top layer and transfer the middle layer containing peripheral blood mononuclear cells to a fresh 50 milliliter tube and add FBS supplemented PBS up to 50 milliliters. Centrifuge at 120 g's at room temperature for 10 minutes. After the spin, remove the containing platelet-containing supernatant.Following the final centrifugation and collection, resuspend the pellet in 50 milliliters of FBS supplemented PBS and count the peripheral blood mononuclear cells using a hemocytometer. After centrifuging the cells at 120 g's, resuspend the pellet in FBS supplemented PBS containing one millimolar EDTA to a final concentration of 50 million cells per milliliter. Then begin to enrich for monocytes by adding 50 microliters of negative selection antibody cocktail for each milliliter of cell suspension and mix.Incubate for 10 minutes at room temperature. After the incubation, add 50 microliters of magnetic beads per milliliter, mix and incubate for another 10 minutes. Then add PBS with FBS and EDTA up to 25 milliliters and place the peripheral blood mononuclear mixture in a magnet that can accommodate a 50 milliliter tube.After incubating for 10 minutes at room temperature, the magnetic beads will adhere to the walls of the tube and sequester the non-monocytic cells from the solution. Use a 25 milliliter pipette to remove solution containing monocytes from the tube while being careful not to touch the sides of the tube with the pipette. After centrifuging and removing the supernatant, resuspend the pellet containing monocytes in RPMI medium containing 10%TET-free FBS and 1%pen-strep.Begin the assay by seeding 40, 000 HCT-116 or MDA-MB-231 cells in a 0.5 milliliter volume in the wells of a 24-well plate in triplicate. The next day, add a filter to the well. Then plate 8, 000 monocytes in a 0.3 milliliter volume onto a BSA-treated porous membrane insert placed on the top of the cancer cells and incubate at 37 degrees Celsius and 5%carbon dioxide.Collect the inserts after 48 hours. Shake off the excess medium and precisely swipe the inner surface with a cotton-tipped applicator to remove cells that did not migrate. Stain the outer side of the insert using the Wright-Giemsa method.After mounting the filters with the migrated macrophages side up, image the slides using a light microscope with a 20 power objective. Take pictures of nine fields per filter and count migrated macrophages in all fields. The Boyden Chamber Assay was used to quantify the migration of monocytes towards cancer cells.In the presence of MDA-MB-231 breast cancer cells, the migration of monocytes was inhibited by 33%after addition of doxycycline to the co-culture to down regulate PAI-1. This inhibition of monocyte migration was more pronounced in the presence of HCT-116 colon cancer cells where knockdown of PAI-1 by doxycycline administration reduced monocyte migration by 74%Similar results were observed when conditions medium for doxycycline-treated cancer cells was placed in the bottom of the wells as a source of chemoattractants. After watching this video, you should have a good understanding on how to use a functional tet-on system for gene expression knockdown in human cancer cell lines to study the chemoattractant effect of cancer-derived secreted protein PAI-1 on the human monocytes.

Research

JoVE Journal

Cancer Research

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