Name: analysis of cap-binding proteins in human cells exposed to physiological oxygen conditions
Uploaded: 2016-12-28T15:00:00
Description: Watch this Scientific Journal Video about Analysis of Cap-binding Proteins in Human Cells Exposed to Physiological Oxygen Conditions at JoVE.com

This work was supported by the Natural Sciences and Engineering Council of Canada and the Ontario Ministry of Research and Innovation.

1. Preparations for Cell Culture
<ol>
	<li>Purchase commercially available stocks of human cells. 
	NOTE: This protocol utilizes HCT116 colorectal carcinoma and primary human renal proximal tubular epithelial cells (HRPTEC).</li>
	<li>Make 500 ml medium for culture of HCT116: Dulbecco&#39;s Modified Eagle Medium (DMEM)/High glucose medium supplemented with 7.5% Fetal Bovine Serum (FBS) and 1% Penicillin/Streptomycin (P/S).</li>
	<li>Make 500 ml medium for culture of HRPTEC: Epithelial cell medium supplemented with...

<ol>
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The analysis of cap-binding proteins in human cells exposed to physiological oxygen conditions can allow for the identification of novel oxygen-regulated translation initiation factors. The affinity of these factors for the 5&#39; cap of mRNA or other cap-associated proteins can be measured by the strength of their association to m7GTP-linked Agarose beads. One caveat of this technique is that it measures the cap-binding potential of proteins post-lysis, but it is performed under non-denaturing conditions that...

Translational control is emerging as an equally important step to transcriptional regulation in gene expression, especially during periods of cellular stress1. A focal point of translation control is at the rate-limiting step of initiation where the first steps of protein synthesis involve the binding of the eukaryotic initiation factor 4E (eIF4E) to the 7-methylguanosine (m7GTP) 5&#39; cap of mRNAs2. eIF4E is part of a trimeric complex named eIF4F that includes eIF4A, an RNA helicase, and eIF4G, a scaffolding protein required for the recruitment of other translation factors and the 40S ribosome3. Under normal physiological conditions, the vast majority of mRNAs are translated via a cap-dependent mechanism, but under periods of cellular stress approximately 10% of human mRNAs contain 5&#39; UTRs that could allow cap-independent translation intiation1,4. Cap-dependent translation has been historically synonymous with eIF4F, however, stress-specific variations of eIF4F have become a trending topic5-8.
Various cellular stresses cause eIF4E activity to be repressed via the mammalian target of rapamycin complex 1 (mTORC1). This kinase becomes impaired under stress, which results in the increased activity of one of its targets, the 4E-binding protein (4E-BP). Non-phosphorylated 4E-BP binds to eIF4E and blocks its ability to interact with eIF4G causing the repression of cap-dependent translation9,10. Interestingly, a homolog of eIF4E named eIF4E2 (or 4EHP) has a much lower affinity for 4E-BP11, perhaps allowing it to evade stress-mediated repression. Indeed, initially characterized as a repressor of translation due to its lack of interaction with eIF4G12, eIF4E2 initiates the translation of hundreds of mRNAs that contain RNA hypoxia response elements in their 3&#39; UTR during hypoxic stress6,13. This activation is achieved through interactions with eIF4G3, RNA binding protein motif 4, and the hypoxia inducible factor (HIF) 2&#945; to constitute a hypoxic eIF4F complex, or eIF4FH6,13. As a repressor under normal conditions, eIF4E2 binds with GIGYF2 and ZNF59814. These complexes were, in part, identified through Agarose-linked m7GTP affinity resins. This classic method15 is standard in the field of translation and is the best and most commonly used technique to isolate cap-binding complexes in pull down and in vitro binding assays16-19. As the cap-dependent translation machinery is emerging as flexible and adaptable with inter-changing parts6-8,13, this method is a powerful tool to rapidly identify novel cap-binding proteins involved in the stress response. Furthermore, variations in eIF4F could have broad implications as several eukaryotic model systems appear to use an eIF4E2 homolog for stress responses such as A. thaliana20, S. Pombe21, D. melanogaster22, and C. elegans23.
Evidence suggests that variations in eIF4F may not be strictly limited to stress conditions, but be involved in normal physiology24. The oxygen supply to tissues (at capillary ends) or within tissues (measured via microelectrodes) varies from 2-6% in the brain25, 3-12% in the lungs26, 3.5-6% in the intestine27, 4% in the liver28, 7-12% in the kidney29, 4% in muscle30, and 6-7% in bone marrow31. Cells and mitochondria contain less than 1.3% oxygen32. These values are much closer to hypoxia than the ambient air where cells are routinely cultured. This suggests that what were previously thought of as hypoxia-specific cellular processes may be relevant in a physiological setting. Interestingly, eIF4F and eIF4FH actively participate in the translation initiation of distinct pools or classes of mRNAs in several different human cell lines exposed to physiological oxygen or &#34;physioxia&#34;24. Low oxygen also drives proper fetal development33 and cells generally have higher proliferation rates, longer lifespans, less DNA damage and less general stress responses in physioxia34. Therefore, eIF4FH is likely a key factor in the expression of select genes under physiological conditions.
Here, we provide a protocol to culture cells in fixed physiological oxygen conditions or in a dynamic fluctuating range that is likely more representative of tissue microenvironments. One advantage of this method is that cells are lysed within the hypoxia workstation. It is not often clear how the transition from hypoxic cell culture to cell lysis is performed in other protocols. Cells are often first removed from a small hypoxia incubator before lysis, but this exposure to oxygen could affect biochemical pathways as the cellular response to oxygen is rapid (one or two min)35. Certain cap-binding proteins require interactions with a second base or can hydrolyze the m7GTP, therefore some cap interactors may be missed in the purification process. Agarose-linked to enzymatically resistant cap analogs may be substituted in this protocol. Exploring the activity and composition of eIF4FH and other variations of eIF4F through the method described here will shed light on the intricate gene expression machineries that cells utilize during physiological conditions or stress responses.

<table border="0" cellpadding="0" cellspacing="0" width="901">
	<tbody>
		<tr height="26">
			<td height="26" style="height:26px;width:380px;">&#947;-aminophenyl-m7GTP agarose C10-linked beads</td>
			<td style="width:151px;">Jena Bioscience</td>
			<td style="width:165px;">AC-1555</td>
			<td style="width:205px;">Agarose-linked m7GTP</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">100 mm culture dish</td>
			<td>Corning</td>
			<td>877222</td>
			<td>10-cm culture dish</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">150 mm culture dish</td>
			<td>Thermofisher</td>
			<td>130183</td>
			<td>15-cm culture dish</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">AEBSF Hydrochloride</td>
			<td>ACROS Organics</td>
			<td>A0356829</td>
			<td>AEBSF</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Agarose Beads</td>
			<td>Jena Bioscience&#160;</td>
			<td>AC-0015</td>
			<td>Agarose bead control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bromophenol Blue</td>
			<td>Fisher</td>
			<td>BP112-25</td>
			<td>Component of SDS-PAGE loading buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1.5 mL Centrifuge Tubes</td>
			<td>FroggaBio</td>
			<td>1210-00S</td>
			<td>Used to centrifuge small volumes</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">15 mL Conical Centrifuge Tubes</td>
			<td>Fisher</td>
			<td>1495970C</td>
			<td>Used in culturing primary cells</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Defined trypsin inhibitor</td>
			<td>Fisher</td>
			<td>R007100</td>
			<td>DTI</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dithiothreital</td>
			<td>Fisher</td>
			<td>BP172-25</td>
			<td>DTT</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Epithelial cell medium (complete kit)</td>
			<td>ScienCell</td>
			<td>4101</td>
			<td>Includes serum and growth factor supplements)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glycerol</td>
			<td>Fisher</td>
			<td>BP229-1</td>
			<td>Component of SDS-PAGE loading buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">100 mM Guanosine 5&#39;-triphosphate, 1 mL</td>
			<td>Jena Bioscience</td>
			<td>272076-0251M</td>
			<td>GTP</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HCT116 colorectal carcinoma</td>
			<td>ATCC</td>
			<td>CCL-247</td>
			<td>Human cancer cell line</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Human renal proximal tubular epithelial cells</td>
			<td>ATCC</td>
			<td>PCS-400-010</td>
			<td>HRPTEC</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hyclone DMEM/High Glucose</td>
			<td>GE Life Sciences</td>
			<td>SH30022.01</td>
			<td>Standard media for human cell culture</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hyclone Penicillin-Streptomycin solution</td>
			<td>GE Life Sciences</td>
			<td>SV30010</td>
			<td>Antibiotic component of DMEM</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">H35 HypOxystation</td>
			<td>Hypoxygen</td>
			<td>N/A</td>
			<td>Hypoxia workstation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Igepal CA-630</td>
			<td>MP Biomedicals</td>
			<td>2198596</td>
			<td>Detergent component of lysis buffer</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">Monopotassium phosphate</td>
			<td>Fisher</td>
			<td>P288-500</td>
			<td>KH2PO4</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Potassium chloride</td>
			<td>Fisher</td>
			<td>P217-500</td>
			<td>KCl</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Magnesium chloride</td>
			<td>Fisher</td>
			<td>M33-500</td>
			<td>MgCl2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium chloride</td>
			<td>Fisher</td>
			<td>BP358-10</td>
			<td>NaCl</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium fluoride</td>
			<td>Fisher</td>
			<td>5299-100</td>
			<td>NaF (phosphatase inhibitor component of lysis buffer)</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Disodium phosphate</td>
			<td>Fisher</td>
			<td>5369-500</td>
			<td>Na2HPO4</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Premium Grade Fetal Bovine Serum</td>
			<td>Seradigm</td>
			<td>1500-500</td>
			<td>FBS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Protease Inhibitor Cocktail (100 x)</td>
			<td>Cell Signalling</td>
			<td>58715</td>
			<td>Component of lysis buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium Dodecyl Sulfate</td>
			<td>Fisher</td>
			<td>BP166-100</td>
			<td>SDS</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;">Sodium Orthovanadate</td>
			<td>Sigma</td>
			<td>56508</td>
			<td>Na3VO4</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tris Base</td>
			<td>Fisher</td>
			<td>BP152-5</td>
			<td>Component of buffers</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">0.05% Trypsin-EDTA (1x)</td>
			<td>Life Technologies</td>
			<td>2500-067</td>
			<td>Trypsin used to detach adherent cells</td>
		</tr>
	</tbody>
</table>

analysis of cap-binding proteins in human cells exposed to physiological oxygen conditions

Translational control is a focal point of gene regulation, especially during periods of cellular stress. Cap-dependent translation via the eIF4F complex is by far the most common pathway to initiate protein synthesis in eukaryotic cells, but stress-specific variations of this complex are now emerging. Purifying cap-binding proteins with an affinity resin composed of Agarose-linked m7GTP (a 5' mRNA cap analog) is a useful tool to identify factors involved in the regulation of translation initiation. Hypoxia (low oxygen) is a cellular stress encountered during fetal development and tumor progression, and is highly dependent on translation regulation. Furthermore, it was recently reported that human adult organs have a lower oxygen content (physioxia 1-9% oxygen) that is closer to hypoxia than the ambient air where cells are routinely cultured. With the ongoing characterization of a hypoxic eIF4F complex (eIF4FH), there is increasing interest in understanding oxygen-dependent translation initiation through the 5' mRNA cap. We have recently developed a human cell culture method to analyze cap-binding proteins that are regulated by oxygen availability. This protocol emphasizes that cell culture and lysis be performed in a hypoxia workstation to eliminate exposure to oxygen. Cells must be incubated for at least 24 hr for the liquid media to equilibrate with the atmosphere within the workstation. To avoid this limitation, pre-conditioned media (de-oxygenated) can be added to cells if shorter time points are required. Certain cap-binding proteins require interactions with a second base or can hydrolyze the m7GTP, therefore some cap interactors may be missed in the purification process. Agarose-linked to enzymatically resistant cap analogs may be substituted in this protocol. This method allows the user to identify novel oxygen-regulated translation factors involved in cap-dependent translation.

Analysis of Cap-binding Ability in Response to Oxygen of eIF4E and eIF4E2 in an m7GTP Affinity Column
Figures 1 and 2 represent western blots of typical m7GTP affinity purification of two major cap-binding proteins in response to oxygen fluctuations in two human cell lines: primary human renal proximal tubular epithelial cells (HRPTEC) in Figure 1 and colorect...

Watch this Scientific Journal Video about Analysis of Cap-binding Proteins in Human Cells Exposed to Physiological Oxygen Conditions at JoVE.com

Analysis of Cap-binding Proteins in Human Cells Exposed to Physiological Oxygen Conditions

Here, we present human cell culture protocols to analyze translation initiation factors that bind the 5' cap of mRNA during physiological oxygen conditions. This method utilizes an Agarose-linked m7GTP cap analog and is suitable to investigate cap-binding factors and their interacting partners.

Translational control is a focal point of gene regulation, especially during periods of cellular stress. Cap-dependent translation via the eIF4F complex ...

The overall goal of this experiment is to capture cap-binding proteins in conditions of low oxygen. This method utilizes an agarose linked seven methyl-guanosine cap analog to investigate cap-binding factors and their interacting partners. This method will help answer key questions in the field of protein synthesis such as identifying novel oxygen regulated factors involved in cap dependent translation.The main advantage of this technique is that cells are kept in a hypoxia workstation up until the point of lysis. The implications of this technique extend towards cancer therapy because cancer cells within a tumor are exposed to very low levels of oxygen and translational control plays a key role in tumor progression. We first had the idea for this method when we read a recent publication from Corona's colleagues reporting that tissue oxygenation is actually closer to what we call hypoxia rather than the normaxia that cells are routinely cultured in.Begin this procedure will cell culture as described in the text protocol. After counting the cells using a hemocytometer feed 150 millimeter cultured dishes containing 15 milliliters of complete medium to obtain a cell density of 2500 to 5000 cells per square centimeter. Use two 150 millimeter dishes for each cap-binding assay.Place the seeded culture dishes in the incubator at 37 degrees celsius and a five percent carbon dioxide atmosphere. After the cells have incubated at least 24 hours place the cells into a hypoxia workstation for the desired time. Then, set the workstation to the appropriate physioxia.Pre-warm one X phosphate buffered saline, or PBS, and trypsin in a 37 degree celsius water bath for 30 minutes. Aliquot 980 microliters of lysis buffer into a 1.5 microliter centrifuge tube for each cap-binding assay being performed. 10 microliters of 100X protease inhibitor cocktail and 10 microliters of 4-benzenesulfonyl fluoride hydrocloride to the 980 microliters of lysis buffer on ice.Discard the media from each 150 millimeter dish in a waste container within the hypoxia workstation. Then, wash the cells with three to four milliliters of warm one X PBS and discard the liquid. Add one milliliter of warm 05 percent trypsin EDTA to each dish and let the dishes sit for two minutes or until the cells are no longer adhered to the plate.Using a pipette transfer the cells of one plate to a 1.5 milliliter micro-centrifuge tube. Repeat as needed so that each plate of cells is transferred to a separate 1.5 milliliter micro-centrifuge tube. Centrifuge the micro-centrifuge tubes at 6000 times g for 90 seconds to pellet the cells.Following centrifugation aspirate the trypsin using a pipette without disturbing the pellet. Wash the cells with warm one X PBS by gently pipetting 200 microliters of PBS into the tube just above the pellet. Then aspirate the PBS without disturbing the pellet.Next, pipette 500 microliters from the one milliliter prepared lysis buffer solution onto the first cellular pellet. Re-suspend the pellet entirely by pipetting up and down. Combine the re-suspended cells with the second cell pellet and re-suspend the second pellet by pipetting up and down.Repeat this process until all pellets have been combined and re-suspended for each sample. Next, combine the lysate with the remaining 500 microliters of lysis buffer in a 1.5 liter micro-centrifuge tube. Remove the samples from the hypoxia workstation.Lyse the cells using gentle agitation by rotating the samples at four degrees celsisus for 1.5 to two hours. Following incubation, centrifuge the lysed cells at 1200 times g for 15 minutes at four degrees celsius to remove cellular debris. Transfer the lysate to a new 1.5 milliliter micro-centrifuge tube and discard the pellet.Reserve a portion of the supernatant to be used as whole cell lysate input control for western blot analysis. To prepare for the cap-binding assay use scissors to remove the tip of the pipette to facilitate collection of the bead slurry. For each sample transfer 50 microliters of the blank agarose bead control slurry and 50 microliters of the m7GTP agarose C10-linked beads slurry to separate 1.5 milliliter micro-centrifuge tubes.Then, pellet the beads by centrifuging the slurry at 500 times g for 30 seconds. Remove the supernatant carefully and re-suspend the beads in 500 microliters of TBS. After repeating these steps pellet the beads at 500 times g for 30 seconds and remove the supernatant.Next, transfer the supernatant containing the lysate to the 1.5 milliliter micro-centrifuge tube containing the blank agarose beads. Incubate for 10 minutes at four degrees celsius with gentle agitation. After 10 minutes, pellet the blank agarose beads by centrifuging at 500 times g for 30 seconds.Following centrifugation transfer the lysate that doesn't bind to the beads to the 1.5 milliliter micro-centrifuge tube containing the m7GTP agarose C10-linked beads. Wash the blank agarose beads by re-suspending the beads in 500 microliters of lysis buffer, pelleting the beads by centrifuging at 500 time g for 30 seconds, and discarding the supernatant. Repeat this four times for a total of five washes.Re-suspend the blank agarose beads in one X SDS-PAGE sample buffer. And boil the beads for 90 seconds at 95 degrees celsius. Store the sample at 20 degrees celsius for future western blot analysis to observe weather the protein of interest binds non-specifically to the bead.Incubate the lysate with the m7GTP agarose C10-linked beads with gentle agitation for one hour at four degrees celsuis to capture cap-binding proteins. Following agitation, pellet the m7GTP agarose C10-linked beads by centrifuging at 500 times g for 30 seconds. After discarding the supernatant, wash the m7GTP agarose C10-linked beads as before.Re-suspend the beads in 600 microliters of lysis buffer and add GTP to a final concentration of one millimolar. Incubate the m7GTP agarose C10-linked beads plus one millimolar GTP with gentle agitation for one hour at four degrees celsius. This will dissociate proteins that non-specifically interact with m7GTP.Pellet the m7GTP agarose C10-linked beads by centrifuging at 500 time g for 30 seconds. Transfer the supernatant to a new 1.5 milliliter micro-centrifuge tube, and add 200 microliters of four X SDS-PAGE sample buffer. After washing the beads as before, re-suspend the beads in one X SDS-PAGE sample buffer and boil at 95 degrees celsius for 90 seconds.Shown here are representative western blots of a typical m7GTP affinity purification of two major cap-binding proteins in response to oxygen fluctuations in primary human renal proximal tubule epithelial cells. The cell lysates were exposed to eight percent, five percent, three percent, or one percent oxygen for 24 hours. The lanes include 10 percent of the whole cell lysate as the input, a GTP washed to measure the specificity for m7GTP, and the proteins bound to m7GTP beads after the GTP wash.Data from at least three independent experiments were quantified by Image J and expressed as relative density units relative to 10 percent input of the whole cell lysate. Results indicate that human cells cultured under physiological oxygen utilize two cap-binding proteins to recruit distinct mRNAs for translation. After watching this video you should have a good understanding of how to capture cap-binding proteins in low oxygen conditions.While attempting this procedure it's important to remember to keep cells in the hypoxia workstation up until the point of lysis, as oxygen can rapidly alter the biochemical properties of these translation initiation factors. Following this procedure other methods like polysome fractionation can be performed to answer additional questions such as which cap-binding proteins associate with active translation under conditions of low oxygen.

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