Name: biochemical assays for analyzing activities of atp-dependent chromatin remodeling enzymes
Uploaded: 2014-10-25T14:00:00.000+00:00
Duration: 10 min 14 s
Description: Watch this Scientific Journal Video about Biochemical Assays for Analyzing Activities of ATP-dependent Chromatin Remodeling Enzymes at JoVE.com

Work in the authors' laboratory is supported by a grant from the National Institute of General Medical Sciences (GM41628) and by a grant to the Stowers Institute for Medical Research from the Helen Nelson Medical Research Fund at the Greater Kansas City Community Foundation.

1. ATP-dependent Nucleosome Remodeling Assays
To measure ATP-dependent nucleosome remodeling activities, immunopurified INO80 or INO80 subcomplexes are incubated with ATP and a mononucleosomal substrate, which contains a single nucleosome positioned at one end of a 216-bp, 32P-labeled DNA fragment. The reaction products are then subjected to electrophoresis in native poly-acrylamide gels.
<ol>
	<li>To generate the 32P-labeled, &#39;601&#39; DNA fragment, amplify from pGEM-3Z-6014 a 216 bp DNA fragment containing an end-positioned 601 nucleosome positioning sequence, using the oligonucleotides 5&#8242;-ACAGGATGTATATATCTGACACGTGCCTGG and 5&#8242;-AATACTCAAGCTTGGATGCCTGCAG as forward and reverse primers.
	<ol>
		<li>Set up a 100 &#956;l PCR reaction as described in Table 1.</li>
		<li>Perform the PCR reactions in a thermal cycler using the following program: 1 min at 96 &#176;C, followed by 45 sec at 94 &#176;C, 30 sec at 57 &#176;C, 60 sec at 72 &#176;C for 30 cycles; ending with 7 min at 72 &#176;C.</li>
		<li>After the PCR reaction is finished, remove the unincorporated nucleotides by passing the reaction products twice through nuclease-free spin columns.</li>
		<li>Run 5 &#956;l of the purified PCR product in a 1.2% agarose gel to confirm that the PCR reaction generated the desired ~216 bp DNA fragment.</li>
		<li>Dilute 5 &#956;l of the purified PCR product 20-fold, and measure the DNA concentration using a UV spectrophotometer. The average yield is ~40 ng/&#956;l.</li>
		<li>Measure the radioactivity of 1 &#956;l of the purified PCR product in a scintillation counter. Estimate the labeling efficiency by calculating the cpm/ng. A successful labeling reaction is expected to yield ~15,000 cpm/ng of 601 DNA fragment.</li>
	</ol>
	</li>
	<li>Transfer Hela cell nucleosomes onto the labeled 601 DNA using a serial dilution method 5.
	<ol>
		<li>Mix 2 pmol of 32P-labeled 601 DNA fragment with 6 &#181;g of Hela nucleosomes (prepared as described 5) in 50 &#181;l of a buffer containing 1.0 M NaCl, 10 mM Tris-HCl, pH 8.0, 1 mM EDTA, 0.1 mM PMSF, and 1 mM DTT and incubate at 30 &#176;C for 30 min.</li>
		<li>Sequentially dilute the mixture to 0.8 M, 0.6 M, and 0.4 M NaCl by dilution with 12.5 &#181;l, 20.8 &#181;l, and 41.6 &#181;l, respectively, of 10 mM Tris-HCl (pH 8.0), 1 mM EDTA, 0.1 mM PMSF, and 1 mM DTT, with a 30 min incubation at 30 &#176;C after each dilution.</li>
		<li>Further dilute the mixture to 0.2 M and then to 0.1 M NaCl by addition of 125 &#181;l and then 250 &#181;l of the same buffer containing 0.1% Nonidet P-40, 20% glycerol, and 200 &#181;g/ml BSA, with a 30 min incubation at 30 &#176;C between the final two dilutions. Store the mononucleosome substrate at 4 &#176;C for up to 3 months.</li>
	</ol>
	</li>
	<li>Perform ATP-dependent nucleosome sliding reactions in a total volume of 10 &#181;l. The reaction components are listed in Table 2. Since the optimal NaCl concentration for INO80 nucleosome remodeling activity is ~50 mM NaCl (unpublished results), adjust the total concentration of NaCl in each reaction to 50 mM, taking into account the amount of NaCl contained in preparations of nucleosomes and enzyme.
	<ol>
		<li>Before beginning to set up the assays, cast native poly-acrylamide gels (18 x 16 cm). To prepare a single gel containing 5% acrylamide (acrylamide:bisacrylamide 37.5:1), 0.5x TBE (45 mM Tris borate, 1 mM EDTA), 0.01% ammonium persulfate (APS), and 0.001% N,N,N&#180;,N&#180;-tetramethylethylenediamine (TEMED), mix the ingredients listed in Table 3. Allow the gel to polymerize for at least 2 hr at RT.</li>
		<li>Meanwhile, for each reaction to be performed, combine in a pre-chilled siliconized 1.5 ml microcentrifuge tube ~20 nM INO80 or INO80 subcomplex (prepared as described 3) with an amount of EB100 buffer (Table 4) sufficient to give a volume of 4.75 &#956;l. Immediately re-freeze any remaining INO80-containing fractions in powdered dry ice or liquid nitrogen.</li>
		<li>Set up a master cocktail with the rest of the ingredients, scaling up by a factor of &#39;X&#39; (where X = total number of reactions +3). The amount of each ingredient needed for a single 10 &#956;l reaction is listed in Table 5; the recipe should be scaled up according to the number of reactions to be performed. Mix well by tapping the tube or by pipetting up and down with a Pipetman and spin the tube for a few seconds in a benchtop microcentrifuge.</li>
		<li>Dispense 5.25 &#181;l of the master cocktail to each of the reaction tubes set up in step 1.3.2. Mix well by pipetting up and down. Start the reactions by transferring reaction tubes to a 30 &#176;C heat block or water bath and incubate for 2 hr.</li>
		<li>Meanwhile, prepare &#39;removing mix&#39; cocktail containing competitor DNA and nucleosomes, scaling up by a factor of X (X = total number of reactions + 4). The amount of each ingredient needed to prepare 1.5 &#181;l removing mix for a single reaction is listed in Table 6; the recipe should be scaled up depending on the number of assays to be performed.</li>
		<li>Terminate reactions by adding 1.5 &#956;l of the removing mix. Mix well, spin down, and incubate at 30 &#176;C for a further 30 min.</li>
		<li>Meanwhile, pre-run the native polyacrylamide gel in a vertical electrophoresis unit at 100 V for 30 min at 4 &#176;C, using 0.5x TBE as running buffer with a magnetic stir bar inside the lower chamber to maintain constant buffer circulation.</li>
		<li>To load the sample, add 2.5 &#181;l of loading dye containing 3x TBE, 30% glycerol, 0.25% Bromophenol Blue, and 0.25% Xylene Cyanol FF. Mix well, briefly spin the samples, and load onto the gel using loading tips.</li>
		<li>Run the gel at 200 V for 4.5 hr at 4 &#176;C with buffer circulation.</li>
		<li>To detect the signal, transfer the gel to a stack of two sheets of filter paper. Wrap the filter paper with the gel on top using clear plastic wrap, and then expose it to a storage phosphor screen at 4 &#176;C for the desired time.</li>
		<li>Scan the screen with an isotope imaging scanner system and analyze the data using suitable software.</li>
	</ol>
	</li>
</ol>
2. Mononucleosome Binding Assays
To assay the binding affinity of a given INO80 complex for mononucleosomes, perform an Electrophoretic Mobility Shift Assay (EMSA) using the mononucleosomal substrate generated in Step 1.2.
<ol>
	<li>Set up the reaction mixes for binding assays as described for nucleosome remodeling assays but omit the ATP and removing mix from the reactions; incubate at 30 &#176;C for 30 min.</li>
	<li>Add 2.5 &#181;l of loading dye to each reaction mixture, and apply to a native polyacrylamide gel containing 3.5% acrylamide (acrylamide:bis 37.5:1), 1% Glycerol, 0.5x TBE, 0.01% APS, and 0.001% TEMED.</li>
	<li>Using 0.5x TBE as running buffer, run the gel at 200 V for 2.5 hr at 4 &#176;C with buffer circulation and expose to a storage phosphor screen.</li>
</ol>
3. DNA- and Nucleosome-dependent ATPase Assays
Perform ATPase assays in 5 &#956;l reaction mixtures containing 20 mM Tris-HCl (pH 7.5), 60 mM NaCl, 6.6 mM MgCl2, 0.8 mM EDTA, 0.015% Nonidet P-40, 2.5% glycerol, 0.1 mg/ml BSA, 1 mM DTT, 0.1 mM PMSF, 2 mM ATP, 2 &#956;Ci of [&#945;-32P] ATP (3,000 Ci/mmol). For each INO80 complex or amount of INO80 complex to be assayed set up three parallel reactions, one containing EB100 buffer to measure DNA- or nucleosome-independent ATPase, one containing closed circular plasmid DNA (5,000 bp, ~30 nM) to measure DNA-dependent ATPase, and one containing Hela oligonucleosomes (~185 nM) to measure nucleosome-dependent ATPase. Set up all reactions on ice.
<ol>
	<li>For each reaction, combine 10-50 nM of the immunopurified INO80 or INO80 subcomplexes with an amount of EB100 buffer sufficient to give a volume of 2.2 &#956;l in pre-chilled lubricated 1.5 ml microcentrifuge tubes. Immediately re-freeze any INO80-containing fractions in powdered dry ice or liquid nitrogen.</li>
	<li>Set up a master cocktail. The amount of each ingredient needed for a single reaction is listed in Table 7. Scale up the recipe by scaling up by a factor of 3(X+2) +1, where X = the number of INO80 preparations to be assayed.</li>
	<li>To prepare &#39;sub-cocktails&#39; containing buffer only, DNA, or nucleosomes, dispense 2.5(X+2) &#956;l of the master cocktail into three separate tubes. Add 0.3(X+2) &#956;l of either EB100, closed circular plasmid DNA (1.5 &#181;g/&#181;l), or Hela oligonucleosomes (1.5 &#956;g/&#956;l) and mix well.</li>
	<li>Dispense 2.8 &#956;l of the appropriate sub-cocktail to the enzyme-containing reaction tubes set up in step 3.1. Gently pipette up and down to mix; avoid introducing bubbles.</li>
	<li>To start reactions, transfer the reaction tubes to a 30 &#176;C heat block.</li>
	<li>After 5, 15, 30, and 60 min of incubation, spot 0.5 &#956;l of each reaction mixture onto a cellulose polyethyleneimine thin layer chromatography (TLC) plate (20 x 10 cm) in a straight line at least 1.5 cm away from the bottom edge. Immediately return reaction tubes to the 30 &#176;C heat block so multiple time points can be taken from a single tube. After spotting, dry the TLC plates using a blow dryer.</li>
	<li>Transfer the TLC plates to a glass chamber containing enough 0.375 M potassium phosphate (pH 3.5) to allow the bottom 0.5 cm of the TLC plate to be submerged in the solution.</li>
	<li>Cover the chamber, and develop until the front of the liquid phase reaches the top of the TLC plates. Immediate dry the plates thoroughly using a blow dryer.</li>
	<li>Expose the dried TLC plates to a storage Phosphor screen at RT. Scan the screen with an isotope imaging scanner system and determine the amount of radioactive ATP substrate and ADP product.</li>
	<li>To calculate the amount of ATP hydrolyzed, multiply the % ATP hydrolyzed by the amount of ATP present in the starting reaction mixture using the following formula: pmol ATP hydrolyzed = 10 pmol ATP in starting reaction x [ADP/(ATP+ADP)]</li>
</ol>

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The authors declare that they have no competing financial interests.

To ensure that nucleosome remodeling and ATPase activities we observe in assays depend on the catalytic activity of INO80 complexes, and not on contaminating remodeling and/or ATPase enzymes, we routinely assay nucleosome remodeling and ATPase activity of catalytically inactive versions of INO80 complexes, purified in parallel with wild type INO80 using the same procedure. A negative control reaction lacking ATP should also be performed when assaying nucleosome remodeling activity to test for the presence of contaminatin...

SNF2 family chromatin remodeling complexes include a central SNF2-like ATPase subunit 1,2. Some SNF2-like ATPases function as single subunit enzymes, while others function as the catalytic subunit of larger multi-subunit complexes. Elucidating the molecular mechanisms by which each of the subunits of chromatin remodeling complexes contribute to their activities requires the ability to perform biochemical assays that dissect the remodeling process.
ATP-dependent nucleosome remodeling by the human INO80 complex and other chromatin remodeling enzymes can be envisioned as a multi-step process that starts with binding of the remodeling enzyme to nucleosomes, followed by activation of its DNA- and/or nucleosome-dependent ATPase, translocation of the remodeling enzyme on nucleosomal DNA, and eventual repositioning of nucleosomes 1,2. Understanding the molecular details of the ATP-dependent chromatin remodeling process requires dissection of the remodeling reaction into its individual steps and definition of the contributions of individual subunits of the chromatin remodeling complex to each step of the reaction. Such analyses require the ability to analyze nucleosome remodeling and other activities using defined molecular substrates in vitro.
In a previous JOVE protocol, we described procedures used to generate INO80 chromatin remodeling complexes and subcomplexes with defined subunit compositions 3. Here, we present three biochemical assays that enable quantitative analysis of the nucleosome binding, DNA- and nucleosome-activated ATPase, and nucleosome remodeling activities associated with such complexes.

<table><tbody><tr><td>Protease Inhibitor Cocktail</td><td>Sigma</td><td>P8340</td><td></td></tr><tr><td>10x PCR reaction buffer&amp;nbsp;</td><td>Roche Applied Science&amp;nbsp;</td><td>11435094001</td><td></td></tr><tr><td>Roche Taq DNA Polymerase</td><td>Roche Applied Science&amp;nbsp;</td><td>11435094001</td><td></td></tr><tr><td>NucAway Nuclease-free Spin Columns&amp;nbsp;</td><td>Ambion</td><td>Cat. # AM10070</td><td></td></tr><tr><td>ultrapure ATP&amp;nbsp;</td><td>USB/Affymetrix</td><td>77241 25 UM</td><td></td></tr><tr><td>bovine serum albumin&amp;nbsp;</td><td>Sigma</td><td>A9418&amp;nbsp;</td><td></td></tr><tr><td>40% Acrylamide/Bis 37.5:1</td><td>Amresco</td><td>0254-500ML</td><td></td></tr><tr><td>Sonicated salmon sperm DNAs&amp;nbsp;</td><td>GE Healthcare</td><td>27-4565-01</td><td></td></tr><tr><td>10% ammonium persulfate (APS)</td><td>Thermo Scientific</td><td>17874</td><td></td></tr><tr><td>benzonase&amp;nbsp;</td><td>Novagen</td><td>Cat. No. 70664</td><td></td></tr><tr><td>dCTP, [&amp;alpha;-&lt;sup&gt;32&lt;/sup&gt;P]- 6,000 Ci/mmol</td><td>PerkinElmer</td><td>BLU013Z250UC</td><td></td></tr><tr><td>PCR thermal cycler PTC 200</td><td>MJ Research</td><td>PTC 200</td><td></td></tr><tr><td>Hoefer vertical electrophoresis unit</td><td>Hoefer</td><td>SE600X-15-1.5</td><td></td></tr><tr><td>lubricated 1.5 ml microcentrifuge tubes&amp;nbsp;</td><td>Costar</td><td>3207</td><td></td></tr><tr><td>Storage Phosphor Screen&amp;nbsp;</td><td>Molecular Dynamics</td><td>63-0034-79</td><td></td></tr><tr><td>3MM filter paper</td><td>Whatman&amp;nbsp;</td><td>28458-005</td><td>VWR</td></tr><tr><td>Typhoon PhosphorImager&amp;nbsp;</td><td>GE Healthcare</td><td>8600</td><td></td></tr><tr><td>ImageQuant software</td><td>GE Healthcare</td><td>ver2003.02</td><td></td></tr><tr><td>TLC Glass Plates, PEI-Cellulose F</td><td>Millipore</td><td>5725-7</td><td></td></tr><tr><td>Immobilon-FL Transfer Membrane 7 x 8.4</td><td>Millipore</td><td>IPFL07810</td><td></td></tr><tr><td>General purpose survey meter with end-window or pancake GM (Geiger-Mueller) probe</td><td>Biodex</td><td>Model 14C</td><td></td></tr></tbody></table>

biochemical assays for analyzing activities of atp-dependent chromatin remodeling enzymes

Members of the SNF2 family of ATPases often function as components of multi-subunit chromatin remodeling complexes that regulate nucleosome dynamics and DNA accessibility by catalyzing ATP-dependent nucleosome remodeling. Biochemically dissecting the contributions of individual subunits of such complexes to the multi-step ATP-dependent chromatin remodeling reaction requires the use of assays that monitor the production of reaction products and measure the formation of reaction intermediates. This JOVE protocol describes assays that allow one to measure the biochemical activities of chromatin remodeling complexes or subcomplexes containing various combinations of subunits. Chromatin remodeling is measured using an ATP-dependent nucleosome sliding assay, which monitors the movement of a nucleosome on a DNA molecule using an electrophoretic mobility shift assay (EMSA)-based method. Nucleosome binding activity is measured by monitoring the formation of remodeling complex-bound mononucleosomes using a similar EMSA-based method, and DNA- or nucleosome-dependent ATPase activity is assayed using thin layer chromatography (TLC) to measure the rate of conversion of ATP to ADP and phosphate in the presence of either DNA or nucleosomes. Using these assays, one can examine the functions of subunits of a chromatin remodeling complex by comparing the activities of the complete complex to those lacking one or more subunits. The human INO80 chromatin remodeling complex is used as an example; however, the methods described here can be adapted to the study of other chromatin remodeling complexes.

The figures show representative results of biochemical assays used to characterize INO80 activities, including nucleosome sliding (Figure 1) and binding (Figure 2) assays and DNA- or nucleosome-dependent ATPase assays (Figure 3).
The experiment shown in Figure 1 compares the ability of intact INO80 complexes purified through FLAG-Ies2 or FLAG-INO80E and of INO80 subcomplexes purified through either FLAG-Ino80&#916;N or Ino80&#...

Watch this Scientific Journal Video about Biochemical Assays for Analyzing Activities of ATP-dependent Chromatin Remodeling Enzymes at JoVE.com

Biochemical Assays for Analyzing Activities of ATP-dependent Chromatin Remodeling Enzymes

Here we describe biochemical assays that can be used to characterize ATP-dependent chromatin remodeling enzymes for their abilities to 1) catalyze ATP-dependent nucleosome sliding, 2) engage with nucleosome substrates, and 3) hydrolyze ATP in a nucleosome- or DNA-dependent manner.

Members of the SNF2 family of ATPases often function as components of multi-subunit chromatin remodeling complexes that regulate nucleosome dynamics and ...

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Research

JoVE Journal

Biology

14.8K Views.  Stowers Institute for Medical Research. Here we describe biochemical assays that can be used to characterize ATP-dependent chromatin remodeling enzymes for their abilities to 1) catalyze ATP-dependent nucleosome sliding, 2) engage with nucleosome substrates, and 3) hydrolyze ATP in a nucleosome- or DNA-dependent manner.

Video: Biochemical Assays for Analyzing Activities of ATP-dependent Chromatin Remodeling Enzymes

Sequential Salt Extractions for the Analysis of Bulk Chromatin Binding Properties of Chromatin Modifying Complexes

Elucidation of the binding properties of chromatin-targeting proteins can be very challenging due to the complex nature of chromatin and the heterogeneous nature of most mammalian chromatin-modifying complexes. In order to overcome these hurdles, we have adapted a sequential salt extraction (SSE) assay for evaluating the relative binding affinities of chromatin-bound complexes. This easy and straightforward assay can be used by non-experts to evaluate the relative difference in binding affinity of two related complexes, the changes in affinity of a complex when a subunit is lost or an individual domain is inactivated, and the change in binding affinity after alterations to the chromatin landscape. By sequentially re-suspending bulk chromatin in increasing amounts of salt, we are able to profile the elution of a particular protein from chromatin. Using these profiles, we are able to determine how alterations in a chromatin-modifying complex or alterations to the chromatin environment affect binding interactions. Coupling SSE with other in vitro and in vivo assays, we can determine the roles of individual domains and proteins on the functionality of a complex in a variety of chromatin environments.

Sequential salt extraction of chromatin bound proteins is a useful tool for determining the binding properties of large protein complexes. This method can be employed to evaluate the role of individual subunits or domains in the overall affinity of a protein complex to bulk chromatin.

Elucidation of the binding properties of chromatin-targeting proteins can be very challenging due to the complex nature of chromatin and the heterogeneous ...

Genetics

Real-time Analysis of Transcription Factor Binding, Transcription, Translation, and Turnover to Display Global Events During Cellular Activation

Upon activation, cells rapidly change their functional programs and, thereby, their gene expression profile. Massive changes in gene expression occur, for example, during cellular differentiation, morphogenesis, and functional stimulation (such as activation of immune cells), or after exposure to drugs and other factors from the local environment. Depending on the stimulus and cell type, these changes occur rapidly and at any possible level of gene regulation. Displaying all molecular processes of a responding cell to a certain type of stimulus/drug is one of the hardest tasks in molecular biology. Here, we describe a protocol that enables the simultaneous analysis of multiple layers of gene regulation. We compare, in particular, transcription factor binding (Chromatin-immunoprecipitation-sequencing (ChIP-seq)), de novo transcription (4-thiouridine-sequencing (4sU-seq)), mRNA processing, and turnover as well as translation (ribosome profiling). By combining these methods, it is possible to display a detailed and genome-wide course of action.
Sequencing newly transcribed RNA is especially recommended when analyzing rapidly adapting or changing systems, since this depicts the transcriptional activity of all genes during the time of 4sU exposure (irrespective of whether they are up- or downregulated). The combinatorial use of total RNA-seq and ribosome profiling additionally allows the calculation of RNA turnover and translation rates. Bioinformatic analysis of high-throughput sequencing results allows for many means for analysis and interpretation of the data. The generated data also enables tracking co-transcriptional and alternative splicing, just to mention a few possible outcomes.
The combined approach described here can be applied for different model organisms or cell types, including primary cells. Furthermore, we provide detailed protocols for each method used, including quality controls, and discuss potential problems and pitfalls.

This protocol describes the combinatorial use of ChIP-seq, 4sU-seq, total RNA-seq, and ribosome profiling for cell lines and primary cells. It enables tracking changes in transcription-factor binding, de novo transcription, RNA processing, turnover and translation over time, and displaying the overall course of events in activated and/or rapidly changing cells.

Upon activation, cells rapidly change their functional programs and, thereby, their gene expression profile. Massive changes in gene expression occur, for ...

In Vitro Ubiquitination and Deubiquitination Assays of Nucleosomal Histones

Ubiquitination is a post-translational modification that plays important roles in various signaling pathways and is notably involved in the coordination of chromatin function and DNA-associated processes. This modification involves a sequential action of several enzymes including E1 ubiquitin-activating, E2 ubiquitin-conjugating and E3 ubiquitin-ligase and is reversed by deubiquitinases (DUBs). Ubiquitination induces degradation of proteins or alteration of protein function including modulation of enzymatic activity, protein-protein interaction and subcellular localization. A critical step in demonstrating protein ubiquitination or deubiquitination is to perform in vitro reactions with purified components. Effective ubiquitination and deubiquitination reactions could be greatly impacted by the different components used, enzyme co-factors, buffer conditions, and the nature of the substrate.&#160; Here, we provide step-by-step protocols for conducting ubiquitination and deubiquitination reactions. We illustrate these reactions using minimal components of the mouse Polycomb Repressive Complex 1 (PRC1), BMI1, and RING1B, an E3 ubiquitin ligase that monoubiquitinates histone H2A on lysine 119. Deubiquitination of nucleosomal H2A is performed using a minimal Polycomb Repressive Deubiquitinase (PR-DUB) complex formed by the human deubiquitinase BAP1 and the DEUBiquitinase ADaptor (DEUBAD) domain of its co-factor ASXL2. These ubiquitination/deubiquitination assays can be conducted in the context of either recombinant nucleosomes reconstituted with bacteria-purified proteins or native nucleosomes purified from mammalian cells. We highlight the intricacies that can have a significant impact on these reactions and we propose that the general principles of these protocols can be swiftly adapted to other E3 ubiquitin ligases and deubiquitinases.

Ubiquitination is a post-translational modification that plays important roles in cellular processes and is tightly coordinated by deubiquitination. Defects in both reactions underlie human pathologies. We provide protocols for conducting ubiquitination and deubiquitination reaction in vitro using purified components.

Ubiquitination is a post-translational modification that plays important roles in various signaling pathways and is notably involved in the coordination ...

Biochemistry

Assays for Validating Histone Acetyltransferase Inhibitors

Lysine acetyltransferases (KATs) catalyze acetylation of lysine residues on histones and other proteins to regulate chromatin dynamics and gene expression. KATs, such as CBP/p300, are under intense investigation as therapeutic targets due to their critical role in tumorigenesis of diverse cancers. The development of novel small molecule inhibitors targeting the histone acetyltransferase (HAT) function of KATs is challenging and requires robust assays that can validate the specificity and potency of potential inhibitors.
This article outlines a pipeline of three methods that provide rigorous in vitro validation for novel HAT inhibitors (HATi). These methods include a test tube HAT assay, Chromatin Hyperacetylation Inhibition (ChHAI) assay, and Chromatin Immunoprecipitation-quantitative PCR (ChIP-qPCR). In the HAT assay, recombinant HATs are incubated with histones in a test tube reaction, allowing for acetylation of specific lysine residues on the histone tails. This reaction can be blocked by a HATi and the relative levels of site-specific histone acetylation can be measured via immunoblotting. Inhibitors identified in the HAT assay need to be confirmed in the cellular environment.
The ChHAI assay uses immunoblotting to screen for novel HATi that attenuate the robust hyperacetylation of histones induced by a histone deacetylase inhibitor (HDACi). The addition of an HDACi is helpful because basal levels of histone acetylation can be difficult to detect via immunoblotting.
The HAT and ChHAI assays measure global changes in histone acetylation, but do not provide information regarding acetylation at specific genomic regions. Therefore, ChIP-qPCR is used to investigate the effects of HATi on histone acetylation levels at gene regulatory elements. This is accomplished through selective immunoprecipitation of histone-DNA complexes and analysis of the purified DNA through qPCR. Together, these three assays allow for the careful validation of the specificity, potency, and mechanism of action of novel HATi.

Inhibitors of histone acetyltransferases (HATs, also known as lysine acetyltransferases), such as CBP/p300, are potential therapeutics for treating cancer. However, rigorous methods for validating these inhibitors are needed. Three in vitro methods for validation include HAT assays with recombinant acetyltransferases, immunoblotting for histone acetylation in cell culture, and ChIP-qPCR.

Lysine acetyltransferases (KATs) catalyze acetylation of lysine residues on histones and other proteins to regulate chromatin dynamics and gene ...

Cancer Research

CD Spectroscopy to Study DNA-Protein Interactions

Circular dichroism (CD) spectroscopy is a simple and convenient method to investigate the secondary structure and interactions of biomolecules. Recent advancements in CD spectroscopy have enabled the study of DNA-protein interactions and conformational dynamics of DNA in different microenvironments in detail for a better understanding of transcriptional regulation in vivo. The area around a potential transcription zone needs to be unwound for transcription to occur. This is a complex process requiring the coordination of histone modifications, binding of the transcription factor to DNA, and other chromatin remodeling activities. Using CD spectroscopy, it is possible to study conformational changes in the promoter region caused by regulatory proteins, such as ATP-dependent chromatin remodelers, to promote transcription. The conformational changes occurring in the protein can also be monitored. In addition, queries regarding the affinity of the protein towards its target DNA and sequence specificity can be addressed by incorporating mutations in the target DNA. In short, the unique understanding of this sensitive and inexpensive method can predict changes in chromatin dynamics, thereby improving the understanding of transcriptional regulation.

The interaction of an ATP-dependent chromatin remodeler with a DNA ligand is described using CD spectroscopy. The induced conformational changes on a gene promoter analyzed by the peaks generated can be used to understand the mechanism of transcriptional regulation.

Circular dichroism (CD) spectroscopy is a simple and convenient method to investigate the secondary structure and interactions of biomolecules. Recent ...

In Vitro Characterization of Histone Chaperones using Analytical, Pull-Down and Chaperoning Assays

Histone proteins associate with DNA to form the eukaryotic chromatin. The basic unit of chromatin is a nucleosome, made up of a histone octamer consisting of two copies of the core histones H2A, H2B, H3, and H4, wrapped around by the DNA. The octamer is composed of two copies of an H2A/H2B dimer and a single copy of an H3/H4 tetramer. The highly charged core histones are prone to non-specific interactions with several proteins in the cellular cytoplasm and the nucleus. Histone chaperones form a diverse class of proteins that shuttle histones from the cytoplasm into the nucleus and aid their deposition onto the DNA, thus assisting the nucleosome assembly process. Some histone chaperones are specific for either H2A/H2B or H3/H4, and some function as chaperones for both. This protocol describes how in vitro laboratory techniques such as pull-down assays, analytical size-exclusion chromatography, analytical ultra-centrifugation, and histone chaperoning assay could be used in tandem to confirm whether a given protein is functional as a histone chaperone.

In Vitro Characterization of Histone Chaperones using Analytical, Pull-Down and Chaperoning Assays

This protocol describes a battery of methods that includes analytical size-exclusion chromatography to study histone chaperone oligomerization and stability, pull-down assay to unravel histone chaperone-histone interactions, AUC to analyze the stoichiometry of the protein complexes, and histone chaperoning assay to functionally characterize a putative histone chaperone in vitro.

Histone proteins associate with DNA to form the eukaryotic chromatin. The basic unit of chromatin is a nucleosome, made up of a histone octamer consisting ...

Deciphering Molecular Mechanism of Histone Assembly by DNA Curtain Technique

Chromatin is a higher-order structure that packages eukaryotic DNA. Chromatin undergoes dynamic alterations according to the cell cycle phase and in response to environmental stimuli. These changes are essential for genomic integrity, epigenetic regulation, and DNA metabolic reactions such as replication, transcription, and repair. Chromatin assembly is crucial for chromatin dynamics and is catalyzed by histone chaperones. Despite extensive studies, the mechanisms by which histone chaperones enable chromatin assembly remains elusive. Moreover, the global features of nucleosomes organized by histone chaperones are poorly understood. To address these problems, this work describes a unique single-molecule imaging technique named DNA curtain, which facilitates the investigation of the molecular details of nucleosome assembly by histone chaperones. DNA curtain is a hybrid technique that combines lipid fluidity, microfluidics, and total internal reflection fluorescence microscopy (TIRFM) to provide a universal platform for real-time imaging of diverse protein-DNA interactions.Using DNA curtain, the histone chaperone function of Abo1, the Schizosaccharomyces pombe bromodomain-containing AAA+ ATPase, is investigated, and the molecular mechanism underlying histone assembly of Abo1 is revealed. DNA curtain provides a unique approach for studying chromatin dynamics.

DNA curtain, a high-throughput single-molecule imaging technique, provides a platform for real-time visualization of diverse protein-DNA interactions. The present protocol utilizes the DNA curtain technique to investigate the biological role and molecular mechanism of Abo1, a Schizosaccharomyces pombe bromodomain-containing AAA+ ATPase.

Chromatin is a higher-order structure that packages eukaryotic DNA. Chromatin undergoes dynamic alterations according to the cell cycle phase and in ...

Chromatin Immunoprecipitation (ChIP) to Assay Dynamic Histone Modification in Activated Gene Expression in Human Cells

In response to a variety of extracellular ligands, the STAT (signal transducer and activator of transcription) transcription factors are rapidly recruited from their latent state in the cytoplasm to cell surface receptors where they are activated by phosphorylation at a single tyrosine residue1. They then dimerize and translocate to the nucleus to drive the transcription of target genes, affecting growth, differentiation, homeostasis and the immune response. Not surprisingly, given their widespread involvement in normal cell processes, dysregulation of STAT function contributes to human disease, particularly to cancers2 and autoimmune diseases3. It is well established that transcription is regulated by alterations to the chromatin template4,5. These alterations include the activities of ATP-dependent complexes, as well as covalent histone modifications and DNA methylation6. Because STAT activation of gene expression is both rapid and transient, it requires specific mechanisms for modulating the chromatin template at STAT-dependent gene loci. To define these mechanisms, we characterize the histone modifications and the enzymatic activities that generate them at gene loci that respond to STAT signaling. This protocol describes chromatin immunoprecipitation, a method that is valuable for the study of STAT signaling to chromatin in activated gene expression.

Chromatin Immunoprecipitation ChIP to Assay Dynamic Histone Modification in Activated Gene Expression in Human Cells

This protocol describes how chromatin immunoprecipitation (ChIP) is used to study the dynamic alterations to the chromatin template that regulate transcription induced by a signal transduction pathway.

In response to a variety of extracellular ligands, the STAT (signal transducer and activator of transcription) transcription factors are rapidly recruited ...

Development of a Click-Based Assay for Screening HAT1 Enzyme Activity

An Acetyl-Click Chemistry Assay to Measure Histone Acetyltransferase 1 Acetylation

HAT1, also known as Histone acetyltransferase 1, plays a crucial role in chromatin synthesis by stabilizing and acetylating nascent H4 before nucleosome assembly. It is required for tumor growth in various systems, making it a potential target for cancer treatment. To facilitate the identification of compounds that can inhibit HAT1 enzymatic activity, we have devised an acetyl-click assay for rapid screening. In this simple assay, we employ recombinant HAT1/Rbap46, which is purified from activated human cells. The method utilizes the acetyl-CoA analog 4-pentynoyl-CoA (4P) in a click-chemistry approach. This involves the enzymatic transfer of an alkyne handle through a HAT1-dependent acylation reaction to a biotinylated H4 N-terminal peptide. The captured peptide is then immobilized on neutravidin plates, followed by click-chemistry functionalization with biotin-azide. Subsequently, streptavidin-peroxidase recruitment is employed to oxidize amplex red, resulting in a quantitative fluorescent output. By introducing chemical inhibitors during the acylation reaction, we can quantify enzymatic inhibition based on a reduction of the fluorescence signal. Importantly, this reaction is scalable, allowing for high throughput screening of potential inhibitors for HAT1 enzymatic activity.

Author Spotlight: Developing Acetyl-Click Assay for HAT1 Inhibitor Screening

Quick and accurate chemical assays to screen for specific inhibitors are an important tool in the drug development arsenal. Here, we present a scalable acetyl-click chemistry assay to measure the inhibition of HAT1 acetylation activity.

HAT1, also known as Histone acetyltransferase 1, plays a crucial role in chromatin synthesis by stabilizing and acetylating nascent H4 before nucleosome ...

Measuring In Vitro ATPase Activity for Enzymatic Characterization

Adenosine triphosphate-hydrolyzing enzymes, or ATPases, play a critical role in a diverse array of cellular functions. These dynamic proteins can generate energy for mechanical work, such as protein trafficking and degradation, solute transport, and cellular movements. The protocol described here is a basic assay for measuring the in vitro activity of purified ATPases for functional characterization. Proteins hydrolyze ATP in a reaction that results in inorganic phosphate release, and the amount of phosphate liberated is then quantitated using a colorimetric assay. This highly adaptable protocol can be adjusted to measure ATPase activity in kinetic or endpoint assays. A representative protocol is provided here based on the activity and requirements of EpsE, the AAA+ ATPase involved in Type II Secretion in the bacterium Vibrio cholerae. The amount of purified protein needed to measure activity, length of the assay and the timing and number of sampling intervals, buffer and salt composition, temperature, co-factors, stimulants (if any), etc. may vary from those described here, and thus some optimization may be necessary. This protocol provides a basic framework for characterizing ATPases and can be performed quickly and easily adjusted as necessary.

Measuring In Vitro ATPase Activity for Enzymatic Characterization

We describe a basic protocol for quantitating in vitro ATPase activity. This protocol can be optimized based on the level of activity and requirements for a given purified ATPase.

Adenosine triphosphate-hydrolyzing enzymes, or ATPases, play a critical role in a diverse array of cellular functions. These dynamic proteins can generate ...

Biochemical Assays for Analyzing Activities of ATP-dependent Chromatin Remodeling Enzymes

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Sequential Salt Extractions for the Analysis of Bulk Chromatin Binding Properties of Chromatin Modifying Complexes

Real-time Analysis of Transcription Factor Binding, Transcription, Translation, and Turnover to Display Global Events During Cellular Activation

In Vitro Ubiquitination and Deubiquitination Assays of Nucleosomal Histones

Assays for Validating Histone Acetyltransferase Inhibitors

CD Spectroscopy to Study DNA-Protein Interactions

In Vitro Characterization of Histone Chaperones using Analytical, Pull-Down and Chaperoning Assays

Deciphering Molecular Mechanism of Histone Assembly by DNA Curtain Technique

Chromatin Immunoprecipitation (ChIP) to Assay Dynamic Histone Modification in Activated Gene Expression in Human Cells

An Acetyl-Click Chemistry Assay to Measure Histone Acetyltransferase 1 Acetylation

Measuring In Vitro ATPase Activity for Enzymatic Characterization