Method Article

Reconstitution Of β-catenin Degradation In Xenopus Egg Extract

DOI:

10.3791/51425

June 17th, 2014

In This Article

Erratum Notice

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Erratum

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Formal Correction: Erratum: Reconstitution Of β-catenin Degradation In Xenopus Egg Extract
Posted by JoVE Editors on 1/01/1970. Citeable Link.

A correction was made to Reconstitution Of β-catenin Degradation In Xenopus Egg Extract. At the time of publication there were some instances where an incorrect volume notation was used. These instances were corrected from:

2.1.2. Add extract to 1/10 the volume of pelleted antibody or affinity beads (e.g., 20 ml pelleted beads to 200 ml extract). In order to minimize dilution of the extract, withdraw as much liquid from the beads as possible before addition of the extract using gel loading tips with long, tapered tips.

2.2.5. Aliquot the appropriate volumes for degradation assay into pre-chilled microfuge tubes on ice. For radiolabeled β-catenin degradation assays, withdraw 2-5 ml extract for each time point.

3.2.3. At the designated time point, remove 1-5 ml of the sample and mix immediately with SDS sample buffer (5x volume) to stop the reaction. To make sure the degradation reaction is completely terminated, flick tube several times and vortex vigorously.

3.2.4. Perform SDS-PAGE/autoradiography. Run 1 ml equivalents (~50 mg of protein) of the extract for each time point/lane. Degradation of β-catenin in Xenopus egg extract should be evidenced by the time-dependent decrease in intensity of the radiolabeled β-catenin band Figure 2. Quantify results using ImageJ, ImageQuant, or other preferred imaging software if necessary.

4.2.2. Add in vitro-translated β-catenin-luciferase fusion (from 4.1) into prepared Xenopus reaction mix (from 2.2) on ice and mix well as in 3.2.1. NOTE: The activity of the β-catenin luciferase that is added to the extract is typically between 20 - 50,000 relative luminescence units (RLU)/ml of extract (based on measurements obtained from 4.1.2). Starting signal should be approximately 100,000 RLU (2-5 ml of the in vitro-translated β-catenin-luciferase fusion).

to:

2.1.2. Add extract to 1/10 the volume of pelleted antibody or affinity beads (e.g., 20 µl pelleted beads to 200 µl extract). In order to minimize dilution of the extract, withdraw as much liquid from the beads as possible before addition of the extract using gel loading tips with long, tapered tips.

2.2.5. Aliquot the appropriate volumes for degradation assay into pre-chilled microfuge tubes on ice. For radiolabeled β-catenin degradation assays, withdraw 2-5 µl extract for each time point.

3.2.3. At the designated time point, remove 1-5 µl of the sample and mix immediately with SDS sample buffer (5x volume) to stop the reaction. To make sure the degradation reaction is completely terminated, flick tube several times and vortex vigorously.

3.2.4. Perform SDS-PAGE/autoradiography. Run 1 µl equivalents (~50 mg of protein) of the extract for each time point/lane. Degradation of β-catenin in Xenopus egg extract should be evidenced by the time-dependent decrease in intensity of the radiolabeled β-catenin band Figure 2. Quantify results using ImageJ, ImageQuant, or other preferred imaging software if necessary.

4.2.2. Add in vitro-translated β-catenin-luciferase fusion (from 4.1) into prepared Xenopus reaction mix (from 2.2) on ice and mix well as in 3.2.1. NOTE: The activity of the β-catenin luciferase that is added to the extract is typically between 20 - 50,000 relative luminescence units (RLU)/µl of extract (based on measurements obtained from 4.1.2). Starting signal should be approximately 100,000 RLU (2-5 µl of the in vitro-translated β-catenin-luciferase fusion).

Summary

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A method is described for analyzing protein degradation using radiolabeled and luciferase-fusion proteins in Xenopus egg extract and its adaptation for high-throughput screening for small molecule modulators of protein degradation.

Abstract

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Xenopus laevis egg extract is a well-characterized, robust system for studying the biochemistry of diverse cellular processes. Xenopus egg extract has been used to study protein turnover in many cellular contexts, including the cell cycle and signal transduction pathways1-3. Herein, a method is described for isolating Xenopus egg extract that has been optimized to promote the degradation of the critical Wnt pathway component, β-catenin. Two different methods are described to assess β-catenin protein degradation in Xenopus egg extract. One method is visually informative ([35S]-radiolabeled proteins), while the other is more readily scaled for high-throughput assays (firefly luciferase-tagged fusion proteins). The techniques described can be used to, but are not limited to, assess β-catenin protein turnover and identify molecular components contributing to its turnover. Additionally, the ability to purify large volumes of homogenous Xenopus egg extract combined with the quantitative and facile readout of luciferase-tagged proteins allows this system to be easily adapted for high-throughput screening for modulators of β-catenin degradation.

Introduction

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Xenopus laevis egg extract has been used extensively to study many cell biological processes including cytoskeletal dynamics, nuclear assembly and import, apoptosis, ubiquitin metabolism, cell cycle progression, signal transduction, and protein turnover1-17. The Xenopus egg extract system is amenable to the biochemical analysis of a legion of cellular processes because egg extract represents essentially undiluted cytoplasm that contains all the essential cytoplasmic components necessary to execute these processes and enable investigation. Large quantities of egg extract can be prepared at one time for biochemical manipulations that require....

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Protocol

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1. Preparation of Xenopus Egg Extract

NOTE: Each frog yields approximately 1 ml of usable egg extract. Extracts from 10 frogs are typically prepared at one time, and the volume of buffer described below is for performing a 10 frog Xenopus egg extract prep. The buffer volume can be adjusted accordingly for larger or smaller preparations of egg extract. Preps generated in this manner consistently yield protein concentrations ≥ 50 mg/ml. The process of collecting eggs and processing them into extract is most efficient when conducted by two people. (For basic frog husbandry techniques, see Sive et al.

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Results

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A schematic of β-catenin degradation in Xenopus egg extract is shown in Figure 2A. 35S-labeled β-catenin was incubated in Xenopus egg extract, aliquots (1 ml extract equivalent) were removed at the appropriate times, and samples were subjected to SDS-PAGE followed by autoradiography. β-catenin degradation by components of the Wnt pathway is mediated by the ubiquitin-proteasome system2, and degradation of [35S]-radiolabeled β-catenin in Xenopus e.......

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Discussion

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Xenopus egg extract is a robust biochemical system for investigating β-catenin turnover. The concentration of β-catenin in Xenopus egg extract is ~25 nM 2. Under optimal conditions, the egg extract is capable of degrading β-catenin at a rate of 50-100 nM/hr and is half-maximal at 200 nM24. There are several critical steps for successful reconstitution of β-catenin degradation using Xenopus egg extract. These include 1) generating high quality X.......

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Disclosures

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The authors declare that they have no competing financial interests.

Acknowledgements

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We thank Laurie Lee for critical reading of the manuscript. T.W.C is supported by an American Heart Association Predoctoral Fellowship (12PRE6590007). M.R.B. is supported by a National Cancer Institute training grant (T32 CA119925). S.S.H is supported by National Institutes of Health (R01DK078640). E.L. is supported by the National Institutes of Health (R01GM081635 and R01GM103926).

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
Pregnant mare serum gonadotropin (PMSG)ProSpechor-272-AReconstituted with distilled water before use. 
Human chorionic gonadotropinSigmaCG10-10VL
Potassium chlorideFisherBP366-1
Sodium chlorideResearch Products InternationalS23020-5000.0
Magnesium chlorideFisherBP214-500
Calcium chlorideAcros OrganicsAC42352-5000
HEPESFisherBP310-1
CysteineAcros OrganicsAC17360-1000
LeupeptinSigmaL2884-10MG
AprotininSigmaA1153-10MG
PepstatinSigmaP4265-5MG
Cytochalasin BSigmaC8273-10MG
3 ml syringe: Luer Lock tipBecton Dickinson309657
27 G needleBecton Dickinson305109
96 well solid white polystyrene microplate, round bottomedCorning3605
Steady-Glo luciferase assay systemPromegaE2520Store long-term at -80 °C, can store for up to 1 month at -20 °C
TNT Sp6 coupled reticulocyte lysate systemPromegaL4600
TNT Sp6 high-yield wheat germ protein expression systemPromegaL3260Generally higher yield than reticulocyte lysate 
EasyTag Express protein labeling mix [S35]Perkin ElmerNEG772007MC
Creatine phosphateSigma27920-5G
ATPSigmaA2383-5G
Creatine phosphokinaseSigmaC3755-35KU
Dimethyl sulfoxide (DMSO)SigmaD8418-50ML
Dual-Glo luciferase assay systemPromegaE2920Same storage conditions as Steady-Glo
50 ml Centrifuge tubesFisher Scientific0556214D
Sorvall SS-34 fixed angle rotorThermo Scientific28020
115 V 50/60 Hz MinicentrifugeFisher Scientific05-090-128
mMessage mMachine Sp6 kitAmbionAM1340
Anti-firefly luciferase antibodyAbcamab16466
Anti-GSK3 antibodyBD Transduction Laboratories610201
FLUOStar OptimaBMG Labtech
Sorvall RC-6 Plus centrifugeThermo Scientific
16 °C IncubatorPercival Scientific

References

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  1. Glotzer, M., Murray, A. W., Kirschner, M. W. Cyclin is degraded by the ubiquitin pathway. Nature. 349, 132-138 (1991).
  2. Salic, A., Lee, E., Mayer, L., Kirschner, M. W. Control of beta-catenin stability: reconstitution of the cytoplasmic steps of the wnt pathwa....

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Tags

Xenopus Egg ExtractBeta catenin DegradationCell free SystemRadioactive LabelingLuciferase AssayProteasome InhibitionGSK3 InhibitionImmunoblottingEnergy Regeneration MixHigh throughput Screening

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