Name: rhoc gtpase activation assay
Uploaded: 2010-08-22T17:00:00.000+00:00
Duration: 9 min 58 s
Description: Watch this Scientific Journal Video about RhoC GTPase Activation Assay at JoVE.com

Dipartimento della Difesa W81XWH-05-1-0005, W81XWH-06-1-0495, W81XWH-08-1-0029 e W81XWH-08-1-0356

1. Preparare GST-fusione delle proteine <ol><li> Le scorte di glicerolo di batteri competenti JM109 contenenti il ​​primo N-terminale di 90 amminoacidi di Rho rhotekin dominio di legame (RBD) subcloned nel pGEX3x BamH1/EcoR1 vettore sono fatti. Al fine di garantire alta efficienza Le seguenti operazioni devono essere eseguite per ogni esperimento. Nella nostra esperienza, preparati al momento GST-RBD è la chiave per un test GTPasi robusto e preciso di attivazione. </li><li> Aggiungere 50 microlitri (approssimativo, senza scongelare) di brodo glicerolo a 50 mL di amplificatore LB e far crescere a 37 ° C durante la notte con agitazione. </li><li> Diluire 1:10 in 500 ml LB-amp e crescere per 1 h. </li><li> Indurre GST-produzione di proteine ​​con 0,1 mM IPTG per 2 ore. </li><li> Distribuire uniformemente in bottiglie da centrifuga e centrifugare, Sorval GSA3 rotore a 5000 giri 4 ° C per 20 min. </li><li> Risospendere le sfere in bottiglie di centrifuga, 10 ml di tampone di lisi *. * Buffer di lisi batterica: 20% di saccarosio, 10% glicerolo, 50 mM Tris pH 8.0, 0,2 mM Na 2 S 2 O 5, 2 mM MgCl 2, 2 mM DTT, Aggiungi fresca PMSF, benzamide, aprotinina e leupeptina. </li><li> Sonicare 2-3 minuti (dipende dal tipo di ultrasuoni. Usiamo un Fischer di Sonic Dismembranator modello 500 fissato a segno 6, ciclo 50%). </li><li> Centrifuga, Sorvall SS34, 20 min 10.000 rpm a 4 ° C. A questo punto una piccola aliquota può essere estratto e gestito da SDS-PAGE. Il gel può essere colorato Coomassie e una band dovrebbe essere evidente a 46 kDa. </li><li> Rimuovere il surnatante e aggiungere 1 ml di 50% di glutatione-Sepharose liquami 4B. </li><li> Incubare per 30 minuti a 4 ° C con rotazione. Lavare 3 volte con tampone di lisi. </li><li> Risospendere le sfere GST-RBD/glutatione-Sepharose ad un impasto 50% (circa 1 mL) con GST-pesce tampone **. ** GST-Fish Buffer: 10% glicerolo, 50 mM Tris pH 7.4, 100 mM NaCl, 1% NP-4, 2 mM MgCl 2, Aggiungere fresco PMSF, benzamide, aprotinina e leupeptina </li></ol> 2. Fusione GST-pull down assay <ol><li> Usa 5-10 x 10 6 cellule / test </li><li> Lavare le cellule una volta nel ghiaccio PBS freddo, tenere le piastre in ghiaccio (usiamo un piatto di vetro piano riempito di ghiaccio) e lisare con 0,5 ml di GST-pesce buffer. </li><li> Incubare 5 minuti in ghiaccio, le cellule raccolta con un poliziotto in gomma o scrapper piatto, trasferimento in microcentrifuga tubo e centrifugare 20.000 rpm 5 minuti a 4 ° C. </li><li> Trasferire il surnatante in una provetta per microcentrifuga fresca. Prendere 50 microlitri per determinare totale Rho (cioè il PIL + GTP legato). </li><li> Aggiungere 0,5 ml di perline GST-RBD/glutatione-Sepharose e incubare a 4 ° C, durante la notte con la rotazione. </li><li> Lavare 6x con GST-pesce buffer. </li><li> Perline Risospendere in 40 microlitri 2x-Laemelli tampone campione A questo punto la concentrazione del totale aliquota proteina Rho preso in 2.4 deve essere determinata e 30 mcg pronto per essere eseguito sul gel con il campione di attivazione corrispondenti. </li><li> Campioni bollire a 90 ° C per 5 minuti, centrifugare brevemente e prendere surnatante (cioè evitare le perline), caricare ed eseguire su un 12-ben pendenza 4-20% SDS-PAGE gel. </li><li> Esegui gel senza tensione superiore a 150, il trasferimento alla membrana utilizzando tampone Towbin e costante corrente di 100 W. </li><li> Blocco della membrana con 5% di latte / TBST soluzione e sonda con RhoC-specfic anticorpi. </li></ol> 3. Rappresentante Risultati Buoni risultati dovrebbero produrre una singola banda di circa 22 kDa. Cattivi risultati producono bande multiple o fondo elevato. Questo è indicativo di degradazione delle proteine, lavaggio incompleta di campioni o l&#39;utilizzo di vecchi GST-RBD. <img src="/files/ftp_upload/2083/2083fig1.jpg" alt="Figura 1" /> Figura 1. Tre linee di cellule distinte che esprimono diversi livelli di RhoC GTPasi sono mostrati per dimostrare bassi livelli di RhoC attivo e totale, alti livelli di RhoC attivo e totale o nessuna RhoC. La macchia è stato poi spogliato e reprobed con un anticorpo alla actina house keeping gene per servire come un controllo di carico per la proteina RhoC totale. <img src="/files/ftp_upload/2083/2083fig2.jpg" alt="Figura 2" /> Figura 2. Bande multiple o risultati di elevato background dalla degradazione delle proteine, lavaggio incompleto dei campioni o l&#39;uso di vecchie GST-RBD.

<ol>
	<li>van Golen, K. L., Wu, Z. F., Qiao, X. T., Bao, L. W., Merajver, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RhoC+GTPase,+a+novel+transforming+oncogene+for+human+mammary+epithelial+cells+that+partially+recapitulates+the+inflammatory+breast+cancer+phenotype.">RhoC GTPase, a novel transforming oncogene for human mammary epithelial cells that partially recapitulates the inflammatory breast cancer phenotype.</a> Cancer Res. 60 (20), 5832-5838 (2000).</li><li>van Golen, K. L., Wu, Z. F., Qiao, X. T., Bao, L., Merajver, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RhoC+GTPase+overexpression+modulates+induction+of+angiogenic+factors+in+breast+cells.">RhoC GTPase overexpression modulates induction of angiogenic factors in breast cells.</a> Neoplasia. 2 (5), 418-425 (2000).</li><li>Golen, K. L. v. a. n. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reversion+of+RhoC+GTPase-induced+inflammatory+breast+cancer+phenotype+by+treatment+with+a+farnesyl+transferase+inhibitor.">Reversion of RhoC GTPase-induced inflammatory breast cancer phenotype by treatment with a farnesyl transferase inhibitor.</a> Mol Cancer Ther. 1 (8), 575-583 (2002).</li><li>Golen, K. L. v. a. n. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitogen+activated+protein+kinase+pathway+is+involved+in+RhoC+GTPase+induced+motility,+invasion+and+angiogenesis+in+inflammatory+breast+cancer.">Mitogen activated protein kinase pathway is involved in RhoC GTPase induced motility, invasion and angiogenesis in inflammatory breast cancer.</a> Clin Exp Metastasis. 19 (4), 301-311 (2002).</li><li>Yao, H., Dashner, E. J., van Golen, C. M., van Golen, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RhoC+GTPase+is+required+for+PC-3+prostate+cancer+cell+invasion+but+not+motility.">RhoC GTPase is required for PC-3 prostate cancer cell invasion but not motility.</a> Oncogene. 25 (16), 2285-2296 (2006).</li><li>Hall, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Type+I+Collagen+receptor+(alpha2beta1)+signaling+promotes+prostate+cancer+cell+invasion+through+RhoC+GTPase.">Type I Collagen receptor (alpha2beta1) signaling promotes prostate cancer cell invasion through RhoC GTPase.</a> Neoplasia. 10 (8), 797-803 (2008).</li><li>Sequeira, L., Dubyk, C. W., Riesenberger, T. A., Cooper, C. R., van Golen, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rho+GTPases+in+PC-3+prostate+cancer+cell+morphology,+invasion+and+tumor+cell+diapadesis.">Rho GTPases in PC-3 prostate cancer cell morphology, invasion and tumor cell diapadesis.</a> Clin Exp Metastasis. 25, 569-579 (2008).</li><li>van Golen, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CCL2+Induces+Prostate+Cancer+Transendothelial+Cell+Migration+via+Activation+of+the+Small+GTPase+Rac.">CCL2 Induces Prostate Cancer Transendothelial Cell Migration via Activation of the Small GTPase Rac.</a> J Cell Biochem. 104, 1587-1597 (2008).</li><li>Chatterjee, M., van Golen, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Int J Cancer. , (2010).</li><li>Sander, E. E., ten Klooster, J. P., van Delft, S., van der Kammen, R. A., Collard, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rac+downregulates+Rho+activity:+reciprocal+balance+between+both+GTPases+determines+cellular+morphology+and+migratory+behavior.">Rac downregulates Rho activity: reciprocal balance between both GTPases determines cellular morphology and migratory behavior.</a> J Cell Biol. 147 (5), 1009-1022 (1999).</li></ol>

Nessun conflitto di interessi dichiarati.

La fase più critica della procedura è la generazione di nuove GST-RBD. Il mancato prestare molta attenzione a questo passo è motivo principale per il fallimento. Tutte le fasi, dalla generazione del GST-RBD (1,2) per la notte di incubazione con il lisato cellulare (2,5), dovrebbe essere fatto in un solo giorno. Un altro passo fondamentale è quello di rendere certo che ci sono cellule sufficienti per produrre la lisati cellulari. Questo è di particolare importanza quando si guarda RhoC GTPasi, che tende ad essere pr...

<table><tbody><tr><td>Gluthione-sepharose 4B beads</td><td>GE Healthcare</td><td>17-0756-01</td><td></td></tr><tr><td>Criterion 4-20% Tris-HCl gels</td><td>Bio-Rad</td><td>345-0032</td><td></td></tr></tbody></table>

rhoc gtpase activation assay

RhoC GTPasi ha il 91% di omologia RhoA GTPasi. A causa della sua diffusione nelle cellule, reagenti e tecniche per molti RhoA GTPasi sono stati sviluppati. Tuttavia, RhoC GTPasi è espressa nelle cellule tumorali metastatiche a livelli relativamente bassi. Quindi, pochi RhoC reagenti specifici sono stati sviluppati. Abbiamo adattato un test per rilevare l&#39;attivazione Rho GTPasi RhoC. Questa tecnica utilizza un GST-Rho legame proteina di fusione del dominio a tirare fuori attivo GTPasi RhoC. Inoltre, siamo in grado di raccogliere proteine ​​totali all&#39;inizio del test per determinare i livelli di totale (GTP e PIL legato) GTPasi RhoC. Questo permette la determinazione di principi attivi rispetto al totale delle GTPasi RhoC nella cella. Diverse versioni commerciali di questa procedura sono stati sviluppati tuttavia, i kit commerciali sono ottimizzati per RhoA GTPasi e di solito non funzionano bene per RhoC GTPasi. Parti del test sono stati modificati, nonché lo sviluppo di una RhoC-anticorpo specifico.

Watch this Scientific Journal Video about RhoC GTPase Activation Assay at JoVE.com

RhoC GTPase Activation Assay

Questo protocollo utilizza un pull down di analisi per determinare i livelli di attivo GTPasi RhoC all&#39;interno delle cellule.

RhoC GTPasi attivazione di analisi

RhoC GTPase has 91% homology to RhoA GTPase.  Because of its prevalence in cells, many reagents and techniques for RhoA GTPase have been developed.  ...

Universidad de Cartagena UDEC

Research

JoVE Journal

Biology

12.4K Views.  University of Delaware. Questo protocollo utilizza un pull down di analisi per determinare i livelli di attivo GTPasi RhoC all'interno delle cellule.

Video: RhoC GTPase Activation Assay

Measuring G-protein-coupled Receptor Signaling via Radio-labeled GTP Binding

G-Protein-Coupled Receptors (GPCRs) are a large family of transmembrane receptors that play critical roles in normal cellular physiology and constitute a major pharmacological target for multiple indications, including analgesia, blood pressure regulation, and the treatment of psychiatric disease. Upon ligand binding, GPCRs catalyze the activation of intracellular G-proteins by stimulating the incorporation of guanosine triphosphate (GTP). Activated G-proteins then stimulate signaling pathways that elicit cellular responses. GPCR signaling can be monitored by measuring the incorporation of a radiolabeled and non-hydrolyzable form of GTP, [35S]guanosine-5&#39;-O-(3-thio)triphosphate ([35S]GTP&#947;S), into G-proteins. Unlike other methods that assess more downstream signaling processes, [35S]GTP&#947;S binding measures a proximal event in GPCR signaling and, importantly, can distinguish agonists, antagonists, and inverse agonists. The present protocol outlines a sensitive and specific method for studying GPCR signaling using crude membrane preparations of an archetypal GPCR, the &#181;-opioid receptor (MOR1). Although alternative approaches to fractionate cells and tissues exist, many are cost-prohibitive, tedious, and/or require non-standard laboratory equipment. The present method provides a simple procedure that enriches functional crude membranes. After isolating MOR1, various pharmacological properties of its agonist, [D-Ala, N-MePhe, Gly-ol]-enkephalin (DAMGO), and antagonist, naloxone, were determined.

Guanosine triphosphate (GTP) binding is one of the earliest events in G-Protein-Coupled Receptor (GPCR) activation. This protocol describes how to pharmacologically characterize specific GPCR-ligand interactions by monitoring the binding of the radio-labeled GTP analog, [35S]guanosine-5&#39;-O-(3-thio)triphosphate ([35S]GTP&#947;S), in response to a ligand of interest.

Misurazione del segnalatore del ricettore accoppiato con G-proteina mediante la legatura GTP con etichetta radio

G-Protein-Coupled Receptors (GPCRs) are a large family of transmembrane receptors that play critical roles in normal cellular physiology and constitute a ...

Ricerca

Biochimica

Detection of Small GTPase Prenylation and GTP Binding Using Membrane Fractionation and  GTPase-linked Immunosorbent Assay

The Rho GTPase family belongs to the Ras superfamily and includes approximately 20 members in humans. Rho GTPases are important in the regulation of diverse cellular functions, including cytoskeletal dynamics, cell motility, cell polarity, axonal guidance, vesicular trafficking, and cell cycle control. Changes in Rho GTPase signaling play an essential regulatory role in many pathological conditions, such as&#160;cancer, central nervous system diseases, and immune system-dependent diseases. The posttranslational modification of Rho GTPases (i.e., prenylation by mevalonate pathway intermediates) and GTP binding are key factors which affect the activation of this protein. In this paper, two essential and simple methods are provided to detect a broad range of Rho GTPase prenylation and GTP binding activities. Details of the technical procedures that have been used are explained step by step in this manuscript.

Here we describe a protocol to investigate the prenylation and guanosine-5'-triphosphate (GTP)-loading of Rho GTPase. This protocol consists of two detailed methods, namely membrane fractionation and a GTPase-linked immunosorbent assay. The protocol can be used for measuring the prenylation and GTP loading of different other small GTPases.

Rilevazione di piccolo GTPase prenilazione e GTP Binding mediante frazionamento di membrana e GTPase-collegata dell'immunosorbente

The Rho GTPase family belongs to the Ras superfamily and includes approximately 20 members in humans. Rho GTPases are important in the regulation of ...

Imaging G-protein Coupled Receptor (GPCR)-mediated Signaling Events that Control Chemotaxis of Dictyostelium Discoideum

Many eukaryotic cells can detect gradients of chemical signals in their environments and migrate accordingly 1. This guided cell migration is referred as chemotaxis, which is essential for various cells to carry out their functions such as trafficking of immune cells and patterning of neuronal cells 2, 3. A large family of G-protein coupled receptors (GPCRs) detects variable small peptides, known as chemokines, to direct cell migration in vivo 4. The final goal of chemotaxis research is to understand how a GPCR machinery senses chemokine gradients and controls signaling events leading to chemotaxis. To this end, we use imaging techniques to monitor, in real time, spatiotemporal concentrations of chemoattractants, cell movement in a gradient of chemoattractant, GPCR mediated activation of heterotrimeric G-protein, and intracellular signaling events involved in chemotaxis of eukaryotic cells 5-8. The simple eukaryotic organism, Dictyostelium discoideum, displays chemotaxic behaviors that are similar to those of leukocytes, and D. discoideum is a key model system for studying eukaryotic chemotaxis. As free-living amoebae, D. discoideum cells divide in rich medium. Upon starvation, cells enter a developmental program in which they aggregate through cAMP-mediated chemotaxis to form multicullular structures. Many components involved in chemotaxis to cAMP have been identified in D. discoideum. The binding of cAMP to a GPCR (cAR1) induces dissociation of heterotrimeric G-proteins into G&gamma; and G&beta;&gamma; subunits 7, 9, 10. G&beta;&gamma; subunits activate Ras, which in turn activates PI3K, converting PIP2 into PIP3 on the cell membrane 11-13. PIP3 serve as binding sites for proteins with pleckstrin Homology (PH) domains, thus recruiting these proteins to the membrane 14, 15. Activation of cAR1 receptors also controls the membrane associations of PTEN, which dephosphorylates PIP3 to PIP2 16, 17. The molecular mechanisms are evolutionarily conserved in chemokine GPCR-mediated chemotaxis of human cells such as neutrophils 18. We present following methods for studying chemotaxis of D. discoideum cells. 1. Preparation of chemotactic component cells. 2. Imaging chemotaxis of cells in a cAMP gradient. 3. Monitoring a GPCR induced activation of heterotrimeric G-protein in single live cells. 4. Imaging chemoattractant-triggered dynamic PIP3 responses in single live cells in real time. Our developed imaging methods can be applied to study chemotaxis of human leukocytes.

Imaging G-protein Coupled Receptor GPCR-mediated Signaling Events that Control Chemotaxis of Dictyostelium Discoideum

Here, we describe detailed live cell imaging methods for investigating chemotaxis. We present fluorescence microscopic methods to monitor spatiotemporal dynamics of signaling events in migrating cells. Measurement of signaling events permits us to further understand how a GPCR-signaling network achieves gradient sensing of chemoattractants and controls directional migration of eukaryotic cells.

Receptor Imaging proteina G accoppiata (GPCR)-mediata eventi di segnalazione che chemiotassi di controllo di Dictyostelium discoideum</em

Many eukaryotic cells can detect gradients of chemical signals in their environments and migrate accordingly 1.  This guided cell migration is referred as ...

Biologia

Affinity Precipitation of Active Rho-GEFs Using a GST-tagged Mutant Rho Protein (GST-RhoA(G17A)) from Epithelial Cell Lysates

Proteins of the Rho family of small GTPases are central regulators of the cytoskeleton, and control a large variety of cellular processes, including cell migration, gene expression, cell cycle progression and cell adhesion 1. Rho proteins are molecular switches that are active in GTP-bound and inactive in GDP-bound state. Their activation is mediated by a family of Guanine-nucleotide Exchange Factor (GEF) proteins. Rho-GEFs constitute a large family, with overlapping specificities 2. Although a lot of progress has been made in identifying the GEFs activated by specific signals, there are still many questions remaining regarding the pathway-specific regulation of these proteins. The number of Rho-GEFs exceeds 70, and each cell expresses more than one GEF protein. In addition, many of these proteins activate not only Rho, but other members of the family, contributing further to the complexity of the regulatory networks. Importantly, exploring how GEFs are regulated requires a method to follow the active pool of individual GEFs in cells activated by different stimuli. Here we provide a step-by-step protocol for a method used to assess and quantify the available active Rho-specific GEFs using an affinity precipitation assay. This assay was developed a few years ago in the Burridge lab 3,4 and we have used it in kidney tubular cell lines 5,6,7. The assay takes advantage of a "nucleotide free" mutant RhoA, with a high affinity for active GEFs. The mutation (G17A) renders the protein unable to bind GDP or GTP and this state mimics the intermediate state that is bound to the GEF. A GST-tagged version of this mutant protein is expressed and purified from E. coli, bound to glutathione sepharose beads and used to precipitate active GEFs from lysates of untreated and stimulated cells. As most GEFs are activated via posttranslational modifications or release from inhibitory bindings, their active state is preserved in cell lysates, and they can be detected by this assay8. Captured proteins can be probed for known GEFs by detection with specific antibodies using Western blotting, or analyzed by Mass Spectrometry to identify unknown GEFs activated by certain stimuli.

Affinity Precipitation of Active Rho-GEFs Using a GST-tagged Mutant Rho Protein GST-RhoAG17A from Epithelial Cell Lysates

The method presented here describes an assay to follow activation of RhoA specific GDP/GTP Exchange Factors (GEFs) in cultured cells by making use of a mutant RhoA GST fusion protein that has high affinity for activated GEFs. GEFs are precipitated from cell lysates, detected by Western blotting and quantified by densitometry.

Affinità Precipitazioni di Active Rho-GEFs Utilizzo di un GST-tagged Mutant proteina Rho (GST-RhoA (G17A)) da lisati di cellule epiteliali

Proteins of the Rho family of small GTPases are central regulators of the cytoskeleton, and control a large variety of cellular processes, including cell ...

A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators

G protein-coupled receptors (GPCRs) are of great importance to the pharmaceutical industry as they are involved in many human diseases and include well-validated targets for therapeutic intervention. Discovery of lead compounds, including small synthetic molecules, that specifically inhibit the receptor&#39;s function, is an important initial step in drug development and relies on sensitive, specific, and robust cell-based assays. Here, we describe a kinetic cellular assay with a fluorescent readout primarily designed to identify receptor-specific antagonists that inhibit the intracellular Ca2+ release evoked upon the activation of the CXC chemokine receptor 4 (CXCR4) by its endogenous ligand, the CXC chemokine ligand 12 (CXCL12). A key advantage of this method is that it also enables screening of compounds endowed with intrinsic agonistic properties (i.e., compounds eliciting an increase in intracellular Ca2+ concentration in the absence of CXCL12) or compounds modulating the receptor&#39;s function via interaction with allosteric binding sites (i.e., positive and negative allosteric modulators (PAMs and NAMs, respectively)). On the down side, autofluorescent compounds might interfere with the assay&#39;s readout, thereby hampering reliable data interpretation. Most likely this assay can be implemented, with minimal adaptations, as a generic drug discovery assay for many other GPCRs of which the activation leads to a release of intracellular Ca2+.

A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators

The described cellular assay is designed for the identification of CXC chemokine receptor 4 (CXCR4)-interacting agents that inhibit or stimulate, either competitively or allosterically, the intracellular Ca2+ release initiated by CXCR4 activation.

Un'analisi cinetica basata sulla fluorescenza Ca2 + mobilizzazione per identificare il G proteina-ha accoppiato il ricevitore agonisti, antagonisti e modulatori allosterici

G protein-coupled receptors (GPCRs) are of great importance to the pharmaceutical industry as they are involved in many human diseases and include ...

Medicina

Characterization of G Protein-coupled Receptors by a Fluorescence-based Calcium Mobilization Assay

For more than 20 years, reverse pharmacology has been the preeminent strategy to discover the activating ligands of orphan G protein-coupled receptors (GPCRs). The onset of a reverse pharmacology assay is the cloning and subsequent transfection of a GPCR of interest in a cellular expression system. The heterologous expressed receptor is then challenged with a compound library of candidate ligands to identify the receptor-activating ligand(s). Receptor activation can be assessed by measuring changes in concentration of second messenger reporter molecules, like calcium or cAMP. The fluorescence-based calcium mobilization assay described here is a frequently used medium-throughput reverse pharmacology assay. The orphan GPCR is transiently expressed in human embryonic kidney 293T (HEK293T) cells and a promiscuous G&#945;16 construct is co-transfected. Following ligand binding, activation of the G&#945;16 subunit induces the release of calcium from the endoplasmic reticulum. Prior to ligand screening, the receptor-expressing cells are loaded with a fluorescent calcium indicator, Fluo-4 acetoxymethyl. The fluorescent signal of Fluo-4 is negligible in cells under resting conditions, but can be amplified more than a 100-fold upon the interaction with calcium ions that are released after receptor activation. The described technique does not require the time-consuming establishment of stably transfected cell lines in which the transfected genetic material is integrated into the host cell genome. Instead, a transient transfection, generating temporary expression of the target gene, is sufficient to perform the screening assay. The setup allows medium-throughput screening of hundreds of compounds. Co-transfection of the promiscuous G&#945;16, which couples to most GPCRs, allows the intracellular signaling pathway to be redirected towards the release of calcium, regardless of the native signaling pathway in endogenous settings. The HEK293T cells are easy to handle and have proven their efficacy throughout the years in receptor deorphanization assays. However, optimization of the assay for specific receptors may remain necessary.

The here described fluorescence-based calcium mobilization assay is a medium-throughput reverse pharmacology screening system for the identification of functionally activating ligand(s) of orphan G protein-coupled receptors (GPCRs).

Caratterizzazione di G recettori accoppiati alla proteina da un calcio di Mobilitazione Assay Basato sulla fluorescenza

For more than 20 years, reverse pharmacology has been the preeminent strategy to discover the activating ligands of orphan G protein-coupled receptors ...

Comparing the Affinity of GTPase-binding Proteins using Competition Assays

In this protocol we demonstrate a method for comparing the competition between GTPase-binding proteins. Such an approach is important for determining the binding capabilities of GTPases for two reasons: The fact that all interactions involve the same face of the GTPases means that binding events must be considered in the context of competitors, and the fact that the bound nucleotide must also be controlled means that conventional approaches such as immunoprecipitation are unsuitable for GTPase biochemistry. The assay relies on the use of purified proteins. Purified Rac1 immobilized on beads is used as the bait protein, and can be loaded with GDP, a non-hydrolyzable version of GTP or left nucleotide free, so that the signaling stage to be investigated can be controlled. The binding proteins to be investigated are purified from mammalian cells, to allow correct folding, by means of a GFP tag. Use of the same tag on both proteins is important because not only does it allow rapid purification and elution, but also allows detection of both competitors with the same antibody during elution. This means that the relative amounts of the two bound proteins can be determined accurately.

This protocol compares the relative affinities of binding partners for Rho-family GTPases, including Rac1. In vivo, Rac1-binding proteins compete for a single binding interface, the conformation of which is dictated by a bound nucleotide. The nucleotide is both important and difficult to control experimentally, due to the high hydrolysis rate.

Confrontando l&#39;affinità delle proteine-GTPasi legame con saggi Concorso

In this protocol we demonstrate a method for comparing the competition between GTPase-binding proteins. Such an approach is important for determining the ...

Competition Binding Assay to Study Competing GTPase-Binding Protein Partners

Source: Williamson, R. C., et al.&#160; <a href="https://appjove.unicartagenaproxy.elogim.com/v/53254">Comparing the Affinity of GTPase-binding Proteins using Competition Assays.</a> J. Vis. Exp. (2015)
This video demonstrates a competition assay to study GTPase-binding protein partners. Utilizing nucleotide-bound GTPase protein immobilized on magnetic beads, the competitive binding between two interacting protein partners for the same binding site on the GTPase can be studied to assess the binding affinities of the protein partners.

Saggio di legame della competizione per studiare i partner proteici leganti la GTPasi in competizione

Source: Williamson, R. C., et al.&#160; Comparing the Affinity of GTPase-binding Proteins using Competition Assays. J. Vis. Exp. (2015)
This video ...

JoVE Encyclopedia of Experiments

Biological Techniques

Biomolecular Interaction Detection Techniques

Protein-protein interactions

Small GTPases - Ras and Rho

Ras and Rho are small monomeric GTPases that act downstream of receptor tyrosine kinase (RTK) and regulate various cellular processes. These GTPases switch between active and inactive states by binding to guanine nucleotides.
Three regulatory proteins control their activity:
<ul>
	<li>Guanine nucleotide exchange factors or GEF,</li>
	<li>GTPase-activating proteins or GAPs, and</li>
	<li>Guanine nucleotide-dissociation inhibitors or GDIs.</li>
</ul>
The GEF activates the GTPase by exchanging the bound-GDP with GTP. The GTPases&#8217; activity is turned off by GAP. They hydrolyze the bound GTP to GDP. The GDI further arrests the GTPase in its GDP-bound inactive form.
Ras is a membrane-bound GTPase and attaches to the plasma membrane via prenyl chains. There are three types of Ras present in mammals: H-Ras, K-Ras, and N-Ras. The binding of growth factor ligand activates RTKs and triggers Ras-GEF to displace GDP with GTP. The active Ras-GTP can now recruit and activate the first kinase of the MAPK signaling cascade, such as MAPKKK/Raf, triggering MAPK signaling, thereby initiating cell proliferation. However, it quickly hydrolyzes the GTP and is turned off, preventing uncontrolled cell proliferation. Hyperactive mutant forms of Ras stay in the GTP-bound state and often lead to tumorigenesis.
Rho family proteins such as Cdc42, Rho, and Rac modulate cell shape, movement, and migration. Rho can be soluble or membrane-bound. Soluble RhoGDP binds GDI and stays inactive. Following stimulation, GDI dissociates, facilitating membrane localization of Rho in one of the following ways:
<ol>
	<li>Electrostatic attractive forces between positively charged C termini of Rho and the negatively charged plasma membrane lipids promote its localization.</li>
	<li>The truncated tropomyosin-related kinase B receptor or T1 binds RhoGDI and sequesters it on the plasma membrane, allowing Rho to escape to the membrane for activation. Alternatively, displacement factors such as the ezrin (E), radixin (R), and moesin (M) or ERM family proteins interact with the RhoGTPases-GDI complex, subsequently displacing the GDI from Rho.</li>
	<li>Alternatively, phosphorylation of RhoGDI by protein kinases destabilizes the RhoGTPases-GDI complex, releasing Rho for membrane localization.</li>
</ol>
Once localized to the membrane, Rho interacts with a nearby activated RhoGEF and undergoes GDP/GTP exchange. Activated RhoGTP now promotes downstream signaling and regulates various cellular processes.

Piccole GTPasi - Ras e Rho

Ras and Rho are small monomeric GTPases that act downstream of receptor tyrosine kinase (RTK) and regulate various cellular processes. These GTPases ...

Didattica

JoVE Core

Cell Biology

Unit 1

Signaling Networks of Kinase Receptors

TERMINI E CONCETTI CHIAVE

Activation and Inactivation of G Proteins

Heterotrimeric G proteins are guanine nucleotide-binding proteins. As the name suggests, heterotrimeric G proteins are composed of three subunits: alpha, beta, and gamma. They remain GDP-bound or GTP-bound inside the cells and switch between inactive/active states. The G&#945;&#160;subunit possesses the nucleotide-binding pocket that binds guanine nucleotides and switches between GDP or GTP-bound states. In contrast, the G&#42933; and G&#947;&#160;subunits are always bound together with high affinity and are together referred to as G&#42933;&#947;&#160;subunits.
Heterotrimeric G proteins regulate signaling downstream of G protein-coupled receptors&#160; (GPCRs) and remain anchored to the membrane by lipid modifications. Myristoylation or palmitoylation at the N-terminus of the G&#945;&#160;subunit, and prenylation at the C-terminus of the G&#947;&#160;subunit anchor these subunits to the membrane and stabilize the heterotrimeric complex.
Upon ligand binding, GPCRs bind the G&#945;&#160;subunit of heterotrimeric G proteins with high affinity. The receptor-G protein interaction leads to the opening of the nucleotide-binding site of the G&#945;&#160;subunit, releasing the GDP. GPCRs function as guanine nucleotide exchange factors&#160; (GEFs) that facilitate G&#945;-GTP binding.
The activated GTP-G&#945;&#160;subunit undergoes a conformational change and detaches from the receptor and G&#42933;&#947;&#160; subunit.&#160; GTP-G&#945;&#160;and&#160; G&#42933;&#947;&#160;subunits now individually participate in signal transduction pathways and activate effectors like adenylyl cyclase (AC), phospholipase C&#42933; (PLC&#42933;) and&#160; Na+, K+, and Ca2+-specific ion channels, thereby triggering the production of different second messengers.
The human genome encodes&#160; 21 different G&#945;&#160;subunits that can be classified into subfamilies such as G&#945;s, G&#945;i, G&#945;q, Gt&#945;, Golf, G12&#945;, and G13&#945;. Each of these G&#945;&#160;subunits performs a specific function upon binding their effector. For example, the binding of G&#945;s to adenylyl cyclase activates adenylyl cyclase&#160; to produce cAMP, an important second messenger. cAMP regulates muscle contraction and the metabolism of fats or sugars. In contrast, the binding of G&#945;i inhibits adenylyl cyclase activity and cAMP synthesis.
Other subfamilies of G&#945; subunits perform various other cellular processes. The G&#945;q family activates PLC&#42933;, which produces second messengers like inositol trisphosphate (IP3) and diacylglycerol (DAG). Both IP3 and DAG affect various cellular pathways, including growth and differentiation. The transducin or Gt&#945;&#160;family binds to rhodopsin to transmit information from&#160; visual stimuli by activating specific phosphodiesterases, which hydrolyze cGMP to GMP.&#160; Golf is the variant of the G&#945;s family and is used&#160; in odorant signaling pathways. The family of G12&#945; and G13&#945;&#160;&#160;proteins are involved in cytoskeleton regulation.
G&#945;&#160;subunits have intrinsic GTPase activity, and binding of GTP-G&#945;&#160;to the effector enhances their rate of GTP hydrolysis. The activated GTP-G&#945;&#160;form is thus short-lived and hydrolyzed to GDP-G&#945;&#160; within minutes, switching back to the inactive state. This feedback mechanism helps avoid the overstimulation of cells in response to a signal. G proteins are also regulated by another family of GAP, Regulators of G protein Signaling (RGS). The human genome encodes 25 RGS proteins, each interacting with a particular set of G&#945;&#160;subunits, and helps shut off G protein-mediated cellular responses.

Attivazione e inattivazione delle proteine G

Heterotrimeric G proteins are guanine nucleotide-binding proteins. As the name suggests, heterotrimeric G proteins are composed of three subunits: alpha, ...

RhoC GTPasi attivazione di analisi

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