High Throughput Screen for Inhibitors of Rac1 GTPase by Flow Cytometry

High throughput (HT) screening is at the starting point for most drug discovery programs. As the range of targets being pursued widens new technologies have to be deployed to enable assays built to measure the activity of proteins previously deemed challenging. Flow cytometry is a technology providing multi-parametric analysis of single cells or other particles in suspension, such as beads. High throughput (HT) flow cytometry has become a very attractive screening platform for drug discovery. In this chapter we describe a 1536 well format high throughput screen of 500,000 compounds to find inhibitors of Rac1 GTPase to prevent allergic airway hyper-responsiveness in asthma. We discuss the assay development, miniaturization and validation carried out prior to the full screening campaign. We then describe how we have automated our iQue® HD screener instruments and how we proceed with the data analysis and explain why we chose to run this screen on a flow cytometer and how it enabled us to reduce cost and timelines for the project

Transglutaminase-dependent RhoA Activation and Depletion by Serotonin in Vascular Smooth Muscle Cells

The small G protein RhoA plays a major role in several vascular processes and cardiovascular disorders. Here we analyze the mechanisms of RhoA regulation by serotonin (5-HT) in arterial smooth muscle. 5-HT (0.1-10 microM) induced activation of RhoA followed by RhoA depletion at 24-72 h. Inhibition of 5-HT1 receptors reduced the early phase of RhoA activation but had no effect on 5-HT-induced delayed RhoA activation and depletion, which were suppressed by the 5-HT transporter inhibitor fluoxetine and the transglutaminase inhibitor monodansylcadaverin and in type 2 transglutaminase-deficient smooth muscle cells. Coimmunoprecipitations demonstrated that 5-HT associated with RhoA both in vitro and in vivo. This association was calcium-dependent and inhibited by fluoxetine and monodansylcadaverin. 5-HT promotes the association of RhoA with the E3 ubiquitin ligase Smurf1, and 5-HT-induced RhoA depletion was inhibited by the proteasome inhibitor MG132 and the RhoA inhibitor Tat-C3. Simvastatin, the Rho kinase inhibitor Y-27632, small interfering RNA-mediated RhoA gene silencing, and long-term 5-HT stimulation induced Akt activation. In contrast, inhibition of 5-HT-mediated RhoA degradation by MG132 prevented 5-HT-induced Akt activation. Long-term 5-HT stimulation also led to the inhibition of the RhoA/Rho kinase component of arterial contraction. Our data provide evidence that 5-HT, internalized through the 5-HT transporter, is transamidated to RhoA by transglutaminase. Transamidation of RhoA leads to RhoA activation and enhanced proteasomal degradation, which in turn is responsible for Akt activation and contraction inhibition. The observation of transamidation of 5-HT to RhoA in pulmonary artery of hypoxic rats suggests that this process could participate in pulmonary artery remodeling and hypertension

0341: AMPK exerts an insulin-sensitizing effect on cardiac glucose uptake by multiple molecular mechanisms including cytoskeleton reorganization

BackgroundInsulin-resistant cardiomyocytes are characterized by a decreased ability of insulin to stimulate glucose uptake. We have previously shown that the activation of AMPK by metformin or phenformin restores insulin-sensitivity in insulin-resistant cardiomyocytes. The aim of our present work is to understand by which molecular mechanisms AMPK exerts its insulin sensitizing effect. In this study we focused on the mTOR/p70S6K pathway and on cytoskeleton reorganization. mTOR/p70S6K, which is known to be inhibited by AMPK, is able to reduce insulin signaling via a negative feedback loop involving serine phosphorylation of IRS-1. On the other hand, cytoskeleton reorganization, which is a known target of AMPK, is responsible for the translocation of the glucose transporter GLUT4 to the plasma membrane.MethodsAdult rat cardiomyocytes were primary cultured and treated with different agents including insulin, AMPK activator (phenformin), mTOR inhibitor rapamycin and/or actin cytoskeleton inhibitor latrunculin B. Glucose uptake was assessed by detritiation of 2-3H-glucose.ResultsFirst, we tested if rapamycin was able to mimic AMPK activators. Similarly to phenformin, rapamycin increased the insulin-dependent phosphorylation of Akt involved in the regulation of glucose uptake. Despite the ability of rapamycin to induce this Akt over-phosphorylation, rapamycin was not able to restore the insulin-dependent stimulation of glucose uptake like phenformin did. On the other hand, latrunculin B abolished the insulin-sensitizing action of phenformin on glucose uptake, in insulin-sensitive as well as in insulinresistant cells.Conclusionsactin cytoskeleton reorganization but not mTOR/p70S6K, is involved in the insulin-sensitizing effect of AMPK on cardiac glucose uptake. The role played by Small G proteins, known to be involved in the regulation of actin cytoskeleton is under investigation

Caracterisation electrophysiologique des canaux calciques des cellules musculaires lisses vasculaires par la technique du patch-clamp

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Rho Kinases in Health and Disease: From Basic Science to Translational Research

International audienceRho-associated kinases ROCK1 and ROCK2 are key regulators of actin cytoskeleton dynamics downstream of Rho GTPases that participate in the control of important physiologic functions, S including cell contraction, migration, proliferation, adhesion, and inflammation. Several excellent review articles dealing with ROCK function and regulation have been published over the past few years. Although a brief overview of general molecular, biochemical, and functional properties of ROCKs is included, an effort has been made to produce an original work by collecting and synthesizing recent studies aimed at translating basic discoveries from cell and experimental models into knowledge of human physiology, pathophysiological mechanisms, and medical therapeutics. This review points out the specificity and distinct roles of ROCK1 and ROCK2 isoforms highlighted in the last few years. Results obtained from genetically modified mice and genetic analysis in humans are discussed. This review also addresses the involvement of ROCKs in human diseases and the potential use of ROCK activity as a biomarker or a pharmacological target for specific inhibitors

In Vitro and In Vivo Approaches to Assess Rho Kinase Activity

International audienceIncreased arterial tone and the resulting rise in peripheral vascular resistance are major determinants of the elevated arterial pressure in hypertension. The RhoA/Rho kinase signaling pathways are now recognized as a major regulator of vascular smooth muscle contraction and arterial tone. Here we describe methods to directly and indirectly assess Rho kinase activity in vitro and in cells and tissues

Étude des voies de signalisation dans le phénomène de resténose intra-stent (implication de la protéine G monomérique RhoA et de son effecteur Rho-kinase)

La resténose intra-stent est une nouvelle pathologie induite par l'implantation d'une endoprothèse (stent). Elle résulte d'une prolifération des cellules musculaires lisses (CML), une migration et une production excessive de matrice extracellulaire. Le but de ce travail est d'analyser (i) les conséquences histologiques de l'implantation du stent dans un modèle de culture d'artère mammaires "ex-vivo"; (ii) l'activité de RhoA, régulateur majeur de la prolifération et la migration des CML, après implantation du stent et de déterminer son rôle dans la formation de la néointima; (iii) l'impact du mode d'implantation du stent sur l'épaississement néointimal dans le segment stenté et dans la zone bordante. Notre étude montre que le modèle d'artères mammaires humaines est fiable pour l'étude des conséquences histologiques de l'implantation d'un stent. Le stent induit une activation de RhoA, et l'effet inhibiteur de la rapamycine sur l'expression de RhoA a un rôle clé dans son effet limitant de la resténose. Par l'utilisation de stent actif libérant la rapamycine, nous démontrons l'intérêt de l'implantation directe du stent pour limiter l'effet de bord.In-stent restenosis is a novel pathobiologic process resulting from vascular smooth muscle cell (VSMC) proliferation, migration and excessive matrix production. The aims of this study were to analyze (i) the histological consequences of the healing process following stent implantation in an "ex-vivo" model of human internal mammary arteries; (ii) the activity of RhoA, a major regulator of VSMC proliferation and migration, after stenting and to determine its role in the neointimal formation; (iii) the influence of the stent insertion procedure on neointimal thickening in the stented segment of the artery and at the stent edge. Our study shows that the artery culture model can provide valuable information regarding histological consequences and healing process after balloon dilatation and stent implantation. Stent implantation induces maintained RhoA activation and inhibition of Rho-kinase reduces neointimal thickening. Rapamycin (sirolimus) decreases RhoA expression and this effect plays a key role in its antirestenotic action. Finally, by the use of sirolimus eluting stent, we show the benefit of direct stenting to limit the edge effect.NANTES-BU Sciences (441092104) / SudocSudocFranceF

RhoA Phosphorylation Induces Rac1 Release from Guanine Dissociation Inhibitor α and Stimulation of Vascular Smooth Muscle Cell Migration▿

Although overactivation of RhoA is recognized as a common component of vascular disorders, the molecular mechanisms regulating RhoA activity in vascular smooth muscle cells (VSMC) are still unclear. We have previously shown that in VSMC, RhoA is phosphorylated on Ser188 by nitric oxide (NO)-stimulated cGMP-dependent kinase (PKG), which leads to RhoA-Rho kinase pathway inhibition. In this study, we showed that expression of phosphoresistant RhoA mutants prevented the stimulation of VSMC migration and adhesion induced by NO-PKG pathway activation. In contrast, under basal conditions, phosphomimetic RhoA mutants stimulated VSMC adhesion and migration through a signaling pathway requiring Rac1 and the Rho exchange factor Vav3. RhoA phosphorylation or phosphomimetic RhoA mutants induced Rac1 activation but did not activate Vav3. Indeed, phosphorylated RhoA or phosphomimetic mutants trapped guanine dissociation inhibitor α (GDIα), leading to the release of Rac1 and its translocation to the membrane, where it was then activated by the basal Vav3 nucleotide exchange activity. In vivo, RhoA phosphorylation induced by PKG activation in the aortas of rats treated with sildenafil induced dissociation of Rac1 from GDIα and activation of the Rac1 signaling pathway. These results suggest that the phosphorylation of RhoA represents a novel potent and physiological GDIα displacement factor that leads to Rac1 activation and regulation of Rac1-dependent VSMC functions