Articles de revues : « GTPasi »

1

Irving, Helen R. « Abscisic acid induction of GTP hydrolysis in maize coleoptile plasma membranes ». Functional Plant Biology 25, n^o 5 (1998) : 539. http://dx.doi.org/10.1071/pp98009.

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Since receptor-coupled G proteins increase GTP hydrolysis (GTPase) activity upon ligands binding to the receptor, a study was undertaken to determine if abscisic acid (ABA) induced such an effect. Plasma membranes isolated from etiolated maize (Zea mays L.) coleoptiles were enriched in GTPase activity relative to microsomal fractions. Vanadate was included in the assay to inhibit the high levels of vanadate sensitive low affinity GTPases present. Under these conditions, GTPase activity was enhanced by Mg2+, stimulated by mastoparan, and inhibited by GTPγS indicating the presence of either monomeric or heterotrimeric G proteins. The combination of NaF and AlCl3 is expected to inhibit heterotrimeric G protein activity but had little effect on GTPase activity in maize coleoptile membranes. Cholera toxin enhanced basal GTPase activity, confirming the presence of heterotrimeric G proteins in maize plasma membranes. Pertussis toxin also slightly enhanced basal GTPase activity in maize membranes. Abscisic acid enhanced GTPase activity optimally at 5 mmol/L Mg2+ in a concentration dependent manner by 1.5-fold at 10 µmol/L and up to three-fold at 100 µmol/L ABA. Abscisic acid induced GTPase activity was inhibited by GTPγS, the combination of NaF and AlCl3, and pertussis toxin. Overall, these results are typical of a receptor-coupled G protein responding to its ligand.

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Estevez, Ana Y., Tamara Bond et Kevin Strange. « Regulation of I Cl,swell in neuroblastoma cells by G protein signaling pathways ». American Journal of Physiology-Cell Physiology 281, n^o 1 (1 juillet 2001) : C89—C98. http://dx.doi.org/10.1152/ajpcell.2001.281.1.c89.

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Guanosine 5′- O-(3-thiotriphosphate) (GTPγS) activated the I Cl,swell anion channel in N1E115 neuroblastoma cells in a swelling-independent manner. GTPγS-induced current was unaffected by ATP removal and broadly selective tyrosine kinase inhibitors, demonstrating that phosphorylation events do not regulate G protein-dependent channel activation. Pertussis toxin had no effect on GTPγS-induced current. However, cholera toxin inhibited the current ∼70%. Exposure of cells to 8-bromoadenosine 3′,5′-cyclic monophosphate did not mimic the effect of cholera toxin, and its inhibitory action was not prevented by treatment of cells with an inhibitor of adenylyl cyclase. These results demonstrate that GTPγS does not act through Gαi/o GTPases and that Gαs/Gβγ G proteins inhibit the channel and/or channel regulatory mechanisms through cAMP-independent mechanisms. Swelling-induced activation of I Cl,swell was stimulated two- to threefold by GTPγS and inhibited by 10 mM guanosine 5′- O-(2-thiodiphosphate). The Rho GTPase inhibitor Clostridium difficile toxin B inhibited both GTPγS- and swelling-induced activation of I Cl,swell. Taken together, these findings indicate that Rho GTPase signaling pathways regulate the I Cl,swell channel via phosphorylation-independent mechanisms.

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Uno, Tomohide, Tsubasa Moriwaki, Yuri Isoyama, Yuichi Uno, Kengo Kanamaru, Hiroshi Yamagata, Masahiko Nakamura et Michihiro Takagi. « Rab14 from Bombyx mori (Lepidoptera : Bombycidae) shows ATPase activity ». Biology Letters 6, n^o 3 (13 janvier 2010) : 379–81. http://dx.doi.org/10.1098/rsbl.2009.0878.

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Rab GTPases are essential for vesicular transport, whereas adenosine triphosphate (ATP) is the most important and versatile of the activated carriers in the cell. But there are little reports to clarify the connection between ATP and Rab GTPases. A cDNA clone (Rab14) from Bombyx mori was expressed in Escherichia coli as a glutathione S-transferase fusion protein and purified. The protein bound to [ 3 H]-GDP and [ 35 S]-GTPγS. Binding of [ 35 S]-GTPγS was inhibited by guanosine diphosphate (GDP), guanosine triphosphate (GTP) and ATP. Rab14 showed GTP- and ATP-hydrolysis activity. The Km value of Rab14 for ATP was lower than that for GTP. Human Rab14 also showed an ATPase activity. Furthermore, bound [ 3 H]-GDP was exchanged efficiently with GTP and ATP. These results suggest that Rab14 is an ATPase as well as GTPase and gives Rab14 an exciting integrative function between cell metabolic status and membrane trafficking.

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Herrmann, Andrea, Britta A. M. Tillmann, Janine Schürmann, Michael Bölker et Paul Tudzynski. « Small-GTPase-Associated Signaling by the Guanine Nucleotide Exchange Factors CpDock180 and CpCdc24, the GTPase Effector CpSte20, and the Scaffold Protein CpBem1 in Claviceps purpurea ». Eukaryotic Cell 13, n^o 4 (31 janvier 2014) : 470–82. http://dx.doi.org/10.1128/ec.00332-13.

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ABSTRACTMonomeric GTPases of the Rho subfamily are important mediators of polar growth and NADPH (Nox) signaling in a variety of organisms. These pathways influence the ability ofClaviceps purpureato infect host plants. GTPase regulators contribute to the nucleotide loading cycle that is essential for proper functionality of the GTPases. Scaffold proteins gather GTPase complexes to facilitate proper function. The guanine nucleotide exchange factors (GEFs) CpCdc24 and CpDock180 activate GTPase signaling by triggering nucleotide exchange of the GTPases. Here we show that CpCdc24 harbors nucleotide exchange activity for both Rac and Cdc42 homologues. The GEFs partly share the cellular distribution of the GTPases and interact with the putative upstream GTPase CpRas1. Interaction studies show the formation of higher-order protein complexes, mediated by the scaffold protein CpBem1. Besides the GTPases and GEFs, these complexes also contain the GTPase effectors CpSte20 and CpCla4, as well as the regulatory protein CpNoxR. Functional characterizations suggest a role of CpCdc24 mainly in polarity, whereas CpDock180 is involved in stress tolerance mechanisms. These findings indicate the dynamic formation of small GTPase complexes and improve the model for GTPase-associated signaling inC. purpurea.

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Shan, Shu-ou, Sowmya Chandrasekar et Peter Walter. « Conformational changes in the GTPase modules of the signal reception particle and its receptor drive initiation of protein translocation ». Journal of Cell Biology 178, n^o 4 (6 août 2007) : 611–20. http://dx.doi.org/10.1083/jcb.200702018.

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During cotranslational protein targeting, two guanosine triphosphatase (GTPase) in the signal recognition particle (SRP) and its receptor (SR) form a unique complex in which hydrolyses of both guanosine triphosphates (GTP) are activated in a shared active site. It was thought that GTP hydrolysis drives the recycling of SRP and SR, but is not crucial for protein targeting. Here, we examined the translocation efficiency of mutant GTPases that block the interaction between SRP and SR at specific stages. Surprisingly, mutants that allow SRP–SR complex assembly but block GTPase activation severely compromise protein translocation. These mutations map to the highly conserved insertion box domain loops that rearrange upon complex formation to form multiple catalytic interactions with the two GTPs. Thus, although GTP hydrolysis is not required, the molecular rearrangements that lead to GTPase activation are essential for protein targeting. Most importantly, our results show that an elaborate rearrangement within the SRP–SR GTPase complex is required to drive the unloading and initiate translocation of cargo proteins.

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Nur-E-Kamal, M. S., et H. Maruta. « The role of Gln61 and Glu63 of Ras GTPases in their activation by NF1 and Ras GAP. » Molecular Biology of the Cell 3, n^o 12 (décembre 1992) : 1437–42. http://dx.doi.org/10.1091/mbc.3.12.1437.

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Two distinct GAPs of 120 and 235 kDa called GAP1 and NF1 serve as attenuators of Ras, a member of GTP-dependent signal transducers, by stimulating its intrinsic guanosine triphosphatase (GTPase) activity. The GAP1 (also called Ras GAP) is highly specific for Ras and does not stimulate the intrinsic GTPase activity of Rap1 or Rho. Using GAP1C, the C-terminal GTPase activating domain (residues 720-1044) of bovine GAP1, we have shown previously that the GAP1 specificity is determined by the Ras domain (residues 61-65) where Gln61 plays the primary role. The corresponding domain (residues 1175-1531) of human NF1 (called NF1C), which shares only 26% sequence identity with the GAP1C, also activates Ras GTPases. In this article, we demonstrate that the NF1C, like the GAP1C, is highly specific for Ras and does not activate either Rap1 or Rho GTPases. Furthermore, using a series of chimeric Ras/Rap1 and mutated Ras GTPases, we show that Gln at position 61 of the GTPases primarily determines that NF1C as well as GAP1C activates Ras GTPases, but not Rap1 GTPases, and Glu at position 63 of the GTPases is required for maximizing the sensitivity of Ras GTPases to both NF1C and GAP1C. Interestingly, replacement of Glu63 of c-HaRas by Lys reduces its intrinsic GTPase activity and abolishes the GTPase activation by both NF1C and GAP1C. Thus, the potentiation of oncogenicity by Lys63 mutation of c-HaRas appears primarily to be due to the loss of its sensitivity to the two major Ras signal attenuators (NF1 and GAP1).

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Kötting, Carsten, et Klaus Gerwert. « What vibrations tell us about GTPases ». Biological Chemistry 396, n^o 2 (1 février 2015) : 131–44. http://dx.doi.org/10.1515/hsz-2014-0219.

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Abstract In this review, we discuss how time-resolved Fourier transform infrared (FTIR) spectroscopy is used to understand how GTP hydrolysis is catalyzed by small GTPases and their cognate GTPase-activating proteins (GAPs). By interaction with small GTPases, GAPs regulate important signal transduction pathways and transport mechanisms in cells. The GTPase reaction terminates signaling and controls transport. Dysfunctions of GTP hydrolysis in these proteins are linked to serious diseases including cancer. Using FTIR, we resolved both the intrinsic and GAP-catalyzed GTPase reaction of the small GTPase Ras with high spatiotemporal resolution and atomic detail. This provided detailed insight into the order of events and how the active site is completed for catalysis. Comparisons of Ras with other small GTPases revealed conservation and variation in the catalytic mechanisms. The approach was extended to more nearly physiological conditions at a membrane. Interactions of membrane-anchored GTPases and their extraction from the membrane are studied using the attenuated total reflection (ATR) technique.

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Killoran, Ryan C., et Matthew J. Smith. « Conformational resolution of nucleotide cycling and effector interactions for multiple small GTPases determined in parallel ». Journal of Biological Chemistry 294, n^o 25 (14 mai 2019) : 9937–48. http://dx.doi.org/10.1074/jbc.ra119.008653.

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Small GTPases alternatively bind GDP/GTP guanine nucleotides to gate signaling pathways that direct most cellular processes. Numerous GTPases are implicated in oncogenesis, particularly the three RAS isoforms HRAS, KRAS, and NRAS and the RHO family GTPase RAC1. Signaling networks comprising small GTPases are highly connected, and there is some evidence of direct biochemical cross-talk between their functional G-domains. The activation potential of a given GTPase is contingent on a codependent interaction with the nucleotide and a Mg2+ ion, which bind to individual variants with distinct affinities coordinated by residues in the GTPase nucleotide-binding pocket. Here, we utilized a selective-labeling strategy coupled with real-time NMR spectroscopy to monitor nucleotide exchange, GTP hydrolysis, and effector interactions of multiple small GTPases in a single complex system. We provide insight into nucleotide preference and the role of Mg2+ in activating both WT and oncogenic mutant enzymes. Multiplexing revealed guanine nucleotide exchange factor (GEF), GTPase-activating protein (GAP), and effector-binding specificities in mixtures of GTPases and resolved that the three related RAS isoforms are biochemically equivalent. This work establishes that direct quantitation of the nucleotide-bound conformation is required to accurately determine an activation potential for any given GTPase, as small GTPases such as RAS-like proto-oncogene A (RALA) or the G12C mutant of KRAS display fast exchange kinetics but have a high affinity for GDP. Furthermore, we propose that the G-domains of small GTPases behave autonomously in solution and that nucleotide cycling proceeds independently of protein concentration but is highly impacted by Mg2+ abundance.

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Kesseler, Christoph, Julian Kahr, Natalie Waldt, Nele Stroscher, Josephine Liebig, Frank Angenstein, Elmar Kirches et Christian Mawrin. « EXTH-64. SMALL GTPASES IN MENINGIOMAS : PROLIFERATION, MIGRATION, SURVIVAL, POTENTIAL TREATMENT AND INTERACTIONS ». Neuro-Oncology 22, Supplement_2 (novembre 2020) : ii101. http://dx.doi.org/10.1093/neuonc/noaa215.418.

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Abstract PURPOSE To evaluate the role of the small GTPases RhoA, Rac1 and Cdc42 in meningiomas as therapeutic targets and their interactions in meningiomas. EXPERIMENTAL DESIGN We analyzed expression of GTPases in human meningioma samples and meningioma cell lines of various WHO grades. Malignant IOMM-Lee meningioma cells were used to generate shRNA mediated knockdowns of GTPases RhoA, Rac1 or Cdc42 and to study knockdown effects on proliferation and migration, as well as analysis of cell morphology by confocal microscopy. The same tests were used to investigate effects of the two inhibitors Fasudil and EHT-1864 of malignant IOMM-Lee, KT21 and benign Ben-Men cells and the effects of these drugs on IOMM-Lee knockdown cells. The effects of GTPase knockdowns and Fasudil treatment were studied in terms of overall survival by intracranial xenografts of mice. Potential interactions of GTPases regarding NF2, mTOR and FAK-Paxillin were examined. RESULTS Small GTPases were upregulated in meningiomas of higher tumor grades. Reduced proliferation and migration could be achieved by GTPase knockdown in IOMM-Lee cells. Additionally, the ROCK-inhibitor Fasudil and Rac1-inhibitor EHT-1864 reduced proliferation in different meningioma cell lines and reduced proliferation and migration independent of GTPase knockdowns/status. Moreover, overall survival in vivo could also be increased by knockdowns of RhoA and Rac1 as well as Fasudil treatment. GTPase expression was affected dependent on the NF2 status but effects were not very distinct, indicating that NF2 is not strongly involved in GTPase regulation in meningiomas. In terms of mTOR and FAK-Paxillin signaling, each GTPase changes those pathways in a different manner. CONCLUSION Small GTPases are important effectors in meningioma proliferation and migration in vitro as well as survival in vivo and their inhibition should be considered as potential treatment option.

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Humphries, Brock A., Zhishan Wang et Chengfeng Yang. « MicroRNA Regulation of the Small Rho GTPase Regulators—Complexities and Opportunities in Targeting Cancer Metastasis ». Cancers 12, n^o 5 (28 avril 2020) : 1092. http://dx.doi.org/10.3390/cancers12051092.

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The small Rho GTPases regulate important cellular processes that affect cancer metastasis, such as cell survival and proliferation, actin dynamics, adhesion, migration, invasion and transcriptional activation. The Rho GTPases function as molecular switches cycling between an active GTP-bound and inactive guanosine diphosphate (GDP)-bound conformation. It is known that Rho GTPase activities are mainly regulated by guanine nucleotide exchange factors (RhoGEFs), GTPase-activating proteins (RhoGAPs), GDP dissociation inhibitors (RhoGDIs) and guanine nucleotide exchange modifiers (GEMs). These Rho GTPase regulators are often dysregulated in cancer; however, the underlying mechanisms are not well understood. MicroRNAs (miRNAs), a large family of small non-coding RNAs that negatively regulate protein-coding gene expression, have been shown to play important roles in cancer metastasis. Recent studies showed that miRNAs are capable of directly targeting RhoGAPs, RhoGEFs, and RhoGDIs, and regulate the activities of Rho GTPases. This not only provides new evidence for the critical role of miRNA dysregulation in cancer metastasis, it also reveals novel mechanisms for Rho GTPase regulation. This review summarizes recent exciting findings showing that miRNAs play important roles in regulating Rho GTPase regulators (RhoGEFs, RhoGAPs, RhoGDIs), thus affecting Rho GTPase activities and cancer metastasis. The potential opportunities and challenges for targeting miRNAs and Rho GTPase regulators in treating cancer metastasis are also discussed. A comprehensive list of the currently validated miRNA-targeting of small Rho GTPase regulators is presented as a reference resource.

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Guo, Daji, Xiaoman Yang et Lei Shi. « Rho GTPase Regulators and Effectors in Autism Spectrum Disorders : Animal Models and Insights for Therapeutics ». Cells 9, n^o 4 (31 mars 2020) : 835. http://dx.doi.org/10.3390/cells9040835.

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The Rho family GTPases are small G proteins that act as molecular switches shuttling between active and inactive forms. Rho GTPases are regulated by two classes of regulatory proteins, guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Rho GTPases transduce the upstream signals to downstream effectors, thus regulating diverse cellular processes, such as growth, migration, adhesion, and differentiation. In particular, Rho GTPases play essential roles in regulating neuronal morphology and function. Recent evidence suggests that dysfunction of Rho GTPase signaling contributes substantially to the pathogenesis of autism spectrum disorder (ASD). It has been found that 20 genes encoding Rho GTPase regulators and effectors are listed as ASD risk genes by Simons foundation autism research initiative (SFARI). This review summarizes the clinical evidence, protein structure, and protein expression pattern of these 20 genes. Moreover, ASD-related behavioral phenotypes in animal models of these genes are reviewed, and the therapeutic approaches that show successful treatment effects in these animal models are discussed.

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Cherfils, Jacqueline, et Mahel Zeghouf. « Regulation of Small GTPases by GEFs, GAPs, and GDIs ». Physiological Reviews 93, n^o 1 (janvier 2013) : 269–309. http://dx.doi.org/10.1152/physrev.00003.2012.

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Small GTPases use GDP/GTP alternation to actuate a variety of functional switches that are pivotal for cell dynamics. The GTPase switch is turned on by GEFs, which stimulate dissociation of the tightly bound GDP, and turned off by GAPs, which accelerate the intrinsically sluggish hydrolysis of GTP. For Ras, Rho, and Rab GTPases, this switch incorporates a membrane/cytosol alternation regulated by GDIs and GDI-like proteins. The structures and core mechanisms of representative members of small GTPase regulators from most families have now been elucidated, illuminating their general traits combined with scores of unique features. Recent studies reveal that small GTPase regulators have themselves unexpectedly sophisticated regulatory mechanisms, by which they process cellular signals and build up specific cell responses. These mechanisms include multilayered autoinhibition with stepwise release, feedback loops mediated by the activated GTPase, feed-forward signaling flow between regulators and effectors, and a phosphorylation code for RhoGDIs. The flipside of these highly integrated functions is that they make small GTPase regulators susceptible to biochemical abnormalities that are directly correlated with diseases, notably a striking number of missense mutations in congenital diseases, and susceptible to bacterial mimics of GEFs, GAPs, and GDIs that take command of small GTPases in infections. This review presents an overview of the current knowledge of these many facets of small GTPase regulation.

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Mulloy, James C., Jose A. Cancelas, Marie-Dominique Filippi, Theodosia A. Kalfa, Fukun Guo et Yi Zheng. « Rho GTPases in hematopoiesis and hemopathies ». Blood 115, n^o 5 (4 février 2010) : 936–47. http://dx.doi.org/10.1182/blood-2009-09-198127.

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AbstractRho family GTPases are intracellular signaling proteins regulating multiple pathways involved in cell actomyosin organization, adhesion, and proliferation. Our knowledge of their cellular functions comes mostly from previous biochemical studies that used mutant overexpression approaches in various clonal cell lines. Recent progress in understanding Rho GTPase functions in blood cell development and regulation by gene targeting of individual Rho GTPases in mice has allowed a genetic understanding of their physiologic roles in hematopoietic progenitors and mature lineages. In particular, mouse gene–targeting studies have provided convincing evidence that individual members of the Rho GTPase family are essential regulators of cell type–specific functions and stimuli-specific pathways in regulating hematopoietic stem cell interaction with bone marrow niche, erythropoiesis, and red blood cell actin dynamics, phagocyte migration and killing, and T- and B-cell maturation. In addition, deregulation of Rho GTPase family members has been associated with multiple human hematologic diseases such as neutrophil dysfunction, leukemia, and Fanconi anemia, raising the possibility that Rho GTPases and downstream signaling pathways are of therapeutic value. In this review we discuss recent genetic studies of Rho GTPases in hematopoiesis and several blood lineages and the implications of Rho GTPase signaling in hematologic malignancies, immune pathology. and anemia.

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Voena et Chiarle. « RHO Family GTPases in the Biology of Lymphoma ». Cells 8, n^o 7 (26 juin 2019) : 646. http://dx.doi.org/10.3390/cells8070646.

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RHO GTPases are a class of small molecules involved in the regulation of several cellular processes that belong to the RAS GTPase superfamily. The RHO family of GTPases includes several members that are further divided into two different groups: typical and atypical. Both typical and atypical RHO GTPases are critical transducers of intracellular signaling and have been linked to human cancer. Significantly, both gain-of-function and loss-of-function mutations have been described in human tumors with contradicting roles depending on the cell context. The RAS family of GTPases that also belong to the RAS GTPase superfamily like the RHO GTPases, includes arguably the most frequently mutated genes in human cancers (K-RAS, N-RAS, and H-RAS) but has been extensively described elsewhere. This review focuses on the role of RHO family GTPases in human lymphoma initiation and progression.

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Zhang, Lingye, Anni Zhou, Shengtao Zhu, Li Min, Si Liu, Peng Li et Shutian Zhang. « The role of GTPase-activating protein ARHGAP26 in human cancers ». Molecular and Cellular Biochemistry 477, n^o 1 (30 octobre 2021) : 319–26. http://dx.doi.org/10.1007/s11010-021-04274-3.

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AbstractRho GTPases are molecular switches that play an important role in regulating the behavior of a variety of tumor cells. RhoA GTPase-activating protein 26 (ARHGAP26) is a GTPase-activating protein and inhibits the activity of Rho GTPases by promoting the hydrolytic ability of Rho GTPases. It also affects tumorigenesis and progression of various tumors through several methods, including formation of abnormal fusion genes and circular RNA. This review summarizes the biological functions and molecular mechanisms of ARHGAP26 in different tumors, proposes the potential clinical value of ARHGAP26 in cancer treatment, and discusses current issues that need to be addressed.

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Anderson, Erik L., et Michael J. Hamann. « Detection of Rho GEF and GAP activity through a sensitive split luciferase assay system ». Biochemical Journal 441, n^o 3 (16 janvier 2012) : 869–80. http://dx.doi.org/10.1042/bj20111111.

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Rho GTPases regulate the assembly of cellular actin structures and are activated by GEFs (guanine-nucleotide-exchange factors) and rendered inactive by GAPs (GTPase-activating proteins). Using the Rho GTPases Cdc42, Rac1 and RhoA, and the GTPase-binding portions of the effector proteins p21-activated kinase and Rhophilin1, we have developed split luciferase assays for detecting both GEF and GAP regulation of these GTPases. The system relies on purifying split luciferase fusion proteins of the GTPases and effectors from bacteria, and our results show that the assays replicate GEF and GAP specificities at nanomolar concentrations for several previously characterized Rho family GEFs (Dbl, Vav2, Trio and Asef) and GAPs [p190, Cdc42 GAP and PTPL1-associated RhoGAP]. The assay detected activities associated with purified recombinant GEFs and GAPs, cell lysates expressing exogenous proteins, and immunoprecipitates of endogenous Vav1 and p190. The results demonstrate that the split luciferase system provides an effective sensitive alternative to radioactivity-based assays for detecting GTPase regulatory protein activities and is adaptable to a variety of assay conditions.

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Shah, Bhavin, et Andreas W. Püschel. « Regulation of Rap GTPases in mammalian neurons ». Biological Chemistry 397, n^o 10 (1 octobre 2016) : 1055–69. http://dx.doi.org/10.1515/hsz-2016-0165.

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Abstract Small GTPases are central regulators of many cellular processes. The highly conserved Rap GTPases perform essential functions in the mammalian nervous system during development and in mature neurons. During neocortical development, Rap1 is required to regulate cadherin- and integrin-mediated adhesion. In the adult nervous system Rap1 and Rap2 regulate the maturation and plasticity of dendritic spine and synapses. Although genetic studies have revealed important roles of Rap GTPases in neurons, their regulation by guanine nucleotide exchange factors (GEFs) that activate them and GTPase activating proteins (GAPs) that inactivate them by stimulating their intrinsic GTPase activity is just beginning to be explored in vivo. Here we review how GEFs and GAPs regulate Rap GTPases in the nervous system with a focus on their in vivo function.

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Peurois, François, Gérald Peyroche et Jacqueline Cherfils. « Small GTPase peripheral binding to membranes : molecular determinants and supramolecular organization ». Biochemical Society Transactions 47, n^o 1 (17 décembre 2018) : 13–22. http://dx.doi.org/10.1042/bst20170525.

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AbstractSmall GTPases regulate many aspects of cell logistics by alternating between an inactive, GDP-bound form and an active, GTP-bound form. This nucleotide switch is coupled to a cytosol/membrane cycle, such that GTP-bound small GTPases carry out their functions at the periphery of endomembranes. A global understanding of the molecular determinants of the interaction of small GTPases with membranes and of the resulting supramolecular organization is beginning to emerge from studies of model systems. Recent studies highlighted that small GTPases establish multiple interactions with membranes involving their lipid anchor, their lipididated hypervariable region and elements in their GTPase domain, which combine to determine the strength, specificity and orientation of their association with lipids. Thereby, membrane association potentiates small GTPase interactions with GEFs, GAPs and effectors through colocalization and positional matching. Furthermore, it leads to small GTPase nanoclustering and to lipid demixing, which drives the assembly of molecular platforms in which proteins and lipids co-operate in producing high-fidelity signals through feedback and feedforward loops. Although still fragmentary, these observations point to an integrated model of signaling by membrane-attached small GTPases that involves a diversity of direct and indirect interactions, which can inspire new therapeutic strategies to block their activities in diseases.

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Pai, Sung-Yun, Chaekyun Kim et David A. Williams. « Rac GTPases in Human Diseases ». Disease Markers 29, n^o 3-4 (2010) : 177–87. http://dx.doi.org/10.1155/2010/380291.

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Rho GTPases are members of the Ras superfamily of GTPases that regulate a wide variety of cellular functions. While Rho GTPase pathways have been implicated in various pathological conditions in humans, to date coding mutations in only the hematopoietic specific GTPase,RAC2, have been found to cause a human disease, a severe phagocytic immunodeficiency characterized by life-threatening infections in infancy. Interestingly, the phenotype was predicted by a mouse knock-out ofRAC2and resembles leukocyte adhesion deficiency (LAD). Here we review Rho GTPases with a specific focus on Rac GTPases. In particular, we discuss a new understanding of the unique and overlapping roles of Rac2 in blood cells that has developed since the generation of mice deficient in Rac1, Rac2 and Rac3 proteins. We propose that Rac2 mutations leading to disease be termed LAD type IV.

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deCathelineau, Aimee M., et Gary M. Bokoch. « Inactivation of Rho GTPases by Statins Attenuates Anthrax Lethal Toxin Activity ». Infection and Immunity 77, n^o 1 (20 octobre 2008) : 348–59. http://dx.doi.org/10.1128/iai.01005-08.

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ABSTRACT Anthrax lethal factor (LF), secreted by Bacillus anthracis, interacts with protective antigen to form a bipartite toxin (lethal toxin [LT]) that exerts pleiotropic biological effects resulting in subversion of the innate immune response. Although the mitogen-activated protein kinase kinases (MKKs) are the major intracellular protein targets of LF, the pathology induced by LT is not well understood. The statin family of HMG-coenzyme A reductase inhibitors have potent anti-inflammatory effects independent of their cholesterol-lowering properties, which have been attributed to modulation of Rho family GTPase activity. The Rho GTPases regulate vesicular trafficking, cytoskeletal dynamics, and cell survival and proliferation. We hypothesized that disruption of Rho GTPase function by statins might alter LT action. We show here that statins delay LT-induced death and MKK cleavage in RAW macrophages and that statin-mediated effects on LT action are attributable to disruption of Rho GTPases. The Rho GTPase-inactivating toxin, toxin B, did not significantly affect LT binding or internalization, suggesting that the Rho GTPases regulate trafficking and/or localization of LT once internalized. The use of drugs capable of inhibiting Rho GTPase activity, such as statins, may provide a means to attenuate intoxication during B. anthracis infection.

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Taymans, Jean-Marc. « The GTPase function of LRRK2 ». Biochemical Society Transactions 40, n^o 5 (19 septembre 2012) : 1063–69. http://dx.doi.org/10.1042/bst20120133.

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LRRK2 (leucine-rich repeat kinase 2) is a large protein encoding multiple functional domains, including two catalytically active domains, a kinase and a GTPase domain. The LRRK2 GTPase belongs to the Ras-GTPase superfamily of GTPases, more specifically to the ROC (Ras of complex proteins) subfamily. Studies with recombinant LRRK2 protein purified from eukaryotic cells have confirmed that LRRK2 binds guanine nucleotides and catalyses the hydrolysis of GTP to GDP. LRRK2 is linked to PD (Parkinson's disease) and GTPase activity is impaired for several PD mutants located in the ROC and COR (C-terminal of ROC) domains, indicating that it is involved in PD pathogenesis. Ras family GTPases are known to function as molecular switches, and several studies have explored this possibility for LRRK2. These studies show that there is interplay between the LRRK2 GTPase function and its kinase function, with most data pointing towards a role for the kinase domain as an upstream regulator of ROC. The GTPase function is therefore a pivotal functionality within the LRRK2-mediated signalling cascade which includes partners encoded by other LRRK2 domains as well as other cellular signalling partners. The present review examines what is known of the enzymatic properties of the LRRK2 GTPase, the interplay between ROC and other LRRK2 domains, and the interplay between ROC and other cellular proteins with the dual goal to understand how LRRK2 GTPase affects cellular functions and point to future research venues.

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Jung, Haiyoung, Suk Ran Yoon, Jeewon Lim, Hee Jun Cho et Hee Gu Lee. « Dysregulation of Rho GTPases in Human Cancers ». Cancers 12, n^o 5 (7 mai 2020) : 1179. http://dx.doi.org/10.3390/cancers12051179.

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Rho GTPases play central roles in numerous cellular processes, including cell motility, cell polarity, and cell cycle progression, by regulating actin cytoskeletal dynamics and cell adhesion. Dysregulation of Rho GTPase signaling is observed in a broad range of human cancers, and is associated with cancer development and malignant phenotypes, including metastasis and chemoresistance. Rho GTPase activity is precisely controlled by guanine nucleotide exchange factors, GTPase-activating proteins, and guanine nucleotide dissociation inhibitors. Recent evidence demonstrates that it is also regulated by post-translational modifications, such as phosphorylation, ubiquitination, and sumoylation. Here, we review the current knowledge on the role of Rho GTPases, and the precise mechanisms controlling their activity in the regulation of cancer progression. In addition, we discuss targeting strategies for the development of new drugs to improve cancer therapy.

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Zhang, Zheng, Ming Liu et Yi Zheng. « Role of Rho GTPases in stem cell regulation ». Biochemical Society Transactions 49, n^o 6 (2 décembre 2021) : 2941–55. http://dx.doi.org/10.1042/bst20211071.

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The future of regenerative medicine relies on our understanding of stem cells which are essential for tissue/organ generation and regeneration to maintain and/or restore tissue homeostasis. Rho family GTPases are known regulators of a wide variety of cellular processes related to cytoskeletal dynamics, polarity and gene transcription. In the last decade, major new advances have been made in understanding the regulatory role and mechanism of Rho GTPases in self-renewal, differentiation, migration, and lineage specification in tissue-specific signaling mechanisms in various stem cell types to regulate embryonic development, adult tissue homeostasis, and tissue regeneration upon stress or damage. Importantly, implication of Rho GTPases and their upstream regulators or downstream effectors in the transformation, migration, invasion and tumorigenesis of diverse cancer stem cells highlights the potential of Rho GTPase targeting in cancer therapy. In this review, we discuss recent evidence of Rho GTPase signaling in the regulation of embryonic stem cells, multiple somatic stem cells, and cancer stem cells. We propose promising areas where Rho GTPase pathways may serve as useful targets for stem cell manipulation and related future therapies.

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Dipankar, Pankaj, Puneet Kumar, Shiba Prasad Dash et Pranita P. Sarangi. « Functional and Therapeutic Relevance of Rho GTPases in Innate Immune Cell Migration and Function during Inflammation : An In Silico Perspective ». Mediators of Inflammation 2021 (13 février 2021) : 1–10. http://dx.doi.org/10.1155/2021/6655412.

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Systematic regulation of leukocyte migration to the site of infection is a vital step during immunological responses. Improper migration and localization of immune cells could be associated with disease pathology as seen in systemic inflammation. Rho GTPases act as molecular switches during inflammatory cell migration by cycling between Rho-GDP (inactive) to Rho-GTP (active) forms and play an essential role in the precise regulation of actin cytoskeletal dynamics as well as other immunological functions of leukocytes. Available reports suggest that the dysregulation of Rho GTPase signaling is associated with various inflammatory diseases ranging from mild to life-threatening conditions. Therefore, it is crucial to understand the step-by-step activation and inactivation of GTPases and the functioning of different Guanine Nucleotide Exchange Factors (GEFs) and GTPase-Activating Proteins (GAPs) that regulate the conversion of GDP to GTP and GTP to GDP exchange reactions, respectively. Here, we describe the molecular organization and activation of various domains of crucial elements associated with the activation of Rho GTPases using solved PDB structures. We will also present the latest evidence available on the relevance of Rho GTPases in the migration and function of innate immune cells during inflammation. This knowledge will help scientists design promising drug candidates against the Rho-GTPase-centric regulatory molecules regulating inflammatory cell migration.

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Tsukuba, Takayuki, Yu Yamaguchi et Tomoko Kadowaki. « Large Rab GTPases : Novel Membrane Trafficking Regulators with a Calcium Sensor and Functional Domains ». International Journal of Molecular Sciences 22, n^o 14 (19 juillet 2021) : 7691. http://dx.doi.org/10.3390/ijms22147691.

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Rab GTPases are major coordinators of intracellular membrane trafficking, including vesicle transport, membrane fission, tethering, docking, and fusion events. Rab GTPases are roughly divided into two groups: conventional “small” Rab GTPases and atypical “large” Rab GTPases that have been recently reported. Some members of large Rab GTPases in mammals include Rab44, Rab45/RASEF, and Rab46. The genes of these large Rab GTPases commonly encode an amino-terminal EF-hand domain, coiled-coil domain, and the carboxyl-terminal Rab GTPase domain. A common feature of large Rab GTPases is that they express several isoforms in cells. For instance, Rab44’s two isoforms have similar functions, but exhibit differential localization. The long form of Rab45 (Rab45-L) is abundantly distributed in epithelial cells. The short form of Rab45 (Rab45-S) is predominantly present in the testes. Both Rab46 (CRACR2A-L) and the short isoform lacking the Rab domain (CRACR2A-S) are expressed in T cells, whereas Rab46 is only distributed in endothelial cells. Although evidence regarding the function of large Rab GTPases has been accumulating recently, there are only a limited number of studies. Here, we report the recent findings on the large Rab GTPase family concerning their function in membrane trafficking, cell differentiation, related diseases, and knockout mouse phenotypes.

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Rubio, I. « Use of the Ras binding domain of c-Raf for biochemical and live-cell analysis of Ras activation ». Biochemical Society Transactions 33, n^o 4 (1 août 2005) : 662–63. http://dx.doi.org/10.1042/bst0330662.

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Small modular GBDs (GTPase-binding domains) derived from GTPase-effector proteins are useful tools for the selective detection of the active GTP-loaded GTPase conformation, be it in biochemical assays or for imaging purposes. Use of GBD probes requires careful consideration of all features of the GDB–GTPase interaction. It is innate to the strong and specific interaction with the GTP-loaded GTPase, that GBDs will protect their partner GTPases from GAP (GTPase-activating protein) action. This feature is likely to cause an increase in cellular Ras-GTP levels, in particular in leucocytes and other cells with high steady-state Ras-GDP/GTP cycling rates. By the same token, high levels of GBD expression will interrupt GTPase-initiated signalling, with implications for the activation of the very same GTPase since feedback regulatory mechanisms can impinge on this process.

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Mosaddeghzadeh, Niloufar, et Mohammad Reza Ahmadian. « The RHO Family GTPases : Mechanisms of Regulation and Signaling ». Cells 10, n^o 7 (20 juillet 2021) : 1831. http://dx.doi.org/10.3390/cells10071831.

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Much progress has been made toward deciphering Rho GTPase functions, and many studies have convincingly demonstrated that altered signal transduction through Rho GTPases is a recurring theme in the progression of human malignancies. It seems that 20 canonical RHO GTPases are likely regulated by three GDIs, 85 GEFs, and 66 GAPs, and eventually interact with >70 downstream effectors. A recurring theme is the challenge in understanding the molecular determinants of the specificity of these four classes of interacting proteins that, irrespective of their functions, bind to common sites on the surface of RHO GTPases. Identified and structurally verified hotspots as functional determinants specific to RHO GTPase regulation by GDIs, GEFs, and GAPs as well as signaling through effectors are presented, and challenges and future perspectives are discussed.

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Bai, Yanyang, Xiaoliang Xiang, Chunmei Liang et Lei Shi. « Regulating Rac in the Nervous System : Molecular Function and Disease Implication of Rac GEFs and GAPs ». BioMed Research International 2015 (2015) : 1–17. http://dx.doi.org/10.1155/2015/632450.

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Rho family GTPases, including RhoA, Rac1, and Cdc42 as the most studied members, are master regulators of actin cytoskeletal organization. Rho GTPases control various aspects of the nervous system and are associated with a number of neuropsychiatric and neurodegenerative diseases. The activity of Rho GTPases is controlled by two families of regulators, guanine nucleotide exchange factors (GEFs) as the activators and GTPase-activating proteins (GAPs) as the inhibitors. Through coordinated regulation by GEFs and GAPs, Rho GTPases act as converging signaling molecules that convey different upstream signals in the nervous system. So far, more than 70 members of either GEFs or GAPs of Rho GTPases have been identified in mammals, but only a small subset of them have well-known functions. Thus, characterization of important GEFs and GAPs in the nervous system is crucial for the understanding of spatiotemporal dynamics of Rho GTPase activity in different neuronal functions. In this review, we summarize the current understanding of GEFs and GAPs for Rac1, with emphasis on the molecular function and disease implication of these regulators in the nervous system.

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Zhu, Min, et Xiu-qi Wang. « Regulation of mTORC1 by Small GTPases in Response to Nutrients ». Journal of Nutrition 150, n^o 5 (21 janvier 2020) : 1004–11. http://dx.doi.org/10.1093/jn/nxz301.

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ABSTRACT Mechanistic target of rapamycin complex 1 (mTORC1) is a highly evolutionarily conserved serine/threonine kinase that regulates cell growth and metabolism in response to multiple environmental cues, such as nutrients, hormones, energy, and stress. Deregulation of mTORC1 can lead to diseases such as diabetes, obesity, and cancer. A series of small GTPases, including Rag, Ras homolog enriched in brain (Rheb), adenosine diphosphate ribosylation factor 1 (Arf1), Ras-related protein Ral-A, Ras homolog (Rho), and Rab, are involved in regulating mTORC1 in response to nutrients, and mTORC1 is differentially regulated via these small GTPases according to specific conditions. Leucine and arginine sensing are considered to be well-confirmed amino acid–sensing signals, activating mTORC1 via a Rag GTPase–dependent mechanism as well as the Ragulator complex and vacuolar H+-adenosine triphosphatase (v-ATPase). Glutamine promotes mTORC1 activation via Arf1 independently of the Rag GTPase. In this review, we summarize current knowledge regarding the regulation of mTORC1 activity by small GTPases in response to nutrients, focusing on the function of small GTPases in mTORC1 activation and how small GTPases are regulated by nutrients.

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Saliani, Mahsa, Amin Mirzaiebadizi, Niloufar Mosaddeghzadeh et Mohammad Reza Ahmadian. « RHO GTPase-Related Long Noncoding RNAs in Human Cancers ». Cancers 13, n^o 21 (27 octobre 2021) : 5386. http://dx.doi.org/10.3390/cancers13215386.

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RHO GTPases are critical signal transducers that regulate cell adhesion, polarity, and migration through multiple signaling pathways. While all these cellular processes are crucial for the maintenance of normal cell homeostasis, disturbances in RHO GTPase-associated signaling pathways contribute to different human diseases, including many malignancies. Several members of the RHO GTPase family are frequently upregulated in human tumors. Abnormal gene regulation confirms the pivotal role of lncRNAs as critical gene regulators, and thus, they could potentially act as oncogenes or tumor suppressors. lncRNAs most likely act as sponges for miRNAs, which are known to be dysregulated in various cancers. In this regard, the significant role of miRNAs targeting RHO GTPases supports the view that the aberrant expression of lncRNAs may reciprocally change the intensity of RHO GTPase-associated signaling pathways. In this review article, we summarize recent advances in lncRNA research, with a specific focus on their sponge effects on RHO GTPase-targeting miRNAs to crucially mediate gene expression in different cancer cell types and tissues. We will focus in particular on five members of the RHO GTPase family, including RHOA, RHOB, RHOC, RAC1, and CDC42, to illustrate the role of lncRNAs in cancer progression. A deeper understanding of the widespread dysregulation of lncRNAs is of fundamental importance for confirmation of their contribution to RHO GTPase-dependent carcinogenesis.

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Raghavan, Somasundaram, Masuma Akter Brishti et M. Dennis Leo. « Rab GTPases as Modulators of Vascular Function ». Cells 11, n^o 19 (29 septembre 2022) : 3061. http://dx.doi.org/10.3390/cells11193061.

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Rab GTPases, the largest family of small GTPases, are ubiquitously expressed proteins that control various aspects of cellular function, from cell survival to exocytosis. Rabs cycle between the GDP-bound inactive form and the GTP-bound active form. When activated, specific Rab GTPase-positive vesicles mediate cellular networks involved in intracellular trafficking, recycling, and/or exocytosis of cargo proteins. Dysfunctional Rab signaling pathways have been implicated in various disease processes. The precise cellular functions of several members of the Rab GTPase family are still unknown. A lack of pharmacological tools and the lethality of gene knockouts have made more detailed characterizations of their protein interaction networks difficult. Nevertheless, available evidence suggests that these proteins are vital for normal cell function. Endothelial and smooth muscle cells control vascular lumen diameter and modulate blood flow. Endothelial cells also secrete several pro- and antithrombotic factors and vasoactive substances to coordinate local inflammatory responses and angiogenesis. Rab GTPase function in endothelial cells has been relatively well-explored, while only a handful of reports are available on these proteins in vascular smooth muscle. This review summarizes the present knowledge on Rab GTPases in the vasculature.

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Jones, Arwyn T., Ian G. Mills, Axel J. Scheidig, Kirill Alexandrov et Michael J. Clague. « Inhibition of Endosome Fusion by Wortmannin Persists in the Presence of Activated rab5 ». Molecular Biology of the Cell 9, n^o 2 (février 1998) : 323–32. http://dx.doi.org/10.1091/mbc.9.2.323.

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Rab5-dependent endosome fusion is sensitive to the phosphoinositide 3-kinase inhibitor, wortmannin. It has been proposed that phosphoinositide 3-kinase activity may be required for activation of rab5 by influencing its nucleotide cycle such as to promote its active GTP state. In this report we demonstrate that endosome fusion remains sensitive to wortmannin despite preloading of endosomes with stimulatory levels of a GTPase-defective mutant rab5Q79L or of a xanthosine triphosphate-binding mutant, rab5D136N, in the presence of the nonhydrolysable analogue XTPγS. These results suggest that activation of rab5 cannot be the principal function of the wortmannin-sensitive factor on the endosome fusion pathway. This result is extrapolated to all GTPases by demonstrating that endosome fusion remains wortmannin sensitive despite prior incubation with the nonhydrolysable nucleotide analogue GTPγS. Consistent with these results, direct measurement of clathrin-coated vesicle-stimulated nucleotide dissociation from exogenous rab5 was insensitive to the presence of wortmannin. A large excess of rab5Q79L, beyond levels required for maximal stimulation of the fusion assay, afforded protection against wortmannin inhibition, and partial protection was also observed with an excess of wild-type rab5 independent of GTPγS.

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Bruewer, Matthias, Ann M. Hopkins, Michael E. Hobert, Asma Nusrat et James L. Madara. « RhoA, Rac1, and Cdc42 exert distinct effects on epithelial barrier via selective structural and biochemical modulation of junctional proteins and F-actin ». American Journal of Physiology-Cell Physiology 287, n^o 2 (août 2004) : C327—C335. http://dx.doi.org/10.1152/ajpcell.00087.2004.

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Epithelial intercellular junctions regulate cell-cell contact and mucosal barrier function. Both tight junctions (TJs) and adherens junctions (AJs) are regulated in part by their affiliation with the F-actin cytoskeleton. The cytoskeleton in turn is influenced by Rho family small GTPases such as RhoA, Rac1, and Cdc42, all of which constitute eukaryotic targets for several pathogenic organisms. With a tetracycline-repressible system to achieve regulated expression in Madin-Darby canine kidney (MDCK) epithelial cells, we used dominant-negative (DN) and constitutively active (CA) forms of RhoA, Rac1, and Cdc42 as tools to evaluate the precise contribution of each GTPase to epithelial structure and barrier function. All mutant GTPases induced time-dependent disruptions in epithelial gate function and distinct morphological alterations in apical and basal F-actin pools. TJ proteins occludin, ZO-1, claudin-1, claudin-2, and junctional adhesion molecule (JAM)-1 were dramatically redistributed in the presence of CA RhoA or CA Cdc42, whereas only claudins-1 and -2 were redistributed in response to CA Rac1. DN Rac1 expression also induced selective redistribution of claudins-1 and -2 in addition to JAM-1, whereas DN Cdc42 influenced only claudin-2 and DN RhoA had no effect. AJ protein localization was unaffected by any mutant GTPase, but DN Rac1 induced a reduction in E-cadherin detergent solubility. All CA GTPases increased the detergent solubility of claudins-1 and -2, but CA RhoA alone reduced claudin-2 and ZO-1 partitioning to detergent-insoluble membrane rafts. We conclude that Rho family GTPases regulate epithelial intercellular junctions via distinct morphological and biochemical mechanisms and that perturbations in barrier function reflect any imbalance in active/resting GTPase levels rather than simply loss or gain of GTPase activity.

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Peterson, J., Y. Zheng, L. Bender, A. Myers, R. Cerione et A. Bender. « Interactions between the bud emergence proteins Bem1p and Bem2p and Rho-type GTPases in yeast. » Journal of Cell Biology 127, n^o 5 (1 décembre 1994) : 1395–406. http://dx.doi.org/10.1083/jcb.127.5.1395.

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The SH3 domain-containing protein Bem1p is needed for normal bud emergence and mating projection formation, two processes that require asymmetric reorganizations of the cortical cytoskeleton in Saccharomyces cerevisiae. To identify proteins that functionally and/or physically interact with Bem1p, we screened for mutations that display synthetic lethality with a mutant allele of the BEM1 gene and for genes whose products display two-hybrid interactions with the Bem1 protein. CDC24, which is required for bud emergence and encodes a GEF (guanine-nucleotide exchange factor) for the essential Rho-type GTPase Cdc42p, was identified during both screens. The COOH-terminal 75 amino acids of Cdc24p, outside of the GEF domain, can interact with a portion of Bem1p that lacks both SH3 domains. Bacterially expressed Cdc24p and Bem1p bind to each other in vitro, indicating that no other yeast proteins are required for this interaction. The most frequently identified gene that arose from the bem1 synthetic-lethal screen was the bud-emergence gene BEM2 (Bender and Pringle. 1991. Mol. Cell Biol. 11:1295-1395), which is allelic with IPL2 (increase in ploidy; Chan and Botstein, 1993. Genetics. 135:677-691). Here we show that Bem2p contains a GAP (GTPase-activating protein) domain for Rho-type GTPases, and that this portion of Bem2p can stimulate in vitro the GTPase activity of Rho1p, a second essential yeast Rho-type GTPase. Cells deleted for BEM2 become large and multinucleate. These and other genetic, two-hybrid, biochemical, and phenotypic data suggest that multiple Rho-type GTPases control the reorganization of the cortical cytoskeleton in yeast and that the functions of these GTPases are tightly coupled. Also, these findings raise the possibility that Bem1p may regulate or be a target of action of one or more of these GTPases.

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Roy, Mrinalini, Sanket Kaushik, Anupam Jyoti et Vijay Kumar Srivastava. « Probing the Peculiarity of EhRabX10, a pseudoRab GTPase, from the Enteric Parasite Entamoeba histolytica through In Silico Modeling and Docking Studies ». BioMed Research International 2021 (6 octobre 2021) : 1–13. http://dx.doi.org/10.1155/2021/9913625.

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Entamoeba histolytica (Eh) is a pathogenic eukaryote that often resides silently in humans under asymptomatic stages. Upon indeterminate stimulus, it develops into fulminant amoebiasis that causes severe hepatic abscesses with 50% mortality. This neglected tropical pathogen relies massively on membrane modulation to flourish and cause disease; these modulations range from the phagocytic mode for food acquisition to a complex trogocytosis mechanism for tissue invasion. Rab GTPases form the largest branch of the Ras-like small GTPases, with a diverse set of roles across the eukaryotic kingdom. Rab GTPases are vital for the orchestration of membrane transport and the secretory pathway responsible for transporting the pathogenic effectors, such as cysteine proteases (EhCPs) which help in tissue invasion. Rab GTPases thus play a crucial role in executing the cytolytic effect of E. histolytica. First, they interact with Gal/Nac lectins required for adhering to the host cells, and then, they assist in the secretion of EhCPs. Additionally, amoebic Rab GTPases are vital for encystation because substantial vesicular trafficking is required to create dormant amoebic cysts. These cysts are the infective agent and help to spread the disease. The absence of a “bonafide” vesicular transport machinery in Eh and the existence of a diverse repertoire of amoebic Rab GTPases (EhRab) hint at their contribution in supporting this atypical machinery. Here, we provide insights into a pseudoRab GTPase, EhRabX10, by performing physicochemical analysis, predictive 3D structure modeling, protein-protein interaction studies, and in silico molecular docking. Our group is the first one to classify EhRabX10 as a pseudoRab GTPase with four nonconserved G-motifs. It possesses the basic fold of the P-loop containing nucleotide hydrolases. Through this in silico study, we provide an introduction to the characterization of the atypical EhRabX10 and set the stage for future explorations into the mechanisms of nucleotide recognition, binding, and hydrolysis employed by the pseudoEhRab GTPase family.

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Fritz, Rafael Dominik, et Olivier Pertz. « The dynamics of spatio-temporal Rho GTPase signaling : formation of signaling patterns ». F1000Research 5 (26 avril 2016) : 749. http://dx.doi.org/10.12688/f1000research.7370.1.

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Rho GTPases are crucial signaling molecules that regulate a plethora of biological functions. Traditional biochemical, cell biological, and genetic approaches have founded the basis of Rho GTPase biology. The development of biosensors then allowed measuring Rho GTPase activity with unprecedented spatio-temporal resolution. This revealed that Rho GTPase activity fluctuates on time and length scales of tens of seconds and micrometers, respectively. In this review, we describe Rho GTPase activity patterns observed in different cell systems. We then discuss the growing body of evidence that upstream regulators such as guanine nucleotide exchange factors and GTPase-activating proteins shape these patterns by precisely controlling the spatio-temporal flux of Rho GTPase activity. Finally, we comment on additional mechanisms that might feed into the regulation of these signaling patterns and on novel technologies required to dissect this spatio-temporal complexity.

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Voss, Stephanie, Dennis M. Krüger, Oliver Koch et Yao-Wen Wu. « Spatiotemporal imaging of small GTPases activity in live cells ». Proceedings of the National Academy of Sciences 113, n^o 50 (29 novembre 2016) : 14348–53. http://dx.doi.org/10.1073/pnas.1613999113.

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Ras-like small GTPases function as molecular switches and regulate diverse cellular events. To examine the dynamics of signaling requires spatiotemporal visualization of their activity in the cell. Current small GTPase sensors rely on specific effector domains that are available for only a small number of GTPases and compete for endogenous regulator/effector binding. Here, we describe versatile conformational sensors for GTPase activity (COSGAs) based on the conserved GTPase fold. Conformational changes upon GDP/GTP exchange were directly observed in solution, on beads, and in live cells by Förster resonance energy transfer (FRET). The COSGAs allow for monitoring of Rab1 and K-Ras activity in live cells using fluorescence lifetime imaging microscopy. We found that Rab1 is largely active in the cytoplasm and inactive at the Golgi, suggesting that the Golgi serves as the terminal of the Rab1 functional cycle. K-Ras displays polarized activity at the plasma membrane, with less activity at the edge of the cell and membrane ruffles.

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Dandamudi, Akhila, Huzoor Akbar, Jose Cancelas et Yi Zheng. « Rho GTPase Signaling in Platelet Regulation and Implication for Antiplatelet Therapies ». International Journal of Molecular Sciences 24, n^o 3 (28 janvier 2023) : 2519. http://dx.doi.org/10.3390/ijms24032519.

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Platelets play a vital role in regulating hemostasis and thrombosis. Rho GTPases are well known as molecular switches that control various cellular functions via a balanced GTP-binding/GTP-hydrolysis cycle and signaling cascade through downstream effectors. In platelets, Rho GTPases function as critical regulators by mediating signal transduction that drives platelet activation and aggregation. Mostly by gene targeting and pharmacological inhibition approaches, Rho GTPase family members RhoA, Rac1, and Cdc42 have been shown to be indispensable in regulating the actin cytoskeleton dynamics in platelets, affecting platelet shape change, spreading, secretion, and aggregation, leading to thrombus formation. Additionally, studies of Rho GTPase function using platelets as a non-transformed model due to their anucleated nature have revealed valuable information on cell signaling principles. This review provides an updated summary of recent advances in Rho GTPase signaling in platelet regulation. We also highlight pharmacological approaches that effectively inhibited platelet activation to explore their possible development into future antiplatelet therapies.

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Bokoch, Gary M., et Becky A. Diebold. « Current molecular models for NADPH oxidase regulation by Rac GTPase ». Blood 100, n^o 8 (15 octobre 2002) : 2692–95. http://dx.doi.org/10.1182/blood-2002-04-1149.

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Reactive oxygen species (ROS) have been increasingly recognized as important components of cell signaling in addition to their well-established roles in host defense. The formation of ROS in phagocytic and nonphagocytic cells involves membrane-localized and Rac guanosine triphosphatase (GTPase)–regulated reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase(s). We discuss here the current molecular models for Rac GTPase action in the control of the phagocytic leukocyte NADPH oxidase. As a mechanistically detailed example of Rac GTPase signaling, the NADPH oxidase provides a potential paradigm for signaling by Rho family GTPases in general.

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Rodríguez-Fdez, Sonia, et Xosé R. Bustelo. « Rho GTPases in Skeletal Muscle Development and Homeostasis ». Cells 10, n^o 11 (2 novembre 2021) : 2984. http://dx.doi.org/10.3390/cells10112984.

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Rho guanosine triphosphate hydrolases (GTPases) are molecular switches that cycle between an inactive guanosine diphosphate (GDP)-bound and an active guanosine triphosphate (GTP)-bound state during signal transduction. As such, they regulate a wide range of both cellular and physiological processes. In this review, we will summarize recent work on the role of Rho GTPase-regulated pathways in skeletal muscle development, regeneration, tissue mass homeostatic balance, and metabolism. In addition, we will present current evidence that links the dysregulation of these GTPases with diseases caused by skeletal muscle dysfunction. Overall, this information underscores the critical role of a number of members of the Rho GTPase subfamily in muscle development and the overall metabolic balance of mammalian species.

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LIANG, Zhimin, Timothy MATHER et Guangpu LI. « GTPase mechanism and function : new insights from systematic mutational analysis of the phosphate-binding loop residue Ala30 of Rab5 ». Biochemical Journal 346, n^o 2 (22 février 2000) : 501–8. http://dx.doi.org/10.1042/bj3460501.

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Structural and biochemical data indicate the importance of the phosphate-binding loop residues Gly12 and Gly13 of Ras both in the GTP hydrolysis reaction and in biological activity, but these two residues are not conserved in other Ras-related GTPases. To gain a better understanding of this region in GTP hydrolysis and GTPase function, we used the Ras-related Rab5 GTPase as a model for comparison, and substituted the Ala30 residue (the equivalent of Gly13 of Ras) with all the other 19 amino acids. The resulting mutants were analysed for GTP hydrolysis, GTP binding, GTP dissociation and biological activity. Only the substitution of alanine with proline reduced the GTPase activity by an order of magnitude. This effect is in sharp contrast with the observation that a proline substitution at the neighbouring position (Gly12 of Ras) has little effect on the GTPase activity. Whereas most other substitutions showed either a small negative effect or no effect on the GTPase activity, the arginine substitution surprisingly stimulated the GTPase activity by 5-fold. Molecular modelling suggests that this built-in arginine mimics the catalytic arginine residues found in trimeric GTPases and GTPase-activating proteins in providing the positive charge to facilitate the GTP hydrolysis reaction. We investigated further the biological activity of the Rab5 mutants in relation to stimulating endocytosis. When expressed in cultured baby hamster kidney cells, both arginine and proline mutants, like wild-type Rab5, stimulated endocytosis. However, the arginine mutant was a more potent stimulator than the proline mutant (3-fold stimulation as against 1.7-fold). The tryptophan mutant, on the other hand, was completely deficient in activity in terms of the stimulation of endocytosis, demonstrating the importance of the phosphate-binding loop in Rab GTPase function.

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Elvers, Margitta. « RhoGAPs und Rho-GTPasen in Thrombozyten ». Hämostaseologie 36, n^o 03 (2016) : 168–77. http://dx.doi.org/10.5482/hamo-14-09-0046.

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ZusammenfassungDie Reorganisation des Zytoskeletts in Thrombozyten ist essenziell für die Thrombozytenadhäsion und Thrombusbildung in Hämostase und Thrombose. Die Rho-GTPasen RhoA, Rac1 und Cdc42 spielen eine entscheidende Rolle bei der Reorganisation des Zytoskeletts, indem sie die Bildung von Filopodien und Lamellipodien induzieren und somit für die Oberflächenvergrößerung der Thrombozyten wäh-rend der Aktivierung verantwortlich sind. Rho-GTPasen beeinflussen zudem die Prozesse der Thrombozytenaktivität und Aggregatbildung durch Modulation der Sekretion, Integrinaktivierung und arteriellen Thrombusbildung. Die Aktivität der Rho-GTPasen wird von verschiedenen Proteinen kontrolliert, z. B. den GTPase aktivierenden Proteinen (GTPase activating proteins, GAPs). GAPs lösen die Inaktivierung des Guaninnukleotidbindenden Proteins durch Stimulierung der GTPase-Aktivität aus. Die Rolle und Bedeutung von GAPs in Thrombozyten ist nur wenig verstanden und viele der bekannten Rho-GAPs sind bisher nicht in Thrombozyten identifiziert oder hinsichtlich ihrer Funktion charakterisiert worden. Die kürzlich entdeckten RhoGAPs Oligophrenin1 (OPHN1) und Nadrin regulieren die Aktivität von RhoA, Rac1 und Cdc42 und nachfolgend die Reorganisation des Zytoskeletts und die Aktivierung von Thrombozyten sowie die Thrombusbildung. In den letzten Jahren trug die Analyse gene-tisch-modifizierter Mäuse dazu bei, grundlegende Erkenntnisse zur Bedeutung von RhoGTPasen und ihren Regulatoren für die Reorganisation des Zytoskeletts und andere Rhovermittelte zelluläre Prozesse in Thrombozyten zu gewinnen.

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Héraud, Pinault, Lagrée et Moreau. « p190RhoGAPs, the ARHGAP35- and ARHGAP5-Encoded Proteins, in Health and Disease ». Cells 8, n^o 4 (12 avril 2019) : 351. http://dx.doi.org/10.3390/cells8040351.

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Small guanosine triphosphatases (GTPases) gathered in the Rat sarcoma (Ras) superfamily represent a large family of proteins involved in several key cellular mechanisms. Within the Ras superfamily, the Ras homolog (Rho) family is specialized in the regulation of actin cytoskeleton-based mechanisms. These proteins switch between an active and an inactive state, resulting in subsequent inhibiting or activating downstream signals, leading finally to regulation of actin-based processes. The On/Off status of Rho GTPases implicates two subsets of regulators: GEFs (guanine nucleotide exchange factors), which favor the active GTP (guanosine triphosphate) status of the GTPase and GAPs (GTPase activating proteins), which inhibit the GTPase by enhancing the GTP hydrolysis. In humans, the 20 identified Rho GTPases are regulated by over 70 GAP proteins suggesting a complex, but well-defined, spatio-temporal implication of these GAPs. Among the quite large number of RhoGAPs, we focus on p190RhoGAP, which is known as the main negative regulator of RhoA, but not exclusively. Two isoforms, p190A and p190B, are encoded by ARHGAP35 and ARHGAP5 genes, respectively. We describe here the function of each of these isoforms in physiological processes and sum up findings on their role in pathological conditions such as neurological disorders and cancers.

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Reichman, Melvin, Amanda Schabdach, Meera Kumar, Tom Zielinski, Preston S. Donover, Lisa D. Laury-Kleintop et Robert G. Lowery. « A High-Throughput Assay for Rho Guanine Nucleotide Exchange Factors Based on the Transcreener GDP Assay ». Journal of Biomolecular Screening 20, n^o 10 (20 juillet 2015) : 1294–99. http://dx.doi.org/10.1177/1087057115596326.

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Ras homologous (Rho) family GTPases act as molecular switches controlling cell growth, movement, and gene expression by cycling between inactive guanosine diphosphate (GDP)- and active guanosine triphosphate (GTP)-bound conformations. Guanine nucleotide exchange factors (GEFs) positively regulate Rho GTPases by accelerating GDP dissociation to allow formation of the active, GTP-bound complex. Rho proteins are directly involved in cancer pathways, especially cell migration and invasion, and inhibiting GEFs holds potential as a therapeutic strategy to diminish Rho-dependent oncogenesis. Methods for measuring GEF activity suitable for high-throughput screening (HTS) are limited. We developed a simple, generic biochemical assay method for measuring GEF activity based on the fact that GDP dissociation is generally the rate-limiting step in the Rho GTPase catalytic cycle, and thus addition of a GEF causes an increase in steady-state GTPase activity. We used the Transcreener GDP Assay, which relies on selective immunodetection of GDP, to measure the GEF-dependent stimulation of steady-state GTP hydrolysis by small GTPases using Dbs (Dbl’s big sister) as a GEF for Cdc42, RhoA, and RhoB. The assay is well suited for HTS, with a homogenous format and far red fluorescence polarization (FP) readout, and it should be broadly applicable to diverse Rho GEF/GTPase pairs.

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Jiang, Shu-Ye, et Srinivasan Ramachandran. « Comparative and evolutionary analysis of genes encoding small GTPases and their activating proteins in eukaryotic genomes ». Physiological Genomics 24, n^o 3 (mars 2006) : 235–51. http://dx.doi.org/10.1152/physiolgenomics.00210.2005.

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Both small GTPase and its activating protein (GAP) superfamilies exist in various eukaryotes. The small GTPases regulate a wide variety of cellular processes by cycling between active GTP- and inactive GAP-bound conformations. The GAPs promote GTPase inactivation by stimulating the GTP hydrolysis. In this study, we identified 111 small GTPases and 85 GAPs in rice, 65 GAPs in Arabidopsis, 90 small GTPases in Drosophila melanogaster, and 35 GAPs in Saccharomyces cerevisiaeby genome-wide analysis. We then analyzed and compared a total of 498 small GTPases and 422 GAPs from these four eukaryotic and human genomes. Both animals and yeast genomes contained five families of small GTPases and their GAPs. However, plants had only four of these five families because of a lack of the Ras and RasGAP genes. Small GTPases were conserved with common motifs, but GAPs exhibited higher and much more rapid divergence. On the basis of phylogenetic analysis of all small GTPases and GAPs in five eukaryotic organisms, we estimated that their ancestors had small sizes of small GTPases and GAPs and their large-scale expansions occurred after the divergence from their ancestors. Further investigation showed that genome duplications represented the major mechanism for such expansions. Nonsynonymous substitutions per site ( Ka) and synonymous substitutions per site ( Ks) analyses showed that most of the divergence due to a positive selection occurred in common ancestors, suggesting a major functional divergence in an ancient era.

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Dautt-Castro, Mitzuko, Montserrat Rosendo-Vargas et Sergio Casas-Flores. « The Small GTPases in Fungal Signaling Conservation and Function ». Cells 10, n^o 5 (28 avril 2021) : 1039. http://dx.doi.org/10.3390/cells10051039.

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Monomeric GTPases, which belong to the Ras superfamily, are small proteins involved in many biological processes. They are fine-tuned regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Several families have been identified in organisms from different kingdoms. Overall, the most studied families are Ras, Rho, Rab, Ran, Arf, and Miro. Recently, a new family named Big Ras GTPases was reported. As a general rule, the proteins of all families have five characteristic motifs (G1–G5), and some specific features for each family have been described. Here, we present an exhaustive analysis of these small GTPase families in fungi, using 56 different genomes belonging to different phyla. For this purpose, we used distinct approaches such as phylogenetics and sequences analysis. The main functions described for monomeric GTPases in fungi include morphogenesis, secondary metabolism, vesicle trafficking, and virulence, which are discussed here. Their participation during fungus–plant interactions is reviewed as well.

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Barlow, Haley Rose, et Ondine Cleaver. « Building Blood Vessels—One Rho GTPase at a Time ». Cells 8, n^o 6 (6 juin 2019) : 545. http://dx.doi.org/10.3390/cells8060545.

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Blood vessels are required for the survival of any organism larger than the oxygen diffusion limit. Blood vessel formation is a tightly regulated event and vessel growth or changes in permeability are linked to a number of diseases. Elucidating the cell biology of endothelial cells (ECs), which are the building blocks of blood vessels, is thus critical to our understanding of vascular biology and to the development of vascular-targeted disease treatments. Small GTPases of the Rho GTPase family are known to regulate several processes critical for EC growth and maintenance. In fact, many of the 21 Rho GTPases in mammals are known to regulate EC junctional remodeling, cell shape changes, and other processes. Rho GTPases are thus an attractive target for disease treatments, as they often have unique functions in specific vascular cell types. In fact, some Rho GTPases are even expressed with relative specificity in diseased vessels. Interestingly, many Rho GTPases are understudied in ECs, despite their known expression in either developing or mature vessels, suggesting an even greater wealth of knowledge yet to be gleaned from these complex signaling pathways. This review aims to provide an overview of Rho GTPase signaling contributions to EC vasculogenesis, angiogenesis, and mature vessel barrier function. A particular emphasis is placed on so-called “alternative” Rho GTPases, as they are largely understudied despite their likely important contributions to EC biology.

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Olayioye, Monilola A., Bettina Noll et Angelika Hausser. « Spatiotemporal Control of Intracellular Membrane Trafficking by Rho GTPases ». Cells 8, n^o 12 (21 novembre 2019) : 1478. http://dx.doi.org/10.3390/cells8121478.

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As membrane-associated master regulators of cytoskeletal remodeling, Rho GTPases coordinate a wide range of biological processes such as cell adhesion, motility, and polarity. In the last years, Rho GTPases have also been recognized to control intracellular membrane sorting and trafficking steps directly; however, how Rho GTPase signaling is regulated at endomembranes is still poorly understood. In this review, we will specifically address the local Rho GTPase pools coordinating intracellular membrane trafficking with a focus on the endo- and exocytic pathways. We will further highlight the spatiotemporal molecular regulation of Rho signaling at endomembrane sites through Rho regulatory proteins, the GEFs and GAPs. Finally, we will discuss the contribution of dysregulated Rho signaling emanating from endomembranes to the development and progression of cancer.

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Mukhopadhyay, Amitabha, Alejandro M. Barbieri, Kouichi Funato, Richard Roberts et Philip D. Stahl. « Sequential Actions of Rab5 and Rab7 Regulate Endocytosis in the Xenopus Oocyte ». Journal of Cell Biology 136, n^o 6 (24 mars 1997) : 1227–37. http://dx.doi.org/10.1083/jcb.136.6.1227.

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To explore the role of GTPases in endocytosis, we developed an assay using Xenopus oocytes injected with recombinant proteins to follow the uptake of the fluid phase marker HRP. HRP uptake was inhibited in cells injected with GTPγS or incubated with aluminum fluoride, suggesting a general role for GTPases in endocytosis. Injection of Rab5 into oocytes, as well as Rab5:Q79L, a mutant with decreased GTPase activity, increased HRP uptake. Injection of Rab5:S34N, the dominant-negative mutant, inhibited HRP uptake. Injection of N-ethylmaleimide–sensitive factor (NSF) stimulated HRP uptake, and ATPase-defective NSF mutants inhibited HRP uptake when coinjected with Rab5:Q79L, confirming a requirement for NSF in endocytosis. Surprisingly, injection of Rab7:WT stimulated both uptake and degradation/activation of HRP. The latter appears to be due to enhanced transport to a late endosomal/prelysosomal degradative compartment that is monensin sensitive. Enhancement of uptake by Rab7 appears to function via an Rab5-sensitive pathway in oocytes since the stimulatory effect of Rab7 was blocked by coinjection of Rab5:S34N. Stimulation of uptake by Rab5 was blocked by Rab5:S34N but not by Rab7:T22N. Our results suggest that Rab7, while functioning downstream of Rab5, may be rate limiting for endocytosis in oocytes.

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Schöpel, Miriam, Veena Nambiar Potheraveedu, Thuraya Al-Harthy, Raid Abdel-Jalil, Rolf Heumann et Raphael Stoll. « The small GTPases Ras and Rheb studied by multidimensional NMR spectroscopy : structure and function ». Biological Chemistry 398, n^o 5-6 (1 mai 2017) : 577–88. http://dx.doi.org/10.1515/hsz-2016-0276.

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Abstract Ras GTPases are key players in cellular signalling because they act as binary switches. These states manifest through toggling between an active (GTP-loaded) and an inactive (GDP-loaded) form. The hydrolysis and replenishing of GTP is controlled by two additional protein classes: GAP (GTPase-activating)- and GEF (Guanine nucleotide exchange factors)-proteins. The complex interplay of the proteins is known as the GTPase-cycle. Several point mutations of the Ras protein deregulate this cycle. Mutations in Ras are associated with up to one-third of human cancers. The three isoforms of Ras (H, N, K) exhibit high sequence similarity and mainly differ in a region called HVR (hypervariable region). The HVR governs the differential action and cellular distribution of the three isoforms. Rheb is a Ras-like GTPase that is conserved from yeast to mammals. Rheb is mainly involved in activation of cell growth through stimulation of mTORC1 activity. In this review, we summarise multidimensional NMR studies on Rheb and Ras carried out to characterise their structure-function relationship and explain how the activity of these small GTPases can be modulated by low molecular weight compounds. These might help to design GTPase-selective antagonists for treatment of cancer and brain disease.

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