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Ryan T Terry-Lorenzo, Viviana I Torres, Dhananjay Wagh, Jose Galaz, Selene K Swanson, Laurence Florens, Michael P Washburn, Clarissa L Waites, Eckart D Gundelfinger, Richard J Reimer, Craig C Garner
Synaptic vesicles (SVs) fuse with the plasma membrane at a precise location called the presynaptic active zone (AZ). This fusion is coordinated by proteins embedded within a cytoskeletal matrix assembled at the AZ (CAZ). In the present study, we have identified a novel binding partner for the CAZ proteins Piccolo and Bassoon. This interacting protein, Trio, is a member of the Dbl family of guanine nucleotide exchange factors (GEFs) known to regulate the dynamic assembly of actin and growth factor dependent axon guidance and synaptic growth...
2016: PloS One
Marco Seifermann, Bernd Epe
The generation of DNA modifications in cells is in most cases accidental and associated with detrimental consequences such as increased mutation rates and an elevated risk of malignant transformation. Accordingly, repair enzymes involved in the removal of the modifications have primarily a protective function. Among the well-established exceptions of this rule are 5-methylcytosine and uracil, which are generated in DNA enzymatically under controlled conditions and fulfill important regulatory functions in DNA as epigenetic marks and in antibody diversification, respectively...
November 18, 2016: Free Radical Biology & Medicine
Binod Kumar, Bala Chandran
Kaposi's sarcoma associated herpesvirus (KSHV) is etiologically associated with human endothelial cell hyperplastic Kaposi's sarcoma and B-cell primary effusion lymphoma. KSHV infection of adherent endothelial and fibroblast cells are used as in vitro models for infection and KSHV enters these cells by host membrane bleb and actin mediated macropinocytosis or clathrin endocytosis pathways, respectively. Infection in endothelial and fibroblast cells is initiated by the interactions between multiple viral envelope glycoproteins and cell surface associated heparan sulfate (HS), integrins (α3β1, αVβ3 and αVβ5), and EphA2 receptor tyrosine kinase (EphA2R)...
November 14, 2016: Viruses
Janina Hendrick, Monilola A Olayioye
The spatial regulation of cellular Rho signaling by GEF and GAP proteins and the molecular mechanisms controlling the Rho regulators themselves are still incompletely understood. We previously reported that the poorly characterized RhoGAP protein DLC3 localizes to cell-cell adhesions and Rab8-positive membrane tubules. However, it was unclear how DLC3 is targeted to these subcellular sites to execute its functions. In our recent work, protein partners of DLC3 were identified by mass spectrometry, identifying the basolateral polarity protein Scribble as a scaffold for DLC3 at cell-cell contacts...
November 16, 2016: Small GTPases
Oliver A Kent, María-José Sandí, Helen E Burston, Kevin R Brown, Robert Rottapel
Activating mutations of KRAS are nearly ubiquitous in pancreatic adenocarcinomas occurring in greater than 90% of cases. Cellular transformation by oncogenic RAS requires the RHO guanine exchange factor ARHGEF2 (also known as GEF-H1) for tumor growth and survival. Here, we find oncogenic KRAS activates ARHGEF2 through a minimal RAS responsive promoter. We have determined the endogenous ARHGEF2 promoter is positively regulated by the transcription factors ELK1, ETS1, SP1 and SP3 and negatively regulated by the RAS responsive element binding protein (RREB1)...
November 7, 2016: Oncotarget
Jakobus van Unen, Taofei Yin, Yi I Wu, Marieke Mastop, Theodorus W J Gadella, Joachim Goedhart
Rho GTPases are master regulators of the eukaryotic cytoskeleton. The activation of Rho GTPases is governed by Rho guanine nucleotide exchange factors (GEFs). Three RhoGEF isoforms are produced by the gene ARHGEF25; p63RhoGEF(580), GEFT and a recently discovered longer isoform of 619 amino acids (p63RhoGEF(619)). The subcellular distribution of p63RhoGEF(580) and p63RhoGEF(619) is strikingly different in unstimulated cells, p63RhoGEF(580) is located at the plasma membrane and p63RhoGEF(619) is confined to the cytoplasm...
November 11, 2016: Scientific Reports
Nadine Platet, Isabelle Hinkel, Ludovic Richert, Devadarssen Murdamoothoo, Ahlam Moufok-Sadoun, Marie Vanier, Philippe Lavalle, Christian Gaiddon, Dominique Vautier, Jean-Noel Freund, Isabelle Gross
The vast majority of cancer deaths are caused by the formation of metastases rather than the primary tumor itself. Despite this clinical importance, the molecular and cellular events that support the dissemination of cancer cells are not yet fully unraveled. We have previously shown that CDX2, a homeotic transcription factor essential for gut development, acts as a colon-specific tumor suppressor and opposes metastasis. Here, using a combination of biochemical, biophysical, and immunofluorescence techniques, we further investigated the mechanisms promoted by CDX2 that might antagonize tumor cell dissemination...
November 2, 2016: Cancer Letters
Juan Carlos Montero, Samuel Seoane, Sara García-Alonso, Atanasio Pandiella
P-Rex proteins are guanine nucleotide exchange factors (GEFs) that act on the Rho/Rac family of GTP binding proteins. The activity of P-Rex proteins is regulated by several extracellular stimuli. In fact, activation of growth factor receptors has been reported to activate a phosphorylation/dephosphorylation cycle of P-Rex1. Such cycle includes dephosphorylation of serines 313 and 319 which negatively regulate the GEF activity of P-Rex1, together with phosphorylation of serines 605 and 1169 which favour P-Rex1 GEF activity...
October 24, 2016: Oncotarget
Lianggong Ding, Ye Lei, Yanping Han, Yuhong Li, Xunming Ji, Lei Liu
As fundamental processes in mitochondrial dynamics, mitochondrial fusion, fission and transport are regulated by several core components, including Miro. As an atypical Rho-like small GTPase with high molecular mass, the exchange of GDP/GTP in Miro may require assistance from a guanine nucleotide exchange factor (GEF). However, the GEF for Miro has not been identified. While studying mitochondrial morphology in Drosophila, we incidentally observed that the loss of vimar, a gene encoding an atypical GEF, enhanced mitochondrial fission under normal physiological conditions...
October 2016: PLoS Genetics
Anna Bagnato, Laura Rosanò
Metastatization is a complex multistep process requiring fine-tuned regulated cytoskeleton re-modeling, mediated by the cross-talk of actin with interacting partners, such as the Rho GTPases. Our expanding knowledge of invadopodia, small invasive membrane protrusions composed of a core of F-actin, actin regulators and actin-binding proteins, and hotspots for secretion of extracellular matrix (ECM) proteinases, contributes to clarify critical steps of the metastatic program. Growth factor receptors and their intermediate signaling molecules, along with matrix adhesion and rigidity, pH and hypoxia, act as drivers of cytoskeleton changes and invadopodia formation...
October 3, 2016: Small GTPases
Raquel B Haga, Anne J Ridley
Rho GTPases are well known for their roles in regulating cell migration, and also contribute to a variety of other cellular responses. They are subdivided into 2 groups: typical and atypical. The typical Rho family members, including RhoA, Rac1 and Cdc42, cycle between an active GTP-bound and inactive GDP-bound conformation, and are regulated by GEFs, GAPs and GDIs, whereas atypical Rho family members have amino acid substitutions that alter their ability to interact with GTP/GDP and hence are regulated by different mechanisms...
October 2016: Small GTPases
Y Komiya, Y Onodera, M Kuroiwa, S Nomimura, Y Kubo, J-M Nam, K Kajiwara, S Nada, C Oneyama, H Sabe, M Okada
Epithelial tumor cells often acquire malignant properties, such as invasion/metastasis and uncontrolled cell growth, by undergoing epithelial-mesenchymal transition (EMT). However, the mechanisms by which EMT contributes to malignant progression remain elusive. Here we show that the Rho guanine nucleotide exchange factor (GEF) ARHGEF5 promotes tumor malignancy in a manner dependent on EMT status. We previously identified ARHGEF5, a member of the Dbl family of GEFs, as a multifunctional mediator of Src-induced cell invasion and tumor growth...
2016: Oncogenesis
Yufeng Tian, Grzegorz Gawlak, Xinyong Tian, Alok S Shah, Nicolene Sarich, Sandra Citi, Anna A Birukova
Agonist-induced activation of Rho GTPase signaling leads to endothelial cell (EC) permeability and may culminate in pulmonary edema, a devastating complication of acute lung injury. Cingulin is an adaptor protein first discovered in epithelium and is involved in the organization of the tight junctions. This study investigated the role of cingulin in control of agonist-induced lung EC permeability via interaction with RhoA-specific activator GEF-H1. The siRNA-induced cingulin knockdown augmented thrombin-induced EC permeability monitored by measurements of transendothelial electrical resistance and endothelial cell permeability for macromolecules...
November 4, 2016: Journal of Biological Chemistry
Ru-Feng Wu, Chengxu Liao, Guosheng Fu, Heather N Hayenga, Kejia Yang, Zhenyi Ma, Zhe Liu, Lance S Terada
Tissue cells respond to changes in tensional forces with proliferation or death through the control of RhoA. However, the response coupling mechanisms that link force with RhoA activation are poorly understood. We found that tension applied to fibronectin-coated microbeads caused recruitment of all three isoforms of the Shc adapter (p66(Shc), p52(Shc), and p46(Shc)) to adhesion complexes. The Shc PTB domain was necessary and sufficient for this recruitment, and screening studies revealed direct interactions with the FERM domain of FAK that were required for Shc translocation to adhesion complexes...
August 29, 2016: Molecular and Cellular Biology
W Ba, N Nadif Kasri
Activity-dependent modifications in the strength of excitatory synapses are considered to be major cellular mechanisms that contribute to the plasticity of neuronal networks underlying learning and memory. Key mechanisms for the regulation of synaptic efficacy involve the dynamic changes in size and number of dendritic spines, as well as the synaptic incorporation and removal of AMPA-type glutamate receptors (AMPAr). As key regulators of the actin cytoskeleton, the Rho subfamily of GTP-binding proteins play a critical role in synaptic development and plasticity...
August 5, 2016: Small GTPases
Melanie J Grubisha, Chien-Wei Lin, George C Tseng, Peter Penzes, Etienne Sibille, Robert A Sweet
KALRN (KAL) is a Rho GEF that is highly involved in regulation of the actin cytoskeleton within dendrites. There are several isoforms of the protein that arise from differential splicing of KALRN's 66 exons. KAL isoforms have different functions in development. For example, overexpression of the KAL9 and KAL12 isoforms induce dendritic elongation in early development. However, in mature neurons KAL9 overexpression reduces dendritic length, a phenotype also observed in normal human ageing. We therefore hypothesized that KAL9 would have increased expression with age, and undertook to evaluate the expression of individual KALRN exons throughout the adult lifespan...
October 2016: European Journal of Neuroscience
Megan B Miller, Yan Yan, Yi Wu, Bing Hao, Richard E Mains, Betty A Eipper
Kalirin (Kal), a dual Rho GDP/GTP exchange factor (GEF), plays essential roles within and outside the nervous system. Tissue-specific, developmentally regulated alternative splicing generates isoforms with one (Kal7) or two (Kal9, Kal12) GEF domains along with a kinase (Kal12) domain; while Kal9 and Kal12 are crucial for neurite outgrowth, Kal7 plays important roles in spine maintenance and synaptic plasticity. Tissue-specific usage of alternate Kalrn promoters (A, B, C, D) places four different peptides before the Sec14 domain...
July 28, 2016: Journal of Neurochemistry
Huibo Ren, Xie Dang, Yanqiu Yang, Dingquan Huang, Mengting Liu, Xiaowei Gao, Deshu Lin
Plant organ growth and final shape rely on cell proliferation and, particularly, on cell expansion that largely determines the visible growth of plant organs. Arabidopsis (Arabidopsis thaliana) petals serve as an excellent model for dissecting the coordinated regulation of patterns of cell expansion and organ growth, but the molecular signaling mechanisms underlying this regulation remain largely unknown. Here, we demonstrate that during the late petal development stages, SPIKE1 (SPK1), encoding a guanine nucleotide exchange factor, activates Rho of Plants (ROP) GTPase proteins (ROP2, ROP4, and ROP6) to affect anisotropic expansion of epidermal cells in both petal blades and claws, thereby affecting anisotropic growth of the petal and the final characteristic organ shape...
September 2016: Plant Physiology
Pauline Croisé, Laurent Brunaud, Petra Tóth, Stéphane Gasman, Stéphane Ory
Altered Rho GTPase signaling has been linked to many types of cancer. As many small G proteins, Rho GTPases cycle between an active and inactive state thanks to specific regulators that catalyse exchange of GDP into GTP (Rho-GEF) or hydrolysis of GTP into GDP (Rho-GAP). Recent studies have shown that alteration takes place either at the level of Rho proteins themselves (expression levels, point mutations) or at the level of their regulators, mostly RhoGEFs and RhoGAPs. Most reports describe Rho GTPases gain of function that may participate to the tumorigenesis processes...
June 29, 2016: Small GTPases
Mariam Mansour, Sue Haupt, Ai-Leen Chan, Nathan Godde, Alexandra Rizzitelli, Sherene Loi, Franco Caramia, Siddhartha Deb, Elena A Takano, Mark Bishton, Cameron Johnstone, Brendon Monahan, Yarra Levav-Cohen, Yong-Hui Jiang, Alpha S Yap, Stephen Fox, Ora Bernard, Robin Anderson, Ygal Haupt
Metastatic disease is the major cause of breast cancer-related death and despite many advances, current therapies are rarely curative. Tumor cell migration and invasion require actin cytoskeletal reorganization to endow cells with capacity to disseminate and initiate the formation of secondary tumors. However, it is still unclear how these migratory cells colonize distant tissues to form macrometastases. The E6-associated protein, E6AP, acts both as an E3 ubiquitin-protein ligase and as a coactivator of steroid hormone receptors...
July 15, 2016: Cancer Research
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