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Sanchaita Das, David G Lambright
Long-range tethering is a ubiquitous recognition event preceding membrane fusion. A new study shows that Rab GTPase binding causes 'entropic collapse' of the coiled-coil endosome tether EEA1, driving membrane apposition and facilitating short-range interactions required for fusion.
October 24, 2016: Current Biology: CB
Zheng Zhang, Hannah A Ledford, Seojin Park, Wenying Wang, Sassan Rafizadeh, Hyo Jeong Kim, Wilson Xu, Ling Lu, Victor C Lau, Anne A Knowlton, Xiao-Dong Zhang, Ebenezer N Yamoah, Nipavan Chiamvimonvat
The normal function of ion channels depends critically on the precise subcellular localization and the number of channel proteins on the cell surface membrane. Small-conductance, Ca(2+) -activated K(+) channels (SK, KCa 2) are expressed in human atrial myocytes and responsible for shaping atrial action potentials. Understanding the mechanisms of SK channel trafficking may provide new insights into the regulation controlling the repolarization of atrial myocytes. We have previously demonstrated that the C and N termini of SK2 channels interact with actin-binding proteins, α-actinin2 and filamin A, respectively...
October 25, 2016: Journal of Physiology
Yohei Yamauchi, Yuki Miura, Yasunori Kanaho
The Small GTPase ADP-ribosylation factor 6 (Arf6) functions as the molecular switch in cellular signaling pathways by cycling between GDP-bound inactive and GTP-bound active form, which is precisely regulated by two regulators, guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Numerous studies have shown that these machineries play critical roles in tumor angiogenesis/growth and cancer cell invasion/metastasis through regulating the cycling of Arf6. Here, we summarize accumulating knowledge for involvement of Arf6 GEFs/GAPs and small molecule inhibitors of Arf6 signaling/cycling in cancer progression, and discuss possible strategies for developing innovative anti-cancer drugs targeting Arf6 signaling/cycling...
October 18, 2016: Advances in Biological Regulation
Elisabeth Salzer, Deniz Cagdas, Miroslav Hons, Emily M Mace, Wojciech Garncarz, Özlem Yüce Petronczki, René Platzer, Laurène Pfajfer, Ivan Bilic, Sol A Ban, Katharina L Willmann, Malini Mukherjee, Verena Supper, Hsiang Ting Hsu, Pinaki P Banerjee, Papiya Sinha, Fabienne McClanahan, Gerhard J Zlabinger, Winfried F Pickl, John G Gribben, Hannes Stockinger, Keiryn L Bennett, Johannes B Huppa, Loïc Dupré, Özden Sanal, Ulrich Jäger, Michael Sixt, Ilhan Tezcan, Jordan S Orange, Kaan Boztug
RASGRP1 is an important guanine nucleotide exchange factor and activator of the RAS-MAPK pathway following T cell antigen receptor (TCR) signaling. The consequences of RASGRP1 mutations in humans are unknown. In a patient with recurrent bacterial and viral infections, born to healthy consanguineous parents, we used homozygosity mapping and exome sequencing to identify a biallelic stop-gain variant in RASGRP1. This variant segregated perfectly with the disease and has not been reported in genetic databases. RASGRP1 deficiency was associated in T cells and B cells with decreased phosphorylation of the extracellular-signal-regulated serine kinase ERK, which was restored following expression of wild-type RASGRP1...
October 24, 2016: Nature Immunology
Anshuk Sarkar, Markus Pech, Matthias Thoms, Roland Beckmann, Ed Hurt
Nuclear export of preribosomal subunits is a key step during eukaryotic ribosome formation. To efficiently pass through the FG-repeat meshwork of the nuclear pore complex, the large pre-60S subunit requires several export factors. Here we describe the mechanism of recruitment of the Saccharomyces cerevisiae RNA-export receptor Mex67-Mtr2 to the pre-60S subunit at the proper time. Mex67-Mtr2 binds at the premature ribosomal-stalk region, which later during translation serves as a binding platform for translational GTPases on the mature ribosome...
October 24, 2016: Nature Structural & Molecular Biology
Hiroaki Iwata, Mayumi Kamaguchi, Hideyuki Ujiie, Machiko Nishimura, Kentaro Izumi, Ken Natsuga, Satoru Shinkuma, Wataru Nishie, Hiroshi Shimizu
Macropinocytosis is an endocytic pathway that is involved in the nonselective fluid uptake of extracellular fluid. Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease associated with autoantibodies to type XVII collagen (COL17), which is a component of hemidesmosome. When keratinocytes are treated with BP-IgG, COL17 internalizes into cells by way of the macropinocytosis. We investigated the mechanism of COL17 macropinocytosis using DJM-1 cells, a cutaneous squamous cell carcinoma cell line...
October 24, 2016: Laboratory Investigation; a Journal of Technical Methods and Pathology
Viviana Guadagni, Chiara Cerri, Ilaria Piano, Elena Novelli, Claudia Gargini, Carla Fiorentini, Matteo Caleo, Enrica Strettoi
Retinitis pigmentosa (RP) comprises a group of inherited pathologies characterized by progressive photoreceptor degeneration. In rodent models of RP, expression of defective genes and retinal degeneration usually manifest during the first weeks of postnatal life, making it difficult to distinguish consequences of primary genetic defects from abnormalities in retinal development. Moreover, mouse eyes are small and not always adequate to test pharmacological and surgical treatments. An inducible paradigm of retinal degeneration potentially extensible to large animals is therefore desirable...
October 24, 2016: Scientific Reports
Bor L Tang
Hexanucleotide repeat expansion in an intron of Chromosome 9 open reading frame 72 (C9orf72) is the most common genetic cause of Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD). While functional haploinsufficiency of C9orf72 resulting from the mutation may play a role in ALS/FTD, the actual cellular role of the protein has been unclear. Recent findings have now shown that C9orf72 physically and functionally interacts with multiple members of the Rab small GTPases family, consequently exerting important influences on cellular membrane traffic and the process of autophagy...
2016: Frontiers in Cellular Neuroscience
Richard Wong, Larry Feig
RalGDS is a guanine nucleotide exchange factor that promotes the active GTP-bound form of Ral GTPases, RalA and RalB. GTP-bound Ras has the capacity to activate Ral GTPases at least in part by binding to the C-terminal Ras-binding domain (RBD) of RalGDS and directing the protein to Ral GTPases in the plasma membrane. In many cases, activation of Ral proteins complements other Ras effector pathways to carry out a cell function, but in others it opposes them. Moreover, in many cases activation of Ral proteins contributes to the oncogenic potential of Ras...
October 20, 2016: Biochemical and Biophysical Research Communications
Justin P Ingram, Igor E Brodsky, Siddharth Balachandran
Salmonella enterica is a facultative intracellular bacterium that is the leading cause of food borne illnesses in humans. The cytokine IFN-γ has well-established antibacterial properties against Salmonella and other intracellular microbes, for example its capacity to activate macrophages, promote phagocytosis, and destroy phagocytosed microbes by free radical-driven toxification of phagosomes. But IFN-γ induces the expression of hundreds of uncharacterized genes, suggesting that this cytokine deploys additional antimicrobial strategies that await discovery...
October 20, 2016: Cytokine
Yubai Zhang, Maya Nolan, Hiroshi Yamada, Masami Watanabe, Yasutomo Nasu, Kohji Takei, Tetsuya Takeda
Cancer cell invasion is mediated by actin-based membrane protrusions termed invadopodia. Invadopodia consist of "core" F-actin bundles associated with adhesive and proteolytic machineries promoting cell invasion by degrading extracellular matrix (ECM). Formation of the F-actin core in invadopodia is regulated by various actin-binding proteins including Arp2/3 complex and cortactin. Dynamin GTPase localizes to the invadopodia and is implicated in cancer cell invasion, but its precise role at the invadopodia remained elusive...
October 19, 2016: Biochemical and Biophysical Research Communications
P Gómez-Contreras, J M Ramiro-Díaz, A Sierra, C Stipp, F E Domann, R J Weigel, G Lal
ECM1 overexpression is an independent predictor of poor prognosis in primary breast carcinomas, however the mechanisms by which ECM1 affects tumor progression have not been completely elucidated. ECM1 was silenced in the triple-negative breast cancer cell lines Hs578T and MDAMB231 using siRNA and the cells were evaluated for changes in morphology, migration, invasion and adhesion. Actin cytoskeleton alterations were evaluated by fluorescent staining and levels of activated Rho GTPases by pull down assays. ECM1 downregulation led to significantly diminished cell migration (p = 0...
October 21, 2016: Clinical & Experimental Metastasis
Hisateru Komatsu, Tomohiro Iguchi, Takaaki Masuda, Hidenari Hirata, Masami Ueda, Shinya Kidogami, Yushi Ogawa, Kuniaki Sato, Qingjiang Hu, Sho Nambara, Tomoko Saito, Shotaro Sakimura, Ryutaro Uchi, Shuhei Ito, Hidetoshi Eguchi, Keishi Sugimachi, Hidetoshi Eguchi, Yuichiro Doki, Masaki Mori, Koshi Mimori
BACKGROUND: The RND1 gene encodes a protein that belongs to the Rho GTPase family, which regulates various cellular functions. Depletion of RND1 expression activates the oncogenic Ras signaling pathway. In this study, we aimed to clarify the clinical significance of RND1 expression in predicting prognosis and to investigate its biological role in human hepatocellular carcinoma (HCC). METHODS: The association between RND1 expression and clinical outcomes in patients with HCC was analyzed in three independent cohorts: 120 cases resected in our hospital; 370 cases in The Cancer Genome Atlas (TCGA); and 242 cases in GSE14520...
October 21, 2016: Annals of Surgical Oncology
Sha Xu, Ge-Yuan Zhang, Huijie Zhang, Toshihiko Kitajima, Hideki Nakanishi, Xiao-Dong Gao
BACKGROUND: To humanize yeast N-glycosylation pathways, genes involved in yeast specific hyper-mannosylation must be disrupted followed by the introduction of genes catalyzing the synthesis, transport, and addition of human sugars. However, deletion of these genes, for instance, OCH1, which initiates hyper-mannosylation, could cause severe defects in cell growth, morphogenesis and response to environmental challenges. RESULTS: In this study, overexpression of RHO1, which encodes the Rho1p small GTPase, is confirmed to partially recover the growth defect of Saccharomyces cerevisiae Δalg3Δoch1 double mutant strain...
October 21, 2016: Microbial Cell Factories
Christopher P Webster, Emma F Smith, Andrew J Grierson, Kurt J De Vos
A GGGGCC hexanucleotide repeat expansion in the first intron of the C9orf72 gene is the most common genetic defect associated with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) (C9ALS/FTD). Haploinsufficiency and a resulting loss of C9orf72 protein function has been suggested as a possible pathogenic mechanism in C9ALS/FTD. C9ALS/FTD patients exhibit specific ubiquitin and p62/sequestosome-1 positive but TDP-43 negative inclusions in the cerebellum and hippocampus, indicating possible autophagy deficits in these patients...
October 21, 2016: Small GTPases
Ana Rolo, Sarah Escuin, Nicholas D E Greene, Andrew J Copp
Neural tube closure is an important morphogenetic event that involves dramatic reshaping of both neural and non-neural tissues. Rho GTPases are key cytoskeletal regulators involved in cell motility and in several developmental processes, and are thus expected to play pivotal roles in neurulation. Here, we discuss 2 recent studies that shed light on the roles of distinct Rho GTPases in different tissues during neurulation. RhoA plays an essential role in regulating actomyosin dynamics in the neural epithelium of the elevating neural folds, while Rac1 is required for the formation of cell protrusions in the non-neural surface ectoderm during neural fold fusion...
October 21, 2016: Small GTPases
Francesco Parmeggiani, Vanessa Barbaro, Angelo Migliorati, Paolo Raffa, Patrizia Nespeca, Katia De Nadai, Claudia Del Vecchio, Giorgio Palù, Cristina Parolin, Enzo Di Iorio
PURPOSE: To identify novel mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene and retinitis pigmentosa 2 (RP2) gene underlying X-linked retinitis pigmentosa (XLRP) and assess genotype-phenotype correlations. METHODS: The patient cohort, consisting of 13 individuals from 3 unrelated XLRP families, underwent comprehensive ophthalmologic examination. The open reading frames of RPGR and RP2 were analyzed with Sanger sequencing in each patient. The identified genetic variants were defined as mutations or polymorphisms on the basis of their pathological effect...
October 21, 2016: European Journal of Ophthalmology
Nicole S Nicholas, Aikaterini Pipili, Michaela S Lesjak, Simon M Ameer-Beg, Jenny L C Geh, Ciaran Healy, Alistair D MacKenzie Ross, Maddy Parsons, Frank O Nestle, Katie E Lacy, Claire M Wells
Cancer cells are thought to use actin rich invadopodia to facilitate matrix degradation. Formation and maturation of invadopodia requires the co-ordained activity of Rho-GTPases, however the molecular mechanisms that underlie the invadopodia lifecycle are not fully elucidated. Previous work has suggested a formation and disassembly role for Rho family effector p-21 activated kinase 1 (PAK1) however, related family member PAK4 has not been explored. Systematic analysis of isoform specific depletion using in vitro and in vivo invasion assays revealed there are differential invadopodia-associated functions...
September 27, 2016: Oncotarget
Katsuya Sato, Masashi Kimura, Kazue Sugiyama, Masashi Nishikawa, Yukio Okano, Hitoshi Nagaoka, Takahiro Nagase, Yukio Kitade, Hiroshi Ueda
PLEKHG2/FLJ00018 is a Gβγ-dependent guanine nucleotide exchange factor for the small GTPases Rac and Cdc42 and has been shown to mediate the signaling pathways leading to actin cytoskeleton reorganization. Here we showed that the zinc finger domain-containing protein four-and-a-half LIM domains 1 (FHL1) acts as a novel interaction partner of PLEKHG2 by the yeast two-hybrid system. Among the isoforms of FHL1 (i.e., FHL1A, FHL1B and FHL1C), FHL1A and FHL1B interacted with PLEKHG2. We found that there was an FHL1-binding region at amino acids 58-150 of PLEKHG2...
October 20, 2016: Journal of Biological Chemistry
Soula Danopoulos, Michael Krainock, Omar Toubat, Matthew Thornton, Brendan Grubbs, Denise Al Alam
Lung branching morphogenesis relies on a number of factors, including proper epithelial cell proliferation and differentiation, cell polarity and migration. Rac1, a small Rho GTPase, orchestrates a number of these cellular processes, including cell proliferation and differentiation, cellular alignment and polarization. Furthermore, Rac1 modulates both non-canonical and canonical Wnt signaling, important pathways in lung branching morphogenesis. Culture of embryonic mouse lung explants in the presence of the Rac1 inhibitor (NSC23766) resulted in a dose-dependent decrease in branching...
October 7, 2016: American Journal of Physiology. Lung Cellular and Molecular Physiology
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