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Molecular Biology of the Cell

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https://www.readbyqxmd.com/read/28331075/myosin-activity-drives-actomyosin-bundle-formation-and-organization-in-contractile-cells-of-the-c-elegans-spermatheca
#1
Alison C E Wirshing, Erin J Cram
Stress fibers, contractile actomyosin bundles, are important for cellular force production and adaptation to physical stress and have been well-studied within the context of cell migration. However, less is known about actomyosin bundle formation and organization in vivo and in specialized contractile cells, such as smooth muscle and myoepithelial cells. The Caenorhabditis elegans spermatheca is a bag-like organ of 24 myoepithelial cells that houses the sperm and is the site of fertilization. During ovulation, spermathecal cells are stretched by oocyte entry and then coordinately contract to expel the fertilized embryo into the uterus...
March 22, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28331074/osteopontin-inhibits-osteoblast-responsiveness-through-the-downregulation-of-focal-adhesion-kinase-mediated-by-the-induction-of-low-molecular-weight-protein-tyrosine-phosphatase
#2
Joji Kusuyama, Kenjiro Bandow, Tomokazu Ohnishi, Mitsuhiro Hisadome, Kaori Shima, Ichiro Semba, Tetsuya Matsuguchi
Osteopontin (OPN) is an osteogenic marker protein. Osteoblast functions are affected by inflammatory cytokines and pathological conditions. OPN is highly expressed in bone legions such as rheumatoid arthritis. However, local regulatory effects of OPN on osteoblasts remain ambiguous. Here, we examined how OPN influences osteoblast responses to mechanical stress and growth factors. Expression of NO synthase 1 (Nos1) and Nos2 was increased by low intensity pulsed ultrasound (LIPUS) in MC3T3-E1 cells and primary osteoblasts...
March 22, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28331073/stability-and-function-of-a-putative-microtubule-organizing-center-in-the-human-parasite-toxoplasma-gondii
#3
Jacqueline M Leung, Yudou He, Fangliang Zhang, Yu-Chen Hwang, Eiji Nagayasu, Jun Liu, John M Murray, Ke Hu
The organization of the microtubule cytoskeleton is dictated by microtubule nucleators or organizing centers.  Toxoplasma gondii, an important human parasite, has an array of 22 regularly spaced cortical microtubules stemming from a hypothesized organizing center, the apical polar ring. Here, we examine the functions of the apical polar ring by characterizing two of its components, KinesinA and APR1, and discovered that its putative role in templating can be separated from its mechanical stability. Parasites that lack both KinesinA and APR1 (ΔkinesinAΔapr1) are capable of generating 22 cortical microtubules...
March 22, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28331072/direct-measurement-of-microtubule-attachment-strength-to-yeast-centrosomes
#4
Kimberly K Fong, Krishna K Sarangapani, Erik C Yusko, Michael Riffle, Aida Llauró, Beth Graczyk, Trisha N Davis, Charles L Asbury
Centrosomes, or spindle pole bodies (SPBs) in yeast, are vital mechanical hubs that maintain load-bearing attachments to microtubules during mitotic spindle assembly, spindle positioning, and chromosome segregation. However, the strength of microtubule-centrosome attachments is unknown, and the possibility that mechanical force might regulate centrosome function has scarcely been explored. To uncover how centrosomes sustain and regulate force, we purified SPBs from budding yeast and used laser trapping to manipulate single attached microtubules in vitro Our experiments reveal that SPB-microtubule attachments are extraordinarily strong, rupturing at forces about 4-fold higher than kinetochore attachments under identical loading conditions...
March 22, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28331071/cell-cell-and-cell-ecm-adhesions-cooperate-to-organize-actomyosin-networks-and-maintain-force-transmission-during-dorsal-closure
#5
Katharine Goodwin, Emily E Lostchuck, Kaitlyn M L Cramb, Teresa Zulueta-Coarasa, Rodrigo Fernandez-Gonzalez, Guy Tanentzapf
Tissue morphogenesis relies on the coordinated action of actin networks, cell-cell adhesions, and cell-ECM adhesions. Such coordination can be achieved through crosstalk between cell-cell and cell-ECM adhesions. Drosophila Dorsal Closure (DC), a morphogenetic process wherein an extra-embryonic tissue called the amnioserosa contracts and ingresses to close a discontinuity in the dorsal epidermis of the embryo, requires both cell-cell and cell-ECM adhesions. However, whether the function of these two types of adhesion is coordinated during DC is not known...
March 22, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28331070/cytoplasmic-flows-as-signatures-for-the-mechanics-of-mitotic-positioning
#6
Ehssan Nazockdast, Abtin Rahimian, Daniel Needleman, Michael Shelley
The proper positioning of mitotic spindle in the single-cell Caenorhabditis elegans embryo is achieved initially by the migration and rotation of the pronuclear complex (PNC) and its two associated astral microtubules (MTs). Pronuclear migration produces global cytoplasmic flows that couple the mechanics of all microtubules, the PNC, and the cell periphery with each other through their hydrodynamic interactions (HIs). We present the first computational study that explicitly accounts for detailed HIs between the cytoskeletal components and demonstrate the key consequences of HIs on the mechanics of pronuclear migration...
March 22, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28331069/efficiency-of-lamellipodia-protrusion-is-determined-by-the-extent-of-cytosolic-actin-assembly
#7
Georgi Dimchev, Anika Steffen, Frieda Kage, Vanessa Dimchev, Julien Pernier, Marie-France Carlier, Klemens Rottner
Cell migration and cell-cell communication involves the protrusion of actin-rich cell surface projections such as lamellipodia and filopodia. Lamellipodia are networks of actin filaments generated and turned over by filament branching through Arp2/3 complex. Inhibition of branching is commonly agreed to eliminate formation and maintenance of lamellipodial actin networks, but the regulation of nucleation or elongation of Arp2/3-independent filament populations within the network e.g. by formins or Ena/VASP family members and its impact on the effectivity of protrusion have remained unclear...
March 22, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28298493/deubiquitinating-enzymes-ubp2-and-ubp15-regulate-endocytosis-by-limiting-ubiquitination-and-degradation-of-arts
#8
Hsuan-Chung Ho, Jason A MacGurn, Scott D Emr
Endocytic downregulation of cell-surface proteins is a fundamental cellular process for cell survival and adaptation to environmental stimuli. Ubiquitination of cargo proteins serves as the sorting signal for downstream trafficking, and relies on the Rsp5-ART (arrestin-related trafficking adaptors) ubiquitin ligase adaptor network in yeast. Hence, proper regulation of the abundance and activity of these ligase-adaptor complexes is critical for maintenance of optimal plasma membrane (PM) protein composition...
March 15, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28298492/-wait-anaphase-signals-are-not-confined-to-the-mitotic-spindle
#9
Lydia Reńe Heasley, Steven M Markus, Jennifer G DeLuca
The Spindle Assembly Checkpoint ensures the faithful inheritance of chromosomes by arresting mitotic progression in the presence of kinetochores that are not attached to spindle microtubules. This is achieved through inhibition of the Anaphase Promoting Complex/Cyclosome by a kinetochore-derived 'wait anaphase' signal known as the Mitotic Checkpoint Complex. It remains unclear whether the localization and activity of these inhibitory complexes are restricted to the mitotic spindle compartment or are diffusible throughout the cytoplasm...
March 15, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28298491/cyk-4-regulates-rac-but-not-rho-during-cytokinesis
#10
Yelena Zhuravlev, Sophia M Hirsch, Shawn N Jordan, Julien Dumont, Mimi Shirasu-Hiza, Julie C Canman
Cytokinesis is driven by constriction of an actomyosin contractile ring that is controlled by Rho family small GTPases. Rho, activated by the Guanine-nucleotide Exchange Factor (GEF) ECT-2, is upstream of both myosin-II activation and diaphanous formin-mediated filamentous actin (f-actin) assembly, which drive ring constriction. The role for Rac and its regulators is more controversial but, based on the finding that Rac inactivation can rescue cytokinesis failure when the GTPase Activating Protein (GAP) CYK-4 is disrupted, Rac activity was proposed to be inhibitory to contractile ring constriction and thus specifically inactivated by CYK-4 at the division plane...
March 15, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28298490/aberrant-caveolin-1-mediated-smad-signaling-and-proliferation-identified-by-analysis-of-adenine-474-deletion-mutation-c-474dela-in-patient-fibroblasts-a-new-perspective-in-the-mechanism-of-pulmonary-hypertension
#11
Glenn Marsboom, Zhenlong Chen, Yang Yuan, Yanmin Zhang, Chinnaswamy Tiruppathi, James E Loyd, Eric D Austin, Roberto F Machado, Richard D Minshall, Jalees Rehman, Asrar B Malik
A heterozygous Caveolin-1 c.474delA mutation has been identified in a family with heritable pulmonary arterial hypertension (PAH). This frameshift mutation leads to caveolin-1 protein that contains all known functional domains but has a change only in the final 20 amino acids of the C terminus. Here we studied how this mutation alters caveolin-1 function using patient-derived fibroblasts. Transmission electron microscopy showed that fibroblasts carrying the c.474delA mutation formed typical caveolae. Expression of mutated caveolin-1 in caveolin-1-null mouse fibroblasts failed to induce formation of caveolae due to retention of the mutated protein in the endoplasmic reticulum...
March 15, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28298489/mechanisms-of-kinetic-stabilization-by-the-drugs-paclitaxel-and-vinblastine
#12
Brian T Castle, Seth McCubbin, Louis S Prahl, Jordan N Bernens, David Sept, David J Odde
Microtubule-targeting agents (MTAs), widely used as biological probes and chemotherapeutic drugs, bind directly to tubulin subunits and "kinetically stabilize" microtubules, suppressing the characteristic self-assembly process of dynamic instability. However, the molecular-level mechanisms of kinetic stabilization are still unclear, and the fundamental thermodynamic and kinetic requirements for dynamic instability and its elimination by MTAs have yet to be defined. Here we integrate a computational model for microtubule assembly with nanometer-scale fluorescence microscopy measurements to identify the kinetic and thermodynamic basis of kinetic stabilization by the MTAs paclitaxel, an assembly promoter, and vinblastine, a disassembly promoter...
March 15, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28298488/the-ribosome-bound-quality-control-complex-remains-associated-to-aberrant-peptides-during-their-proteasomal-targeting-and-interacts-with-tom1-to-limit-protein-aggregation
#13
Quentin Defenouillère, Abdelkader Namane, John Mouaikel, Alain Jacquier, Micheline Fromont-Racine
Protein quality control mechanisms eliminate defective polypeptides to ensure proteostasis and to avoid the toxicity of protein aggregates. In eukaryotes, the Ribosome-bound Quality Control (RQC) complex detects aberrant nascent peptides that remain stalled in 60S ribosomal particles due to a dysfunction in translation termination. The RQC complex polyubiquitylates aberrant polypeptides and recruits a Cdc48 hexamer to extract them from 60S particles in order to escort them to the proteasome for degradation...
March 15, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28298487/tgf-%C3%AE-triggers-rapid-fibrillogenesis-via-a-novel-t%C3%AE-rii-dependent-fibronectin-trafficking-mechanism
#14
Archana Varadaraj, Laura M Jenkins, Priyanka Singh, Anindya Chanda, John Snider, N Y Lee, Ayelet R Amsalem-Zafran, Marcelo Ehrlich, Yoav I Henis, Karthikeyan Mythreye
Fibronectin (FN) is a critical regulator of extra cellular matrix (ECM) remodeling through its availability and stepwise polymerization for fibrillogenesis. Availability of FN is regulated by its synthesis and turnover, while fibrillogenesis is a multistep integrin dependent process essential for cell migration, proliferation and tissue function. Transforming growth factor beta (TGF-β) is an established regulator of ECM remodeling through transcriptional control of ECM proteins. Here, we show that TGF-β, through increased FN trafficking in a transcription and SMAD independent manner, is a direct and rapid inducer of fibrillogenesis required for TGF-β induced cell migration...
March 15, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28298486/protein-arginine-methyltransferases-interact-with-ift-particles-and-change-location-during-flagellar-growth-and-resorption
#15
Katsutoshi Mizuno, Roger D Sloboda
Changes in protein activity driven by post translational modifications comprise an important mechanism for the control of many cellular processes. Several flagellar proteins are methylated on arginine residues during flagellar resorption; however, the function is not understood. To learn more about the role of protein methylation during flagellar dynamics, we have focused on protein arginine methyltransferases (PRMTs) 1, 3, 5, and 10. These PRMTs localize to the tip of flagella and in a punctate pattern along the length, very similar, but not identical, to that of intraflagellar transport (IFT) components...
March 15, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28298485/mcak-mediated-regulation-of-endothelial-cell-microtubule-dynamics-is-mechano-sensitive-to-myosin-ii-contractility
#16
Lauren D'Angelo, Nicole M Myer, Kenneth A Myers
Compliance and dimensionality mechanosensing, the processes by which cells sense the physical attributes of the extracellular environment (ECM), are known to drive cell branching and shape change largely through a myosin-II-mediated reorganization of the actin and microtubule (MT) cytoskeletons. Subcellular regulation of MT dynamics is spatially controlled through a Rac1-Aurora-A kinase pathway that locally inhibits the MT depolymerizing activity of MCAK, thereby promoting leading-edge MT growth and cell polarization...
March 15, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28251926/phospho-regulation-of-tau-modulates-inhibition-of-kinesin-1-motility
#17
Jamie L Stern, Dominique V Lessard, Gregory J Hoeprich, Gerardo A Morfini, Christopher L Berger
Microtubule-based axonal transport is tightly regulated by numerous pathways ensuring appropriate delivery of specific organelle cargoes to selected subcellular domains. Highlighting the importance of this process, pathological evidence has linked alterations in these pathways to the pathogenesis of several neurodegenerative diseases. An important regulator of this system, the microtubule associated protein Tau has been shown to participate in signaling cascades, modulate microtubule dynamics and preferentially inhibit kinesin-1 motility...
March 1, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28251925/the-rhogap-protein-arhgap18-senex-localises-to-microtubules-and-regulates-their-stability-in-endothelial-cells
#18
Michael D Lovelace, Elizabeth E Powter, Paul R Coleman, Yang Zhao, Amelia Parker, Garry H Chang, Angelina J Lay, Julie Hunter, Aaron P McGrath, Mika Jormakka, Patrick Bertolino, Geoffrey McCaughan, Maria Kavallaris, Mathew A Vadas, Jennifer R Gamble
RhoGTPases are important regulators of the cell cytoskeleton, controlling cell shape, migration and proliferation. Previously, we showed ARHGAP18 in endothelial cells is important in cell junctions. Here we show using structured illumination microscopy (SIM), ground state depletion (GSD) and total internal reflection fluorescence (TIRF) that a proportion of ARHGAP18 localises to microtubules in endothelial cells as well as non-endothelial cells, an association confirmed biochemically. In endothelial cells some ARHGAP18 puncta also colocalised to Weibel-Palade Bodies on the microtubules...
March 1, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28251924/differential-role-of-nonmuscle-myosin-ii-isoforms-during-blebbing-of-mcf-7-cells
#19
Sumit K Dey, Raman K Singh, Shyamtanu Chattoraj, Shekhar Saha, Alakesh Das, Kankan Bhattacharyya, Kaushik Sengupta, Shamik Sen, Siddhartha S Jana
Bleb formation has been correlated with nonmuscle myosin II (NM-II) activity. Whether three isoforms of NM-II (NM-IIA, -IIB, and -IIC) have the same or differential roles in bleb formation is not well understood. Here, we report that ectopically expressed GFP-tagged NM-II isoforms exhibit different types of membrane protrusions such as multiple blebs, lamellipodia, combination of both or absence of any such protrusions in MCF-7 cells. Quantification suggests that 50% of NM-IIA-GFP, 29% of NM-IIB-GFP and 19% of NM-IIC1-GFP expressing MCF-7 cells show multiple blebs formation compared with 36% of GFP alone expressing cells...
March 1, 2017: Molecular Biology of the Cell
https://www.readbyqxmd.com/read/28251923/binding-of-zo-1-to-%C3%AE-5%C3%AE-1-integrins-regulates-the-mechanical-properties-of-%C3%AE-5%C3%AE-1-fibronectin-links
#20
Víctor González-Tarragó, Alberto Elosegui-Artola, Elsa Bazellières, Roger Oria, Carlos Pérez-González, Pere Roca-Cusachs
Fundamental processes in cell adhesion, motility, and rigidity adaptation are regulated by integrin-mediated adhesion to the extracellular matrix (ECM). The link between the ECM component fibronectin (fn) and integrin α5β1 forms a complex with ZO-1 in cells at the edge of migrating monolayers, regulating cell migration. However, how this complex affects the α5β1-fn link is unknown. Here we show that the α5β1/ZO-1 complex decreases the resistance to force of α5β1-fn adhesions located at at the edge of migrating cell monolayers, while also increasing α5β1 recruitment...
March 1, 2017: Molecular Biology of the Cell
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