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Molecular Biology of the Cell

Shannon N Rhoads, Zachary T Monahan, Debra S Yee, Andrew Y Leung, Cameron G Newcombe, Robert N O'Meally, Robert N Cole, Frank P Shewmaker
FUS is an abundant, predominantly nuclear protein involved in RNA processing. Under various conditions, FUS functionally associates with RNA and other macromolecules to form distinct, reversible phase-separated liquid structures. Persistence of the phase-separated state and increased cytoplasmic localization are both hypothesized to predispose FUS to irreversible aggregation, which is a pathological hallmark of subtypes of amyotrophic lateral sclerosis and frontotemporal dementia. We previously showed that phosphorylation of FUS's prion-like domain suppressed phase separation and toxic aggregation, proportionally to the number of added phosphates...
June 13, 2018: Molecular Biology of the Cell
Sandeep Dave, Samuel J Anderson, Pallavi Sinha Roy, Emmanuel T Nsamba, Angela R Bunning, Yusuke Fukuda, Mohan L Gupta
To function in diverse cellular processes, the dynamic properties of microtubules must be tightly regulated. Cellular microtubules are influenced by a multitude of regulatory proteins, but how their activities are spatiotemporally coordinated within the cell, or on specific microtubules remains mostly obscure. The conserved kinesin-8 motor proteins are important microtubule regulators, and family members from diverse species combine directed motility with the ability to modify microtubule dynamics. Yet, how kinesin-8 activities are appropriately deployed in the cellular context is largely unknown...
June 6, 2018: Molecular Biology of the Cell
Agila Somasundaram, Justin Taraska
Calcium triggered exocytosis is key to many physiological processes, including neurotransmitter and hormone release by neurons and endocrine cells. Dozens of proteins regulate exocytosis, yet the temporal and spatial dynamics of these factors during vesicle fusion remain unclear. Here we use total internal reflection fluorescence microscopy to visualize local protein dynamics at single sites of exocytosis of small synaptic-like microvesicles in live cultured neuroendocrine PC12 cells. We employ two-color imaging to simultaneously observe membrane fusion (using vesicular acetylcholine transporter (VAChT) tagged to pHluorin) and the dynamics of associated proteins at the moments surrounding exocytosis...
June 6, 2018: Molecular Biology of the Cell
Pallabi Roy, Benjamin J Perrin
Stereocilia are mechanosensitive protrusions on the surface of sensory hair cells in the inner ear that detect sound, gravity and head movement. Their core is comprised of parallel actin filaments that are crosslinked and stabilized by several actin-binding proteins including fascin-2, plastin-1, espin and XIRP2. The actin filaments are the most stable known, with actin turnover primarily occurring at the stereocilia tip. While stereocilia actin dynamics have been well-studied, little is known about the behavior of the actin crosslinking proteins, which are the most abundant type of protein in stereocilia after actin and are critical for stereocilia morphogenesis and maintenance...
June 6, 2018: Molecular Biology of the Cell
Ha Neul Lee, Mithun Mitra, Oye Bosompra, David C Corney, Elizabeth L Johnson, Nadine Rashed, Linda D Ho, Hilary A Coller
Cell migration is a highly conserved process involving cytoskeletal reorganization and restructuring of the surrounding extracellular matrix. Although there are many studies describing mechanisms underlying cell motility, little has been reported about the contribution of alternative isoform use towards cell migration. Here, we investigated whether alternative isoform use can affect cell migration focusing on REversion-inducing-Cysteine-rich protein with Kazal motifs (RECK), an established inhibitor of cell migration...
June 6, 2018: Molecular Biology of the Cell
Hana M Odeh, Etienne Coyaud, Brian Raught, Michael J Matunis
Sumoylation regulates a wide range of essential cellular functions, many of which are associated with activities in the nucleus. Although there is also emerging evidence for the involvement of SUMO at intracellular membranes, the mechanisms by which sumoylation is regulated at membranes is largely unexplored. In this study, we report that the SUMO-specific isopeptidase, SENP2, uniquely associates with intracellular membranes. Using in vivo analyses and in vitro binding assays, we show that SENP2 is targeted to intracellular membranes via a predicted N-terminal amphipathic α-helix that promotes direct membrane binding...
June 6, 2018: Molecular Biology of the Cell
Meenakshi Agarwal, Hui Jin, Melainia McClain, Jinbo Fan, Bailey A Koch, Sue L Jaspersen, Hong-Guo Yu
The budding yeast centrosome, often called the spindle pole body (SPB), nucleates microtubules for chromosome segregation during cell division. An appendage, called the half bridge, attaches to one side of the SPB and regulates SPB duplication and separation. Like DNA, the SPB is duplicated only once per cell cycle. During meiosis, however, after one round of DNA replication, two rounds of SPB duplication and separation are coupled with homolog segregation in meiosis I and sister-chromatid segregation in meiosis II...
May 30, 2018: Molecular Biology of the Cell
Sawako Yamashiro, Soichiro Tanaka, Laura M McMillen, Daisuke Taniguchi, Dimitrios Vavylonis, Naoki Watanabe
How mechanical stress applied to the actin network modifies actin turnover has attracted considerable attention. Actomyosin exerts the major force on the actin network, which has been implicated in actin stability regulation. However, direct monitoring of immediate changes in F-actin stability upon alteration of actomyosin contraction has not been achieved. Here we reexamine myosin regulation of actin stability by using single-molecule speckle analysis of actin. To avoid possible errors attributable to actin-binding probes, we employed DyLight-labeled actin that distributes identical to F-actin in lamellipodia (Yamashiro et al...
May 30, 2018: Molecular Biology of the Cell
Jongmin Lee, David E Levin
Stress-activated MAPKs (SAPKs) respond to a wide variety of stressors. In most cases, the pathways through which specific stress signals are transmitted to the SAPKs are not known. In this study, we delineate the intracellular signaling pathway by which the trivalent toxic metalloid arsenite [As(III)] activates the yeast SAPK Hog1. We demonstrate that, to activate Hog1, As(III) must enter the cell through the glycerol channel Fps1 and requires metabolism to methylarsenite [MAs(III)] by the dimeric methyltransferase Mtq2:Trm112...
May 30, 2018: Molecular Biology of the Cell
Chantal A Coles, Jovana Maksimovic, Jenny Wadeson, Fahri T Fahri, Tracie Webster, Carolina Leyton, Matthew B McDonagh, Jason D White
Mouse models have shown ADAM12 is implicated during adipogenesis, the molecular pathways are not well understood. Stealth RNAiTM was used to knockdown ADAM12 in 3T3-L1 cells. Using gene profiling and metabolic enzymatic markers we have identified signalling pathways ADAM12 impacts upon during proliferation, differentiation and maturation of adipocytes. ADAM12 reduced cell numbers in proliferating pre-adipocytes, delayed differentiation of pre-adipocytes to adipocytes and increased lipid accumulation in mature adipocytes...
May 30, 2018: Molecular Biology of the Cell
Hem Sapkota, Emilia Wasiak, John R Daum, Gary J Gorbsky
Cells delayed in metaphase with intact mitotic spindles undergo cohesion fatigue, where sister chromatids separate asynchronously, while cells remain in mitosis. Cohesion fatigue requires release of sister chromatid cohesion. However, the pathways that breach sister chromatid cohesion during cohesion fatigue remain unknown. Using moderate-salt buffers to remove loosely bound chromatin Cohesin, we show that "cohesive" Cohesin is not released during chromatid separation during cohesion fatigue. Using a regulated protein heterodimerization system to lock different Cohesin ring interfaces at specific times in mitosis, we show that the Wapl-mediated pathway of Cohesin release is not required for cohesion fatigue...
May 30, 2018: Molecular Biology of the Cell
Marc A Vittoria, Elizabeth M Shenk, Kevin P O'Rourke, Amanda F Bolgioni, Sanghee Lim, Victoria Kacprzak, Ryan J Quinton, Neil J Ganem
Tetraploid cells, which are most commonly generated by errors in cell division, are genomically unstable and have been shown to promote tumorigenesis. Recent genomic studies have estimated that ∼40% of all solid tumors have undergone a genome-doubling event during their evolution, suggesting a significant role for tetraploidy in driving the development of human cancers. To safeguard against the deleterious effects of tetraploidy, non transformed cells that fail mitosis and become tetraploid activate both the Hippo and p53 tumor suppressor pathways to restrain further proliferation...
May 23, 2018: Molecular Biology of the Cell
Zachary N Wilson, Amber L Scott, Robin D Dowell, Greg Odorizzi
Lysosomes are dynamic organelles with critical roles in cellular physiology. The lysosomal signaling lipid phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2 ) is a key regulator that has been implicated to control lysosome ion homeostasis, but the scope of ion transporters targeted by PI(3,5)P2 and the purpose of this regulation is not well understood. Through an unbiased screen in Saccharomyces cerevisiae, we identified loss-of-function mutations in the vacuolar H+ -ATPase (V-ATPase) and in Vnx1, a vacuolar monovalent cation/proton antiporter, as suppressor mutations that relieve the growth defects and osmotic swelling of vacuoles (lysosomes) in yeast lacking PI(3,5)P2 ...
May 23, 2018: Molecular Biology of the Cell
Chiye Sakurai, Makoto Itakura, Daiki Kinoshita, Seisuke Arai, Hitoshi Hashimoto, Ikuo Wada, Kiyotaka Hatsuzawa
SNAP-23 is a plasma membrane-localized SNARE protein involved in Fc receptor (FcR)-mediated phagocytosis. However, the regulatory mechanism underlying its function remains elusive. Using phosphorylation specific-antibodies, SNAP-23 was found to be phosphorylated at Ser95 in macrophages. To understand the role of this phosphorylation, we established macrophage lines overexpressing the non-phosphorylatable S95A or the phospho-mimicking S95D mutation. The efficiency of phagosome formation and maturation was severely reduced in SNAP-23-S95D-overexpressing cells...
May 17, 2018: Molecular Biology of the Cell
Anushree C Gulvady, Fatemeh Dubois, Nicholas O Deakin, Gregory J Goreczny, Christopher E Turner
The focal adhesion proteins, Hic-5 and Paxillin have been previously identified as key regulators of MDA-MB-231 breast cancer cell migration and morphologic mesenchymal-amoeboid plasticity in three-dimensional extracellular matrices. However, their respective roles in other cancer cell types has not been evaluated. Herein, utilizing 3D cell-derived matrices and fibronectin-coated 1D substrates, we show that across a variety of cancer cell lines, the level of Hic-5 expression serves as the major indicator of the cells primary morphology, plasticity and in vitro invasiveness...
May 17, 2018: Molecular Biology of the Cell
Elisa Dultz, Roberta Mancini, Guido Polles, Pascal Vallotton, Frank Alber, Karsten Weis
Chromatin organization is highly dynamic and regulates transcription. Upon transcriptional activation, chromatin is remodeled and referred to as "open", but quantitative and dynamic data of this decompaction process are lacking. Here, we have developed a quantitative high-resolution microscopy assay in living yeast cells to visualize and quantify chromatin dynamics using the GAL7-10-1 locus as a model system. Upon transcriptional activation of these three clustered genes, we detect an increase of the mean distance across this locus by >100 nm...
May 17, 2018: Molecular Biology of the Cell
Christina M Ketchum, Xiaoyu Sun, Alexandra Suberi, John T Fourkas, Wenxia Song, Arpita Upadhyaya
B cell signaling activation is most effectively triggered by the binding of B cell receptors (BCRs) to membrane-bound antigens.  In vivo, B cells encounter antigen on antigen presenting cells (APC), which possess complex surfaces with convoluted topographies, a fluid membrane and deformable cell bodies. However, whether and how the physical properties of antigen presentation affect B cell activation is not well understood. Here, we use nanotopographic surfaces that allow systematic variation of geometric parameters to show that surface features on a subcellular scale influence B cell signaling and actin dynamics...
May 17, 2018: Molecular Biology of the Cell
Joanna Kim, John A Cooper
Junctional integrity of endothelial monolayers is crucial to control movement of molecules and cells across the endothelium. Examining the structure and dynamics of cell junctions in endothelial monolayers, we discovered a role for septins. Contacts between adjacent endothelial cells were dynamic, with protrusions extending above or below neighboring cells. VE-cadherin was present at cell junctions, with a membrane-associated layer of F-actin. Septins localized at cell-junction membranes, in patterns distinct from VE-cadherin and F-actin...
May 17, 2018: Molecular Biology of the Cell
T McHugh, H Drechsler, A D McAinsh, N J Carter, R A Cross
Kif15 is a kinesin-12 that contributes critically to bipolar spindle assembly in humans. Here we use force-ramp experiments in an optical trap to probe the mechanics of single Kif15 molecules under hindering or assisting loads and in a variety of nucleotide states. Whilst unloaded Kif15 is established to be highly processive, we find that under hindering loads, Kif15 takes <∼10 steps. As hindering load is increased, Kif15 forestep:backstep ratio decreases exponentially, with stall occurring at 6 pN. By contrast, under assisting loads, Kif15 detaches readily and rapidly, even from its AMPPNP state...
May 17, 2018: Molecular Biology of the Cell
Yuki Hamada, Yuta Tsurumi, Shohei Nozaki, Yohei Katoh, Kazuhisa Nakayama
The dynein-2 complex mediates trafficking of ciliary proteins by powering the intraflagellar transport (IFT) machinery containing IFT-A and IFT-B complexes. Although 11 subunits are known to constitute the dynein-2 complex, with several light chain subunits shared by the dynein-1 complex, the overall architecture of the dynein-2 complex has not been fully clarified. Utilizing the visible immunoprecipitation assay, we demonstrated the interaction modes among the dynein-2 subunits, including previously undefined interactions, such as that between WDR60 and the TCTEX1D2-DYNLT1/DYNLT3 dimer...
May 9, 2018: Molecular Biology of the Cell
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