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Molecular Biology of the Cell

Calvin Tiengwe, Carolina M Koeller, James D Bangs
Misfolded secretory proteins are retained by ER quality control (ERQC) and degraded in the proteasome by ER associated degradation (ERAD). However, in yeast and mammals misfolded glycosylphosphatidylinositol (GPI)-anchored proteins are preferentially degraded in the vacuole/lysosome. We investigate this process in the divergent eukaryotic pathogen Trypanosoma brucei using a misfolded GPI-anchored subunit (HA:E6) of the trypanosome transferrin receptor. HA:E6 is N-glycosylated and GPI-anchored, and accumulates in the ER as aggregates...
August 9, 2018: Molecular Biology of the Cell
Braulio Vargas Möller-Hergt, Andreas Carlström, Katharina Stephan, Axel Imhof, Martin Ott
Mitochondrial gene expression in Saccharomyces cerevisiae is responsible for the production of highly hydrophobic subunits of the oxidative phosphorylation system. Membrane insertion occurs co-translationally on membrane bound mitochondrial ribosomes. Here, by employing a systematic mass-spectrometric-based approach, we discovered the previously uncharacterized membrane protein Mrx15 that interacts via a soluble C-terminal domain with the large ribosomal subunit. Mrx15 contacts mitochondrial translation products during their synthesis and plays, together with the ribosome receptor Mba1, an overlapping role in co-translational protein insertion...
August 9, 2018: Molecular Biology of the Cell
Keren E Shapira, Marcelo Ehrlich, Yoav I Henis
Transforming growth factor-β (TGF-β) plays critical roles in numerous physiological and pathological responses. Cholesterol, a major plasma membrane component, can have pronounced effects on signaling responses. Cells continually monitor cholesterol content and activate multi-layered transcriptional and translational signaling programs, following perturbations to cholesterol homeostasis ( e.g., statins, the commonly used cholesterol reducing drugs). However, the crosstalk of such programs with ligand-induced signaling responses ( e...
August 9, 2018: Molecular Biology of the Cell
Alison C E Wirshing, Erin J Cram
Disruption to the contractility of cells, including smooth muscle cells of the cardiovascular system and myoepithelial cells of the glandular epithelium, contributes to the pathophysiology of contractile tissue diseases including asthma, hypertension, and Primary Sjögren's syndrome. Cell contractility is determined by myosin activity and actomyosin network organization and is mediated by hundreds of protein-protein interactions, many directly involving actin. Here we use a candidate RNAi screen of more than 100 C...
August 9, 2018: Molecular Biology of the Cell
Shujun Cai, Désirée Böck, Martin Pilhofer, Lu Gan
The in situ 3-D organization of chromatin at the nucleosome and oligonucleosome levels is unknown. Here we use cryo-electron tomography (cryo-ET) to determine the in situ structures of HeLa nucleosomes, which have canonical core structures and asymmetric, flexible linker DNA. Subtomogram remapping suggests that sequential nucleosomes in heterochromatin follow irregular paths at the oligonucleosome level. This basic principle of higher-order repressive chromatin folding is compatible with the conformational variability of the two linker DNAs at the single-nucleosome level...
August 9, 2018: Molecular Biology of the Cell
Ziad Jowhar, Sigal Shachar, Prabhakar R Gudla, Darawalee Wangsa, Erin Torres, Jill L Russ, Gianluca Pegoraro, Thomas Ried, Armin Raznahan, Tom Misteli
Sex chromosome aneuploidies (SCAs) are common genetic syndromes characterized by the presence of an aberrant number of X and Y chromosomes due to meiotic defects. These conditions impact structure and function of diverse tissues, but the proximal effects of SCA on genome organization are unknown. Here, to determine the consequences of SCAs on global genome organization, we have analyzed multiple architectural features of chromosome organization in a comprehensive set of primary cells from SCA patients with various ratios of X and Y chromosomes by use of imaging-based high-throughput Chromosome Territory Mapping (HiCTMap)...
August 9, 2018: Molecular Biology of the Cell
Michael Kirmiz, Stephanie Palacio, Parashar Thapa, Anna N King, Jon T Sack, James S Trimmer
Endoplasmic reticulum (ER) and plasma membrane (PM) form junctions crucial to ion and lipid signaling and homeostasis. The Kv2.1 ion channel is localized at ER-PM junctions in brain neurons and is unique among PM proteins in its ability to remodel these specialized membrane contact sites. Here, we show that this function is conserved between Kv2.1 and Kv2.2, which differ in their biophysical properties, modulation and cellular expression. Kv2.2 ER-PM junctions are present at sites deficient in the actin cytoskeleton, and disruption of actin cytoskeleton affects their spatial organization...
August 9, 2018: Molecular Biology of the Cell
Lena Wullkopf, Ann-Katrine V West, Natascha Leijnse, Thomas R Cox, Chris D Madsen, Lene B Oddershede, Janine T Erler
Increased tissue stiffness is a classic characteristic of solid tumors. One of the major contributing factors is increased density of collagen fibers in the extracellular matrix (ECM). Here, we investigate how cancer cells biomechanically interact with and respond to the stiffness of the ECM. Probing the adaptability of cancer cells to altered ECM stiffness using optical tweezers based micro-rheology and deformability cytometry, we find that only malignant cancer cells have the ability to adjust to collagen matrices of different densities...
August 9, 2018: Molecular Biology of the Cell
P D Arora, T He, K Ng, C A McCulloch
Flightless I (FliI) is a calcium-dependent, actin severing and capping protein that localizes to cell matrix adhesions, contributes to the generation of cell extensions and co-localizes with Ras. Currently the mechanism by which FliI interacts with Ras to enable assembly of actin-based cell protrusions is not defined. R-Ras but not K-ras, H-ras or N-ras, associated with the leucine-rich region (LRR) of FliI. Mutations of the proline-rich region of R-ras (P202A, P203A) prevented this association. Knockdown of Ras-GTPase-activating SH3 domain binding protein (G3BP1) or Rasgap120 by siRNA inhibited the formation of cell extensions and prevented interaction of R-ras and G3BP1 in FliI WT cells...
August 9, 2018: Molecular Biology of the Cell
Pil Jung Kang, Kristi E Miller, Julia Guegueniat, Laure Beven, Hay-Oak Park
The Cdc42 GTPase plays a central role in polarity development in many species. In budding yeast, Cdc42 is essential for polarized growth at the proper site and also for spontaneous cell polarization in the absence of spatial cues. Cdc42 polarization is critical for multiple events in the G1 phase prior to bud emergence, including bud-site assembly, polarization of the actin cytoskeleton, and septin filament assembly to form a ring at the new bud site. Yet the mechanism by which Cdc42 polarizes is not fully understood...
August 9, 2018: Molecular Biology of the Cell
Kuan-Chung Su, Mary-Jane Tsang, Neil Emans, Iain M Cheeseman
A key goal for cell biological analyses is to assess the phenotypes that result from eliminating a target gene. For the past 25 years, the predominant strategy utilized in human tissue culture cells has been RNAi-mediated protein depletion. However, RNAi suffers well-documented off-target effects as well as incomplete and reversible protein depletion. The implementation of CRISPR/Cas9-based DNA cleavage has revolutionized the capacity to conduct functional studies in human cells. However, this approach is still under-utilized for conducting visual phenotypic analyses, particularly for essential genes that require conditional strategies to eliminate their gene products...
August 9, 2018: Molecular Biology of the Cell
Elad Prinz, Sharon Aviram, Ami Aronheim
The mitogen-activated protein kinases (MAPKs) regulate a variety of cellular processes. The three main MAPK cascades are the ERK, JNK and p38 kinases. A typical MAPK cascade is composed of MAP3K-MAP2K-MAPK kinases that are held by scaffold proteins. Scaffolds function to assemble the protein tier and contribute to the specificity and efficacy of signal transmission. WDR62 is a JNK scaffold protein, interacting with JNK, MKK7 and several MAP3Ks. The loss of WDR62 in human leadsto microcephaly and pachygyria...
August 9, 2018: Molecular Biology of the Cell
Sandeep Krishna, Sunil Laxman
A minimal model for oscillating between quiescent and growth/proliferation states, dependent on the availability of a central metabolic resource, is presented. From the yeast metabolic cycles (YMCs), metabolic oscillations in oxygen consumption are represented as transitions between quiescent and growth states. We consider metabolic resource availability, growth rates, and switching rates (between states) to model a relaxation oscillator explaining transitions between these states. This frustrated bistability model reveals a required communication between the metabolic resource that determines oscillations, and the quiescent and growth state cells...
July 25, 2018: Molecular Biology of the Cell
Michele Haltiner Jones, Eileen T O'Toole, Amy S Fabritius, Eric G Muller, Janet B Meehl, Sue L Jaspersen, Mark Winey
Phosphorylation modulates many cellular processes during cell cycle progression. The yeast centrosome (called the spindle pole body, SPB) is regulated by the protein kinases Mps1 and Cdc28/Cdk1 as it nucleates microtubules to separate chromosomes during mitosis. Previously we completed an SPB phosphoproteome, identifying 297 sites on 17 of the 18 SPB components. Here we describe mutagenic analysis of phosphorylation events on Spc29 and Spc42, two SPB core components that were shown in the phosphoproteome to be heavily phosphorylated...
July 25, 2018: Molecular Biology of the Cell
Yingfan Zhang, Chengyu Liu, Robert S Adelstein, Xuefei Ma
Three paralogs of nonmuscle myosin 2 (NM 2A, 2B, and 2C) are expressed in mammals and the heavy chains are the products of three different genes, Myh9, Myh10 and Myh14, respectively. NM 2A and 2B are essential for mouse development, while 2C is not. Studies on NM 2C are limited and the in vivo function of this paralog is not clear. Using homologous recombination, cDNA expressing nonmuscle myosin heavy chain 2C1 fused with GFP was introduced into the first coding exon of Myh9, thereby replacing NM 2A expression with NM 2C1 in mice...
July 25, 2018: Molecular Biology of the Cell
Yi-Hua Zhu, Joanne Hyun, Yun-Zu Pan, James E Hopper, Josep Rizo, Jian-Qiu Wu
Cytokinesis is a complicated yet conserved step of the cell-division cycle that requires the coordination of multiple proteins and cellular processes. Here we describe a previously uncharacterized protein Ync13 and its roles during fission yeast cytokinesis. Ync13 is a member of the UNC-13/Munc13 protein family, whose animal homologues are essential priming factors for SNARE complex assembly during exocytosis in various cell types, but no roles in cytokinesis have been reported. We find that Ync13 binds to lipids in vitro and dynamically localizes to the plasma membrane at cell tips during interphase and at the division site during cytokinesis...
July 25, 2018: Molecular Biology of the Cell
Youngbin Cho, Minjeong Son, Hyuntae Jeong, Jennifer H Shin
During wound healing, cells migrate with electrotactic bias as a collective entity. Unlike the case of EF-induced single cell migration, the sensitivity of electrotactic response depends primarily on the integrity of the cell-cell junctions in the monolayer. Although there exist biochemical clues on how cells sense EF, well-defined physical portrait to illustrate how collective cells respond to directional EF remains elusive. Here, we developed an EF stimulating system integrated with a hydrogel-based traction measurement platform to quantify the EF-induced changes in cellular tractions, from which the complete in-plane intercellular stress tensor can be calculated...
July 25, 2018: Molecular Biology of the Cell
WeiTing Chen, Holly A Ping, Laura L Lackner
Mitochondrial transport and anchoring mechanisms work in concert to position mitochondria to meet cellular needs. In yeast, Mmr1 functions as a mitochondrial adaptor for Myo2 to facilitate actin-based transport of mitochondria to the bud. Post-transport, Mmr1 is proposed to anchor mitochondria at the bud tip. Although both functions require an interaction between Mmr1 and mitochondria, the molecular basis of the Mmr1-mitochondria interaction is poorly understood. Our in vitro phospholipid binding assays indicate Mmr1 can directly interact with phospholipid membranes...
July 25, 2018: Molecular Biology of the Cell
Barbara Noethel, Lena Ramms, Georg Dreissen, Marco Hoffmann, Ronald Springer, Matthias Rübsam, Wolfgang H Ziegler, Carien M Niessen, Rudolf Merkel, Bernd Hoffmann
The skin's epidermis is a multi-layered epithelial tissue and the first line of defense against mechanical stress. Its barrier function depends on an integrated assembly and reorganization of cell-matrix and cell-cell junctions in the basal layer and on different intercellular junctions in suprabasal layers. However, how mechanical stress is recognized and which adhesive and cytoskeletal components are involved is poorly understood. Here, we subjected keratinocytes to cyclic stress in the presence or absence of intercellular junctions...
July 25, 2018: Molecular Biology of the Cell
Julie K Monda, Iain M Cheeseman
Nde1 is a key regulator of cytoplasmic dynein, binding directly to both dynein itself and the dynein adaptor, Lis1. Nde1 and Lis1 are thought to function together to promote dynein function, yet mutations in each result in distinct neurodevelopment phenotypes. To reconcile these phenotypic differences, we sought to dissect the contribution of Nde1 to dynein regulation and explore the cellular functions of Nde1. Here, we show that an Nde1-Lis1 interaction is required for spindle pole focusing and Golgi organization, but is largely dispensable for centrosome placement, despite Lis1 itself being required...
July 19, 2018: Molecular Biology of the Cell
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