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Cayla E Jewett, Rytis Prekeris
The creation of cellular tubes is one of the most vital developmental processes, resulting in the formation of most organ types. Cells have co-opted a number of different mechanisms for tube morphogenesis that vary among tissues and organisms; however, generation and maintenance of cell polarity is fundamental for successful lumenogenesis. Polarized membrane transport has emerged as a key driver not only for establishing individual epithelial cell polarity, but also for coordination of epithelial polarization during apical lumen formation and tissue morphogenesis...
May 16, 2018: Traffic
Luis-Carlos Tábara, Juan-Jesús Vicente, Joanna Biazik, Eeva-Liisa Eskelinen, Olivier Vincent, Ricardo Escalante
The multispanning membrane protein VMP1 (Vacuole membrane protein 1) marks and regulates endoplasmic reticulum (ER)-domains associated with diverse ER-organelle membrane contact sites (MCSs). A proportion of these domains associate with endosomes during their maturation and remodeling. We found that these VMP1-domains are enriched in CEPT1 and PIS1, two ER enzymes required for the synthesis of various phospholipids. Interestingly, the lack of VMP1 impairs the formation of PIS1-enriched ER domains, suggesting a role in the distribution of phosphoinositides...
May 14, 2018: Traffic
Yi Xie, Hui Miao, J Todd Blankenship
Our understanding of how membrane trafficking pathways function to direct morphogenetic movements and the planar polarization of developing tissues is a new and emerging field. While a central focus of developmental biology has been on how protein asymmetries and cytoskeletal force generation direct cell shaping, the role of membrane trafficking in these processes has been less clear. Here, we review recent advances in Drosophila and vertebrate systems in our understanding of how trafficking events are coordinated with planar cytoskeletal function to drive lasting changes in cell and tissue topologies...
May 14, 2018: Traffic
Anthony R Mele, Jamie Marino, Kenneth Chen, Vanessa Pirrone, Chris Janetopoulos, Brian Wigdahl, Zachary Klase, Michael R Nonnemacher
The human immunodeficiency virus type 1 (HIV-1) transactivator of transcription (Tat) protein functions both intracellularly and extracellularly. Intracellularly the main function is to enhance transcription of the viral promoter. However, this process only requires a small amount of intracellular Tat. The majority of Tat is secreted through an unconventional mechanism by binding to phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2 ), a phospholipid in the inner leaflet of the plasma membrane that is required for secretion...
April 30, 2018: Traffic
Sarah C Charnaud, Thorey K Jonsdottir, Paul R Sanders, Hayley E Bullen, Benjamin K Dickerman, Betty Kouskousis, Catherine S Palmer, Halina M Pietrzak, Annamarrie E Laumaea, Anna-Belen Erazo, Emma McHugh, Leann Tilley, Brendan S Crabb, Paul R Gilson
Plasmodium falciparum, which causes malaria, extensively remodels its human host cells, particularly erythrocytes. Remodelling is essential for parasite survival by helping to avoid host immunity and assisting in the uptake of plasma nutrients to fuel rapid growth. Host cell renovation is carried out by hundreds of parasite effector proteins that are exported into the erythrocyte across an enveloping parasitophorous vacuole membrane (PVM). The Plasmodium translocon for exported proteins (PTEX) is thought to span the PVM and provide a channel that unfolds and extrudes proteins across the PVM into the erythrocyte...
April 26, 2018: Traffic
Stella M Lu, Gregory D Fairn
The plasma membrane is inhomogeneously organized containing both highly ordered and disordered nanodomains. 7-Ketocholesterol (7KC), an oxysterol formed from the non-enzymatic oxidation of cholesterol, is a potent disruptor of membrane order. Importantly, 7KC is a component of oxidized LDL and accumulates in macrophage and foam cells found in arterial plaques. Using a murine macrophage cell line, J774, we report that both IgG-mediated and phosphatidylserine (PtdSer)-mediated phagocytic pathways are inhibited by the accumulation of 7KC...
April 24, 2018: Traffic
Michael W Hess, Georg F Vogel, Teodor E Yordanov, Barbara Witting, Karin Gutleben, Hannes L Ebner, Mariana E G de Araujo, Przemyslaw Filipek, Lukas A Huber
Immunogold labeling of permeabilized whole-mount cells or thin-sectioned material is widely used for the subcellular localization of biomolecules at the high spatial resolution of electron microscopy (EM). Those approaches are well compatible with either three-dimensional (3D) reconstruction of organelle morphology and antigen distribution or with rapid cryofixation - but not easily with both at once. We describe here a specimen preparation and labeling protocol for animal cell cultures, which represents a novel blend of specifically adapted versions of established techniques...
April 19, 2018: Traffic
Jing Wang, Alina Fedoseienko, Bayou Chen, Ezra Burstein, Da Jia, Daniel D Billadeau
The tubular endolysosomal network is a quality control system that ensures the proper delivery of internalized receptors to specific subcellular destinations in order to maintain cellular homeostasis. Although retromer was originally described in yeast as a regulator of endosome-to-Golgi receptor recycling, mammalian retromer has emerged as a central player in endosome-to-plasma membrane recycling of a variety of receptors. Over the past decade, information regarding the mechanism by which retromer facilitates receptor trafficking has emerged, as has the identification of numerous retromer-associated molecules including the WASH complex, sorting nexins and TBC1d5...
April 18, 2018: Traffic
Trey Farmer, Naava Naslavsky, Steve Caplan
The mitochondrion is a unique organelle that serves as the main site of adenosine triphosphate (ATP) generation needed for energy in the cell. However, mitochondria also play essential roles in cell death through apoptosis and necrosis, as well as a variety of crucial functions related to stress regulation, autophagy, lipid synthesis, and calcium storage. There is a growing appreciation that mitochondrial function is regulated by the dynamics of its membrane fusion and fission; longer, fused mitochondria are optimal for ATP generation, whereas fission of mitochondria facilitates mitophagy and cell division...
April 16, 2018: Traffic
Peishan Yi, Chao Xie, Guangshuo Ou
Kinesin-2 motors power anterograde intraflagellar transport (IFT), a highly ordered process that assembles and maintains cilia. However, it remains elusive how kinesin-2 motors are regulated in vivo. Here, we performed forward genetic screens to isolate suppressors that rescue the ciliary defects of OSM-3-kinesin (homolog of mammalian homodimeric kinesin-2 KIF17) mutants in C. elegans. We identified the C. elegans dyf-5 and dyf-18, which encode the homologs of mammalian male germ cell-associated kinase (MAK) and cell cycle-related kinase (CCRK), respectively...
April 14, 2018: Traffic
Pearl V Ryder, Dorothy A Lerit
At the nexus of specialized cellular responses are localized enrichments of protein activity. The localization of messenger RNA (mRNA) coupled with translational control often plays a crucial role in the generation of protein concentrations at defined subcellular domains. Although mRNA localization is classically associated with large specialized cells, such as neurons and embryos, RNA localization is a highly conserved paradigm of post-transcriptional regulation observed in diverse cellular contexts. Functions of localized mRNAs extend far beyond the well-studied examples of neuronal polarization and developmental patterning...
April 13, 2018: Traffic
Emily K Herman, Moazzam Ali, Mark C Field, Joel B Dacks
Endocytosis is a crucial process in eukaryotic cells. The GTPases Rab 5, 21 and 22 that mediate endocytosis are ancient eukaryotic features and all available evidence suggests conserved function. In animals and fungi, these GTPases are regulated in part by proteins possessing Vps9 domains. However, the diversity, evolution and functions of Vps9 proteins beyond animals or fungi are poorly explored. Here we report a comprehensive analysis of the Vps9 family of GTPase regulators, combining molecular evolutionary data with functional characterization in the non-opisthokont model organism Trypanosoma brucei...
March 30, 2018: Traffic
Dakota J Brock, Lauren Kustigian, Mengqiu Jiang, Kristin Graham, Ting-Yi Wang, Alfredo Erazo-Oliveras, Kristina Najjar, Junjie Zhang, Hays Rye, Jean-Philippe Pellois
Various densely charged polycationic species, whether of biological or synthetic origin, can penetrate human cells, albeit with variable efficiencies. The molecular underpinnings involved in such transport remain unclear. Herein, we assemble one, two, or three copies of the HIV peptide TAT on a synthetic scaffold to generate branched cell-permeable prototypes with increasing charge density. We establish that increasing TAT copies dramatically increases the cell penetration efficiency of the peptides while simultaneously enabling the efficient cytosolic delivery of macromolecular cargos...
March 26, 2018: Traffic
Khan Umaer, Peter J Bush, James D Bangs
Trypanosoma brucei possesses a streamlined secretory system that guarantees efficient delivery to the cell surface of the critical GPI-anchored virulence factors, variable surface glycoprotein (VSG) and transferrin receptor (TfR). Both are thought to be constitutively endocytosed and returned to the flagellar pocket via TbRab11+ recycling endosomes. We use conditional knockdown with established reporters to investigate the role of TbRab11 in specific endomembrane trafficking pathways in bloodstream trypanosomes...
March 26, 2018: Traffic
Zenia Kaul, Oishee Chakrabarti
The endosomal sorting complexes required for transport (ESCRT) proteins help in the recognition, sorting and degradation of ubiquitinated cargoes from the cell surface, long-lived proteins or aggregates, and aged organelles present in the cytosol. These proteins take part in the endo-lysosomal system of degradation. The ESCRT proteins also play an integral role in cytokinesis, viral budding and mRNA transport. Many neurodegenerative diseases are caused due to toxic accumulation of cargo in the cell, which causes stress and ultimately leads to neuronal death...
March 25, 2018: Traffic
Jessica Bailey Blackburn, Tetyana Kudlyk, Irina Pokrovskaya, Vladimir V Lupashin
The Conserved Oligomeric Golgi (COG) complex controls membrane trafficking and ensures Golgi homeostasis by orchestrating retrograde vesicle trafficking within the Golgi. Human COG defects lead to severe multi-systemic diseases known as COG-Congenital Disorders of Glycosylation (COG-CDG). To gain better understanding of COG-CDGs we compared COG knockout cells to cells deficient to two key enzymes, Alpha-1,3-mannosyl-glycoprotein 2-beta-N-acetylglucosaminyltransferase (MGAT1) and UDP-glucose 4-epimerase (GALE), which contribute to proper N- and O-glycosylation...
March 23, 2018: Traffic
Guillaume Kulakowski, Hugo Bousquet, Jean-Baptiste Manneville, Patricia Bassereau, Bruno Goud, Lena K Oesterlin
Specific intracellular localization of RAB GTPases has been reported to be dependent on protein factors but the contribution of the membrane physicochemical properties to this process has been poorly described. Here, we show that three RAB proteins (RAB1/RAB5/RAB6) preferentially bind in vitro to disordered and curved membranes, and that this feature is uniquely dependent on their prenyl group. Our results imply that the addition of a prenyl group confers to RAB proteins, and most probably also to other prenylated proteins, the ability to sense lipid packing defects induced by unsaturated conical-shaped lipids and curvature...
March 23, 2018: Traffic
Christina Müdsam, Paul Wollschläger, Norbert Sauer, Sabine Schneider
Adaptor protein (AP) complexes mediate cargo selection and vesicle trafficking to different cellular membranes in all eukaryotic cells. Information on the role of AP4 in plants is still limited. Here we present analyses of Arabidopsis thaliana mutants lacking different subunits of AP4. These mutants show abnormalities in their development and in protein sorting. We found that growth of roots and etiolated hypocotyls, as well as male fertility and trichome morphology are disturbed in ap4. Analyses of GFP-fusions transiently expressed in mesophyll protoplasts demonstrated that the tonoplast proteins MOT2, NRAMP3 and NRAMP4, but not INT1, are partially sorted to the plasma membrane in the absence of a functional AP4 complex...
March 23, 2018: Traffic
Thomas O Tolsma, Lena M Cuevas, Santiago M Di Pietro
Clathrin mediated endocytosis is a fundamental transport pathway that depends on numerous protein-protein interactions. Testing the importance of the adaptor protein-clathrin interaction for coat formation and progression of endocytosis in vivo has been difficult due to experimental constrains. Here we addressed this question using the yeast clathrin adaptor Sla1, which is unique in showing a cargo endocytosis defect upon substitution of three amino acids in its clathrin-binding motif (sla1AAA ) that disrupt clathrin binding...
March 15, 2018: Traffic
Muhmmad Omar-Hmeadi, Nikhil Gandasi, Sebastian Barg
Phosphoinositides (PtdIns) play important roles in exocytosis and are thought to regulate secretory granule docking by co-clustering with the SNARE protein syntaxin to form a docking receptor in the plasma membrane. Here we tested this idea by high-resolution TIRF imaging of EGFP-labeled PtdIns markers or syntaxin-1 at secretory granule release sites in live insulin-secreting cells. In intact cells, PtdIns markers distributed evenly across the plasma membrane with no preference for granule docking sites. In contrast, syntaxin-1 was found clustered in the plasma membrane, mostly beneath docked granules...
March 14, 2018: Traffic
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